CMS Bulletin

LS1 overview

In general the LS1 project is progressing well and the workflow is holding to the original December 2012 schedule within two–three weeks, acceptable at this stage, with about 400 work packages already completed. In particular, the critical logistic configuration planned for summer 2013, giving simultaneous access to both ends of the vacuum tank interior and the exterior, plus the YE1 nose zones, was achieved significantly before the deadline at the end of June. The safety awareness of all those working on the CMS detector is currently very satisfactory and the general atmosphere at Point 5 is good, despite many concurrent activities and inevitable last minute adjustments to the day-to-day planning.

LS1 services infrastructure work

The “once-in-ten years” maintenance of the water-cooling infrastructure has been completed successfully by EN department teams; underground circuits were available again from 12 June. In the shadow of this activity, consolidation and maintenance of sub-detector water-cooling plants has been carried out, while fluorocarbon plants are being revised for lower-temperature operation of the tracking detectors. A further pre-requisite for this is the complete revision of the dry-gas supply and distribution system, which helps maintain low-humidity conditions in the Tracker and other subsystems. The external pipework installation and testing for this is now nearing completion. Finally, a vast programme of pipe-work and cabling modifications and additions in preparation for the installation of the fourth endcap muon stations has just passed the halfway mark.

Meanwhile, the re-cabling of the detector power distribution to extend UPS coverage to all the S1- and S2-based systems has also been completed.  Restoration of power throughout the USC awaits completion of the preventive replacement programme for turbine modules, expected to be complete by mid-July.

LS1 logistics and on-detector work

Since mid-June the solenoid vacuum tank outer surface has become accessible for the first time since 2008. Both endcaps are fully open and the YB-wheels of both ends are parked between the end of the vactank and the YE1s. The thermal shields of the vactank and YB0 have been removed and all ECAL cables covering sectors where DT chambers require maintenance have been disconnected from their patch panels and folded back. By the beginning of the CMS Week, access scaffolding will surround YB0, allowing installation of the on-detector pipe-work supplying dry gas (nitrogen or air, depending on operation conditions) to the tracker volume, additional sniffer pipes monitoring the dew point inside the vactank, cabling for additional temperature and humidity sensors, new HB low-voltage cables, with larger cross-section, for use with the Phase 1 upgraded electronics (foreseen for LS2) and an insulated cooling line at each end for the PLT. In addition, the path of the concentric vacuum-insulated CO₂ cooling lines for the Phase 1 Pixel detector upgrade can now be defined in detail. If available, the supports will be installed now, to minimise work during the actual pipe installation and testing at low temperature, planned for December 2013, which will take place without scaffolding. In parallel with these service installations, all HO photo-detectors on YB0 will be exchanged and maintenance on all accessible DT-mini-crates will be performed. Alongside this very packed programme on YB0 and the outside of the vactank, the humidity sealing of the Tracker’s service channels inside the vactank is about to start. This activity, the top priority task of LS1, will continue for up to one year.

On the YE1 nose zones, the extraction of ME1/1 chambers is progressing well, with two chambers per day being extracted, according to schedule. All chambers at the +Z end are expected to have been removed and transferred to the refitting laboratory in SX5, before the July CMS Week.

Phase 1 upgrade detector infrastructure

On 14 June, the assembly tooling for the YE4 endcap shielding walls successfully passed its safety inspection, after which three sectors were assembled vertically onto the support beam in the ISR, testing the underground installation procedure. From the middle of August, the barrel wheels at the +Z end will be temporarily moved back over the vacuum tank and the endcap will be closed by 6m, making space for the assembly of the first YE4 disk, after which a mirror-symmetrical logistic configuration will be set up to allow the second disk to be assembled.

All elements of the new central beam pipe (designed for the Phase 1 Pixel Tracker) are now complete at the manufacturer and the replacement support collars, for those lost in transit from CERN in May, have now also been delivered.

Authorisation to proceed with e-beam welding of the sections awaits a full understanding of the weld-test samples received recently.

Detector systems oversight

On 14 June, a follow-up took place of the ME1/1 Manufacturing Progress Review held in March 2013. The reviewers were pleased to note that the CSC laboratory in SX5 is fully operational with currently two refurbished spare chambers under test. In view of the excellent progress in nearly all areas that caused concern in the March MPR, the review committee was confident that the revision programme of the ME1/1 system is likely to conclude successfully. It was therefore concluded that the refurbishment of the removed ME1/1 chambers should start at the discretion of the endcap muon project manager, once details of the necessary testing infrastructure are complete.

The operation of the PLT demonstrator during the 2012 LHC physics run was extremely valuable in understanding the device and the conditions necessary for it to deliver an independent luminosity measurement. However a drawback became apparent with the diamond sensors currently used. Under irradiation they develop a rate-dependent signal shape and amplitude, most probably due to polarisation effects, leading to reduced efficiency. This would make an independent luminosity measurement impossible. As a consequence, on 28 June, a combined Engineering Change and Design Review was held, considering the proposal to change the sensor material from diamond to silicon. As the readout is the same for both sensors, the exchange of the sensor material is almost independent from the rest of the design. Silicon sensors and readout chips are available in the necessary quantities. The main difficulty arises from the necessity to cool the silicon sensors. The Integration Office is working with high priority to establish the routing of a cooling line from the Tracker SS2 distribution to the PLT carriage and the carriage itself, which also houses the BCM1F, is being re-designed to include cooling circuits. Though giving an overall positive recommendation, the committee has raised some questions and will require close monitoring of the progress through a series of subsequent reviews.

Other technical reviews since the last CMS Week include the ESR for the DAQ “Ferol” board, the PRR for the endcap radio-protection shielding and a follow-up to the pixel CO₂ cooling PRR, which endorsed the plan to install the new vacuum-insulated concentric distribution pipes mentioned above.

The review process for Phase 1 TDR detectors proper has started with a PRR authorising the procurement of all the barrel silicon sensors.

The recommendations arising from these recent reviews will be published shortly.

Phase 2 upgrade: logistics and planning

Following the TC workshop held on 23 May and the CMS-DESY workshop in June, Technical Coordination is focussing on three main issues: replacement of the HE scintillator (which may be forced by ageing), replacement of the whole endcap nose with a new calorimeter system and first muon station (with options to extend coverage of both to higher η) and comparative planning for completing the key elements of Phase 2 in a single shutdown (preferred) or two shutdowns.

The magnet is fully stopped and at room temperature. The maintenance works and consolidation activities on the magnet sub-systems are progressing.

To consolidate the cryogenic installation, two redundant helium compressors will be installed as ‘hot spares’, to avoid the risk of a magnet downtime in case of a major failure of a compressor unit during operation. The screw compressors, their motors, the mechanical couplings and the concrete blocks are already available and stored at P5. The metallic structure used to access the existing compressors in SH5 will be modified to allow the installation of the two redundant ones. The plan is to finish the installation and commissioning of the hot spare compressors before the summer 2014.

In the meantime, a bypass on the high-pressure helium piping will be installed for the connection of a helium drier unit later during the Long Shutdown 1, keeping this installation out of the schedule critical path.

A proposal is now being prepared for the consolidation of the compressor lubricant separator unit, against the risk of polluting the downstream helium piping with the lubricant in case of a degradation of the filtering units.

The overhaul of the two existing compressors and their motors is planned for the end of 2013, and the re-installation will take place in mid-March 2013.

The low-voltage electrical distribution for the cryogenic process control has been consolidated. The consolidation works for the redundant compressors on the 3.3 kV distribution network at Point 5 will take place in the second half of 2013 and extend until the beginning of 2014, before the redundant compressors will be commissioned.

For the other magnet sub-systems, namely the vacuum pumping groups, the magnet control and safety systems and the powering circuit, minor consolidations are planned. A thorough maintenance will be made well ahead of the scheduled magnet restart.

