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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 829 records · Page 46Linked to original sources

arXiv2018

Search for a singly produced third-generation scalar leptoquark decaying to a $τ$ lepton and a bottom quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search is presented for a singly produced third-generation scalar leptoquark decaying to a $τ$ lepton and a bottom quark. Associated production of a leptoquark and a $τ$ lepton is considered, leading to a final state with a bottom quark and two $τ$ leptons. The search uses proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Upper limits are set at 95% confidence level on the production cross section of the third-generation scalar leptoquarks as a function of their mass. From a comparison of the results with the theoretical predictions, a third-generation scalar leptoquark decaying to a $τ$ lepton and a bottom quark, assuming unit Yukawa coupling ($λ$), is excluded for masses below 740 GeV. Limits are also set on $λ$ of the hypothesized leptoquark as a function of its mass. Above $λ=$ 1.4, this result provides the best upper limit on the mass of a third-generation scalar leptoquark decaying to a $τ$ lepton and a bottom quark.

hep-ex↗

arXiv2018

Electroweak production of two jets in association with a Z boson in proton-proton collisions at $\sqrt{s}= $ 13 TeV

A measurement of the electroweak (EW) production of two jets in association with a Z boson in proton-proton collisions at $\sqrt{s} = $ 13 TeV is presented, based on data recorded in 2016 by the CMS experiment at the LHC corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The measurement is performed in the $\ell\ell\mathrm{jj}$ final state with $\ell$ including electrons and muons, and the jets j corresponding to the quarks produced in the hard interaction. The measured cross section in a kinematic region defined by invariant masses $m_{\ell\ell} > $ 50 GeV, $m_{\mathrm{jj}} > $ 120 GeV, and transverse momenta $p_{\mathrm{T j}} > $ 25 GeV is $σ_\mathrm{EW}(\ell\ell\mathrm{jj})= $ 534 $\pm$ 20 (stat) $\pm$ 57 (syst) fb, in agreement with leading-order standard model predictions. The final state is also used to perform a search for anomalous trilinear gauge couplings. No evidence is found and limits on anomalous trilinear gauge couplings associated with dimension-six operators are given in the framework of an effective field theory. The corresponding 95% confidence level intervals are $-2.6 < c_{WWW}/Λ^2 < 2.6 $ TeV$^{-2}$ and $-8.4 < c_{W}/Λ^2 < 10.1 $ TeV$^{-2}$. The additional jet activity of events in a signal-enriched region is also studied, and the measurements are in agreement with predictions.

hep-ex↗

arXiv2018

Search for a heavy resonance decaying into a Z boson and a vector boson in the $ν\overlineν\mathrm{q}\overline{\mathrm{q}}$ final state

A search is presented for a heavy resonance decaying into either a pair of Z bosons or a Z boson and a W boson (ZZ or WZ), with a Z boson decaying into a pair of neutrinos and the other boson decaying hadronically into two collimated quarks that are reconstructed as a highly energetic large-cone jet. The search is performed using the data collected with the CMS detector at the CERN LHC during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 35.9 fb$^{-1}$. No excess is observed in data with regard to background expectations. Results are interpreted in scenarios of physics beyond the standard model. Limits at 95% confidence level on production cross sections are set at 0.9 fb (63 fb) for spin-1 W$'$ bosons, included in the heavy vector triplet model, with mass 4.0 TeV (1.0 TeV), and at 0.5 fb (40 fb) for spin-2 bulk gravitons with mass 4.0 TeV (1.0 TeV). Lower limits are set on the masses of W$'$ bosons in the context of two versions of the heavy vector triplet model of 3.1 TeV and 3.4 TeV, respectively.

hep-ex↗

arXiv2018

Azimuthal correlations for inclusive 2-jet, 3-jet, and 4-jet events in pp collisions at $\sqrt{s}= $ 13 TeV

Azimuthal correlations between the two jets with the largest transverse momenta $ {p_{\mathrm{T}}} $ in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet $ {p_{\mathrm{T}}} $ up to 4 TeV. For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or four leading $ {p_{\mathrm{T}}} $ jets are also presented. The analysis is based on data from proton-proton collisions collected by the CMS Collaboration at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Calculations based on leading-order matrix elements supplemented with parton showering and hadronization do not fully describe the data, so next-to-leading-order calculations matched with parton shower and hadronization models are needed to better describe the measured distributions. Furthermore, we show that azimuthal jet correlations are sensitive to details of the parton showering, hadronization, and multiparton interactions. A next-to-leading-order calculation matched with parton showers in the MC@NLO method, as implemented in HERWIG 7, gives a better overall description of the measurements than the POWHEG method.

