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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

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arXiv2019

Azimuthal separation in nearly back-to-back jet topologies in inclusive 2- and 3-jet events in pp collisions at $\sqrt{s} =$ 13 TeV

A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, $Δϕ_{12}$ , is presented. The measurement considers events where the two leading jets are nearly collinear ("back-to-back") in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb$^{-1}$ are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with the measurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177$^\circ$ $<$ $Δϕ_{12}$ $<$ 180$^\circ$. The 2- and 3-jet measurements are not simultaneously described by any of models.

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arXiv2019

Search for a light charged Higgs boson decaying to a W boson and a CP-odd Higgs boson in final states with e$μμ$ or $μμμ$ in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for a light charged Higgs boson (H$^+$) decaying to a W boson and a CP-odd Higgs boson (A) in final states with e$μμ$ or $μμμ$ is performed using data from pp collisions at $\sqrt{s}=$ 13 TeV, recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. In this search, it is assumed that the H$^+$ boson is produced in decays of top quarks, and the A boson decays to two oppositely charged muons. The presence of signals for H$^+$ boson masses between 100 and 160 GeV and A boson masses between 15 and 75 GeV is investigated. No evidence for the production of the H$^+$ boson is found. Upper limits at 95% confidence level are obtained on the combined branching fraction for the decay chain t $\to$ bH$^+$ $\to$ bW$^+$A $\to$ bW$^+μ^+μ^-$, of 1.9 $\times$ 10$^{-6}$ to 8.6 $\times$ 10$^{-6}$, depending on the masses of the H$^+$ and A bosons. These are the first limits for these decay modes of the H$^+$ and A bosons.

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arXiv2019

Search for supersymmetry with a compressed mass spectrum in the vector boson fusion topology with 1-lepton and 0-lepton final states in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for supersymmetric particles produced in the vector boson fusion topology in proton-proton collisions is presented. The search targets final states with one or zero leptons, large missing transverse momentum, and two jets with a large separation in rapidity. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 13 TeV collected in 2016 with the CMS detector at the LHC. The observed dijet invariant mass and lepton-neutrino transverse mass spectra are found to be consistent with the standard model predictions. Upper limits are set on the cross sections for chargino ($\widetildeχ_1^\pm$) and neutralino ($\widetildeχ_2^0$) production with two associated jets. For a compressed mass spectrum scenario in which the $\widetildeχ_1^\pm$ and $\widetildeχ_2^0$ decays proceed via a light slepton and the mass difference between the lightest neutralino $\widetildeχ_1^0$ and the mass-degenerate particles $\widetildeχ_1^\pm$ and $\widetildeχ_2^0$ is 1 (30) GeV, the most stringent lower limit to date of 112 (215) GeV is set on the mass of these latter two particles.

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arXiv2019

Search for vector-like leptons in multilepton final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for vector-like leptons in multilepton final states is presented. The data sample corresponds to an integrated luminosity of 77.4 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016 and 2017. Events are categorized by the multiplicity of electrons, muons, and hadronically decaying $τ$ leptons. The missing transverse momentum and the scalar sum of the lepton transverse momenta are used to distinguish the signal from background. The observed results are consistent with the expectations from the standard model hypothesis. The existence of a vector-like lepton doublet, coupling to the third generation standard model leptons in the mass range of 120-790 GeV, is excluded at 95% confidence level. These are the most stringent limits yet on the production of a vector-like lepton doublet, coupling to the third generation standard model leptons.

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arXiv2019

Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

Evidence for the light-by-light scattering process, $γγ$ $\to$ $γγ$, in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is reported. The analysis is conducted using a data sample corresponding to an integrated luminosity of 390 $μ$b$^{-1}$ recorded by the CMS experiment at the LHC. Light-by-light scattering processes are selected in events with two photons exclusively produced, each with transverse energy E$_\mathrm{T}^γ$ $>$ 2 GeV, pseudorapidity $|η^γ|$ $\lt$ 2.4, diphoton invariant mass $m^{γγ}$ $\gt$ 5 GeV, diphoton transverse momentum $p_\mathrm{T}^{γγ}$ $\lt$ 1 GeV, and diphoton acoplanarity below 0.01. After all selection criteria are applied, 14 events are observed, compared to expectations of 9.0 $\pm$ 0.9 (theo) events for the signal and 4.0 $\pm$ 1.2 (stat) for the background processes. The excess observed in data relative to the background-only expectation corresponds to a significance of 3.7 standard deviations, and has properties consistent with those expected for the light-by-light scattering signal. The measured fiducial light-by-light scattering cross section, $σ_\mathrm{fid} (γγ$ $\to$ $γγ) =$ 120 $\pm$ 46 (stat) $\pm$ 28 (syst) $\pm$ 12 (theo) nb, is consistent with the standard model prediction. The $m^{γγ}$ distribution is used to set new exclusion limits on the production of pseudoscalar axion-like particles, via the $γγ$ $\to$ a $\to$ $γγ$ process, in the mass range $m_{\mathrm{a}} =$ 5-90 GeV.

