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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 721 records · Page 40Linked to original sources

arXiv2019

Search for nonresonant Higgs boson pair production in the $\mathrm{b\overline{b}b\overline{b}}$ final state at $\sqrt{s} =$ 13 TeV

Results of a search for nonresonant production of Higgs boson pairs, with each Higgs boson decaying to a $\mathrm{b\overline{b}}$ pair are presented. This search uses data from proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$, collected by the CMS detector at the LHC. No signal is observed, and a 95% confidence level upper limit of 847 fb is set on the cross section for standard model nonresonant Higgs boson pair production times the squared branching fraction of the Higgs boson decay to a $\mathrm{b\overline{b}}$ pair. The same signature is studied, and upper limits are set, in the context of models of physics beyond the standard model that predict modified couplings of the Higgs boson.

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arXiv2019

Jet shapes of isolated photon-tagged jets in PbPb and pp collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The modification of jet shapes in PbPb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta ($p_\mathrm{T}$) above 1 GeV/c in annuli around the axes of jets with $p^\mathrm{jet}_\mathrm{T}$ $>$ 30 GeV/c associated with an isolated photon with $p^γ_\mathrm{T}$ $>$ 60 GeV/c. The jet shape distributions are consistent between peripheral PbPb and pp collisions, but are modified for more central PbPb collisions. In these central PbPb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to pp, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.

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arXiv2019

Measurement and interpretation of differential cross sections for Higgs boson production at $\sqrt{s} =$ 13 TeV

Differential Higgs boson (H) production cross sections are sensitive probes for physics beyond the standard model. New physics may contribute in the gluon-gluon fusion loop, the dominant Higgs boson production mechanism at the LHC, and manifest itself through deviations from the distributions predicted by the standard model. Combined spectra for the H $\to$ $γγ$, H $\to$ ZZ, and H $\to$ $\mathrm{b\overline{b}}$ decay channels and the inclusive Higgs boson production cross section are presented, based on proton-proton collision data recorded with the CMS detector at $\sqrt{s} =$ 13 TeV corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The transverse momentum spectrum is used to place limits on the Higgs boson couplings to the top, bottom, and charm quarks, as well as its direct coupling to the gluon field. No significant deviations from the standard model are observed in any differential distribution. The measured total cross section is 61.1 $\pm$ 6.0 (stat) $\pm$ 3.7 (syst) pb, and the precision of the measurement of the differential cross section of the Higgs boson transverse momentum is improved by about 15% with respect to the H $\to$ $γγ$ channel alone.

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arXiv2019

Search for an $L_μ$ $-$ $L_τ$ gauge boson using Z $\to$ 4$μ$ events in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for a narrow Z$'$ gauge boson with a mass between 5 and 70 GeV resulting from an $L_μ$ $-$ $L_τ$ $U(1)$ local gauge symmetry is reported. Theories that predict such a particle have been proposed as an explanation of various experimental discrepancies, including the lack of a dark matter signal in direct-detection experiments, tension in the measurement of the anomalous magnetic moment of the muon, and reports of possible lepton flavor universality violation in B meson decays. A data sample of proton-proton collisions at a center-of-mass energy of 13 TeV is used, corresponding to an integrated luminosity of 77.3 fb$^{-1}$ recorded in 2016 and 2017 by the CMS detector at the LHC. Events containing four muons with an invariant mass near the standard model Z boson mass are analyzed, and the selection is further optimized to be sensitive to the events that may contain Z $\to$ Z$'μμ$ $\to$ 4$μ$ decays. The event yields are consistent with the standard model predictions. Upper limits of 10$^{-8}$-10$^{-7}$ at 95% confidence level are set on the product of branching fractions $\mathcal{B}$(Z $\to$ Z$'μμ$) $\mathcal{B}$(Z$'$ $\to$ $μμ$), depending on the Z$'$ mass, which excludes a Z$'$ boson coupling strength to muons above 0.004-0.3. These are the first dedicated limits on $L_μ$ $-$ $L_τ$ models at the LHC and result in a significant increase in the excluded model parameter space. The results of this search may also be used to constrain the coupling strength of any light Z$'$ gauge boson to muons.

