116 research outputs found

    Measurement of the Higgs boson width and evidence of its off-shell contributions to ZZ production

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    Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width—related to its lifetime—is an important parameter. One way to determine this quantity is to measure its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here we report evidence for such off-shell contributions to the production cross-section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at the 95% confidence level. The scenario with no off-shell contribution is excluded at a p-value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as Γ\GammaH_H=3.21.7+2.4^{+2.4}_{−1.7}MeV, in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs

    Search for new particles in an extended Higgs sector with four b quarks in the final state at √s = 13 TeV

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    A search for a massive resonance X decaying to a pair of spin-0 bosons ϕ that themselves decay to pairs of bottom quarks, is presented. The analysis is restricted to the mass ranges from 25 to 100 GeV and from 1 to 3 TeV. For these mass ranges, the decay products of each ϕ boson are expected to merge into a single large-radius jet. Jet substructure and flavor identification techniques are used to identify these jets. The search is based on CERN LHC proton-proton collision data at , collected with the CMS detector in 2016–2018, corresponding to an integrated luminosity of 138 . Model-specific limits, where the two new particles arise from an extended Higgs sector, are set on the product of the production cross section and branching fraction for as a function of the resonances' masses, where both the and branching fractions are assumed to be 100%. These limits are the first of their kind on this process, ranging between 30 and 1 fb at 95% confidence level for the considered mass ranges

    Search for resonances decaying to three W bosons in the hadronic final state in proton-proton collisions at ps=13 TeV

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    A search for Kaluza-Klein excited vector boson resonances, W KK , decaying in cascade to three W bosons via a scalar radion R , W KK → W R → W W W , in a final state containing two or three massive jets is presented. The search is performed with √ s = 13     TeV proton-proton collision data collected by the CMS experiment at the CERN LHC during 2016–2018, corresponding to an integrated luminosity of 138     fb − 1 . Two final states are simultaneously probed, one where the two W bosons produced by the R decay are reconstructed as separate, large-radius, massive jets, and one where they are merged into a single large-radius jet. The observed data are in agreement with the standard model expectations. Limits are set on the product of the W KK resonance cross section and branching fraction to three W bosons in an extended warped extra-dimensional model and are the first of their kind at the LHC

    Measurement of the Higgs boson width and evidence of its off-shell contributions to ZZ production

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    Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width—related to its lifetime—is an important parameter. One way to determine this quantity is to measure its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here we report evidence for such off-shell contributions to the production cross-section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at the 95% confidence level. The scenario with no off-shell contribution is excluded at a p-value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as ΓH=3.2+2.4−1.7MeV, in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs

    Measurement of the B-s(0) \u2192 mu(+)mu(-) decay properties and search for the B-0 \u2192 mu(+)mu(-) decay in proton-proton collisions at 1as=13 TeV

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    Search for Z\u2032 bosons decaying to pairs of heavy Majorana neutrinos in proton-proton collisions at 1as=13 TeV

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    Abstract: A search for the production of pairs of heavy Majorana neutrinos (N-& ell;) from the decays of Z ' bosons is performed using the CMS detector at the LHC. The data were collected in proton-proton collisions at a center-of-mass energy of root s = 13 TeV, with an integrated luminosity of 138 fb(-1). The signature for the search is an excess in the invariant mass distribution of the final-state objects, two same-flavor leptons (e or mu) and at least two jets. No significant excess of events beyond the expected background is observed. Upper limits at 95% confidence level are set on the product of the Z ' production cross section and its branching fraction to a pair of N-& ell;, as functions of N-& ell; and Z ' boson masses (m(N & ell;) and m(Z '), respectively) for m(Z ') from 0.4 to 4.6 TeV and m(N & ell;) from 0.1 TeV to m(Z ')/2. In the theoretical framework of a left-right symmetric model, exclusion bounds in the m(N & ell;)-m(Z ') plane are presented in both the electron and muon channels. The observed upper limit on m(Z ') reaches up to 4.42 TeV. These are the most restrictive limits to date on the mass of N as a function of the Z ' boson mass

    Measurements of the azimuthal anisotropy of prompt and nonprompt charmonia in PbPb collisions at <tex>\sqrt{s_{NN}}$</tex>=5.02 TeV

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    Abstract: The second-order (v(2)) and third-order (v(3)) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/psi, as well as prompt psi(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.02TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb(-1) recorded with the CMS detector. The J/psi and psi(2S) mesons are reconstructed using their dimuon decay channel. The v(2) and v(3) coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measured v(2) values for prompt J/psi mesons are found to be larger than those for nonprompt J/psi mesons. The prompt J/psi v(2) values at high pT are found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/psi meson v(3) and prompt psi(2S) v(2) and v(3) values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions

    Search for a high-mass dimuon resonance produced in association with b quark jets at 1as=13 TeV

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    Abstract: A search for high-mass dimuon resonance production in association with one or more b quark jets is presented. The study uses proton-proton collision data collected with the CMS detector at the LHC corresponding to an integrated luminosity of 138 fb(-1) at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the number of signal events with exactly one or more than one b quark jet. Results are also interpreted in a lepton-flavor-universal model with Z boson couplings to a bb quark pair (g(b)), an sb quark pair (g(b)delta(bs)), and any same-flavor charged lepton (g(l)) or neutrino pair (g(nu)), with |g(nu)| = |g(l)|. For a Z ' boson with a mass mZ ' = 350 GeV (2 TeV) and |delta(bs)| sll measurements. In this scenario, most of the allowed parameter space is excluded for a Z ' boson with 350 < mZ ' < 500 GeV, while the constraints are less stringent for higher mZ ' hypotheses. This is the first dedicated search at the LHC for a high-mass dimuon resonance produced in association with multiple b quark jets, and the constraints obtained on models with this signature are the most stringent to date

    Evidence for four-top quark production in proton-proton collisions at s=13TeV

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    The production of four top quarks (tt¯tt¯) is studied with LHC proton-proton collision data samples collected by the CMS experiment at a center-of-mass energy of 13 TeV, and corresponding to integrated luminosities of up to 138 fb−1. Events that have no leptons (all-hadronic), one lepton, or two opposite-sign leptons (where lepton refers only to prompt electrons or prompt muons) are considered. This is the first tt¯tt¯ measurement that includes the all-hadronic final state. The observed significance of the tt¯tt¯ signal in these final states of 3.9 standard deviations (1.5 expected) provides evidence for tt¯tt¯ production, with a measured cross section of 36 +12−11 fb. Combined with earlier CMS results in other final states, the signal significance is 4.0 standard deviations (3.2 expected). The combination returns an observed cross section of 17 ± 4 (stat) ± 3 (syst) fb, which is consistent with the standard model prediction

    Measurements of inclusive and differential cross sections for the Higgs boson production and decay to four-leptons in proton-proton collisions at 1as=13 TeV

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    Abstract: Measurements of the inclusive and differential fiducial cross sections for the Higgs boson production in the H -> ZZ -> 4 l ( l = e, mu) decay channel are presented. The results are obtained from the analysis of proton-proton collision data recorded by the CMS experiment at the CERN LHC at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 138 fb(-1). The measured inclusive fiducial cross section is 2.73 +/- 0.26 fb, in agreement with the standard model expectation of 2.86 +/- 0.1 fb. Differential cross sections are measured as a function of several kinematic observables sensitive to the Higgs boson production and decay to four leptons. A set of double-differential measurements is also performed, yielding a comprehensive characterization of the four leptons final state. Constraints on the Higgs boson trilinear coupling and on the bottom and charm quark coupling modifiers are derived from its transverse momentum distribution. All results are consistent with theoretical predictions from the standard model
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