CMS Bulletin

TRIGGER

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.