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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 901 records · Page 50Linked to original sources

arXiv2018

Search for standard model production of four top quarks with same-sign and multilepton final states in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for standard model production of four top quarks ($\mathrm{t}\overline{\mathrm{t}}\mathrm{t}\overline{\mathrm{t}})$ is reported using events containing at least three leptons (e, $μ$) or a same-sign lepton pair. The events are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, and the data sample, recorded in 2016, corresponds to an integrated luminosity of 35.9 fb$^{-1}$. Jet multiplicity and flavor are used to enhance signal sensitivity, and dedicated control regions are used to constrain the dominant backgrounds. The observed and expected signal significances are, respectively, 1.6 and 1.0 standard deviations, and the $\mathrm{t}\overline{\mathrm{t}}\mathrm{t}\overline{\mathrm{t}}$ cross section is measured to be 16.9 $^{+13.8}_{-11.4}$ fb, in agreement with next-to-leading-order standard model predictions. These results are also used to constrain the Yukawa coupling between the top quark and the Higgs boson to be less than 2.1 times its expected standard model value at 95% confidence level.

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arXiv2018

Search for supersymmetry with Higgs boson to diphoton decays using the razor variables at $\sqrt{s} = $ 13 TeV

An inclusive search for anomalous Higgs boson production in the diphoton decay channel and in association with at least one jet is presented, using LHC proton-proton collision data collected by the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The razor variables $M_\mathrm{R}$ and $\mathrm{R}^2$, as well as the momentum and mass resolution of the diphoton system, are used to categorize events into different search regions. The search result is interpreted in the context of strong and electroweak production of supersymmetric particles. We exclude bottom squark pair-production with masses below 450 GeV for bottom squarks decaying to a bottom quark, a Higgs boson, and the lightest supersymmetric particle (LSP) for LSP masses below 250 GeV. For wino-like chargino-neutralino production, we exclude charginos with mass below 170 GeV for LSP masses below 25 GeV. In the GMSB scenario, we exclude charginos with mass below 205 GeV for neutralinos decaying to a Higgs boson and a goldstino LSP with 100% branching fraction.

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arXiv2018

Inclusive search for a highly boosted Higgs boson decaying to a bottom quark-antiquark pair

An inclusive search for the standard model Higgs boson ($\mathrm{H}$) produced with large transverse momentum ($p_\mathrm{T}$) and decaying to a bottom quark-antiquark pair ($\mathrm{b}\overline{\mathrm{b}}$) is performed using a data set of pp collisions at $\sqrt{s}=$ 13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$. A highly Lorentz-boosted Higgs boson decaying to $\mathrm{b}\overline{\mathrm{b}}$ is reconstructed as a single, large radius jet and is identified using jet substructure and dedicated $\mathrm{b}$ tagging techniques. The method is validated with $\mathrm{Z}\to\mathrm{b}\overline{\mathrm{b}}$ decays. The $\mathrm{Z}\to\mathrm{b}\overline{\mathrm{b}}$ process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of $\mathrm{H} \rightarrow \mathrm{b}\overline{\mathrm{b}}$ with $p_\mathrm{T} > $450 GeV and in the pseudorapidity range $-$2.5 $< η<$ 2.5 is 74 $\pm$ 48 (stat) $_{-10}^{+17}$ (syst) fb, which is consistent within uncertainties with the standard model prediction.

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arXiv2018

Constraints on the double-parton scattering cross section from same-sign W boson pair production in proton-proton collisions at $\sqrt{s} =$ 8 TeV

A first search for same-sign WW production via double-parton scattering is performed based on proton-proton collision data at a center-of-mass energy of 8 TeV using dimuon and electron-muon final states. The search is based on the analysis of data corresponding to an integrated luminosity of 19.7 fb$^{-1}$. No significant excess of events is observed above the expected single-parton scattering yields. A 95% confidence level upper limit of 0.32 pb is set on the inclusive cross section for same-sign WW production via the double-parton scattering process. This upper limit is used to place a 95% confidence level lower limit of 12.2 mb on the effective double-parton cross section parameter, closely related to the transverse distribution of partons in the proton. This limit on the effective cross section is consistent with previous measurements as well as with Monte Carlo event generator predictions.