A refurbishment of the data acquisition system for the magnet coil instrumentation is now discussed together with CEA/Saclay.

The instrumentation on the yoke will be completed with about 60 new Hall probes, part of them are ready to be installed on the barrels.

One of the first activities of LS1 has been the refurbishment of the rack ventilation units in the USC55 counting rooms. These rack-mounted turbines have been in service since 2007 and they have largely passed the expected lifetime. Some 450 motor-fans units have been procured in Germany, via the CERN store, and shipped to CMS where a team of technicians has dismounted the old turbines, keeping only the bare chassis, and inserted the new fans. A metallic mesh has also been added to better protect personnel from possible injuries by spinning blades. A full test of several hours has validated the new units, prior to their installation inside the racks. The work, started soon after the beginning of LS1, has been successfully concluded last week.

Figure 1: Drawing of the fan units recently refurbished in the USC55 counting room racks

Image 1: New filter on the main rack water-cooling distribution line

The cooling systems of CMS are gently coming out of their maintenance programme. All water circuits have been put back in operation on 15 June, are in good shape and have no leaks at all, despite the huge interventions completed: full maintenance on the plants – from the towers to the detector circulation systems – cleaning of all filters, installation of an additional filter and the repair of all muon system circuit flow limiters.

The activity still ongoing, guided by the accessibility of the panels, is the replacement of all quick connectors on the radial thermal shields.

Image 2: The TIF CO₂ cooling plant: full-scale prototype for Pixel Phase 1 Upgrade

The fluorocarbon cooling systems serving the Strip Tracker, the Pixel detector and the ECAL Preshower have been completely refurbished to achieve –20 ºC operation and the re-commissioning of the system is reaching its end. By the beginning of July, the full performance tests will have to assess the total power of the system at the lowest design temperatures.

On the surface, the construction of the CO₂ cooling system for Pixel Phase 1 upgrade is completed. All components have been installed and pressure-tested in Building 186 and the first steps towards commissioning are ongoing: I/O verification for the cabling and controls logic verification on a mirror machine, prior to powering of the new plant.

Pixel Tracker

At the beginning of May, the Pixel detector was successfully extracted from inside CMS. The operation lasted one and a half days each for the forward and barrel Pixel detectors. Everything went smoothly: new people were trained during the exercise and care was taken to minimise radiation exposure – see Image 3.  Lessons learned were noted in an updated written extraction procedure.  Care was also taken to prepare for reinsertion around the new beam pipe next year, with new alignment targets placed on the barrel Pixel detector. All pieces were lifted to the surface and are now safely stored at low temperatures in the dedicated Pixel laboratory at Point 5 (see Image 4 and previous Bulletin).

Image 3 (a) and (b): Extracted FPIX and BPIX detector

The subsequent maintenance of the forward Pixel detector started on 27 May.  Since then one of four half cylinders has been repaired and, even more importantly, most of the failures have been fully understood. In particular one failure type was related to the loss of signal bandwidth in some of the readout channels, which made the signal impossible to be interpreted by the back-end electronics. The problem was caused by a misalignment between a cable and the analogue high-density interconnector carrying the analogue electrical signals and power to the disks. Another failure type was related to the reliability of programming of some readout chips. Also in this case, the problem was related to the digital high-density interconnector carrying, just as for the analogue one, the digital electrical signals and power to the disks. The team of experts is in the process of searching for means to mitigate future occurrences of such problems.  So far about 50% (corresponding to a detector total of ~3%) of the failures in FPIX have been repaired, and repairs will continue in the coming months.

Image 4: Pixel laboratory at the CMS site in Cessy. The two white boxes contain one forward Pixel half cylinder each. The DAQ/DCS station is located on the left.

The cause of the barrel Pixel detector failures (in total ~2.3% of BPIX channels) are identified to be either broken modules (i.e. broken wire-bonds) or faulty services (e.g. broken analogue-to-optical transducers and disconnected sense-wires). As a conservative approach the team of experts will repair all broken services and all modules, which are easily accessible (i.e. located on the outer-most layer). A thorough risk assessment will be performed in order to understand whether or not to repair modules on inner layers.

The Pixel community is eager to take full advantage of the current LHC long shutdown period (LS1), not only to repair the detector, but also to fully calibrate the detector at different temperatures for a prompt adaptation of the detector performance to any of the possible running conditions that will be faced after LS1. Also Pixel DOC shifts are re-opened – join the fun.

Strip Tracker

CMS is now in the fully open configuration and operation “Tracker Going Cold” is in full swing. The new dry-gas membrane system has been commissioned including connection to the distribution racks underground and installation of new copper pipes up the cryostat. The installation of multilayer pipes up to the bulkhead is imminent. The C₆F₁₄ cooling refurbishment went exceptionally well and reached the final commissioning stage. The humidity-seal inspection inside the vactank has been done and the team is confident to achieve the final sealing by August, with the deployment of new dew-point instrumentation. A complex gas humidity analysis rack, with five chilled mirrors and 26 industrial Vaisala dew-point sensors, has been delivered to Point 5.

The Online/DAQ group has been active at the former Tracker Integration Facility (TIF) in building 186. The Cosmic Rack (C-Rack) detector has been re-commissioned, including its cosmic trigger. The former Magnet and Cosmic Challenge (MTCC) structure is being made operational again to act as an additional and independent development and testing system at the TIF; especially to test failure scenarios within a larger system.

Online software is being developed and tested for various updates scheduled during LS1, such as the transition to Scientific Linux 6 and the new PCI VME interface card allowing a significant reduction in the number of PCs needed.

A first Strip DAQ hands-on tutorial was organised to train future experts on all the commissioning tasks envisioned for the autumn re-comissioning of the Strip Tracker at lower operating temperatures. The participation in the current LS1 activities is a rare opportunity to create the next generation of experts for the coming LHC run.

Studies have commenced on possible improvements for the cluster-finding algorithm in the Front End Drivers (FEDs) to have the firmware ready for occupancies well beyond the initial design specifications.

In the last few months a renewed effort was put into the study of the Strip Tracker detector ageing. The radiation damage corresponding to several integrated luminosity scenarios and its effect on the evolution of Strip modules leakage currents and depletion voltages was modelled. The leakage current modelling was validated against data; while dedicated Noise and Signal Bias scan results are being analysed to validate the depletion voltage evolution model. Strip calibration conditions (bad components, noise and gain) were produced for upgrade luminosity scenarios. These ageing conditions have been the basis for the upgrade studies simulations ongoing for the ECFA meeting. The Strip Calibration and the Tracker Alignment groups are producing improved calibration constants (bad components and alignment) for the legacy reprocessing of the 2011 data. The new, more accurate algorithms are being used to provide the best data quality and both workflows are being included in the Prompt Calibration Loop (PCL) at T0, ready for the next data-taking period. The Tracker alignment framework has been extended to treat position-sensitive calibration parameters, such as Lorentz Angle and Strip backplane corrections, with the MillePede II algorithm.

New people are welcome to join this exciting effort and take the rare opportunity to participate in the re-commissioning of the detector!

In a break with tradition, the ECAL general meetings during the April CMS Week were devoted to a series of brainstorming sessions, focusing on a small number of hot-topic items. These included sessions on ECAL upgrades, analysis of 2012 detector performance and resolution, software development plans and a review of the ECAL calibration sequence. These sessions were well attended and extremely productive, and have helped to define and guide the direction of the ECAL effort planned for LS1.

The area of ECAL upgrades has been particularly active over the past several months. A note summarising the test-beam performance of crystal matrices, irradiated with proton fluences representative of the end of Phase 1 LHC running, has been prepared and is being reviewed by ECAL. This important note provides data to tune and validate the simulation of ECAL ageing that has been implemented in CMSSW. This simulation is being used by the ECAL group and others to evaluate the physics performance of the ECAL at the end of Phase 1 and during Phase 2 operations, up to ~3000fb^–1. In addition, studies of the longevity and radiation resistance of electronic components and APDs, again up to the end of Phase 2, are being performed.