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arXiv2019

Search for excited leptons in $\ell\ellγ$ final states in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search is presented for excited electrons and muons in $\ell\ellγ$ final states at the LHC. The search is based on a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector in 2016. This is the first search for excited leptons at $\sqrt{s} =$ 13 TeV. The observation is consistent with the standard model background prediction, and the most stringent exclusion limits to date are set on the excited lepton mass and the compositeness scale, at 95% confidence level. Excited electrons and muons are excluded for masses below 3.9 and 3.8 TeV, respectively, under the assumption that the excited lepton mass equals the compositeness scale. The best observed limit on the compositeness scale is obtained with an excited lepton mass of around 1.0 TeV, excluding values below 25 TeV for both excited electrons and muons.

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arXiv2019

Observation of single top quark production in association with a Z boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV

The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017, and correspond to an integrated luminosity of 77.4 fb$^{-1}$. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over five standard deviations. The measured tZq production cross section is $σ$(pp $\to$ tZq $\to$ t$\ell^{+} \ell^{-}$q) = 111 $\pm$ 13 (stat) $ _{-9}^{+11}$ (syst) fb, for dilepton invariant masses above 30 GeV, in agreement with the standard model expectation.

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arXiv2019

Measurement of the top quark mass in the all-jets final state at $\sqrt{s} =$ 13 TeV and combination with the lepton+jets channel

A top quark mass measurement is performed using 35.9 fb$^{-1}$ of LHC proton-proton collision data collected with the CMS detector at $\sqrt{s} =$ 13 TeV. The measurement uses the $\mathrm{t\overline{t}}$ all-jets final state. A kinematic fit is performed to reconstruct the decay of the $\mathrm{t\overline{t}}$ system and suppress the multijet background. Using the ideogram method, the top quark mass ($m_\mathrm{t}$) is determined, simultaneously constraining an additional jet energy scale factor (JSF). The resulting value of $m_\mathrm{t}$ = 172.34 $\pm$ 0.20 (stat+JSF) $\pm$ 0.70 (syst) GeV is in good agreement with previous measurements. In addition, a combined measurement that uses the $\mathrm{t\overline{t}}$ lepton+jets and all-jets final states is presented, using the same mass extraction method, and provides an $m_\mathrm{t}$ measurement of 172.26 $\pm$ 0.07 (stat+JSF) $\pm$ 0.61 (syst) GeV. This is the first combined $m_\mathrm{t}$ extraction from the lepton+jets and all-jets channels through a single likelihood function.

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arXiv2019

Search for resonant $\mathrm{t}\overline{\mathrm{t}}$ production in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for a heavy resonance decaying into a top quark and antiquark ($\mathrm{t\bar{t}}$) pair is performed using proton-proton collisions at $\sqrt{s} =$ 13 TeV. The search uses the data set collected with the CMS detector in 2016, which corresponds to an integrated luminosity of 35.9 fb$^{-1}$. The analysis considers three exclusive final states and uses reconstruction techniques that are optimized for top quarks with high Lorentz boosts, which requires the use of nonisolated leptons and jet substructure techniques. No significant excess of events relative to the expected yield from standard model processes is observed. Upper limits on the production cross section of heavy resonances decaying to a $\mathrm{t\bar{t}}$ pair are calculated. Limits are derived for a leptophobic topcolor Z' resonance with widths of 1, 10, and 30%, relative to the mass of the resonance, and exclude masses up to 3.80, 5.25, and 6.65 TeV, respectively. Kaluza-Klein excitations of the gluon in the Randall-Sundrum model are excluded up to 4.55 TeV. To date, these are the most stringent limits on $\mathrm{t\bar{t}}$ resonances.

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arXiv2019

Combination of searches for Higgs boson pair production in proton-proton collisions at $\sqrt{s} =$ 13 TeV

This Letter describes a search for Higgs boson pair production using the combined results from four final states: bb$γγ$, bb$ττ$, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250-3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.