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arXiv2018

Search for supersymmetry in proton-proton collisions at 13 TeV using identified top quarks

A search for supersymmetry is presented based on proton-proton collision events containing identified hadronically decaying top quarks, no leptons, and an imbalance $p_\mathrm{T}^\text{miss}$ in transverse momentum. The data were collected with the CMS detector at the CERN LHC at a center-of-mass energy of 13 TeV, and correspond to an integrated luminosity of 35.9 fb$^{-1}$. Search regions are defined in terms of the multiplicity of bottom quark jet and top quark candidates, the $p_\mathrm{T}^\text{miss}$, the scalar sum of jet transverse momenta, and the $m_{\mathrm{T2}}$ mass variable. No statistically significant excess of events is observed relative to the expectation from the standard model. Lower limits on the masses of supersymmetric particles are determined at 95% confidence level in the context of simplified models with top quark production. For a model with direct top squark pair production followed by the decay of each top squark to a top quark and a neutralino, top squark masses up to 1020 GeV and neutralino masses up to 430 GeV are excluded. For a model with pair production of gluinos followed by the decay of each gluino to a top quark-antiquark pair and a neutralino, gluino masses up to 2040 GeV and neutralino masses up to 1150 GeV are excluded. These limits extend previous results.

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arXiv2018

Search for higgsino pair production in pp collisions at sqrt(s) = 13 TeV in final states with large missing transverse momentum and two Higgs bosons decaying via H to bb-bar

Results are reported from a search for new physics in 13 TeV proton-proton collisions in the final state with large missing transverse momentum and two Higgs bosons decaying via H to bb-bar. The search uses a data sample accumulated by the CMS experiment at the LHC in 2016, corresponding to an integrated luminosity of 35.9 inverse femtobarns. The search is motivated by models based on gauge-mediated supersymmetry breaking, which predict the electroweak production of a pair of higgsinos, each of which can decay via a cascade process to a Higgs boson and an undetected lightest supersymmetric particle. The observed event yields in the signal regions are consistent with the standard model background expectation obtained from control regions in data. Higgsinos in the mass range 230-770 GeV are excluded at 95% confidence level in the context of a simplified model for the production and decay of approximately degenerate higgsinos.

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arXiv2018

Search for resonant and nonresonant Higgs boson pair production in the bblnulnu final state in proton-proton collisions at sqrt(s) = 13 TeV

Searches for resonant and nonresonant pair-produced Higgs bosons (HH) decaying respectively into ll nu nu, through either W or Z bosons, and bbbar are presented. The analyses are based on a sample of proton-proton collisions at sqrt(s) = 13 TeV, collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 inverse femtobarns. Data and predictions from the standard model are in agreement within uncertainties. For the standard model HH hypothesis, the data exclude at 95% confidence level a product of the production cross section and branching fraction larger than 72 fb, corresponding to 79 times the prediction, consistent with expectations. Constraints are placed on different scenarios considering anomalous couplings, which could affect the rate and kinematics of HH production. Upper limits at 95% confidence level are set on the production cross section of narrow-width spin-0 and spin-2 particles decaying to Higgs boson pairs, the latter produced with minimal gravity-like coupling.

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arXiv2018

Search for the pair production of third-generation squarks with two-body decays to a bottom or charm quark and a neutralino in proton-proton collisions at sqrt(s) = 13 TeV

Results are presented from a search for the pair production of third-generation squarks in proton-proton collision events with two-body decays to bottom or charm quarks and a neutralino, which produces a significant imbalance in the transverse momentum. The search is performed using a sample of proton-proton collision data at sqrt(s) = 13 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 inverse femtobarns. No statistically significant excess of events is observed beyond the expected contribution from standard model processes. Exclusion limits are set in the context of simplified models of bottom or top squark pair production. Models with bottom squark masses up to 1220 GeV are excluded at 95% confidence level for light neutralinos, and models with top squark masses of 510 GeV are excluded assuming that the mass splitting between the top squark and the neutralino is small.

