Studies of ttˉ\rm t\bar{t}+X at CMS

This talk is dedicated to the most recent measurements of the processes that feature the production of a top quark pair either with an electroweak standard model boson, or another pair of top, bottom or light quarks. For the measurement of the production cross-section of top quark pair in association with a photon, 19.7 $\rm fb^{-1}$ of proton-proton collision data collected by CMS detector at $\sqrt{s}$ = 8 TeV is used, while for four top production, $\rm t\bar{t}$ + bb, $\rm t\bar{t}$ + jj, $\rm t\bar{t}$W and $\rm t\bar{t}$Z the data collected at $\sqrt{s}$ = 13 TeV amounting to 35.9 $\rm fb^{-1}$, is used. The measurement of $\rm t\bar{t}\gamma$ is performed in the fiducial phase space corresponding to the semileptonic decay chain of the top quark pair, and the cross section is measured relative to the inclusive top quark pair production cross section. The fiducial cross section for this process is found to be 127 $\pm$ 27 (stat + syst) fb. The most recent search for the four top quark production, that explores the same-sign dilepton final state, set the upper observed (expected) limit to 4.6 ($2.9^{+1.4}_{-0.9}$) times predicted standard model cross section. The measured cross section of the top pair production with two b quarks is found to be $\sigma$($\rm t\bar{t}$ + bb) = 3.9 $\pm$ 0.6 (stat) $\pm$ 1.3 (syst) pb in the full phase space. The measurement of the $\rm t\bar{t}$W and $\rm t\bar{t}$Z processes combines three final states with two same-sign, three and four leptons. The $\rm t\bar{t}$W and $\rm t\bar{t}$Z production cross sections are measured to be $\sigma$($\rm t\bar{t}$Z) = $\rm 1.00^{+0.09}_{-0.08} (stat.)^{+0.12}_{-0.10} (sys.)$ pb and $\sigma$($\rm t\bar{t}$W) = $\rm 0.80^{+0.12}_{-0.11} (stat.)^{+0.13}_{-0.12} (sys.)$ pb with an expected (observed) significance of 4.6 (5.5) and 9.5 (9.9) standard deviations from the background-only hypothesis.Comment: 6 pages, 5 figures, proceedings for the fifth annual conference on Large Hadron Collider Physics , Shanghai, Chine, May 15-20, 201

Measurement of differential cross sections for top quark pair production using the lepton plus jets final state in proton-proton collisions at 13 TeV

National Science Foundation (U.S.

Particle-flow reconstruction and global event description with the CMS detector

The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic tau decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8 TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions

Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV

Many measurements and searches for physics beyond the standard model at the LHC rely on the efficient identification of heavy-flavour jets, i.e. jets originating from bottom or charm quarks. In this paper, the discriminating variables and the algorithms used for heavy-flavour jet identification during the first years of operation of the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, are presented. Heavy-flavour jet identification algorithms have been improved compared to those used previously at centre-of-mass energies of 7 and 8 TeV. For jets with transverse momenta in the range expected in simulated $\mathrm{t}\overline{\mathrm{t}}$ events, these new developments result in an efficiency of 68% for the correct identification of a b jet for a probability of 1% of misidentifying a light-flavour jet. The improvement in relative efficiency at this misidentification probability is about 15%, compared to previous CMS algorithms. In addition, for the first time algorithms have been developed to identify jets containing two b hadrons in Lorentz-boosted event topologies, as well as to tag c jets. The large data sample recorded in 2016 at a centre-of-mass energy of 13 TeV has also allowed the development of new methods to measure the efficiency and misidentification probability of heavy-flavour jet identification algorithms. The heavy-flavour jet identification efficiency is measured with a precision of a few per cent at moderate jet transverse momenta (between 30 and 300 GeV) and about 5% at the highest jet transverse momenta (between 500 and 1000 GeV)

Search for heavy resonances decaying to a top quark and a bottom quark in the lepton+jets final state in proton–proton collisions at 13 TeV

info:eu-repo/semantics/publishe

Evidence for the Higgs boson decay to a bottom quark–antiquark pair

info:eu-repo/semantics/publishe

Pseudorapidity and transverse momentum dependence of flow harmonics in pPb and PbPb collisions

info:eu-repo/semantics/publishe

Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp collisions at √s = 13 TeV

Abstract The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (d̂ t) and chromomagnetic (μ̂ t) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable AFB(1) is used to approximate the asymmetry. Candidate t t ¯ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for t t ¯ final states. The values found for the parameters are AFB(1)=0.048−0.087+0.095(stat)−0.029+0.020(syst),μ̂t=−0.024−0.009+0.013(stat)−0.011+0.016(syst), and a limit is placed on the magnitude of | d̂ t| < 0.03 at 95% confidence level. [Figure not available: see fulltext.

Measurement of t(t)over-bar normalised multi-differential cross sections in pp collisions at root s=13 TeV, and simultaneous determination of the strong coupling strength, top quark pole mass, and parton distribution functions

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