hep-ex↗

arXiv2018

Measurement of the underlying event activity in inclusive Z boson production in proton-proton collisions at $\sqrt{s} = $ 13 TeV

This paper presents a measurement of the underlying event activity in proton-proton collisions at a center-of-mass energy of 13 TeV, performed using inclusive Z boson production events collected with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 2.1 fb$^{-1}$. The underlying event activity is quantified in terms of the charged particle multiplicity, as well as of the scalar sum of the charged particles' transverse momenta in different topological regions defined with respect to the Z boson direction. The distributions are unfolded to the stable particle level and compared with predictions from various Monte Carlo event generators, as well as with similar CDF and CMS measurements at center-of-mass energies of 1.96 and 7 TeV respectively.

hep-ex↗

arXiv2018

Search for a new scalar resonance decaying to a pair of Z bosons in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for a new scalar resonance decaying to a pair of Z bosons is performed in the mass range from 130 GeV to 3 TeV, and for various width scenarios. The analysis is based on proton-proton collisions recorded by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$ at a center-of-mass energy of 13 TeV. The Z boson pair decays are reconstructed using the 4$\ell$, 2$\ell$2q, and 2$\ell$2$ν$ final states, where $\ell =$ e or $μ$. Both gluon fusion and electroweak production of the scalar resonance are considered, with a free parameter describing their relative cross sections. A dedicated categorization of events, based on the kinematic properties of associated jets, and matrix element techniques are employed for an optimal signal and background separation. A description of the interference between signal and background amplitudes for a resonance of an arbitrary width is included. No significant excess of events with respect to the standard model expectation is observed and limits are set on the product of the cross section for a new scalar boson and the branching fraction for its decay to ZZ for a large range of masses and widths.

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arXiv2018

Search for high-mass resonances in final states with a lepton and missing transverse momentum at $\sqrt{s}=$ 13 TeV

A search for new high-mass resonances in proton-proton collisions having final states with an electron or muon and missing transverse momentum is presented. The analysis uses proton-proton collision data collected in 2016 with the CMS detector at the LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The transverse mass distribution of the charged lepton-neutrino system is used as the discriminating variable. No significant deviation from the standard model prediction is found. The best limit, from the combination of electron and muon channels, is 5.2 TeV at 95% confidence level for the mass of a W$'$ boson with the same couplings as those of the standard model W boson. Exclusion limits of 2.9 TeV are set on the inverse radius of the extra dimension in the framework of split universal extra dimensions. In addition, model-independent limits are set on the production cross section and coupling strength of W$'$ bosons decaying into this final state. An interpretation is also made in the context of an R parity violating supersymmetric model with a slepton as a mediator and flavor violating decay.

hep-ex↗

arXiv2018

Nuclear modification factor of D$^0$ mesons in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The transverse momentum ($p_\mathrm{t}$) spectrum of prompt D$^0$ mesons and their antiparticles has been measured via the hadronic decay channels D$^0 \to \mathrm{K}^- π^+$ and $\overline{\mathrm{D}}^0 \to \mathrm{K}^+ π^-$ in pp and PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair with the CMS detector at the LHC. The measurement is performed in the D$^0$ meson $p_\mathrm{t}$ range of 2-100 GeV and in the rapidity range of $|y| < $1. The pp (PbPb) dataset used for this analysis corresponds to an integrated luminosity of 27.4 pb$^{-1}$ (530 $μ$b$^{-1}$). The measured D$^0$ meson $p_\mathrm{t}$ spectrum in pp collisions is well described by perturbative QCD calculations. The nuclear modification factor, comparing D$^0$ meson yields in PbPb and pp collisions, was extracted for both minimum-bias and the 10% most central PbPb interactions. For central events, the D$^0$ meson yield in the PbPb collisions is suppressed by a factor of 5-6 compared to the pp reference in the $p_\mathrm{t}$ range of 6-10 GeV. For D$^0$ mesons in the high-$p_\mathrm{t}$ range of 60-100 GeV, a significantly smaller suppression is observed. The results are also compared to theoretical calculations.

