Abstract
A template fitting technique for reconstructing the amplitude of signals produced by the lead tungstate crystals of the CMS electromagnetic calorimeter is described. This novel approach is designed to suppress the contribution to the signal of the increased number of out-of-time interactions per beam crossing following the reduction of the accelerator bunch spacing from 50 to 25 ns at the start of Run 2 of the LHC. Execution of the algorithm is sufficiently fast for it to be employed in the CMS high-level trigger. It is also used in the offline event reconstruction. Results obtained from simulations and from Run 2 collision data (2015–2018) demonstrate a substantial improvement in the energy resolution of the calorimeter over a range of energies extending from a few GeV to several tens of GeV.
Highlights
The shaped signals are sampled at the LHC bunch-crossing frequency of 40 MHz and digitized by a system of three channels of floating-point Analog-to-Digital Converters (ADCs)
Another effect that has been checked in data is the rejection power for anomalous signals ascribed to direct energy deposition in the avalanche photodiodes (APDs) [18] by traversing particles
A multifit algorithm that uses a template fitting technique to reconstruct the energy of single hits in the CMS electromagnetic calorimeter has been presented
Summary
The results shown in this paper are based on subsets of the data samples recorded by the CMS experiment in proton-proton (pp) collisions at a center-of-mass energy of 13 TeV. One is the full detector simulation used for physics analyses, implemented with G 4 [6], of single photons within the CMS detector with a uniform distribution in η and a flat transverse momentum pT spectrum extending from 1 to 100 GeV. 8.226 [7] package and its CUETP8M1 [8] tune for parton showering, hadronization, and underlying event simulation These events are used to study the performance of the algorithm when the showering of an electromagnetic particle spreads across more than a single crystal, which is typical of most energy deposits in the ECAL. Additional pp interactions in the same or adjacent BXs are added to each simulated event sample, with an average number of 40
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