The ongoing work of the ECAL upgrades group was summarised during the CMS upgrade week at DESY. At this meeting, a working hypothesis for the upgrade of ECAL for Phase 2 LHC operation was presented to the collaboration. This provides, based on the currently available input, an aggressive scenario that involves replacing the EB electronics (providing maximum flexibility for increased CMS triggering capabilities) and replacing the existing EE+ES with a new radiation-hard detector.  This working hypothesis will serve as a focal point for the ECAL upgrade scope and cost-scale determination. Both of these aspects, which are required for the October RRB meeting, will be significant topics for discussion during the July CMS Week.

The recent work of the ECAL Detector Performance Group (DPG) has focused on consolidation of Run 1 performance and preparations for Run 2. A series of topical workshops has been organised, based on the outcome of the brainstorming sessions in April. The first workshop, held in mid-June, focused on planned developments of the ECAL reconstruction software during LS1. Topics discussed included the reorganisation and rewriting of core reconstruction code for better efficiency and maintainability, the design of a new thread-safe data unpacker, and plans to adapt the amplitude reconstruction to reduce the sensitivity to out-of-time pile-up. A second workshop, focused on energy resolution and calibration, is scheduled for the summer.

Regarding Run 1 data, the reference paper for electron/photon energy scale and resolution using 2010/11 data, EGM-11-001, was completed and submitted to the Journal of Instrumentation in early June. New ECAL conditions, with an improved noise description, were provided for the new MC samples that have been recently generated to be used for the Run 1 legacy Higgs analyses.

At Point 5, the disconnecting of EB low-voltage cables at the YB0 patch panels to permit the refurbishment of HCAL photodetectors has been completed according to schedule. The reconnection is planned for later this year (for EB–) and early 2014 (EB+). EE and ES detector checkout, including taking laser calibration data to track crystal recovery in EE, will commence once power to the on- and off-detector racks is restored. This will be followed by interventions to attempt to repair faulty low- and high-voltage lines in EE and ES.

The DAQ-slice in building 904 is nearing completion and is being used as a development and test stand for the ongoing Trigger and DAQ software development work.

Notes and Conference talks

1) Papers:

EGM-11-001, Energy calibration and resolution of the CMS electromagnetic calorimeter in pp collisions at sqrt(s)=7 TeV

2) Detector performance summaries:

CMS-DP-2013-007, 2012 ECAL detector performance plots

CMS-DP-2013-016, 2012 ECAL detector performance plots (2)

3) Conference talks and posters:

CHEF 2013:

M.M. Obertino, The challenges involving the calibration of the CMS Electromagnetic Calorimeter at the LHC

M. Dejardin, Role of the CMS electromagnetic calorimeter in the hunt for the Higgs boson through the two-gamma decay channel

A. Zabi, The electron and photon trigger of the CMS Experiment

A. Bornheim, Evolution of the CMS ECAL response, R&D studies on new scintillators, and possible design options for electromagnetic calorimetry at the HL-LHC

SCINT 2013:

S. Nourbakhsh, Role of the CMS electromagnetic calorimeter in the hunt for the Higgs boson through the two-gamma decay mode

A. Ledovskoy, Evolution of the response of the CMS ECAL, R&D studies on new scintillators, and possible design options for electromagnetic calorimetry at the HL-LHC

IFAE 2013:

L. Soffi, Use of ECAL time in physics analyses at CMS

C. La Licata, Role of the CMS electromagnetic calorimeter in the hunt for the Higgs bosn through the two-gamma decay mode

LHCC, March 2013:

C. Pena, CMS ECAL calibration and the energy scale and resolution for photons

6DW-PTeV:

E. Auffray-Hillemanns, Radiation damage in lead tungstate crystals (PWO) used in the CMS electromagnetic calorimeter

Lake Louise 2013:

N. Daci, Role of the CMS electron and photon trigger in the Higgs boson searches

VCI 2013:

J. Malcles, The CMS electromagnetic calorimeter: performance and role in the discovery of the Higgs boson

M. Diemoz, Podium discussion on the comparison of electromagnetic calorimetery in ATLAS and CMS

DAE-HEP-IN:

S. Jain, Anomalous APD signals in the CMS Electromagnetic Calorimeter

The DT collaboration is undertaking substantial work both for detector maintenance – after three years since the last access to the chambers and their front-end electronics – and upgrade.

The most critical maintenance interventions are chambers and Minicrate repairs, which have not begun yet, because they need proper access to each wheel of the CMS barrel, meaning space for handling the big chambers in the few cases where they have to be extracted, and, more in general, free access from cables and thermal shields in the front and back side of the chambers. These interventions are planned for between the coming Autumn until next spring. Meanwhile, many other activities are happening, like the “pigtail” intervention on the CAEN AC/DC converters which has just taken place.

The upgrade activities continue to evolve in good accordance with the schedule, both for the theta Trigger Board (TTRB) replacement and for the Sector Collector (SC) relocation from the UXC to the USC. The TTRB work aims at reconstituting the stock of spare boards for the long-term operation of the chamber Minicrates. Theta TRB production is going on satisfactorily: soon we will have the first batch of boards at CERN. With the SC work, data and trigger primitives from each of the 250 DT chambers will be available in the USC on optical fibres. This work is the cornerstone for any long-term upgrade plan of the DT system. All but one optical-fibre trunk cables have been received, measured and are ready for installation between the USC and the UXC.
Half of the Wiener crates have been received and tests are satisfactory.
A first batch of final OFCU-RO boards is being tested: no problems so far.
Final production has also been started for the first batch of CUOF mezzanines and of OFCU-TRG boards.
CUOF motherboard slow control tests worked fine.
Cooling tests for the CUOF crate have started at the building 904 site, where a peak of activity is being reached with many tasks carried out in parallel: CAEN modules test stand refurbishment, slow control developments, Minicrate installation logistics etc.

Finally, a DT Upgrade workshop on detector longevity and Phase 2 upgrade strategies was held in Padova: the data on electronics irradiation tests were reviewed and the decision to rebuild the Minicrates was taken in the end, aiming at their installation during LS3. The DT DPG group has started studies for simulating the muon barrel performance in scenarios of increasing degradation due to ageing of the detector.

The ambitious CSC upgrade programme during Long Shutdown 1 (LS1) includes the installation of 67 new ME4/2 chambers, and replacement of the cathode electronics in ME1/1 to use flash ADCs and undo the 3:1 ganging of strips in the inner section that covers pseudorapidity 2.1–2.4. The ME1/1 project passed a follow-up (MPR) review on 14 June and is now proceeding rapidly. A programme to eliminate a tin-gold interface in the low voltage connectors in our 60 peripheral crates is well underway. Meanwhile, a combined muon system (CSC+DT+RPC) performance paper has been submitted to JINST and arXiv at the end of June.

The ME4/2 chamber factory at Prevessin’s building 904 has produced 51 of the needed 67 chambers, and continues to turn out at least the anticipated one chamber per week. Cathode (CFEB) boards are now being recuperated from ME1/1 for use on the ME4/2 chambers. Installation of associated infrastructure including cooling, low-voltage and cabling are going well. High-voltage boards are in full production with completion expected at the end of 2013.

Removal of the ME1/1 chambers is complete for the positive endcap and is proceeding on the negative endcap. The chambers are brought to the CSC surface facility at SX5 (see the Image 5 below), where they are refurbished with the new electronics and cabling, and then thoroughly tested.  The 36 associated patch panels have been removed from the noses of both endcaps, and trial installation of three new patch panels has been made.

The new digital cathode boards (DCFEBs) for ME1/1 are now in full production and more than 100 have been shipped to CERN (seven are needed on each ME1/1 chamber). Additional low-voltage power supplies have been delivered, and on-chamber cables and power distribution boards are mostly in hand. The new off-chamber boards are coming along well, with OTMB (trigger) boards in full production, while ODMB (data-acquisition) boards are nearing their production readiness review.

