Abstract
The performance of the Compact Muon Solenoid detector for measuring missing transverse energy is evaluated using fully simulated pp collisions at a center-of-mass energy of 14 TeV at the Large Hadron Collider. For minimum bias events without pileup, a resolution of 6.1 GeV is computed, corresponding to a stochastic contribution of $0.63\sqrt{\Sigma{}E_{\text{T}}} \mathrm{GeV^{1/2}}$ , where ΣET is the summed transverse energy in all calorimeter towers. When the contribution of pileup is included, the resolution degrades according to the overall deposited ΣET with the same stochastic coefficient. For QCD dijet events with event pileup corresponding to a luminosity $\mathcal{L}=2\times10^{33}\mathrm{cm^{-2}s^{-1}}$ , we compute $\sigma=[({3.8} \mathrm{GeV})^2+({0.97} \mathrm{GeV^{1/2}}\sqrt{\Sigma{}E_{\text{T}}})^2+(0.012\Sigma{}E_{\text{T}})^2]^{1/2}$ resulting in a resolution of 45 GeV for jet events with reconstructed transverse momentum of 800 GeV/c. Monte Carlo samples of tt and W+jet events with high-momentum (pT>20 GeV/c) lepton decays leading to true missing transverse energy were used to determine the azimuthal angle resolution to be 0.1 radians (0.2 radians) for a reconstructed missing transverse energy of 200 GeV (100 GeV).
Highlights
The understanding of detector response to standard model physics from quantum chromodynamics (QCD) is a prerequisite to the search for new phenomena at the Large Hadron Collider (LHC) [1]
Energetic particles produced in the direction of the beam pipe make it impossible to directly measure missing energy longitudinal to the beam direction, the transverse energy balance can be measured with an accuracy good enough to help establish a physics signature involving one or more non-interacting particles
No significant difference is observed in the ETmiss resolution for the QCD samples between two different muon algorithms used in ORCA [23]
Summary
The understanding of detector response to standard model physics from quantum chromodynamics (QCD) is a prerequisite to the search for new phenomena at the Large Hadron Collider (LHC) [1]. Measurement of the missing transverse energy vector (EmTiss) in events at the LHC will be complicated by the presence of pileup collisions. Accurate measurement of the missing transverse energy in individual events is a difficult experimental problem, because various detector factors are known to contribute in subtle ways. These factors include energy resolution, limited detector coverage, nonlinearity of calorimeter response, detector granularity, non-instrumented material, magnetic field and its effect on low pT charged particles, quantization of detector readout, electronic noise, event pileup, and underlying event. A more advanced understanding of ETmiss in the CMS detector has required the large event samples available from the recent data challenge [16]. No significant difference is observed in the ETmiss resolution for the QCD samples between two different muon algorithms used in ORCA [23]
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