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arXiv2019

Search for long-lived particles using nonprompt jets and missing transverse momentum with proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for long-lived particles decaying to displaced, nonprompt jets and missing transverse momentum is presented. The data sample corresponds to an integrated luminosity of 137 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC in 2016-2018. Candidate signal events containing nonprompt jets are identified using the timing capabilities of the CMS electromagnetic calorimeter. The results of the search are consistent with the background prediction and are interpreted using a gauge-mediated supersymmetry breaking reference model with a gluino next-to-lightest supersymmetric particle. In this model, gluino masses up to 2100, 2500, and 1900 GeV are excluded at 95% confidence level for proper decay lengths of 0.3, 1, and 100 m, respectively. These are the best limits to date for such massive gluinos with proper decay lengths greater than $\sim$0.5 m.

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arXiv2019

Measurement of exclusive $ρ^0$(770) photoproduction in ultraperipheral pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

Exclusive $ρ^0$(770) photoproduction is measured for the first time in ultraperipheral pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV with the CMS detector. The cross section $σ(γ$p $\to$ $ρ^0$(770)p) is 11.0 $\pm$ 1.4 (stat) $\pm$ 1.0 (syst) $μ$b at $\langle W_{γ\mathrm{p}}\rangle =$ 92.6 GeV for photon-proton centre-of-mass energies $W_{γ\mathrm{p}}$ between 29 and 213 GeV. The differential cross section d$σ/$d$|t|$ is measured in the interval 0.025 $< |t| < 1$ GeV$^{2}$ as a function of $W_{γ\mathrm{p}}$, where $t$ is the squared four-momentum transfer at the proton vertex. The results are compared with previous measurements and theoretical predictions. The measured cross section $σ(γ$ p$ \to ρ^0$(770)p) has a power-law dependence on the photon-proton centre-of-mass, consistent with electron-proton collision measurements performed at HERA. The $W_{γ\mathrm{p}}$ dependence of the exponential slope of the differential cross section d$σ/$d$|t|$ is also measured.

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arXiv2019

Centrality and pseudorapidity dependence of the transverse energy density in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, $E_\mathrm{T}$, over 13.2 units of pseudorapidity, $η$, for pPb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at $-6.6$ $<$ $η$ $<$ $-5.2$ is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias pPb collisions the maximum value of d$E_\mathrm{T}/$d$η$ is 22 GeV, which implies an $E_\mathrm{T}$ per participant nucleon pair comparable to that of peripheral PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 2.76 TeV. The increase of d$E_\mathrm{T}/$d$η$ with centrality is much stronger for the lead-going side than for the proton-going side. The $η$ dependence of d$E_\mathrm{T}/$d$η$ is sensitive to the $η$ range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the $η$ and centrality dependence of the data and the correlations observed between different $η$ regions.

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arXiv2019

Search for Higgs and Z boson decays to J/$ψ$ or $Υ$ pairs in the four-muon final state in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for decays of the Higgs and Z boson to pairs of J/$ψ$ or $Υ$(nS) (n = 1, 2, 3) mesons, with their subsequent decay to $μ^+μ^-$ pairs, is presented. The analysis uses data from proton-proton collisions at $\sqrt{s} =$ 13 TeV, collected with the CMS detector at the LHC in 2017 and corresponding to an integrated luminosity of 37.5 fb$^{-1}$. While an observation of such a decay with this sample would indicate the presence of physics beyond the standard model, no significant excess is observed. Upper limits at 95% confidence level are placed on the branching fractions of these decays. In the J/$ψ$ pair channel, the limits are 1.8 $\times$ 10$^{-3}$ and 2.2 $\times$ 10$^{-6}$ for the Higgs and Z boson, respectively, while in the combined $Υ$(nS) pair channel, the limits are 1.4 $\times$ 10$^{-3}$ and 1.5 $\times$ 10$^{-6}$, respectively, when the mesons from the Higgs and Z boson decay are assumed to be unpolarized. When fully longitudinal and transverse polarizations are considered the limits reduce by about 22-29% and increase by about 10-13%, respectively.