A comprehensive test suite has been developed that is being used for testing ME4/2 and ME1/1 chambers; this suite will also be applied to the other CSC chambers in the UXC when services are fully restored. A few ME1/1 chambers have been tested at SX5, and it is expected that two chambers will be reinstalled onto the endcap nose in August, well in advance of the reinstallation of the remainder on the positive endcap starting in October.

Image 5: The CSC facility at SX5 with ME1/1 chambers undergoing refurbishment and testing

In the CSC peripheral crates, the low-voltage “fretting” problem due to a tin-to-gold power connection is being fixed by replacement of the tin-plated backplane connectors. Tooling was created to accomplish this replacement in situ, and 12 of the 60 crates have already been repaired

During LS1, the Resistive Plate Chamber (RPC) collaboration is focusing its efforts on installation and commissioning of the fourth endcap station (RE4) and on the reparation and maintenance of the present system (1100 detectors).

The 600 bakelite gaps, needed to build 200 double-gap RE4 chambers are being produced in Korea. Chamber construction and testing sites are located at CERN, in Ghent University, and at BARC (India). At present, 42 chambers have been assembled, 32 chambers have been successfully tested with cosmic rays runs and 7 Super Modules, made by two chambers, have been built at CERN by a Bulgarian/Georgian/Italian team and are now ready to be installed in the positive endcap. The 36 Super Modules needed to complete the positive endcap will be ready in September and installation is scheduled for October 2013.

The Link-Board system for RE4 is under construction in Naples. Half of the system has been delivered at CERN in June. Six crates (Link-Board Boxes) and 75 boards, needed to instrument the positive endcap are now under test in building 904 at the RPC electronic laboratory. The full system will be delivered and tested at CERN by the end of July for thorough testing and subsequent installation at Point 5.

Concurrently, activities in Point 5 are ongoing for maintenance and repair of the present system, which will start in mid-August. Functionality tests of the RPC Detector Control System (DCS) after its migration to the new architecture have started.  In addition, critical annual tests on the power system, gas-leak rates, and bakelite resistivity measurements are being performed.

Integration of the services on the positive endcap started last winter. 36 double gas patch panels were installed on the YE+3 periphery in March. Gas piping between the gas distribution rack and the panels was completed in April. Cooling mini-manifolds were installed and tested for leaks in early May. RPC trigger fibres, high-voltage cables and flexible gas pipes will be installed by the end of August.  RE+4 Link-System will be equipped with link/control boards and cabled by early September. Similarly, installation of all RPC services for the negative endcap (RE–4) should take place in the last trimester of 2013.

Hardware related activities for the RPC upgrade go hand-in-hand with software development. LS1 is the ideal period to extend the existing tools to meet the need of the upgraded detector, to implement all of improvements and changes of the CMS software framework (CMSSW), and to perform ageing studies. The extension of the existing tools to RE4 concerns DQM, reconstruction, simulation, and geometry. Extension of Offline tools is complete and extensive Monte Carlo validation tests are ongoing. Implementation of CMSSW improvements and changes span across different topics, such as: migration to Git, improvements in the geometry description, centralisation of monitoring tools. Finally, a task force has been put together to study and mathematically model detector ageing.

The CMS detector has been gradually opened and whenever a wheel became exposed the first operation was the removal of the MABs, the sensor structures of the Hardware Barrel Alignment System. By the last days of June all 36 MABs have arrived at the Alignment Lab at the ISR where, as part of the Alignment Upgrade Project, they are refurbished with new Survey target holders. Their electronic checkout is on the way and finally they will be recalibrated. During LS1 the alignment system will be upgraded in order to allow more precise reconstruction of the MB4 chambers in Sector 10 and Sector 4. This requires new sensor components, so called MiniMABs (pictured below), that have already been assembled and calibrated.

Image 6: Calibrated MiniMABs are ready for installation

For the track-based alignment, the systematic uncertainties of the algorithm are under scrutiny: this study will enable the production of an improved Monte Carlo misalignment scenario and to update alignment position errors eventually, crucial for high-momentum muon analysis such as Z′ searches.

Trigger Strategy Group

The Strategy for Trigger Evolution And Monitoring (STEAM) group is responsible for the development of future High-Level Trigger menus, as well as of its DQM and validation, in collaboration and with the technical support of the PdmV group.

Taking into account the beam energy and luminosity expected in 2015, a rough estimate of the trigger rates indicates a factor four increase with respect to 2012 conditions. Assuming that a factor two can be tolerated thanks to the increase in offline storage and processing capabilities, a toy menu has been developed using the new OpenHLT workflow to estimate the transverse energy/momentum thresholds that would halve the current trigger rates.

The CPU time needed to run the HLT has been compared between data taken with 25 ns and 50 ns bunch spacing, for equivalent pile-up: no significant difference was observed on the global time per event distribution at the only available data point, corresponding to a pile-up of about 10 interactions.

Using the currently available 8 TeV Monte Carlo samples the HLT rates at have been compared with 8 TeV data, highlighting some discrepancies. A production of samples with a 300 ns out-of-time pile-up window, in both 25 ns and 50 ns bunch spacing configurations, has just been completed and will be used for further study of both HLT rates and CPU timing. A similar production at 13 TeV is in progress.

On the HLT validation side, STEAM is developing an event-by-event comparison workflow, based on the same simulated DIGI-RAW events, which improves the qualification of the CMSSW software releases. The group is currently collaborating with the PAGs to set up data skims of good events to be used in future validation cycles.

During LS1 the Software, Tools, Online Releases and Menus (STORM) group is following the activities of the DAQ, Computing and Offline sectors of CMS, in order to make sure that HLT menus and software can cope with the modifications in the underlying systems.

This is in addition to the usual activity of the group, which consists of providing the HLT menus for the different purposes. In the past months the two main achievements have been:

• the implementation of the so-called "half-rate menu", designed by STEAM, and its integration in the latest CMSSW release: this somewhat artificial menu can be considered the baseline for providing the actual HLT menu when the operation will be resumed in 2015;

• the "2011 legacy menu", currently being tested, for which the latest menu used in 2011 was ported and made compliant to the CMSSW 5.3.x legacy release, so that simulation samples can be produced with this menu.

At the same time the Field Operations Group (FOG) has been primarily concerned with studying the performance of the HLT menu on the online HLT farm. With the likelihood of 25ns running, increased energy and high pile-up conditions in Run 2, the activities have focused on studying the CPU and memory capacity of the most recently purchased machines used in 2012 data taking to estimate conditions in 2015 – while training new experts to replace those that left at the end of Run 1.

The group has also been involved in the planning of the proposed monitoring upgrade, and is closely monitoring the development of the DAQ upgrade to assess its impact on the future HLT operations.

L1 Trigger

Image 7: The cover of the CMS L1 Upgrade TDR

The major activity for the L1 Trigger group this year has been the preparation of the Technical Design Report of the Phase 1 upgrade, which in June was formally presented to the LHCC. An ambitious and extensive upgrade of the electronics for the muon, calorimeter, and global trigger systems is planned making use of state-of-the-art Xilinx FPGAs and high-speed optical data links on a telecommunications platform.

The impact on the physics capability of CMS for the period after LS1 has been studied for several benchmark physics channels and is significant, approaching a factor three improvement for Higgs-to-two-taus. An extended synopsis of the L1 Upgrade TDR can be found here.

The File-based Filter Farm in the CMS DAQ MarkII

The CMS DAQ system will be upgraded after LS1 in order to replace obsolete network equipment, use more homogeneous switching technologies, prepare the ground for future upgrade of the detector front-ends. The experiment parameters for the post-LS1 data taking remain similar to the ones of Run 1: a Level-1 aggregate rate of 100 kHz and an aggregate HLT output bandwidth of up to 2 GB/s. A moderate event-size increase is anticipated from increased pile-up and changes in the detector readout. For the output bandwidth, the figure of 2 GB/s is assumed.

