Measurement of the azimuthal anisotropy of Y(1S) and Y(2S) mesons in PbPb collisions at root s(NN)=5.02 TeV

The second-order Fourier coefficients (v(2)) characterizing the azimuthal distributions of Y(1S) and Y(2S) mesons produced in PbPb collisions at root s(NN) = 5.02 TeV are studied. The Y mesons are reconstructed in their dimuon decay channel, as measured by the CMS detector. The collected data set corresponds to an integrated luminosity of 1.7 nb(-1). The scalar product method is used to extract the v2 coefficients of the azimuthal distributions. Results are reported for the rapidity range vertical bar y vertical bar < 2.4, in the transverse momentum interval 0 < pT < 50 GeV/c, and in three centrality ranges of 10-30%, 30-50% and 50-90%. In contrast to the J/psi mesons, the measured v(2) values for the Y mesons are found to be consistent with zero. (C) 2021 The Author(s). Published by Elsevier B.V.Peer reviewe

Investigation of in-medium effects of charmonia using azimuthal anisotropy and jet fragmentation function in PbPb collisions at 5.02 TeV with the CMS experiment

Quarkonia have been long proposed as the golden probes to study quark-gluon plasma (QGP) in heavy-ion collisions. In this presentation, we present the second- and third-order Fourier coefficients, $v_2$ and $v_3$, for prompt and nonprompt J/$\psi$ mesons in PbPb collisions as functions transverse momentum ($p_{\rm T}$) and PbPb collision centrality. Also, we report the first measurements of $v_2$ and $v_3$ for the prompt $\psi$(2S) mesons in PbPb collisions. The results provide $v_2$ and $v_3$ values over the wide studied kinematics regions of transverse momentum and collision centrality

Measurement of the azimuthal anisotropy of Υ\Upsilon(1S) and Υ\Upsilon(2S) mesons in PbPb collisions at sNN=\sqrt{s_\mathrm{NN}} = 5.02 TeV

The second-order Fourier coefficients ($v_2$) characterizing the azimuthal distribution of $\Upsilon$(1S) and $\Upsilon$(2S) mesons arising from PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV are studied. The $\Upsilon$ mesons are reconstructed in their dimuon decay channel, as measured by the CMS detector. The data set was collected in 2018 and corresponds to an integrated luminosity of 1.7 nb$^{-1}$. The scalar product method is used to extract the $v_2$ coefficients of the azimuthal distribution. Results are reported for the rapidity range $|y|\lt$ 2.4, with the transverse momentum 0 $\lt p_\mathrm{T} \lt$ 50 GeV/$c$, and in three centrality ranges of 10-30, 30-50 and 50-90%. In contrast to the J/$\psi$ mesons, no azimuthal anisotropy is observed for the $\Upsilon$ mesons

Measurements of the azimuthal anisotropy of prompt and nonprompt charmonia in PbPb collisions at sNN\sqrt{s_\mathrm{NN}} = 5.02 TeV

International audienceThe second-order ($v_2$) and third-order ($v_3$) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/$\psi$, as well as prompt $\psi$(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb$^{-1}$ recorded with the CMS detector. The J/$\psi$ and $\psi$(2S) mesons are reconstructed using their dimuon decay channel. The $v_2$ and $v_3$ coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measured $v_2$ values for prompt J/$\psi$ mesons are found to be larger than those for nonprompt J/$\psi$ mesons. The prompt J/$\psi$$v_2$ values at high $p_\mathrm{T}$ are found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/$\psi$ meson $v_3$ and prompt $\psi$(2S) $v_2$ and $v_3$ values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions

Measurement of the τ \tau lepton polarization in Z boson decays in proton-proton collisions at s= \sqrt{s} = 13 TeV

