ELECTROMAGNETIC CALORIMETER (ECAL)

All components of ECAL – EB, EE and ES – operated well throughout 2010 with few problems, and negligible evolution of dead channels. About 2% of the ES silicon sensors were unplugged in the second part of the year due to unacceptable increases in leakage currents attributed to radiation damage of the surfaces.

The LHC winter technical stop allowed many improvements to the ECAL infrastructure at Point 5. For example, the High Voltage distribution systems for the EE and ES were both improved, with further modifications planned for the ES later in the year. Monitoring and alarming of power supplies was also improved, increasing the level of safety. Some cables in the USC and UXC were re-worked, recovering the operation of some environmental monitoring sensors and improving robustness overall.

A thorough Readiness Review Workshop was organised at the end of January 2011 to review 2010 data quality and online and offline operations, and to prepare for the higher luminosities in 2011. All presentations, as well as detailed minutes and outcomes, can be found at: https://indico.cern.ch/conferenceDisplay.py?confId=120490.

The stability of the complete system allowed ECAL shifts to become obsolete, with central shifters providing the necessary day-to-day monitoring, supported by a team of ECAL experts on call. This will be the modus operandi in 2011.

Small transparency changes in the crystals observed in 2010 are consistent with expectations due to radiation damage. The laser and LED monitoring systems follow this evolution excellently and a fast feedback from these systems will be incorporated into the single channel response calibration during 2011 data-taking. Data taken with a special HLT π0 trigger stream, used to calculate inter-calibration constants, provide a cross check of the transparency corrections.

There have been a few changes to firmware of the Data and Trigger Concentrator Cards (DCC and TCC) to protect against minor instabilities in data collection, to improve reliability and performance and to adapt to the expected increase in luminosity and occupancy in the 2011 run. For example, masking of individual problematic crystals, rather than whole trigger towers, has increased the number of working trigger channels to around 98.7% in the endcaps (up from 98% in late 2010). In order to mitigate the impact at the L1 trigger of Anomalous Calorimeter Signals (ACS) due to highly ionising particles in the Avalanche Photo-Diodes (APDs), the trigger front-end readout was modified to tag energy deposits with ACS-like topologies at L1 and was tested in late 2010. This is being further optimised with first 2011 collision data, before being incorporated in the standard running.

Prompt feedback from early 2011 collisions has confirmed the ECAL health status and performance.