The original Filter Farm design has been successfully operated in 2010–2013 and its efficiency and fault tolerance brought to an excellent level. There are, however, a number of disadvantages in that design at the interface between the DAQ data flow and the High-Level Trigger that warrant a careful scrutiny in view of the deployment of DAQ2, after the LS1:

1. The reduction of the number of RU builder output ports in the new DAQ2 design requires the splitting of the BU and FU functionality. The additional synchronous connections would essentially cancel the simplification resulting from fewer RU builder ports.

2. The concurrency of XDAQ and CMSSW tasks in the HLT calls for special releases of CMSSW that integrate the XDAQ framework. This requires synchronisation of common code (compilers, system libraries, tools).

3. The CMSSW runtime environment is not particularly adapted to the DAQ runtime strategy.

4. The synchronous operation of the HLT requires reconciling the DAQ and CMSSW state machine transitions and does not allow for sufficient time decoupling of the DAQ. There are large overheads in certain operations of CMSSW (e.g. at run start for condition loading).

Hardware

The main characteristic of the HLT hardware environment is its rapid evolution. The existing architecture allows to easily and seamlessly accommodate different generations of HLT nodes, and to rapidly deploy new hardware when machine conditions warrant. It is clearly desirable to maintain and increase this flexibility. In 2015, we will also need to integrate the legacy HLT nodes that are not yet at their end of life.

Software

The primary goal of the FBEvF design is decoupling the online and offline code base. There are three main interfaces to the HLT which require special treatment in the DAQ: the raw input interface to feed data from the detector; the control interface that manages the life cycle and state transition of the CMSSW executable; and the monitoring interface, providing at the same time fast feedback to the operator and persistent information like trigger counts which are stored in a database. The output interface, on the other hand, is easily replaceable with a file, at the price of a more complex management of a large number of files in the local storage area.

The most challenging task, from a performance point of view, is to feed input binary data from a single BU into several HLT nodes at a data rate of up to 4 GB/s and an event rate of up to 2 kHz.

The Raw Data format from the detector Front-End Drivers (FEDs) naturally lends itself to provide the building blocks for a simple low-level binary format of the input data. Each FED provides a variable-length, 64-bit aligned block of data consisting of a standardised header (64b) and trailer (64b), encapsulating the variable length payload (detector-dependent). The Common Data Format defines the header and trailer content and bit-field assignments. The trailer provides a word count and a checksum (CRC16). A raw CMS event consists of the concatenation of each and every FED block produced by the detector. The file can be structured as a concatenation of events prepended with a 64-bit aligned event header.

In the DAQ1, Run Control sequences the HLT through its internal CMSSW states via an XDAQ-based adaptor layer on top of the CMSSW state model. The different time scale and inherent variability of the HLT processing time, however, can cause undesirable lead times in completing state transition, sometimes interpreted as malfunctions. In the new file-based design, the execution flow is entirely data-driven and exclusively under the control of the CMSSW executable. The lifetime of the CMSSW processes is controlled by the input data and monitored by independent watchdog processes.

All the monitoring information is generated by either services in the flow of the HLT execution (for rates etc.) or the watchdog processes, looking at the parameter of the system itself (e.g. disk usage etc.).

In the FFF, the Online data-quality monitoring is served events and histograms via files on the local disk of the FUs. The aggregation of the DQM data will follow the same scheme as for the normal event data. The event and histogram data needed by online DQM are saved to dedicated storage, from where the online DQM system can access the files.

Design and implementation 

Figure 2: Principle architecture of the FFF system

The structure of the basic building block of the DAQ2 EvF system is dictated by the form factor chosen for the EVB network, and the CPU and networking requirements for the corresponding per-BU rate. For example, processing a 2 kHz event rate would require, for the typical HLT CPU usage observed during Run 1, roughly 200 cores. The most recent machines currently deployed in DAQ1 are dual 8-core motherboards arranged in a 4-fold 2U chassis, and a complete “BU appliance” would require a minimum of three chassis and the corresponding network interconnect. In order to avoid investing into retrofitting legacy machines with expensive 10 GbE interfaces, these will be connected using the existing 1 GbE and branched into the new 10/40 GbE switch using existing line cards.

A RAMdisk has been chosen as the baseline solution to store HLT input data, as it provides a simple and effective high-bandwidth buffer without the problems inherent to classic storage or SSD. At the scale of interest, it is also the cheapest solution fulfilling all requirements.

A complete appliance test has been carried out by the DAQ group using dummy events of fixed size built out of four fragments generated in four RU machines. The Builder Unit could write events of 1 MB size up to a rate of 5.9 kHz to files resident on a RAM disk of 256 GB. When the RAM disk was exported to the FU using NFSv4, 192 CMSSW processes running on legacy FU machines and connected over 2 GbE links could read concurrently at a rate up to 1.9 kHz, whereas 16 processes connected over 10 GbE could concurrently read at a rate up to 3.9 kHz. The CMSSW modules necessary for reading input and writing output event data in a format supporting concatenation exist and are being finalised. Monitoring uses a self-describing JSON format that is aggregated at the different levels using completely generic software. The CMSSW processes are controlled by a service daemon, which is entirely data-driven. In the coming weeks, the file-based HLT demonstrator will be completed with the hierarchical concatenation of output to provide a small-scale full-chain functional HLT system entirely based on files. The choice of the storage technology for the storage and transfer system, i.e. the Storage Manager replacement, will be discussed in a future article.

Since the LHC ceased operations in February, a lot has been going on at Point 5, and Run Coordination continues to monitor closely the advance of maintenance and upgrade activities.

In the last months, the Pixel detector was extracted and is now stored in the pixel lab in SX5; the beam pipe has been removed and ME1/1 removal has started. We regained access to the vactank and some work on the RBX of HB has started. Since mid-June, electricity and cooling are back in S1 and S2, allowing us to turn equipment back on, at least during the day. 24/7 shifts are not foreseen in the next weeks, and safety tours are mandatory to keep equipment on overnight, but re-commissioning activities are slowly being resumed.

Given the (slight) delays accumulated in LS1, it was decided to merge the two global runs initially foreseen into a single exercise during the week of 4 November 2013. The aim of the global run is to check that we can run (parts of) CMS after several months switched off, with the new VME PCs installed, the Tracker at low temperature, one DT wheel with completed sector collector relocation, some ME11 chambers installed, HCAL new hardware, and a new YE4 disk in place. Clearly, that first global run will be a major milestone for CMS in LS1, even if we do not aim for a cosmic data taking for alignment and calibration (that will take place in 2014).

Discussions are still ongoing with the LHC and all experiments to define the running conditions in 2015.  ATLAS and CMS requests are very similar, aiming at 25ns operations while maintaining the commissioning at 50 ns to the bare minimum. Changes foreseen in machine operations include injection at a β* of 7 m or 5 m, colliding beams during the squeeze process, and luminosity levelling using β*. A slow but relatively steady commissioning of 25 ns would be accepted even if it yielded less integrated luminosity than in 2012. Checkpoints should happen in 2015 to discuss any possible issues that may appear on the way to 25 ns.

Discussions are also taking place to improve CMS operations after LS1. This includes the consolidation of the monitoring infrastructure and the refurbishment of the control room. An informal brainstorming session on this last point took place recently amongst operations experts from all subsystems, TC, DAQ, Trigger etc.

Computing activity had ramped down after the completion of the reprocessing of the 2012 data and parked data, but is increasing with new simulation samples for analysis and upgrade studies. Much of the Computing effort is currently involved in activities to improve the computing system in preparation for 2015.

