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CMS Collaboration

Publications and source records attributed to CMS Collaboration.

At least 847 records · Page 47Linked to original sources

arXiv2018

Search for single production of vector-like quarks decaying to a b quark and a Higgs boson

A search is presented for single production of heavy vector-like quarks (B) that decay to a Higgs boson and a b quark, with the Higgs boson decaying to a highly boosted $\mathrm{b\overline{b}}$ pair reconstructed as a single collimated jet. The analysis is based on data collected by the CMS experiment in proton-proton collisions at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The data are consistent with background expectations, and upper limits at 95% confidence level on the product of the B quark cross section and the branching fraction are obtained in the range 1.28-0.07 pb, for a narrow B quark with a mass between 700 and 1800 GeV. The production of B quarks with widths of 10, 20 and 30% of the resonance mass is also considered, and the sensitivities obtained are similar to those achieved in the narrow width case. This is the first search at the CERN LHC for the single production of a B quark through its fully hadronic decay channel, and the first study considering finite resonance widths of the B quark.

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arXiv2018

Measurement of angular parameters from the decay $\mathrm{B}^0 \to \mathrm{K}^{*0} μ^+ μ^-$ in proton-proton collisions at $\sqrt{s} = $ 8 TeV

Angular distributions of the decay $\mathrm{B}^0 \to \mathrm{K}^{*0} μ^+ μ^-$ are studied using a sample of proton-proton collisions at $\sqrt{s} = $ 8 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb$^{-1}$. An angular analysis is performed to determine the $P_1$ and $P_5'$ parameters, where the $P_5'$ parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the $P_1$ and $P_5'$ parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on the standard model.

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arXiv2018

Search for single production of a vector-like T quark decaying to a Z boson and a top quark in proton-proton collisions at $\sqrt{s} = $13 TeV

A search is presented for single production of a vector-like quark (T) decaying to a Z boson and a top quark, with the Z boson decaying leptonically and the top quark decaying hadronically. The search uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The presence of forward jets is a particular characteristic of single production of vector-like quarks that is used in the analysis. For the first time, different T quark width hypotheses are studied, from negligibly small to 30% of the new particle mass. At the 95% confidence level, the product of cross section and branching fraction is excluded above values in the range 0.26-0.04 pb for T quark masses in the range 0.7-1.7 TeV, assuming a negligible width. A similar sensitivity is observed for widths of up to 30% of the T quark mass. The production of a heavy Z' boson decaying to Tt, with T $\rightarrow$ tZ, is also searched for, and limits on the product of cross section and branching fractions for this process are set between 0.13 and 0.06 pb for Z' boson masses in the range from 1.5 to 2.5 TeV.

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arXiv2018

Study of Bose-Einstein correlations in pp, pPb, and PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 0.9-7 TeV

Quantum statistical (Bose-Einstein) two-particle correlations are measured in pp collisions at $\sqrt{s}=$ 0.9, 2.76, and 7 TeV, as well as in pPb and peripheral PbPb collisions at nucleon-nucleon center-of-mass energies of 5.02 and 2.76 TeV, respectively, using the CMS detector at the LHC. Separate analyses are performed for same-sign unidentified charged particles as well as for same-sign pions and kaons identified via their energy loss in the silicon tracker. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as functions of the pair average transverse momentum ($k_\mathrm{T}$) and the charged-particle multiplicity in the event. For all systems, the extracted correlation radii steadily increase with the event multiplicity, and decrease with increasing $k_\mathrm{T}$. The radii are in the range 1-5 fm, the largest values corresponding to very high multiplicity pPb interactions and to peripheral PbPb collisions with multiplicities similar to those seen in pPb data. It is also observed that the dependencies of the radii on multiplicity and $k_\mathrm{T}$ largely factorize. At the same multiplicity, the radii are relatively independent of the colliding system and center-of-mass energy.

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arXiv2018

Search for dark matter in events with energetic, hadronically decaying top quarks and missing transverse momentum at $\sqrt{s}=$ 13 TeV

A search for dark matter is conducted in events with large missing transverse momentum and a hadronically decaying, Lorentz-boosted top quark. This study is performed using proton-proton collisions at a center-of-mass energy of 13 TeV, in data recorded by the CMS detector in 2016 at the LHC, corresponding to an integrated luminosity of 36 fb$^{-1}$. New substructure techniques, including the novel use of energy correlation functions, are utilized to identify the decay products of the top quark. With no significant deviations observed from predictions of the standard model, limits are placed on the production of new heavy bosons coupling to dark matter particles. For a scenario with purely vector-like or purely axial-vector-like flavor changing neutral currents, mediator masses between 0.20 and 1.75 TeV are excluded at 95% confidence level, given a sufficiently small dark matter mass. Scalar resonances decaying into a top quark and a dark matter fermion are excluded for masses below 3.4 TeV, assuming a dark matter mass of 100 GeV.