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arXiv2019

Measurement of B$^0_\mathrm{s}$ meson production in pp and PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The production cross sections of B$^0_\mathrm{s}$ mesons and charge conjugates are measured in proton-proton (pp) and PbPb collisions via the exclusive decay channel B$^0_\mathrm{s}$ $\to$ $μ^+μ^-$K$^+$K$^-$ at a centre-of-mass energy of 5.02 TeV per nucleon pair and within the rapidity range $|y|$ $\lt$ 2.4 using the CMS detector at the LHC. The pp measurement is performed as a function of transverse momentum (p$_\mathrm{T}$) of the B$^0_\mathrm{s}$ meson in the range of 7 to 50 GeV/$c$ and is compared to the predictions of perturbative QCD calculations. The B$^0_\mathrm{s}$ production yield in PbPb collisions is measured in two p$_\mathrm{T}$ intervals, 7 to 15 and 15 to 50 GeV/$c$, and compared to the yield in pp collisions in the same kinematic region. The nuclear modification factor ($R_\mathrm{AA}$) is found to be 1.5 $\pm$ 0.6 (stat) $\pm$ 0.5 (syst) for 7-15 GeV/$c$, and 0.87 $\pm$ 0.30 (stat) $\pm$ 0.17 (syst) for 15-50 GeV/$c$, respectively. Within current uncertainties, the results are consistent with models of strangeness enhancement and a suppression as observed for the B$^+$ mesons.

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arXiv2019

Search for charged Higgs bosons in the H$^{\pm}$ $\to$ $τ^{\pm}ν_τ$ decay channel in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search is presented for charged Higgs bosons in the H$^{\pm}$ $\to$ $τ^{\pm}ν_τ$ decay mode in the hadronic final state and in final states with an electron or muon. The search is based on proton-proton collision data recorded by the CMS experiment in 2016 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The results agree with the background expectation from the standard model. Upper limits at 95% confidence level are set on the production cross section times branching fraction to $τ^{\pm}ν_τ$ for an H$^{\pm}$ in the mass range of 80 GeV to 3 TeV, including the region near the top quark mass. The observed limit ranges from 6 pb at 80 GeV to 5 fb at 3 TeV. The limits are interpreted in the context of the minimal supersymmetric standard model $m_\mathrm{h}^\mathrm{mod-}$ scenario.

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arXiv2019

Search for the production of W$^\pm$W$^\pm$W$^\mp$ events at $\sqrt{s} =$ 13 TeV

A search for the production of events containing three W bosons predicted by the standard model is reported. The search is based on a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the CMS experiment at the CERN LHC and corresponding to a total integrated luminosity of 35.9 fb$^{-1}$. The search is performed in final states with three leptons (electrons or muons), or with two same-charge leptons plus two jets. The observed (expected) significance of the signal for W$^\pm$W$^\pm$W$^\mp$ production is 0.60 (1.78) standard deviations, and the ratio of the measured signal yield to that expected from the standard model is 0.34 $^{+0.62}_{-0.34}$. Limits are placed on three anomalous quartic gauge couplings and on the production of massive axionlike particles.

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arXiv2019

A search for pair production of new light bosons decaying into muons in proton-proton collisions at 13 TeV

A search for new light bosons decaying into muon pairs is presented using a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy $\sqrt{s} =$ 13 TeV, collected with the CMS detector at the CERN LHC. The search is model independent, only requiring the pair production of a new light boson and its subsequent decay to a pair of muons. No significant deviation from the predicted background is observed. A model independent limit is set on the product of the production cross section times branching fraction to dimuons squared times acceptance as a function of new light boson mass. This limit varies between 0.15 and 0.39 fb over a range of new light boson masses from 0.25 to 8.5 GeV. It is then interpreted in the context of the next-to-minimal supersymmetric standard model and a dark supersymmetry model that allows for nonnegligible light boson lifetimes. In both cases, there is significant improvement over previously published limits.

