ELECTROMAGNETIC CALORIMETER (ECAL)

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