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arXiv2018

Observation of $\mathrm{t\overline{t}}$H production

The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of $\sqrt{s}=$ 7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9 fb$^{-1}$, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, $τ$ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26 ${^{+0.31}_{-0.26}}$.

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arXiv2018

Search for lepton flavour violating decays of the Higgs boson to $μτ$ and e$τ$ in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search for lepton flavour violating decays of the Higgs boson in the $μτ$ and e$τ$ decay modes is presented. The search is based on a data set corresponding to an integrated luminosity of 35.9 fb$^{-1}$ of proton-proton collisions collected with the CMS detector in 2016, at a centre-of-mass energy of 13 TeV. No significant excess over the standard model expectation is observed. The observed (expected) upper limits on the lepton flavour violating branching fractions of the Higgs boson are $\mathcal{B}$(H$\toμτ$) < 0.25% (0.25%) and $\mathcal{B}$(H$\to$e$τ$) < 0.61% (0.37%), at 95% confidence level. These results are used to derive upper limits on the off-diagonal $μτ$ and e$τ$ Yukawa couplings $\sqrt{|{Y_{μτ}}|^{2}+|{Y_{τμ}}|^{2}} < 1.43 \times 10^{-3}$ and $\sqrt{|{Y_{\mathrm{e}τ}}|^{2}+|{Y_{τ\mathrm{e}}}|^{2}} < 2.26 \times 10^{-3}$ at 95% confidence level. The limits on the lepton flavour violating branching fractions of the Higgs boson and on the associated Yukawa couplings are the most stringent to date.

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arXiv2018

Measurements of differential cross sections of top quark pair production as a function of kinematic event variables in proton-proton collisions at $\sqrt{s}=$ 13 TeV

Measurements of differential $\mathrm{t\overline{t}}$ production cross sections are presented in the single-lepton decay channel, as a function of a number of kinematic event variables. The measurements are performed with proton-proton collision data at $\sqrt{s}=$ 13 TeV, collected by the CMS experiment at the LHC during 2016, with an integrated luminosity of 35.9 fb$^{-1}$. The data are compared to a variety of state-of-the-art leading-order and next-to-leading-order $\mathrm{t\overline{t}}$ simulations.

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arXiv2018

Search for a heavy right-handed W boson and a heavy neutrino in events with two same-flavor leptons and two jets at $\sqrt{s}=$ 13 TeV

A search for a heavy right-handed W boson (W$_\mathrm{R}$) decaying to a heavy right-handed neutrino and a charged lepton in events with two same-flavor leptons (e or $μ$) and two jets, is presented. The analysis is based on proton-proton collision data, collected by the CMS Collaboration at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. No significant excess above the standard model expectation is seen in the invariant mass distribution of the dilepton plus dijet system. Assuming that couplings are identical to those of the standard model, and that only one heavy neutrino flavor N$_\mathrm{R}$ contributes significantly to the W$_\mathrm{R}$ decay width, the region in the two-dimensional ($m_\mathrm{W_R}, m_\mathrm{N_R}$) mass plane excluded at 95% confidence level extends to approximately $m_\mathrm{W_R}=$ 4.4 TeV and covers a large range of right-handed neutrino masses below the W$_\mathrm{R}$ boson mass. This analysis provides the most stringent limits on the W$_\mathrm{R}$ mass to date.

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arXiv2018

Search for new physics in final states with an energetic jet or a hadronically decaying W or Z boson and transverse momentum imbalance at $\sqrt{s} = $ 13 TeV

A search for new physics using events containing an imbalance in transverse momentum and one or more energetic jets arising from initial-state radiation or the hadronic decay of W or Z bosons is presented. A data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$, is used. The observed data are found to be in agreement with the expectation from standard model processes. The results are interpreted as limits on the dark matter production cross section in simplified models with vector, axial-vector, scalar, and pseudoscalar mediators. Interpretations in the context of fermion portal and nonthermal dark matter models are also provided. In addition, the results are interpreted in terms of invisible decays of the Higgs boson and set stringent limits on the fundamental Planck scale in the Arkani-Hamed, Dimopoulos, and Dvali model with large extra spatial dimensions.