Operations Office

Since the beginning of 2013, the Computing Operations team successfully re-processed the 2012 data in record time, not only by using opportunistic resources like the San Diego Supercomputer Center which was accessible, to re-process the primary datasets HTMHT and MultiJet in Run2012D much earlier than planned. The Heavy-Ion data-taking period was successfully concluded in February collecting almost 500 T.

Figure 3: Number of events per month (data)

In LS1, our emphasis is to increase efficiency and flexibility of the infrastructure and operation. Computing Operations is working on separating disk and tape at the Tier-1 sites and the full implementation of the xrootd federation to enable processing, production and also analysis more independent of the location of the input samples. The global GlideIn WMS pool will contribute to the efficiency increase as well and allow for more fine-grained prioritisations of jobs, from which also analysis jobs will benefit.

Figure 4: Number of events per month (Monte Carlo)

Figure 4: Number of events per month (Monte Carlo)

For the MC production, the bulk of 8 TeV MC samples have been completed and ramped up again in May with the upgrade samples and additional 7 and 8 TeV requests.

Many members of the Computing Operations team moved on to newer endeavors. Christoph Wissing joined the Computing Operations coordination team and, after four years leading Computing Operations, Markus Klute was succeeded by Christoph Paus.

Physics Support

As part of CMS-wide effort to bring new CMS users up to speed in doing physics analyses, Physics Support recently held two CMS Data Analysis Schools, one at the LPC in Fermilab (8–12 January) and other at the DESY (14–18 January). Over 200 participants took part in the hands-on physics analysis sessions. In addition, there is an upcoming PAT tutorial at CERN (15–19 July) limited to 25 registrants.

Besides smooth and stable running of analysis jobs across Tier-2 centres, during the past year there has been a steady increase in the number of job slots used for CMS analyses, reaching a level of ~26,000 concurrently running analysis jobs on average.

Figure 5: Analysis job slots used per week at T2 sites

Computing Integration

Following a common effort together with ATLAS to incorporate common tools in the distributed computing system, the Computing Integration group is participating in the commissioning and deployment of CRAB3, a new workflow management system for analysis jobs. CRAB3 incorporates new features like asynchronous stage-out of user data, automatic publication in DBS, better monitoring etc. The current CRAB3 prototype is based on the PanDA workflow management system used by ATLAS for production and analysis. A complete PanDA infrastructure is being setup at CERN for CMS by the Integration group in collaboration with CMS analysis operations and ATLAS and CMS developers.

CMS is committed to moving forward in incorporating multicore processing and scheduling into its computing system. The CMSSW framework is incorporating support for multithreaded data processing. The planned strategy is to schedule in the distributed computing infrastructure multicore pilots, which will manage the allocated cores. Multicore pilots can schedule single and multicore applications simultaneously on the same slot. The Computing integration group is performing tests to commission the multicore scheduling infrastructure.

CMS began to incorporate opportunistic resources into its computing system. At the moment we are still working on a seamless integration into the CMS production submission infrastructure (GlideIn WMS), but we already managed to run at limited scale and are in the process of scaling up.

Computing Resource Management Office

The RMO is active in finding and recruiting MnO-A manpower for the coming two years.

The Offline group is now finishing the first production release of 2013, CMSSW_6_2_0. It will contain the latest release of Geant4 as planned. We will use it to start the generation and simulation of 13 TeV datasets for a first round of evaluation of technical and physics performance of the software under the data-taking conditions of 2015. We have also participated in preparing the CMSSW_5_3_X series release to run on 2011 data, and regenerate matching Monte Carlo samples, after the decision this June to create legacy datasets for 2011 that matched 2012.

The Framework group continues its development of a multi-threaded framework. However the big news in this area is the large amount of work that has gone into transitioning the CMSSW source code repository from CVS to Git, and the decision to use a free and robust commercial service for hosting it, github. We recommend people using the UserCode repository also migrate their code there and we provide tools and assistance to do so.

The Fast Simulation team has nearly finished all of the new pile-up Mixing code, including all of the ingredients to use minbias events made with Full Simulation. The hadronic response model has been retuned to take into account the relative times of the energy depositions.  Modelling out-of-time pile-up in FastSim is now possible in the 6_2_X series. Other ongoing work is related to the Phase 2 Upgrades. The simulation of the future forward calorimeters is underway, the ageing models for ECAL and HCAL have now been integrated, and the generalisation of the Tracker geometry description is nearly complete. Future work will concentrate on upgrade integration.

For the Full Simulation, recent work has continued the focus on improving the performance of our implementation of the Geant4 simulation step.  Several rounds of testing of the “Russian Roulette” sampling technique have converged on a default parameter set that will be tried in future Monte Carlo productions for the 13 TeV running.  Several technical improvements in the performance of the digitisation algorithms at very high pile-up have been implemented. As in the Fast Simulation, detailed ageing models for ECAL and HCAL have been implemented in the Geant4 modelling of the detectors.  Ongoing work also includes the development of Geant validation suites and the development of “PreMixing” for modelling of multiple interactions. For this technique, the minbias events that we use to model pile-up are combined into a single “overlay event” before the Monte Carlo production jobs are run. Then, a single overlay event is used for each Monte Carlo hard-scatter event, instead of almost 1000 individual minbias events. This will dramatically simplify large scale MC production.

Major additions were made in the reconstruction algorithms aiming towards completion later in the year:

1. MVA discriminants are now saved for tracks, which can be used for an improved “high purity” selection;

2. the particle-flow-based ECAL clustering has improved both on the CPU performance side and on the physics algorithm side, now using moustache shapes;

3. the electron/photon reconstruction, aiming to give a consistent Global Event Description (GED), using, in particular, the clustering mentioned above, now has the unified eγ candidates and their photon and electron “projections” stored in data for further studies, nearing their use for physics.

Several developments in other areas were completed, including updates in b-taggers, cleanup of older jet collections and addition of collections with substructure information.  Full details will be available in the release notes once the release is made available. Many changes are still ahead of us: some are technical, required to be able to run in multi-threaded environment; some are aiming to improve physics performance.

The Analysis Tools software is very stable and routinely used in physics analyses throughout the collaboration. Latest developments include the final implementation the “unscheduled” processing mode for multi-threaded production with CMSSW. Also the Statistics Tools software is in a mature state, and tutorials are regularly offered in the context of the CMSDAS.

The software for the upgrade projects has been organised in a series of releases in two-week intervals. These releases have been based on the CMSSW_6_1_2 release, which is the most recent fully validated CMSSW release. The upgrade software itself is evolving on a more rapid timescale and has been facilitated by regular releases that move rapidly from new feature integration to production deployment. The Phase 1 Tracker and HCAL upgrades and potential Phase 2 Tracker geometries are currently included in these releases.

Significant progress towards high-pileup reconstruction has been made and large event samples are available with an average of 140 pile-up events per bunch crossing. Current samples include the Phase 1 Pixel detector upgrade and models of degradation due to detector ageing corresponding to integrated luminosities from 300 fb^–1 up to 3000 fb^–1. A new round of samples will soon be generated including the Phase 1 HCAL detector upgrade and an improved ageing model for the HE sub-detector starting from the CMSSW_6_1_2_SLHC5 release.

We anticipate that the upgrade software will soon migrate to the CMSSW_6_2_0 release cycle once it has been validated. This release includes important changes to low-level tracker code and to the fast simulation that could not be easily included in the current CMSSW_6_1_2 based SLHC releases. In addition, the software to simulate and reconstruct the post LS1 shutdown CMS detector is fully integrated into the CMSSW_6_2_0 release cycle and no special release will be needed for its use.

The first part of the Long Shutdown period has been dedicated to the preparation of the samples for the analysis targeting the summer conferences. In particular, the 8 TeV data acquired in 2012, including most of the “parked datasets”, have been reconstructed profiting from improved alignment and calibration conditions for all the sub-detectors.