nucl-ex↗

arXiv2018

Search for high-mass resonances in dilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search is presented for new high-mass resonances decaying into electron or muon pairs. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 36 fb$^{-1}$. Observations are in agreement with standard model expectations. Upper limits on the product of a new resonance production cross section and branching fraction to dileptons are calculated in a model-independent manner. This permits the interpretation of the limits in models predicting a narrow dielectron or dimuon resonance. A scan of different intrinsic width hypotheses is performed. Limits are set on the masses of various hypothetical particles. For the Z$'_\mathrm{SSM}$ (Z$'_ψ$) particle, which arises in the sequential standard model (superstring-inspired model), a lower mass limit of 4.50 (3.90) TeV is set at 95% confidence level. The lightest Kaluza-Klein graviton arising in the Randall-Sundrum model of extra dimensions, with coupling parameters $k/\overline{M}_\mathrm{Pl}$ of 0.01, 0.05, and 0.10, is excluded at 95% confidence level below 2.10, 3.65, and 4.25 TeV, respectively. In a simplified model of dark matter production via a vector or axial vector mediator, limits at 95% confidence level are obtained on the masses of the dark matter particle and its mediator.

hep-ex↗

arXiv2018

Search for $R$-parity violating supersymmetry in pp collisions at $\sqrt{s} = $ 13 TeV using b jets in a final state with a single lepton, many jets, and high sum of large-radius jet masses

Results are reported from a search for physics beyond the standard model in proton-proton collisions at a center-of-mass energy of $\sqrt{s} = $ 13 TeV. The search uses a signature of a single lepton, large jet and bottom quark jet multiplicities, and high sum of large-radius jet masses, without any requirement on the missing transverse momentum in an event. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS experiment at the LHC. No significant excess beyond the prediction from standard model processes is observed. The results are interpreted in terms of upper limits on the production cross section for $R$-parity violating supersymmetric extensions of the standard model using a benchmark model of gluino pair production, in which each gluino decays promptly via $ {\mathrm{\widetilde{g}}} \rightarrow \mathrm{t} \mathrm{b} \mathrm{s} $. Gluinos with a mass below 1610 GeV are excluded at 95% confidence level.

hep-ex↗

arXiv2018

Search for the flavor-changing neutral current interactions of the top quark and the Higgs boson which decays into a pair of b quarks at $\sqrt{s}=$ 13 TeV

A search for flavor-changing neutral currents (FCNC) in events with the top quark and the Higgs boson is presented. The Higgs boson decay to a pair of b quarks is considered. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded by the CMS experiment at the LHC in proton-proton collisions at $\sqrt{s}=$ 13 TeV. Two channels are considered: single top quark FCNC production in association with the Higgs boson (pp $\to$ tH), and top quark pair production with FCNC decay of the top quark (t $\to$ qH). Final states with one isolated lepton and at least three reconstructed jets, among which at least two are associated with b quarks, are studied. No significant deviation is observed from the predicted background. Observed (expected) upper limits at 95% confidence level are set on the branching fractions of top quark decays, $\mathcal{B}$(t $\to$ uH) $<$ 0.47% (0.34%) and $\mathcal{B}$(t $\to$ cH) $<$ 0.47% (0.44%), assuming a single nonzero FCNC coupling.

hep-ex↗

arXiv2018

Search for $\mathrm{t}\overline{\mathrm{t}}$H production in the all-jet final state in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search is presented for the associated production of a Higgs boson with a top quark pair in the all-jet final state. Events containing seven or more jets are selected from a sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV collected with the CMS detector at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. To separate the $\mathrm{t}\overline{\mathrm{t}}$H signal from the irreducible $\mathrm{t}\overline{\mathrm{t}}+\mathrm{b}\overline{\mathrm{b}}$ background, the analysis assigns leading order matrix element signal and background probability densities to each event. A likelihood-ratio statistic based on these probability densities is used to extract the signal. The results are provided in terms of an observed $\mathrm{t}\overline{\mathrm{t}}$H signal strength relative to the standard model production cross section $μ=σ/σ_\mathrm{SM}$, assuming a Higgs boson mass of 125 GeV. The best fit value is $\hatμ =$ 0.9 $\pm$ 0.7 (stat) $\pm$ 1.3 (syst) = 0.9 $\pm$ 1.5 (tot), and the observed and expected upper limits are, respectively, $μ<$ 3.8 and $<$ 3.1 at 95% confidence levels.