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arXiv2018

Search for heavy neutral leptons in events with three charged leptons in proton-proton collisions at $\sqrt{s} =$ 13 TeV

A search for a heavy neutral lepton N of Majorana nature decaying into a W boson and a charged lepton is performed using the CMS detector at the LHC. The targeted signature consists of three prompt charged leptons in any flavor combination of electrons and muons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV, with an integrated luminosity of 35.9 fb$^{-1}$. The search is performed in the N mass range between 1 GeV and 1.2 TeV. The data are found to be consistent with the expected standard model background. Upper limits are set on the values of $|\mathrm{V}_\mathrm{eN}|^2$ and $|\mathrm{V}_{μ\mathrm{N}}|^2$, where $V_{\ell\mathrm{N}}$ is the matrix element describing the mixing of N with the standard model neutrino of flavor $\ell$. These are the first direct limits for N masses above 500 GeV and the first limits obtained at a hadron collider for N masses below 40 GeV.

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arXiv2018

Search for decays of stopped exotic long-lived particles produced in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search is presented for the decays of heavy exotic long-lived particles (LLPs) that are produced in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC and come to rest in the CMS detector. Their decays would be visible during periods of time well separated from proton-proton collisions. Two decay scenarios of stopped LLPs are explored: a hadronic decay detected in the calorimeter and a decay into muons detected in the muon system. The calorimeter (muon) search covers a period of sensitivity totaling 721 (744) hours in 38.6 (39.0) fb$^{-1}$ of data collected by the CMS detector in 2015 and 2016. The results are interpreted in several scenarios that predict LLPs. Production cross section limits are set as a function of the mean proper lifetime and the mass of the LLPs, for lifetimes between 100 ns and 10 days. These are the most stringent limits to date on the mass of hadronically decaying stopped LLPs, and this is the first search at the LHC for stopped LLPs that decay to muons.

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arXiv2018

Search for the X(5568) state decaying into $\mathrm{B}^{0}_{\mathrm{s}}π^{\pm}$ in proton-proton collisions at $\sqrt{s} = $ 8 TeV

A search for resonance-like structures in the $\mathrm{B}^{0}_{\mathrm{s}}π^{\pm}$ invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at $\sqrt{s} = $ 8 TeV, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The $\mathrm{B}^{0}_{\mathrm{s}}$ mesons are reconstructed in the decay chain $\mathrm{B}^{0}_{\mathrm{s}} \rightarrow \mathrm{J}/ψ\,ϕ$, with $\mathrm{J}/ψ\rightarrow μ^+μ^-$ and $ϕ\rightarrow\mathrm{K^{+}}\mathrm{K^{-}}$. The $\mathrm{B}^{0}_{\mathrm{s}}π^{\pm}$ invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed $\mathrm{B}^{0}_{\mathrm{s}}$ and $π^{\pm}$ candidates. Upper limits are set on the relative production rates of the X(5568) and $\mathrm{B}^{0}_{\mathrm{s}}$ states times the branching fraction of the decay $\mathrm{X}(5568)^{\pm} \rightarrow \mathrm{B}^{0}_{\mathrm{s}} π^{\pm} $. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into $\mathrm{B}^{0}_{\mathrm{s}}π^{\pm}$.

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arXiv2018

Jet properties in PbPb and pp collisions at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV

Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity ($Δη$), relative azimuth ($Δϕ$), and relative angular distance from the jet axis $Δ\mathrm{r} = \sqrt{{(Δη)^{2}+(Δϕ)^{2}}}$. This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 $μ$b$^{-1}$ and 27.4 pb$^{-1}$ for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark-gluon plasma.

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arXiv2018

Measurement of prompt D$^0$ meson azimuthal anisotropy in PbPb collisions at $\sqrt{s_\mathrm{NN}} = $5.02 TeV

The prompt D$^0$ meson azimuthal anisotropy coefficients, $v_2$ and $v_3$, are measured at midrapidity ($|y| < 1.0$) in PbPb collisions at a center-of-mass energy $\sqrt{s_\mathrm{NN}} = $5.02 TeV per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum ($p_\mathrm{T}$) range of 1 to 40 GeV/c, for central and midcentral collisions. The $v_2$ coefficient is found to be positive throughout the $p_\mathrm{T}$ range studied. The first measurement of the prompt D$^0$ meson $v_3$ coefficient is performed, and values up to 0.07 are observed for $p_\mathrm{T}$ around 4 GeV/c. Compared to measurements of charged particles, a similar $p_\mathrm{T}$ dependence, but smaller magnitude for $p_\mathrm{T} < $6 GeV/c, is found for prompt D$^0$ meson $v_2$ and $v_3$ coefficients. The results are consistent with the presence of collective motion of charm quarks at low $p_\mathrm{T}$ and a path length dependence of charm quark energy loss at high $p_\mathrm{T}$, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.