A careful planning of the resources was essential in order to deliver the datasets well in time to the analysts, and to schedule the update of all the conditions and calibrations needed at the analysis level.

The newly reprocessed data have undergone detailed scrutiny by the Dataset Certification team allowing to recover some of the data for analysis usage and further improving the certification efficiency, which is now at 91% of the recorded luminosity.

With the aim of delivering a consistent dataset for 2011 and 2012, both in terms of conditions and release (53X), the PPD team is now working to set up a data re-reconstruction and a new MC production also for the 7 TeV dataset. This will serve as legacy for all future analysis of the first LHC run.

Looking even further on the timeline, PPD is contributing to the preparation of post-LS1 data taking and supports all the various productions needed to define the upgrade strategy of the experiment. In this context, the Global Event Description team is following up the work of the POGs to prepare the reconstruction and identification algorithms to the future challenges represented by the LHC running conditions. A workshop focusing on these aspects, both in terms of development and validation, is being organised with all the relevant experts on 23 and 24 July at FNAL.

The PPD core team is also profiting from the shutdown period to develop and consolidate activity on all the central tools for conditions and monitoring. This will allow us to capitalise on the experience acquired in view of the restart of the data taking in 2015.

Alignment and Calibration and Database (AlCaDB)

Since the stop of data taking in early 2013, work in the AlCaDB project moved to a consolidation phase. On the AlCa side, the efforts mainly concentrated on providing and validating new Global Tags as needed for upgrade studies and re-processing campaigns. Improvements on the Global Tag Collector tool to manage these have started and are ongoing. On the Database side, the major redesign of the core conditions software has started and is progressing well.

Data Quality Monitoring (DQM)/Data Certification

The team has completed the certification of 2012 data, which is reprocessed with improved alignment and calibration conditions. The official JSON files have been released in May, and they correspond to a total integrated luminosity of 19.79 fb^–1 in the “golden” scenario, where the data are certified as usable for analysis by all the detectors and POGs. This total includes ~170 pb^–1 of data that was initially unusable for physics analysis due to issues with the Preshower (ES) and Hadron Calorimeter (HCAL) detectors, but was recovered after the reprocessing. The final luminosity-weighted certification efficiency with respect to the recorded luminosity is 91% for 2012 pp data.

As the data certification is completed, we have shifted focus towards increased performance and automation of the DQM system for 2015 data taking. A number of improvements are planned, such as multi-core and multi-thread approaches to data reconstruction and monitoring, multi-run DQM, a new file-based online DQM approach, and a significantly updated data-certification procedure to be tested during the 2013 Global Run.

Physics Data Monte-Carlo Validation (PdmV)

For the first time in CMS, a campaign of era-dependent simulation has been validated and put in production for the 8 TeV MC targeted at Higgs analysis, to reproduce as closely as possible the data-taking conditions during 2012. A first and partial reprocessing of the data collected in 2011 at 7 TeV with the 53X legacy release has been initiated after validation of the updates to the alignment and calibration conditions. The validation for the reprocessing of a corresponding subset of the 7 TeV MC is underway. Both for data and MC, the ultimate legacy dataset will be produced in the summer when the final alignment and calibration conditions and HLT simulation will be available. 

The validation of the upgrade software and conditions has been successfully performed using the standard validation procedures. The validation follows the bi-weekly release schedule of the upgrade project. The validation of the software for the Phase 1 upgrade will be extended to the validation of the simulation of the detector after various ageing and beam conditions. Validation and production of MC samples has been performed under high pressure and tight schedule for the June Upgrade Week with fruitful results.

The McM project, initiated by the generator group and PdmV as PREP2 during 2012, is in a functioning version for a replacement of the MC production management and book-keeping system (PREP). Series of tutorials have been provided and commissioning with pilot campaigns has been made. McM will be put into production as soon as possible.

In the period since the last CMS Bulletin, the LHC – and CMS – have entered LS1. During this time, CMS Physics Analysis Groups have performed more than 40 new analyses, many of which are based on the complete 8 TeV dataset delivered by the LHC in 2012 (and in some cases on the full Run 1 dataset). These results were shown at, and well received by, several high-profile conferences in the spring of 2013, including the inaugural meeting of the Large Hadron Collider    Physics Conference (LHCP) in Barcelona, and the 26^th International Symposium on Lepton Photon Interactions at High Energies (LP) in San Francisco. In parallel, there have been significant developments in preparations for Run 2 of the LHC and on “future physics” studies for both Phase 1 and Phase 2 upgrades of the CMS detector.

The Higgs analysis group produced five new results for LHCP including a new H-to-bb search in VBF production (HIG-13-011), ttH with H to γγ (HIG-13-015), and two new searches for high-mass Higgses (HIG-13-008/014). They also updated the last of the so-called HPAs (High-Priority Analyses), HIG-13-012 (associated production, VH with H to bb) to the full dataset, wherein a 2.1σ excess over background expectations is now observed as shown in Figure 6.  While these and earlier Higgs measurements continue to strengthen the SM Higgs hypothesis, they are not able to exclude BSM physics, for which direct searches continue at CMS in the SUS, EXO and B2G PAGs.

In the time since the last Bulletin, the SUS PAG carried out several new analyses with the full 8 TeV dataset that further constrain “natural” SUSY scenarios, which require relatively light gluinos and third generation squarks. For example, in the search for top squark (stop) pair production (SUS-13-011), stop masses up to 650 GeV are excluded at 95% CL. On the other hand, one manner in which Nature could be supersymmetric and yet evade these searches is if R-parity is not conserved.  The SUS PAG has recently made significant progress in closing this loop-hole with new dedicated searches (SUS-12-027, SUS-13-003) for scenarios that assume one non-zero R-parity-violating coupling at a time and set stringent limits on these models, as can be seen in Figure 7, where supersymmetric particle masses of up to nearly 2 TeV are excluded at 95% CL. 

Figure 6: 2.1σ excess observed in VH with H-to-bb analysis

In other searches for new physics that have unfortunately also yielded null results, EXO PAG has performed an analysis looking for heavy resonances decaying to bottom-quark final states (EXO-12-023), an analysis looking for evidence of jet “extinction” (EXO-12-051), and an update of the LQ2 analysis to the full dataset. Meanwhile, the B2G group produced two new results with the full 8 TeV dataset for LP:  B2G-12-015 that is an inclusive search for top-partners (as might occur in Little Higgs models, for example), and B2G-12-023, a search for baryon-number-violating top quark decays.

In precision physics, the TOP group has confronted NLO QCD calculations with a measurement of the jet multiplicity in di-leptonic top events (TOP-12-041) as well as performing a search for flavour-changing neutral currents in top quark decays (TOP-12-037), both with the 8 TeV dataset. The SMP group has performed the first inclusive differential jet cross-section measurement at 8 TeV (SMP-12-012), a study of final-state radiation via the ratio between inclusive jet cross-sections with different anti-k_T radius parameters (SMP-13-002), and the first measurement of colour coherence effects at the LHC (SMP-12-010). The BPH group has made measurements of the differential Υ (Upsilon) cross-section (BPH-12-006) and prompt J/ψ and ψ(2S) polarisation (BPH-13-003). The forward physics PAG (FSQ) has produced a number of results for DIS 2013 in Marseilles and LP (FSQ-12-005/002/022/028) including the first result using CMS data triggered by TOTEM, a measurement of charged-particle pseudorapidity and transverse-momentum distributions (FSQ-12-026).

Figure 7: 95% CL mass exclusions for various RPV scenarios

In heavy-ion physics, HIN has performed several analyses on the data from the proton-lead run, a study of di-jets (HIN-13-001), a study of the inclusive production of charged hadrons (HIN-12-016), and a paper with detailed studies of the “ridge” in pPb collisions (HIN-13-002).