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arXiv2019

Search for a W' boson decaying to a vector-like quark and a top or bottom quark in the all-jets final state

A search for a heavy W' resonance decaying to one B or T vector-like quark and a top or bottom quark, respectively, is presented. The search uses proton-proton collision data collected in 2016 with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$ at $\sqrt{s} =$ 13 TeV. Both decay channels result in a final state with a top quark, a Higgs boson, and a b quark, each produced with significant energy. The all-hadronic decays of both the Higgs boson and the top quark are considered. The final-state jets, some of which correspond to merged decay products of a boosted top quark and a Higgs boson, are selected using jet substructure techniques, which help to suppress standard model backgrounds. A W' boson signal would appear as a narrow peak in the invariant mass distribution of these jets. No significant deviation in data with respect to the standard model background predictions is observed. Cross section upper limits on W' boson production in the top quark, Higgs boson, and b quark decay mode are set as a function of the W' mass, for several vector-like quark mass hypotheses. These are the first limits for W' boson production in this decay channel, and cover a range of 0.01 to 0.43 pb in the W' mass range between 1.5 and 4.0 TeV.

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arXiv2019

Search for resonant production of second-generation sleptons with same-sign dimuon events in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search is presented for resonant production of second-generation sleptons ($\tildeμ_L$, $\tildeν_μ$) via the $R$-parity-violating coupling $λ'_{211}$ to quarks, in events with two same-sign muons and at least two jets in the final state. The smuon (muon sneutrino) is expected to decay into a muon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton-proton collisions at $\sqrt{s} =$ 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730 fb, are derived in the context of two simplified models representing the dominant signal contributions leading to a same-sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with $λ'_{211}$ as the only nonzero $R$-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.

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arXiv2019

Observation of two excited B$^+_\mathrm{c}$ states and measurement of the B$^+_\mathrm{c}$(2S) mass in pp collisions at $\sqrt{s} =$ 13 TeV

Signals consistent with the B$^+_\mathrm{c}$(2S) and B$^{*+}_\mathrm{c}$(2S) states are observed in proton-proton collisions at $\sqrt{s} =$ 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb$^{-1}$, collected by the CMS experiment during the 2015-2018 LHC running periods. These excited $\bar{\mathrm{b}}$c states are observed in the B$^+_\mathrm{c}π^+π^-$ invariant mass spectrum, with the ground state B$^+_\mathrm{c}$ reconstructed through its decay to J/$ψ\,π^+$. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 $\pm$ 1.5 (stat) $\pm$ 0.7 (syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B$^+_\mathrm{c}$(2S) meson is measured to be 6871.0 $\pm$ 1.2 (stat) $\pm$ 0.8 (syst) $\pm$ 0.8 (B$^+_\mathrm{c}$) MeV, where the last term corresponds to the uncertainty in the world-average B$^+_\mathrm{c}$ mass.

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arXiv2019

Measurement of exclusive $Υ$ photoproduction from protons in pPb collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

The exclusive photoproduction of $Υ$(nS) meson states from protons, $γ$p $ \toΥ$(nS)p (with n = 1, 2, 3), is studied in ultraperipheral pPb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. The measurement is performed using the $Υ$(nS) $\to μ^+μ^-$ decay mode, with data collected by the CMS experiment corresponding to an integrated luminosity of 32.6 nb$^{-1}$. Differential cross sections as functions of the $Υ$(nS) transverse momentum squared $p_\mathrm{T}^2$, and rapidity $y$, are presented. The $Υ$(1S) photoproduction cross section is extracted in the rapidity range $|y|$ $<$ 2.2, which corresponds to photon-proton centre-of-mass energies in the range 91 $<$ W$_{γ\mathrm{p}}$ $<$ 826 GeV. The data are compared to theoretical predictions based on perturbative quantum chromodynamics and to previous measurements.

