693 research outputs found

    Measurement of the Dependence of the Hadron Production Fraction Ratios fs/fuf_s / f_u and fd/fuf_d / f_u on BB Meson Kinematic Variables in Proton-Proton Collisions at s=13TeV\sqrt{s} = 13 TeV

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    The dependence of the ratio between the Bs0B^0_s and B+B^+ hadron production fractions, fs/fuf_s/f_u, on the transverse momentum (pT)(p_T) and rapidity of the BB mesons is studied using the decay channels Bs0J/ψϕB^0_s→J/ψϕ and B+J/ψK+B^+→J/ψK^+. The analysis uses a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 61.6  fb161.6  fb^{−1}. The fs/fuf_s/f_u ratio is observed to depend on the BB pTp_T and to be consistent with becoming asymptotically constant at large pTp_T. No rapidity dependence is observed. The ratio of the B0B^0 to B+B^+ meson production fractions, fd/fuf_d/f_u, is also measured, for the first time in proton-proton collisions, using the B0J/ψK0B^0→J/ψK^{*0} decay channel. The result is found to be within 1 standard deviation of unity and independent of pTpT and rapidity, as expected from isospin invariance

    Search for top squark pair production in a final state with at least one hadronically decaying tau lepton in proton-proton collisions at s \sqrt{s} = 13 TeV

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    Observation of the Rare Decay of the η Meson to Four Muons

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    A search for the rare η→μ+μ−μ+μ− double-Dalitz decay is performed using a sample of proton-proton collisions, collected by the CMS experiment at the CERN LHC with high-rate muon triggers during 2017 and 2018 and corresponding to an integrated luminosity of 101  fb−1. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the η→μ+μ− decay as normalization, the branching fraction B(η→μ+μ−μ+μ−)=[5.0±0.8(stat)±0.7(syst)±0.7(B2μ)]×10−9 is measured, where the last term is the uncertainty in the normalization channel branching fraction. This work achieves an improved precision of over 5 orders of magnitude compared to previous results, leading to the first measurement of this branching fraction, which is found to agree with theoretical predictions

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

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    Performance of the local reconstruction algorithms for the CMS hadron calorimeter with Run 2 data

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    A description is presented of the algorithms used to reconstruct energy deposited in the CMS hadron calorimeter during Run 2 (2015–2018) of the LHC. During Run 2, the characteristic bunch-crossing spacing for proton-proton collisions was 25 ns, which resulted in overlapping signals from adjacent crossings. The energy corresponding to a particular bunch crossing of interest is estimated using the known pulse shapes of energy depositions in the calorimeter, which are measured as functions of both energy and time. A variety of algorithms were developed to mitigate the effects of adjacent bunch crossings on local energy reconstruction in the hadron calorimeter in Run 2, and their performance is compared

    Search for new physics in multijet events with at least one photon and large missing transverse momentum in proton-proton collisions at 13 TeV

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    A search for new physics in final states consisting of at least one photon, multiple jets, and large missing transverse momentum is presented, using proton-proton collision events at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 137 fb−1, recorded by the CMS experiment at the CERN LHC from 2016 to 2018. The events are divided into mutually exclusive bins characterized by the missing transverse momentum, the number of jets, the number of b-tagged jets, and jets consistent with the presence of hadronically decaying W, Z, or Higgs bosons. The observed data are found to be consistent with the prediction from standard model processes. The results are interpreted in the context of simplified models of pair production of supersymmetric particles via strong and electroweak interactions. Depending on the details of the signal models, gluinos and squarks of masses up to 2.35 and 1.43 TeV, respectively, and electroweakinos of masses up to 1.23 TeV are excluded at 95% confidence level

    Search for Higgs Boson and Observation of Z Boson through Their Decay into a Charm Quark-Antiquark Pair in Boosted Topologies in Proton-Proton Collisions at √s = 13 TeV

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    A search for the standard model (SM) Higgs boson (H) produced with transverse momentum (pT) greater than 450 GeV and decaying to a charm quark-antiquark (c¯c) pair is presented. The search is performed using proton-proton collision data collected at √s=13  TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138  fb−1. Boosted H→c¯c decay products are reconstructed as a single large-radius jet and identified using a deep neural network charm tagging technique. The method is validated by measuring the Z→c¯c decay process, which is observed in association with jets at high pT for the first time with a signal strength of 1.00+0.17−0.14(syst)±0.08(theo)±0.06(stat), defined as the ratio of the observed process rate to the SM expectation. The observed (expected) upper limit on σ(H)B(H→c¯c) is set at 47 (39) times the SM prediction at 95% confidence level

    First measurement of the top quark pair production cross section in proton-proton collisions at s \sqrt{s} = 13.6 TeV

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    The first measurement of the top quark pair (tt¯) production cross section in proton-proton collisions at s√ = 13.6 TeV is presented. Data recorded with the CMS detector at the CERN LHC in Summer 2022, corresponding to an integrated luminosity of 1.21 fb−1, are analyzed. Events are selected with one or two charged leptons (electrons or muons) and additional jets. A maximum likelihood fit is performed in event categories defined by the number and flavors of the leptons, the number of jets, and the number of jets identified as originating from b quarks. An inclusive tt¯ production cross section of 881 ± 23 (stat + syst) ± 20 (lumi) pb is measured, in agreement with the standard model prediction of 924+32−40 pb

    Measurements of inclusive and differential cross sections for the Higgs boson production and decay to four-leptons in proton-proton collisions at s \sqrt{s} = 13 TeV

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    Measurements of the inclusive and differential fiducial cross sections for the Higgs boson production in the H → ZZ → 4ℓ (ℓ = e, μ) 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 13 TeV, 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

    Observation of four top quark production in proton-proton collisions at √s = 13 TeV

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