hep-ex↗

arXiv2018

Search for new physics in events with two soft oppositely charged leptons and missing transverse momentum in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search is presented for new physics in events with two low-momentum, oppositely charged leptons (electrons or muons) and missing transverse momentum in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data collected using the CMS detector at the LHC correspond to an integrated luminosity of 35.9 fb$^{-1}$. The observed event yields are consistent with the expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos ($\widetildeχ^\pm_1$ and $\widetildeχ^0_2$) with nearly degenerate masses, as expected in natural supersymmetry models with light higgsinos, as well as in terms of the pair production of top squarks ($\widetilde{\mathrm{t}}$), when the lightest neutralino and the top squark have similar masses. At 95% confidence level, wino-like $\widetildeχ^\pm_1$/$\widetildeχ^0_2$ masses are excluded up to 230 GeV for a mass difference of 20 GeV relative to the lightest neutralino. In the higgsino-like model, masses are excluded up to 168 GeV for the same mass difference. For $\widetilde{\mathrm{t}}$ pair production, top squark masses up to 450 GeV are excluded for a mass difference of 40 GeV relative to the lightest neutralino.

hep-ex↗

arXiv2018

Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $\sqrt{s}=$ 13 TeV

The CMS muon detector system, muon reconstruction software, and high-level trigger underwent significant changes in 2013-2014 in preparation for running at higher LHC collision energy and instantaneous luminosity. The performance of the modified system is studied using proton-proton collision data at center-of-mass energy $\sqrt{s}=$ 13 TeV, collected at the LHC in 2015 and 2016. The measured performance parameters, including spatial resolution, efficiency, and timing, are found to meet all design specifications and are well reproduced by simulation. Despite the more challenging running conditions, the modified muon system is found to perform as well as, and in many aspects better than, previously. We dedicate this paper to the memory of Prof. Alberto Benvenuti, whose work was fundamental for the CMS muon detector.

physics.ins-det↗

arXiv2018

Measurement of prompt and nonprompt charmonium suppression in PbPb collisions at 5.02 TeV

The nuclear modification factors of J/$ψ$ and $ψ$(2S) mesons are measured in PbPb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} =$ 5.02 TeV. The analysis is based on PbPb and pp data samples collected by CMS at the LHC in 2015, corresponding to integrated luminosities of 464 $μ$b$^{-1}$ and 28 pb$^{-1}$, respectively. The measurements are performed in the dimuon rapidity range of $|y| <$ 2.4 as a function of centrality, rapidity, and transverse momentum (p$_\mathrm{T}$) from p$_\mathrm{T}=$ 3 GeV/$c$ in the most forward region and up to 50 GeV/$c$. Both prompt and nonprompt (coming from b hadron decays) mesons are observed to be increasingly suppressed with centrality, with a magnitude similar to the one observed at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV for the two J/$ψ$ meson components. No dependence on rapidity is observed for either prompt or nonprompt J/$ψ$ mesons. An indication of a lower prompt J/$ψ$ meson suppression at p$_\mathrm{T} >$ 25 GeV/$c$ is seen with respect to that observed at intermediate p$_\mathrm{T}$. The prompt $ψ$(2S) meson yield is found to be more suppressed than that of the prompt J/$ψ$ mesons in the entire p$_\mathrm{T}$ range.

nucl-ex↗

arXiv2018

Search for physics beyond the standard model in events with high-momentum Higgs bosons and missing transverse momentum in proton-proton collisions at 13 TeV

A search for physics beyond the standard model in events with one or more high-momentum Higgs bosons, H, decaying to pairs of b quarks in association with missing transverse momentum is presented. The data, corresponding to an integrated luminosity of 35.9 fb$^{-1}$, were collected with the CMS detector at the LHC in proton-proton collisions at the center-of-mass energy $\sqrt{s}=$ 13 TeV. The analysis utilizes a new b quark tagging technique based on jet substructure to identify jets from H $\to$ bb. Events are categorized by the multiplicity of H-tagged jets, jet mass, and the missing transverse momentum. No significant deviation from standard model expectations is observed. In the context of supersymmetry (SUSY), limits on the cross sections of pair-produced gluinos are set, assuming that gluinos decay to quark pairs, H (or Z), and the lightest SUSY particle, LSP, through an intermediate next-to-lightest SUSY particle, NLSP. With large mass splitting between the NLSP and LSP, and 100% NLSP branching fraction to H, the lower limit on the gluino mass is found to be 2010 GeV.