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arXiv2018

Search for pair production of excited top quarks in the lepton+jets final state

A search is performed for the pair production of spin-3/2 excited top quarks, each decaying to a top quark and a gluon. The search uses the data collected with the CMS detector from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 inverse femtobarns. Events are selected by requiring an isolated muon or electron, an imbalance in the transverse momentum, and at least six jets of which exactly two must be compatible with originating from the fragmentation of a bottom quark. No significant excess over the standard model predictions is found. A lower limit of 1.2 TeV is set at 95% confidence level on the mass of the spin-3/2 excited top quark in an extension of the Randall-Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon. These are the best limits to date in a search for excited top quarks and the first at 13 TeV.

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arXiv2018

Search for Higgs boson pair production in events with two bottom quarks and two tau leptons in proton-proton collisions at sqrt(s) = 13 TeV

A search for the production of Higgs boson pairs in proton-proton collisions at a centre-of-mass energy of 13 TeV is presented, using a data sample corresponding to an integrated luminosity of 35.9 inverse femtobarns collected with the CMS detector at the LHC. Events with one Higgs boson decaying into two bottom quarks and the other decaying into two tau leptons are explored to investigate both resonant and nonresonant production mechanisms. The data are found to be consistent, within uncertainties, with the standard model background predictions. For resonant production, upper limits at the 95% confidence level are set on the production cross section for Higgs boson pairs as a function of the hypothesized resonance mass and are interpreted in the context of the minimal supersymmetric standard model. For nonresonant production, upper limits on the production cross section constrain the parameter space for anomalous Higgs boson couplings. The observed (expected) upper limit at 95% confidence level corresponds to about 30 (25) times the prediction of the standard model.

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arXiv2018

Search for low mass vector resonances decaying into quark-antiquark pairs in proton-proton collisions at sqrt(s) = 13 TeV

A search for narrow vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in proton-proton collisions at sqrt(s) = 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 inverse femtobarns. The hypothetical resonance is produced with sufficiently high transverse momentum that its decay products are merged into a single jet with two-prong substructure. A signal would be identified as a peak over a smoothly falling background in the distribution of the invariant mass of the jet, using novel jet substructure techniques. No evidence for such a resonance is observed within the mass range of 50-300 GeV. Upper limits at 95% confidence level are set on the production cross section, and presented in a mass-coupling parameter space. The limits further constrain simplified models of dark matter production involving a mediator interacting between quarks and dark matter particles through a vector or axial-vector current. In the framework of these models, the results are the most sensitive to date, extending for the first time the search region to masses below 100 GeV.

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arXiv2018

Search for dark matter and unparticles in events with a Z boson and missing transverse momentum in proton-proton collisions at sqrt(s) = 13 TeV

A search for dark matter and unparticle production at the LHC has been performed using events containing two charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at the LHC, at a center-of-mass energy of 13 TeV. No excess over the standard model expectation is observed. Compared to previous searches in this topology, which exclusively relied on effective field theories, the results are interpreted in terms of a simplified model of dark matter production for both vector and axial vector couplings between a mediator and dark matter particles. The first study of this class of models using CMS data at sqrt(s) = 13 TeV is presented. Additionally, effective field theories of dark matter and unparticle production are used to interpret the data.

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arXiv2018

Measurements of tt-bar cross sections in association with b jets and inclusive jets and their ratio using dilepton final states in pp collisions at sqrt(s) = 13 TeV

The cross sections for the production of tt-bar bb-bar and tt-bar jj events and their ratio sigma[tt-bar bb-bar]/sigma[tt-bar jj] are measured using data corresponding to an integrated luminosity of 2.3 inverse femtobarns collected in pp collisions at sqrt(s) = 13 TeV with the CMS detector at the LHC. Events with two leptons (e or mu) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is 0.022 +/- 0.003 (stat) +/- 0.006 (syst), the cross section sigma[tt-bar bb-bar] is 4.0 +/- 0.6 (stat) +/- 1.3 (syst) pb and sigma[tt-bar jj] is 184 +/- 6 (stat) +/- 33 (syst) pb. The measurements are compared with the standard model expectations obtained from a POWHEG simulation at next-to-leading-order interfaced with PYTHIA.