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arXiv2019

Search for supersymmetry in final states with photons and missing transverse momentum in proton-proton collisions at 13 TeV

Results are reported for a search for supersymmetry in final states with photons and missing transverse momentum in proton-proton collisions at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$ collected at a center-of-mass energy of 13 TeV using the CMS detector. The results are interpreted in the context of models of gauge-mediated supersymmetry breaking. Production cross section limits are set on gluino and squark pair production in this framework. Gluino masses below 1.86 TeV and squark masses below 1.59 TeV are excluded at 95% confidence level.

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arXiv2019

Studies of beauty suppression via nonprompt D$^0$ mesons in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The transverse momentum spectra of D$^0$ mesons from b hadron decays are measured at midrapidity ($|y|$ $<$ $1$) in pp and PbPb collisions at a nucleon-nucleon center of mass energy of 5.02 TeV with the CMS detector at the LHC. The D$^0$ mesons from b hadron decays are distinguished from prompt D$^0$ mesons by their decay topologies. In PbPb collisions, the B $\to$ D$^0$ yield is found to be suppressed in the measured $p_\mathrm{T}$ range from 2 to 100 GeV$/c$ as compared to pp collisions. The suppression is weaker than that of prompt D$^0$ mesons and charged hadrons for $p_\mathrm{T}$ around 10 GeV$/c$. While theoretical calculations incorporating partonic energy loss in the quark-gluon plasma can successfully describe the measured B $\to$ D$^0$ suppression at higher $p_\mathrm{T}$, the data show an indication of larger suppression than the model predictions in the range of 2 $\lt$ $p_\mathrm{T}$ $\lt$ 5 GeV$/c$.

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arXiv2019

Performance of missing transverse momentum reconstruction in proton-proton collisions at $\sqrt{s} =$ 13 TeV using the CMS detector

The performance of missing transverse momentum (${\vec p}_{\mathrm{T}}^\mathrm{miss}$) reconstruction algorithms for the CMS experiment is presented, using proton-proton collisions at a center-of-mass energy of 13 TeV, collected at the CERN LHC in 2016. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$. The results include measurements of the scale and resolution of ${\vec p}_{\mathrm{T}}^\mathrm{miss}$, and detailed studies of events identified with anomalous ${\vec p}_{\mathrm{T}}^\mathrm{miss}$. The performance is presented of a ${\vec p}_{\mathrm{T}}^\mathrm{miss}$ reconstruction algorithm that mitigates the effects of multiple proton-proton interactions, using the "pileup per particle identification" method. The performance is shown of an algorithm used to estimate the compatibility of the reconstructed ${\vec p}_{\mathrm{T}}^\mathrm{miss}$ with the hypothesis that it originates from resolution effects.

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arXiv2019

Search for a heavy pseudoscalar boson decaying to a Z and a Higgs boson at $\sqrt{s} =$ 13 TeV

A search is presented for a heavy pseudoscalar boson A decaying to a Z boson and a Higgs boson with mass of 125 GeV. In the final state considered, the Higgs boson decays to a bottom quark and antiquark, and the Z boson decays either into a pair of electrons, muons, or neutrinos. The analysis is performed using a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected in 2016 by the CMS experiment at the LHC from proton-proton collisions at a center-of-mass energy of 13 TeV. The data are found to be consistent with the background expectations. Exclusion limits are set in the context of two-Higgs-doublet models in the A boson mass range between 225 and 1000 GeV.

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arXiv2019

Measurement of electroweak WZ boson production and search for new physics in WZ $+$ two jets events in pp collisions at $\sqrt{s} =$ 13 TeV

A measurement of WZ electroweak (EW) vector boson scattering is presented. The measurement is performed in the leptonic decay modes WZ $\to$ $\ellν\ell'\ell'$, where $\ell, \ell' = $ e, $μ$. The analysis is based on a data sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV at the LHC collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The WZ plus two jet production cross section is measured in fiducial regions with enhanced contributions from EW production and found to be consistent with standard model predictions. The EW WZ production in association with two jets is measured with an observed (expected) significance of 2.2 (2.5) standard deviations. Constraints on charged Higgs boson production and on anomalous quartic gauge couplings in terms of dimension-eight effective field theory operators are also presented.

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