hep-ex↗

arXiv2018

Measurement of differential cross sections for the production of top quark pairs and of additional jets in lepton+jets events from pp collisions at $\sqrt{s} =$ 13 TeV

Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at $\sqrt{s} =$ 13 TeV are measured as a function of kinematic variables of the top quarks and the top quark-antiquark ($\mathrm{t}\overline{\mathrm{t}}$) system. In addition, kinematic variables and multiplicities of jets associated with the $\mathrm{t}\overline{\mathrm{t}}$ production are measured. This analysis is based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.8 fb$^{-1}$. The measurements are performed in the lepton+jets decay channels with a single muon or electron and jets in the final state. The differential cross sections are presented at the particle level, within a phase space close to the experimental acceptance, and at the parton level in the full phase space. The results are compared to several standard model predictions that use different methods and approximations. The kinematic variables of the top quarks and the $\mathrm{t}\overline{\mathrm{t}}$ system are reasonably described in general, though none predict all the measured distributions. In particular, the transverse momentum distribution of the top quarks is more steeply falling than predicted. The kinematic distributions and multiplicities of jets are adequately modeled by certain combinations of next-to-leading-order calculations and parton shower models.

hep-ex↗

arXiv2018

Measurement of b hadron lifetimes in pp collisions at $\sqrt{s} =$ 8 TeV

Measurements are presented of the lifetimes of the B$^0$, B$^0_\mathrm{s}$, $Λ^0_\mathrm{b}$, and B$_\mathrm{c}^+$ hadrons using the decay channels B$^0\to$ J/$ψ$K*(892)$^0$, B$^0\to$J/$ψ$K$^0_\mathrm{S}$, B$^0_\mathrm{s}\to$J/$ψπ^+π^-$, B$^0_\mathrm{s}\to$J/$ψϕ$(1020), $Λ^0_\mathrm{b}\to$J/$ψΛ^0$, and B$_\mathrm{c}\to$J/$ψπ^+$. The data sample, corresponding to an integrated luminosity of 19.7 fb$^{-1}$, was collected by the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=$ 8 TeV. The B$^0$ lifetime is measured to be 453.0 $\pm$ 1.6 (stat) $\pm$ 1.8 (syst) $μ$m in J/$ψ$K*(892)$^0$ and 457.8 $\pm$ 2.7 (stat) $\pm$ 2.8 (syst) $μ$m in J/$ψ$K$^0_\mathrm{S}$, which results in a combined measurement of $cτ_{\mathrm{B}^0} =$ 454.1 $\pm$ 1.4 (stat) $\pm$ 1.7 (syst) $μ$m. The effective lifetime of the B$^0_\mathrm{s}$ meson is measured in two decay modes, with contributions from different amounts of the heavy and light eigenstates. This results in two different measured lifetimes: $cτ_{\mathrm{B}^0_\mathrm{s} \to \mathrm{J}/ψπ^+π^-} =$ 502.7 $\pm$ 10.2 (stat) $\pm$ 3.4 (syst) $μ$m and $cτ_{\mathrm{B}^0_\mathrm{s} \to \mathrm{J}/ψϕ(1020)} =$ 443.9 $\pm$ 2.0 (stat) $\pm$ 1.5 (syst) $μ$m. The $Λ^0_\mathrm{b}$ lifetime is found to be 443.9 $\pm$ 8.2 (stat) $\pm$ 2.8 (syst) $μ$m. The precision from each of these channels is as good as or better than previous measurements. The B$_\mathrm{c}^+$ lifetime, measured with respect to the B$^+$ to reduce the systematic uncertainty, is 162.3 $\pm$ 7.8 (stat) $\pm$ 4.2 (syst) $\pm$ 0.1 $(τ_{\mathrm{B}^+})$ $μ$m. All results are in agreement with current world-average values.

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