Abstract

Many physics analyses using the Compact Muon Solenoid (CMS) detector at the LHC require accurate, high-resolution electron and photon energy measurements. Following the excellent performance achieved during LHC Run I at center-of-mass energies of 7 and 8 TeV, the CMS electromagnetic calorimeter (ECAL) is operating at the LHC with proton-proton collisions at 13 TeV center-of-mass energy. The instantaneous luminosity delivered by the LHC during Run II has achieved unprecedented levels. The average number of concurrent proton-proton collisions per bunch-crossing (pileup) has reached up to 40 interactions in 2016 and may increase further in 2017. These high pileup levels necessitate a retuning of the ECAL readout and trigger thresholds and reconstruction algorithms. In addition, the energy response of the detector must be precisely calibrated and monitored. We present new reconstruction algorithms and calibration strategies that were implemented to maintain the excellent performance of the CMS ECAL throughout Run II. We will show performance results from the 2015-2016 data taking periods and provide an outlook on the expected Run II performance in the years to come. Beyond the LHC, challenging running conditions for CMS are expected after the High-Luminosity upgrade of the LHC (HL-LHC) . We review the design and R&D studies for the CMS ECAL and present first test beam studies. Particular challenges at HL-LHC are the harsh radiation environment, the increasing data rates, and the extreme level of pile-up events, with up to 200 simultaneous proton-proton collisions. We present test beam results of hadron irradiated PbWO crystals up to fluences expected at the HL-LHC . We also report on the R&D for the new readout and trigger electronics, which must be upgraded due to the increased trigger and latency requirements at the HL-LHC.

Highlights

  • electromagnetic calorimeter (ECAL) barrelThe raw energy of a supercluster calculated from the sum of individual hits, is further corrected for the material budget in front of the ECAL, as well as partial shower containment due to gaps and cracks between crystals

  • Many physics analyses using the Compact Muon Solenoid (CMS) detector at the LHC require accurate, high-resolution electron and photon energy measurements

  • Following the excellent performance achieved during LHC Run I at center-of-mass energies of 7 and 8 TeV, the CMS electromagnetic calorimeter (ECAL) is operating at the LHC with proton-proton collisions at 13 TeV center-of-mass energy

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Summary

ECAL barrel

The raw energy of a supercluster calculated from the sum of individual hits, is further corrected for the material budget in front of the ECAL, as well as partial shower containment due to gaps and cracks between crystals. Such supercluster energy corrections, denoted by Fe,γ, are derived by a multivariate technique trained with simulated events in which the true energy is known, and is validated with Z → ee events in collision data. The best energy resolution achieved with 2.5 fb−1 data taken in 2015 is between 1% and 2% in the central region of the detector, which is at the level of Run 1, while in the endcaps the resolution is worse due to limited amount of data

Prospects for high-luminosity LHC
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