1,024 research outputs found

    Observation of the B⁰_s → X(3872)ϕ Decay

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    Using a data sample of proton-proton collisions at √s = 13  TeV, corresponding to an integrated luminosity of 140  fb⁻Âč collected by the CMS experiment in 2016–2018, the B⁰_s → X(3872)ϕ decay is observed. Decays into J/ψπâșπ⁻ and KâșK⁻ are used to reconstruct, respectively, the X(3872) and ϕ. The ratio of the product of branching fractions B[B⁰_s → X(3872)ϕ]B[X(3872) → J/ψπâșπ−] to the product B[B⁰_s → ψ(2S)ϕ]B[ψ(2S) → J/ψπâșπ−] is measured to be [2.21±0.29(stat)±0.17(syst)]%. The ratio B[B⁰_s → X(3872)ϕ]/B[B⁰ → X(3872)K⁰] is found to be consistent with one, while the ratio B[B⁰_s → X(3872)ϕ]/B[Bâș → X(3872)Kâș] is two times smaller. This suggests a difference in the production dynamics of the X(3872) in B⁰ and B⁰_s meson decays compared to Bâș. The reported observation may shed new light on the nature of the X(3872) particle

    Search for decays of the 125 GeV Higgs boson into a Z boson and a ρ or ϕ meson

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    Decays of the 125 GeV Higgs boson into a Z boson and a ρ^0(770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at √s = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb⁻Âč. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels

    Search for the lepton flavor violating decay τ → 3ÎŒ in proton-proton collisions at s \sqrt{\mathrm{s}} = 13 TeV

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    Results are reported from a search for the lepton flavor violating decay τ → 3ÎŒ in proton-proton collisions at s \sqrt{\mathrm{s}} = 13 TeV. The data sample corresponds to an integrated luminosity of 33.2 fb−1^{-1} recorded by the CMS experiment at the LHC in 2016. The search exploits τ leptons produced in both W boson and heavy-flavor hadron decays. No significant excess above the expected background is observed. An upper limit on the branching fraction B(τ → 3ÎŒ) of 8.0 x 10−8^{-8} at 90% confidence level is obtained, with an expected upper limit of 6.9 x 10−8^{-8}

    Observation of Forward Neutron Multiplicity Dependence of Dimuon Acoplanarity in Ultraperipheral Pb-Pb Collisions at sNN\sqrt{sNN} =5.02 TeV

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    The first measurement of the dependence of ÎłÎłâ†’ÎŒ+^{+} Ό−^{-} production on the multiplicity of neutrons emitted very close to the beam direction in ultraperipheral heavy ion collisions is reported. Data for lead-lead interactions at sNN\sqrt{^{s}NN}=5.02 TeV, with an integrated luminosity of approximately 1.5nb−1^{-1}, are collected using the CMS detector at the LHC. The azimuthal correlations between the two muons in the invariant mass region 88.3. The back-to-back correlation structure from leading-order photon-photon scattering is found to be significantly broader for events with a larger number of emitted neutrons from each nucleus, corresponding to interactions with a smaller impact parameter. This observation provides a data-driven demonstration that the average transverse momentum of photons emitted from relativistic heavy ions has an impact parameter dependence. These results provide new constraints on models of photon-induced interactions in ultraperipheral collisions. They also provide a baseline to search for possible final-state effects on lepton pairs caused by traversing a quark-gluon plasma produced in hadronic heavy ion collisions

    Inclusive search for highly boosted Higgs bosons decaying to bottom quark-antiquark pairs in proton-proton collisions at <mml:msqrt>s</mml:msqrt>=13 TeV

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    Nuclear modification of Y states in pPb collisions at √SNN_{NN} = 5.02 TeV

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    Production cross sections of ΄(1S), ΄(2S), and ΄(3S) states decaying into ÎŒ+Ό− in proton-lead (pPb) collisions are reported using data collected by the CMS experiment at √sNN = 5.02 TeV. A comparison is made with corresponding cross sections obtained with pp data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for ΄(1S) is found to be RpPb(΄(1S)) = 0.806±0.024 (stat)±0.059 (syst). Similar results for the excited states indicate a sequential suppression pattern, such that RpPb(΄(1S)) > RpPb(΄(2S)) > RpPb(΄(3S)). The suppression of all states is much less pronounced in pPb than in PbPb collisions, and independent of transverse momentum p΄T and center-of-mass rapidity y΄CM of the individual ΄ state in the studied range p ΄T < 30 GeV/c and |y΄CM| <1.93. Models that incorporate final-state effects of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications

    Study of Drell-Yan dimuon production in proton-lead collisions at sNN \sqrt{s_{\mathrm{NN}}} = 8.16 TeV

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    Differential cross sections for the Drell-Yan process, including Z boson production, using the dimuon decay channel are measured in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 173 nb−1. The differential cross section as a function of the dimuon mass is measured in the range 15–600 GeV, for the first time in proton-nucleus collisions. It is also reported as a function of dimuon rapidity over the mass ranges 15–60 GeV and 60–120 GeV, and ratios for the p-going over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum pT and of a geometric variable ϕ* are measured, where ϕ* highly correlates with pT but is determined with higher precision. In the Z mass region, the rapidity dependence of the data indicate a modification of the distribution of partons within a lead nucleus as compared to the proton case. The data are more precise than predictions based upon current models of parton distributions

    Measurement of differential cross sections for Z bosons produced in association with charm jets in pp collisions at s \sqrt{s} = 13 TeV

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    Measurements are presented of differential cross sections for the production of Z bosons in association with at least one jet initiated by a charm quark in pp collisions at s √s = 13 TeV. The data recorded by the CMS experiment at the LHC correspond to an integrated luminosity of 35.9 fb−1. The final states contain a pair of electrons or muons that are the decay products of a Z boson, and a jet consistent with being initiated by a charm quark produced in the hard interaction. Differential cross sections as a function of the transverse momentum pT of the Z boson and pT of the charm jet are compared with predictions from Monte Carlo event generators. The inclusive production cross section 405.4 ± 5.6 (stat) ± 24.3 (exp) ± 3.7 (theo) pb, is measured in a fiducial region requiring both leptons to have pseudorapidity |η| 10 GeV, at least one lepton with pT > 26 GeV, and a mass of the pair in the range 71–111 GeV, while the charm jet is required to have pT > 30 GeV and |η| < 2.4. These are the first measurements of these cross sections in proton-proton collisions at 13 TeV

    Fragmentation of jets containing a prompt J/ψ meson in PbPb and pp collisions at √sNN_{NN} = 5.02 TeV

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