The polarization of $\tau$ leptons is measured using leptonic and hadronic $\tau$ lepton decays in Z $\to\tau^{+}\tau^{-}$ events in proton-proton collisions at $\sqrt{s}=$ 13 TeV recorded by CMS at the CERN LHC with an integrated luminosity of 36.3 fb$^{-1}$. The measured $\tau^{-}$ lepton polarization at the Z boson mass pole is $\mathcal{P}_{\tau}(\mathrm{Z})= -$0.144 $\pm$ 0.006 (stat) $\pm$ 0.014 (syst) $= -$0.144 $\pm$ 0.015, in good agreement with the measurement of the $\tau$ lepton asymmetry parameter of $A_{\tau}=$ 0.1439 $\pm$ 0.0043 $=-\mathcal{P}_{\tau}(\mathrm{Z})$ at LEP. The $\tau$ polarization depends on the ratio of the vector to axial-vector couplings of the $\tau$ leptons in the neutral current expression, and thus on the effective weak mixing angle $\sin^{2}\theta_{\mathrm{W}}^{\, \text{eff}}$, independently of the Z boson production mechanism. The obtained value $\sin^{2}\theta_{\mathrm{W}}^{\, \text{eff}}=$ 0.2319 $\pm$ 0.0008 (stat) $\pm$ 0.0018 (syst) $=$ 0.2319 $\pm$ 0.0019 is in good agreement with measurements at $\mathrm{e}^{+}\mathrm{e}^{-}$ colliders.The polarization of $\tau$ leptons is measured using leptonic and hadronic $\tau$ lepton decays in Z $\to\tau^+\tau^-$ events in proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded by CMS at the CERN LHC with an integrated luminosity of 36.3 fb$^{-1}$. The measured $\tau^-$ polarization at the Z boson mass pole is $\mathcal{P}_{\tau}$(Z) = $-$0.144$\pm$0.006 (stat) $\pm$ 0.014 (syst) = $-$0.144$\pm$0.015, in good agreement with the measurement of the $\tau$ lepton asymmetry parameter of $A_{\tau}$ = 0.1439$\pm$0.0043 = $-\mathcal{P}_{\tau}$(Z) at LEP. The $\tau$ polarization depends on the ratio of the vector to axial-vector couplings of the $\tau$ leptons in the neutral current expression, and thus on the effective weak mixing angle $\sin^{2}\theta_\mathrm{W}^{\text{eff}}$, independently of the Z boson production mechanism. The obtained value $\sin^{2}\theta_\mathrm{W}^{\text{eff}}$ = 0.2319$\pm$0.0008 (stat) $\pm$ 0.0018 (syst) = 0.2319$\pm$0.0019 is in good agreement with measurements at e$^+$e$^-$ colliders

Development of the CMS detector for the CERN LHC Run 3

International audienceSince the initial data taking of the CERN LHC, the CMS experiment has undergone substantial upgrades and improvements. This paper discusses the CMS detector as it is configured for the third data-taking period of the CERN LHC, Run 3, which started in 2022. The entire silicon pixel tracking detector was replaced. A new powering system for the superconducting solenoid was installed. The electronics of the hadron calorimeter was upgraded. All the muon electronic systems were upgraded, and new muon detector stations were added, including a gas electron multiplier detector. The precision proton spectrometer was upgraded. The dedicated luminosity detectors and the beam loss monitor were refurbished. Substantial improvements to the trigger, data acquisition, software, and computing systems were also implemented, including a new hybrid CPU/GPU farm for the high-level trigger

Muon identification using multivariate techniques in the CMS experiment in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceThe identification of prompt and isolated muons, as well as muons from heavy-flavour hadron decays, is an important task. We developed two multivariate techniques to provide highly efficient identification for muons with transverse momentum greater than 10\GeV. One provides a continuous variable as an alternative to a cut-based identification selection and offers a better discrimination power against misidentified muons. The other one selects prompt and isolated muons by using isolation requirements to reduce the contamination from nonprompt muons arising in heavy-flavour hadron decays. Both algorithms are developed using 59.7 fb$^{-1}$ of proton-proton collisions data at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV collected in 2018 with the CMS experiment at the CERN LHC

Search for scalar leptoquarks produced in lepton-quark collisions and coupled to τ\tau leptons

The first search for scalar leptoquarks produced in lepton-quark collisions and coupled to $\tau$ leptons is presented. It is based on a set of proton-proton collision data recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb$^{-1}$. The reconstructed final state consists of a jet, significant missing transverse momentum, and a $\tau$ lepton reconstructed through its hadronic or leptonic decays. Limits are set on the product of the leptoquark production cross section and branching fraction and interpreted as exclusions in the plane of the leptoquark mass and the leptoquark-$\tau$-quark coupling strength

Observation of four top quark production in proton-proton collisions at s\sqrt{s} = 13 TeV

International audienceThe observation of the production of four top quarks in proton-proton collisions is reported, based on a data sample collected by the CMS experiment at a center-of-mass energy of 13 TeV in 2016-2018 at the CERN LHC and corresponding to an integrated luminosity of 138 fb$^{-1}$. Events with two same-sign, three, or four charged leptons (electrons and muons) and additional jets are analyzed. Compared to previous results in these channels, updated identification techniques for charged leptons and jets originating from the hadronization of b quarks, as well as a revised multivariate analysis strategy to distinguish the signal process from the main backgrounds, lead to an improved expected signal significance of 4.9 standard deviations above the background-only hypothesis. Four top quark production is observed with a significance of 5.6 standard deviations, and its cross section is measured to be 17.7$^{+3.7}_{-3.5}$ (stat) $^{+2.3}_{-1.9}$ (syst) fb, in agreement with the available standard model predictions