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arXiv2018

Search for dark matter produced in association with heavy-flavor quarks in proton-proton collisions at sqrt(s) = 13 TeV

A search is presented for an excess of events with heavy-flavor quark pairs (tt-bar and bb-bar) and a large imbalance in transverse momentum in data from proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 2.2 inverse femtobarns collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in tt-bar and bb-bar final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states.

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arXiv2017

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

A search is presented for narrow heavy resonances decaying to a top quark and a bottom quark using data collected by the CMS experiment at sqrt(s) = 13 TeV in 2016. The data set analyzed corresponds to an integrated luminosity of 35.9 inverse femtobarns. Final states that include a single lepton (e, mu), multiple jets, and missing transverse momentum are analyzed. No evidence is found for the production of a W' boson, and the production of right-handed W' bosons is excluded at 95% confidence level for masses up to 3.6 TeV depending on the scenario considered. Exclusion limits for W' bosons are also presented as a function of their coupling strength to left- and right-handed fermions. These limits on a W' boson decaying via a top and a bottom quark are the most stringent published to date.

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arXiv2017

Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at sqrt(s) = 13 TeV

A search for new physics in energetic, high-multiplicity final states has been performed using proton-proton collision data collected with the CMS detector at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 2.3 inverse femtobarns. The standard model background, dominated by multijet production, is determined exclusively from control regions in data. No statistically significant excess of events is observed. Model-independent limits on the product of the cross section and the acceptance of a new physics signal in these final states are set and further interpreted in terms of limits on the production of black holes. Semiclassical black holes and string balls with masses as high as 9.5 TeV, and quantum black holes with masses as high as 9.0 TeV are excluded by this search in the context of models with extra dimensions, thus significantly extending limits set at a center-of-mass energy of 8 TeV with the LHC Run 1 data.

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arXiv2017

Observation of top quark production in proton-nucleus collisions

The first observation of top quark production in proton-nucleus collisions is reported using proton-lead data collected by the CMS experiment at the CERN LHC at a nucleon-nucleon center-of-mass energy of sqrt(s[NN]) = 8.16 TeV. The measurement is performed using events with exactly one isolated electron or muon and at least four jets. The data sample corresponds to an integrated luminosity of 174 inverse nanobarns. The significance of the tt-bar signal against the background-only hypothesis is above five standard deviations. The measured cross section is sigma[tt-bar] = 45 +/- 8 nb, consistent with predictions from perturbative quantum chromodynamics.

nucl-ex↗

arXiv2017

Principal-component analysis of two-particle azimuthal correlations in PbPb and pPb collisions at CMS

For the first time a principle-component analysis is used to separate out different orthogonal modes of the two-particle correlation matrix from heavy ion collisions. The analysis uses data from sqrt(s[NN]) = 2.76 TeV PbPb and sqrt(s[NN]) = 5.02 TeV pPb collisions collected by the CMS experiment at the LHC. Two-particle azimuthal correlations have been extensively used to study hydrodynamic flow in heavy ion collisions. Recently it has been shown that the expected factorization of two-particle results into a product of the constituent single-particle anisotropies is broken. The new information provided by these modes may shed light on the breakdown of flow factorization in heavy ion collisions. The first two modes ("leading" and "subleading") of two-particle correlations are presented for elliptical and triangular anisotropies in PbPb and pPb collisions as a function of pt over a wide range of event activity. The leading mode is found to be essentially equivalent to the anisotropy harmonic previously extracted from two-particle correlation methods. The subleading mode represents a new experimental observable and is shown to account for a large fraction of the factorization breaking recently observed at high transverse momentum. The principle-component analysis technique has also been applied to multiplicity fluctuations. These also show a subleading mode. The connection of these new results to previous studies of factorization is discussed.

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