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arXiv2019

Search for heavy neutrinos and third-generation leptoquarks in hadronic states of two $τ$ leptons and two jets in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for new particles has been conducted using events with two high transverse momentum $τ$ leptons that decay hadronically and at least two energetic jets. The analysis is performed using data from proton-proton collisions at $\sqrt{s} =$ 13 TeV, collected by the CMS experiment at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The observed data are consistent with standard model expectations. The results are interpreted in the context of two physics models. The first model involves right-handed charged bosons, W$_\mathrm{R}$, that decay to heavy right-handed Majorana neutrinos, N$_\ell$ $(\ell = $e, $μ, τ)$, arising in a left-right symmetric extension of the standard model. The model considers that N$_\mathrm{e}$ and N$_μ$ are too heavy to be detected at the LHC. Assuming that the N$_τ$ mass is half of the W$_\mathrm{R}$ mass, masses of the W$_\mathrm{R}$ boson below 3.50 TeV are excluded at 95% confidence level. Exclusion limits are also presented considering different scenarios for the mass ratio between N$_τ$ and W$_\mathrm{R}$, as a function of W$_\mathrm{R}$ mass. In the second model, pair production of third-generation scalar leptoquarks that decay into $ττ$bb is considered, resulting in an observed exclusion region with leptoquark masses below 1.02 TeV, assuming a 100% branching fraction for the leptoquark decay to a $τ$ lepton and a bottom quark. These results represent the most stringent limits to date on these models.

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arXiv2019

Search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for dark matter produced in association with a Higgs boson decaying to a pair of bottom quarks is performed in proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector at the LHC. The analyzed data sample corresponds to an integrated luminosity of 35.9 fb$^{-1}$. The signal is characterized by a large missing transverse momentum recoiling against a bottom quark-antiquark system that has a large Lorentz boost. The number of events observed in the data is consistent with the standard model background prediction. Results are interpreted in terms of limits both on parameters of the type-2 two-Higgs doublet model extended by an additional light pseudoscalar boson a (2HDM+a) and on parameters of a baryonic Z' simplified model. The 2HDM+a model is tested experimentally for the first time. For the baryonic Z' model, the presented results constitute the most stringent constraints to date.

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arXiv2019

Search for dark matter produced in association with a single top quark or a top quark pair in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for dark matter produced in association with top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The data set used corresponds to an integrated luminosity of 35.9 fb$^{-1}$ recorded with the CMS detector at the LHC. Whereas previous searches for neutral scalar or pseudoscalar mediators considered dark matter production in association with a top quark pair only, this analysis also includes production modes with a single top quark. The results are derived from the combination of multiple selection categories that are defined to target either the single top quark or the top quark pair signature. No significant deviations with respect to the standard model predictions are observed. The results are interpreted in the context of a simplified model in which a scalar or pseudoscalar mediator particle couples to a top quark and subsequently decays into dark matter particles. Scalar and pseudoscalar mediator particles with masses below 290 and 300 GeV, respectively, are excluded at 95% confidence level, assuming a dark matter particle mass of 1 GeV and mediator couplings to fermions and dark matter particles equal to unity.

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arXiv2019

Search for a W' boson decaying to a $τ$ lepton and a neutrino in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for a new high-mass resonance decaying to a tau lepton and a neutrino is reported. The analysis uses proton-proton collision data collected by the CMS experiment at the LHC at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search utilizes hadronically decaying tau leptons. No excess in the event yield is observed at high transverse masses of the $τ$ and missing transverse momentum. An interpretation of results within the sequential standard model excludes W' boson masses below 4.0 TeV at 95% confidence level. Existing limits are also improved on models in which the W' boson decays preferentially to fermions of the third generation. Heavy W' bosons with masses less than 1.7-3.9 TeV, depending on the coupling in the non-universal G(221) model, are excluded at 95% confidence level. These are the most stringent limits on this model to date.

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arXiv2019

Measurement of associated production of a W boson and a charm quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV

Measurements are presented of associated production of a W boson and a charm quark (W+c) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 35.7 fb$^{-1}$ collected by the CMS experiment at the CERN LHC. The W bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of D$^*$(2010)$^\pm$ mesons that decay via D$^*$(2010)$^\pm \to$ D$^0$ + $π^\pm \to$ K$^{\mp}$ + $π^\pm$ + $π^\pm$. A cross section is measured in the fiducial region defined by the muon transverse momentum $p_{T}^μ >$ 26 GeV, muon pseudorapidity $|η^μ| <$ 2.4, and charm quark transverse momentum $p_{T}^{c} >$ 5 GeV. The inclusive cross section for this kinematic range is $σ$(W+c) = 1026 $\pm$ 31 (stat) $\substack{+76\\-72}$ (syst) pb. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the W boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.

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