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arXiv2018

Search for natural and split supersymmetry in proton-proton collisions at $\sqrt{s} =$ 13 TeV in final states with jets and missing transverse momentum

A search for supersymmetry (SUSY) is performed in final states comprising one or more jets and missing transverse momentum using data from proton-proton collisions at a centre-of-mass energy of 13 TeV. The data were recorded with the CMS detector at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The number of signal events is found to agree with the expected background yields from standard model processes. The results are interpreted in the context of simplified models of SUSY that assume the production of gluino or squark pairs and their prompt decay to quarks and the lightest neutralino. The masses of bottom, top, and mass-degenerate light-flavour squarks are probed up to 1050, 1000, and 1325 GeV, respectively. The gluino mass is probed up to 1900, 1650, and 1650 GeV when the gluino decays via virtual states of the aforementioned squarks. The strongest mass bounds on the neutralinos from gluino and squark decays are 1150 and 575 GeV, respectively. The search also provides sensitivity to simplified models inspired by split SUSY that involve the production and decay of long-lived gluinos. Values of the proper decay length $cτ$ from $10^{-3}$ to $10^{5}$ mm are considered, as well as a metastable gluino scenario. Gluino masses up to 1750 and 900 GeV are probed for $cτ=$ 1 mm and for the metastable state, respectively. The sensitivity is moderately dependent on model assumptions for $cτ\gtrsim 1$ m. The search provides coverage of the $cτ$ parameter space for models involving long-lived gluinos that is complementary to existing techniques at the LHC.

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arXiv2018

Search for a heavy resonance decaying to a pair of vector bosons in the lepton plus merged jet final state at $\sqrt{s} =$ 13 TeV

A search for a new heavy particle decaying to a pair of vector bosons (WW or WZ) is presented using data from the CMS detector corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected in proton-proton collisions at a centre-of-mass energy of 13 TeV in 2016. One of the bosons is required to be a W boson decaying to e$ν$ or $μν$, while the other boson is required to be reconstructed as a single massive jet with substructure compatible with that of a highly-energetic quark pair from a W or Z boson decay. The search is performed in the resonance mass range between 1.0 and 4.5 TeV. The largest deviation from the background-only hypothesis is observed for a mass near 1.4 TeV and corresponds to a local significance of 2.5 standard deviations. The result is interpreted as an upper bound on the resonance production cross section. Comparing the excluded cross section values and the expectations from theoretical calculations in the bulk graviton and heavy vector triplet models, spin-2 WW resonances with mass smaller than 1.07 TeV and spin-1 WZ resonances lighter than 3.05 TeV, respectively, are excluded at 95% confidence level.

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arXiv2018

Search for lepton-flavor violating decays of heavy resonances and quantum black holes to e$μ$ final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV

A search is reported for heavy resonances decaying into e$μ$ final states in proton-proton collisions recorded by the CMS experiment at the CERN LHC at $\sqrt{s}=$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search focuses on resonance masses above 200 GeV. With no evidence found for physics beyond the standard model in the e$μ$ mass spectrum, upper limits are set at 95% confidence level on the product of the cross section and branching fraction for this lepton-flavor violating signal. Based on these results, resonant $τ$ sneutrino production in R-parity violating supersymmetric models is excluded for masses below 1.7 TeV, for couplings $λ_{132} = λ_{231} = λ'_{311} = 0.01$. Heavy Z$'$ gauge bosons with lepton-flavor violating transitions are excluded for masses up to 4.4 TeV. The e$μ$ mass spectrum is also interpreted in terms of non-resonant contributions from quantum black-hole production in models with one to six extra spatial dimensions, and lower mass limits are found between 3.6 and 5.6 TeV. In all interpretations used in this analysis, the results of this search improve previous limits by about 1 TeV. These limits correspond to the most sensitive values obtained at colliders.

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