Finally, the future physics groups (FTR) have been busy preparing physics projections for both the Phase 1 and Phase 2 upgrades of the CMS detector.  For Phase 1, the L1 Upgrade TDR (CERN-LHCC-2013) has received the endorsement of the LHCC. For Phase 2, using scaled 8 TeV results, parametric and “full” simulations of the CMS detector under several different upgrade scenarios, 14 TeV, 3000 fb^–1 analyses are being performed spanning Higgs, BSM, and SM physics. The earliest of these will go in a whitepaper submitted to Snowmass in late July, with the remainder targeted for the ECFA workshop in October.

There is very good progress in the execution of the LS1 projects and in launching construction of the Phase 1 upgrades. We focus here on two main achievements since the last CMS Week.

The approval of the third Phase 1 TDR

The preparation of the L1 Trigger Upgrade Technical Design Report has been a major effort of the collaboration at the beginning of this year, especially to develop supporting Trigger menu and physics performance studies. These studies have demonstrated the efficiency of the upgraded system to ensure low lepton and jet trigger thresholds, leading to a significant increase of the acceptance for the Higgs measurements, in the associated production mode and in the ττ decays, as well as for the stop searches involving multiple jets in the final state. The TDR was submitted to the LHCC in May and approved at the June committee meeting. It is now a public document, completing the series of the three TDRs describing the Phase 1 upgrades, with the new Pixel system and the HCAL read-out replacement.

The Upgrade Week in DESY and the Phase 2 upgrades

The work on developing the conceptual design for the CMS Phase 2 detector was the main focus of the June upgrade week held at DESY. The meeting was an agreeable and successful week of intense work – many thanks to our DESY and Hamburg University hosts.

The discussions converged on a primary scenario with options for the upgrade, and on the paths towards the shorter- and longer-term deadlines of the project.

The studies of radiation damage and simulation of performance degradation were presented, and clearly demonstrate that new Tracker, and the ECAL and HCAL endcaps (EE and HE respectively) will be needed for the HL-LHC programme. Most likely, all these systems will need replacement after a recorded luminosity of 300 to 500 fb^–1. The ongoing studies will allow further mapping of the operational and performance margins.

The performance of two Tracker configurations, Long Barrel and Barrel Endcap, were compared. A baseline configuration with six outer barrel layers and five forward disks was adopted. A major focus of the project will now be to demonstrate the feasibility of hardware track reconstruction using Associative Memories, and to assess the latency required for implementation in the L1 Trigger.

Two main approaches emerged for the upgrade of the forward calorimetry: replacement of the EE and refurbishment of the HE sensitive material without changing the absorber; or full replacement of both EE and HE, presenting an opportunity for integrated forward calorimetry. An EE shashlik calorimeter and new scintillating or quartz tiles for the HE are considered in the former case, while a dual read-out or imaging calorimetry are investigated in the latter one. Although EB and HE will survive Phase 2 radiation doses, it is proposed to operate the EB at 8–10 ºC to mitigate the increase of noise in the APDs.

The muon system upgrade will include installation of new chambers in the forward region (1.5 < η < 2.4) to improve the L1 Trigger capability. The GEM1/1 project to equip the first station during LS2 is a first step of the project. For farther stations, both GEM and GRPC technologies will be investigated. Due to radiation-induced failures, it is also proposed to replace the DT front-end electronics (minicrates).

To maintain and possibly enhance the L1 Trigger acceptance, it was shown that using Tracker-tracks at this stage will provide significant rate reduction factors. However, to maintain low thresholds for all major triggers, an increase of the overall L1 Trigger rate will be required to allow proper allocation of bandwidth in the Trigger menu. The replacement of the EB front-end electronics (FE), together with the other upgrades foreseen, will allow reaching a 1 MHz rate with an increased latency of 10 µs (increasing the latency beyond this value would require replacement of the CSC FE).

In addition to the main upgrades considered above, pile-up mitigation in the forward region may require specific attention. A preliminary study indicates that an extension of the Pixel system up to η = 4 would almost fully eliminate the large rate of jet-tagging-faking VBF processes due to the high pile-up. R&D on precise timing detectors and their ability to allow discriminating vertex origins are also investigated. Replacing the HE absorber could also allow extended coverage of calorimetry and muon systems up to η = 4 to tag forward tracks associated with a muon. A more complete muon measurement implementing forward toroids in place of the HF could be envisaged if strongly motivated.

The emergence of the upgrade scenario and options will now allow Technical Coordination to establish the subsequent technical constraints at Point 5, simulate the background and radiation generated in the HL-LHC beam conditions and evaluate the scope of work and need for the LS duration. The Tracker and EB FE replacement will be concurrent and will require a shutdown of 26 months. There is also good indication that HE and HF could be removed from the UXC, allowing replacement of the HE absorber. The sequence of work to handle the replacement of Tracker/EB FE, the Forward Calorimeter, the DT minicrate and the YB0 services is being thoroughly investigated. The simulation of the background and radiation conditions will be essential to decide on the extension of the subsystems’ η coverage.

Detector and Physics performance studies are underway to identify main requirements to achieve the HL-LHC physics programme. Benchmark studies for the Snowmass white paper and the ECFA workshop in October are identified. They will use various simulation tools, available or developing. DELPHES will be used for simple implementation of new detector geometries and parameterisation of the measurement performance. This will allow evaluating the benefit of various upgrade options on the timescale of the ECFA workshop. The DELPHES studies will be complemented with fast and full simulations with realistic but less complete detector upgrade descriptions and for a limited set of signals. This will serve as validation of the simplified studies and also to provide performance reach for key physics signals representative of the detector requirements, namely HH→bbγγ and VBF H→ττ. Many new results are expected for discussion during the CMS Week at Taipei.

In parallel, upgrade projects, working group and cross-coordination areas will proceed with cost estimates in preparation of the October 2103 RRB session.  The longer-term goal is to prepare a Technical Proposal for submission to the LHCC in September 2014.

Fire Safety – Essential for a particle detector

The CMS detector is a marvel of high technology, one of the most precise particle measurement devices we have built until now. Of course it has to be protected from external and internal incidents like the ones that can occur from fires. Due to the fire load, the permanent availability of oxygen and the presence of various ignition sources mostly based on electricity this has to be addressed.

Starting from the beam pipe towards the magnet coil, the detector is protected by flooding it with pure gaseous nitrogen during operation. The outer shell of CMS, namely the yoke and the muon chambers are then covered by an emergency inertion system also based on nitrogen. To ensure maximum fire safety, all materials used comply with the CERN regulations IS 23 and IS 41 with only a few exceptions. Every piece of the 30-tonne polyethylene shielding is high-density material, borated, boxed within steel and coated with intumescent (a paint that creates a thick cover if thermally exposed). The same level of detail was considered while analysing all other materials chosen.

Both sides of the detector galleries support additional installations (mostly racks and cryogenic equipment etc.). Most of them are covered by small carbon-dioxide extinguishing systems automatically triggered by melt cables and smoke detectors. Of course, manual intervention is also possible.

Below the detector, a region called “X0” takes up most of the cables leading towards the underground service cavern. Due to the density of the cable trays and their load, a medium-pressure water-mist extinguishing system was installed in situ. In case of activation it will limit the extent of a propagating fire and due to its nature the water will bind and condense smoke and its ingredients like soot, aerosols etc.

In addition an active fire detection system is installed everywhere inside the cavern. Here, the term “active” describes a system that is constantly extracting air from a volume and analysing it with two redundant units. Only if both are triggered a confirmed fire detection is then forwarded to the fire brigade by the detector safety system. Such systems are far more sensitive than the standard smoke detectors.

Last but not the least, a high-expansion foam system could be manually triggered to flood the whole volume of the experimental cavern up to one meter above the detector. This powerful last means of defence is currently undergoing a revision during LS1 to ensure its readiness and operation.

Even if the technical fire safety is state of the art, all users should never stop looking out for unusual incidents. A machine could not replace a vigilant human.