Physics of the standard model with the CMS experiment at the LHC
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ysics of the Standard Model with the CMS Experiment at the LHC S. V. Shmatov Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Dubna State University, Dubna, Moscow oblast, 141980 Russia e-mail: [email protected] Abstract⎯The studies of Standard Model processes with the CMS experiment at the Large Hadron Collider are reviewed. Keywords: Standard Model, QCD, electroweak interactions, top quark, rare decays, LHC DOI: 10.1134/S1063779617050355
By studing the processes predicted by the Standard Model (SM) at the Large Hadron Collider (LHC), one performs important tests of this theory of particle interactions in a new energy region. Therefore, one of the primary goals of the LHC experiments consists in confirming (or “rediscovering”) the Standard Model at high collision energies by thoroughly studing all known particles and their interactions, measuring the cross sections and mass values, etc. Apart from that, at the start of each stage of the LHC operation one had to verify that all detector systems and the selection, reconstruction and event analysis algorithms operate properly and create no physical artifacts. This paper reviews the measurements of Standard Model processes in proton–proton collisions performed with the CMS (Compact Muon Solenoid) experiment at the LHC during the first and second LHC runs at s = 7, 8 TeV (Run 1) and s = 13 TeV (Run 2), respectively. The studies of multiple production of charged hadrons at collision energies of s = 0.9, 2.36, and 7 TeV started immediately after the LHC commissioning in 2009. The measured multiplicity distributions and the energy dependence of the multiplicity pseudorapidity density, dN ch d η, showed significant deviations from theoretical predictions [1]. Therefore, the parameters of Monte-Carlo generators had to be tuned prior to further interpreting the LHC data. Upon this tuning, the predictions well enough reproduced the results of subsequent Run-1 and Run-2 measurements [2] (see the left panel of Fig. 1). The first measurements of inclusive jet production at s = 7 showed good agreement with the the next-leading order (NLO) SM predictions for the jet
transverse momenta up to 2.0 TeV/c and rapidities y ≤ 2.5. Subsequently, the agreement with predictions was confirmed by similar measurements at s = 8 TeV for pT values up to 2.5 TeV/c in six intervals of the rapidity region of y ≤ 3.0, as well as in the initial Run-2 measurements [3] (see the right panel of Fig. 1). The jet pair production was studied by measuring the differential cross section d σ dM jj for invariant masses up to 6.1 TeV/c2[4] (see the left panel of Fig. 2), the jet angular distributions, and their azimuthal decorrelations [5]. Thereby, no deviations from appropriate theoretical predictions were revealed, but restrictions on the parameters of some beyond-SM scenarios were imposed. Through a combined analysis of the inclusive production of jets, pair production of top quarks, and the cross sections for production of two and three jets, the value of the QCD running coupling const
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