15 research outputs found

    Measurement of the top quark mass using events with a single reconstructed top quark in pp collisions at root s=13 TeV

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    Abstract:A measurement of the top quark mass is performed using a data sample en-riched with single top quark events produced in thetchannel. The study is based on proton-proton collision data, corresponding to an integrated luminosity of 35.9 fb−1, recorded at√s= 13TeV by the CMS experiment at the LHC in 2016. Candidate events are selectedby requiring an isolated high-momentum lepton (muon or electron) and exactly two jets,of which one is identified as originating from a bottom quark. Multivariate discriminantsare designed to separate the signal from the background. Optimized thresholds are placedon the discriminant outputs to obtain an event sample with high signal purity. The topquark mass is found to be172.13+0.76−0.77GeV, where the uncertainty includes both the sta-tistical and systematic components, reaching sub-GeV precision for the first time in thisevent topology. The masses of the top quark and antiquark are also determined separatelyusing the lepton charge in the final state, from which the mass ratio and difference aredetermined to be0.9952+0.0079−0.0104and0.83+1.79−1.35GeV, respectively. The results are consistentwithCPTinvariance

    Measurements of Higgs boson production cross sections and couplings in the diphoton decay channel at root s=13 TeV

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    Measurements of Higgs boson production cross sections and couplings in events where the Higgs boson decays into a pair of photons are reported. Events are selected from a sample of proton-proton collisions at root s = 13TeV collected by the CMS detector at the LHC from 2016 to 2018, corresponding to an integrated luminosity of 137 fb(-1). Analysis categories enriched in Higgs boson events produced via gluon fusion, vector boson fusion, vector boson associated production, and production associated with top quarks are constructed. The total Higgs boson signal strength, relative to the standard model (SM) prediction, is measured to be 1.12 +/- 0.09. Other properties of the Higgs boson are measured, including SM signal strength modifiers, production cross sections, and its couplings to other particles. These include the most precise measurements of gluon fusion and vector boson fusion Higgs boson production in several different kinematic regions, the first measurement of Higgs boson production in association with a top quark pair in five regions of the Higgs boson transverse momentum, and an upper limit on the rate of Higgs boson production in association with a single top quark. All results are found to be in agreement with the SM expectations.Peer reviewe

    Whole-exome sequencing identifies rare and low-frequency coding variants associated with LDL cholesterol

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    Elevated low-density lipoprotein cholesterol (LDL-C) is a treatable, heritable risk factor for cardiovascular disease. Genome-wide association studies (GWASs) have identified 157 variants associated with lipid levels but are not well suited to assess the impact of rare and low-frequency variants. To determine whether rare or low-frequency coding variants are associated with LDL-C, we exome sequenced 2,005 individuals, including 554 individuals selected for extreme LDL-C (>98th or <2nd percentile). Follow-up analyses included sequencing of 1,302 additional individuals and genotype-based analysis of 52,221 individuals. We observed significant evidence of association between LDL-C and the burden of rare or low-frequency variants in PNPLA5, encoding a phospholipase-domain-containing protein, and both known and previous

    Evidence for the singly Cabibbo suppressed decay Lambda_c+ --> p eta and search for Lambda_c+ --> p pi0

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    We study the singly Cabibbo suppressed decays Lambda_c+ --> p eta and Lambda_c+ → pπ0 using Lambda+Lambda_c- pairs produced by e+e- collisions at a center-of-mass energy of sqrt(s) =4.6 GeV. The data sample was collected by the BESIII detector at the BEPCII collider and corresponds to an integrated luminosity of 567 pb-1. We find the first evidence for the decay Lambda_c+ --> p eta with a statistical significance of 4.2 sigma and measure its branching fraction to be B( Lambda_c+ --> p eta)=(1.24±0.28(stat)±0.10(syst))10-3. No significant Lambda_c+ --> p pi0 signal is observed. We set an upper limit on its branching fraction B( Lambda_c+ --> p pi0)<2.7x10-4 at the 90% confidence level

    Observation of χc2ηη\chi_{c2}\to\eta'\eta' and χc0,2ηη\chi_{c0,2}\to\eta\eta'

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    Using a sample of 448.1×106  ψ(3686) events collected with the BESIII detector in 2009 and 2012, we study the decays χc0,2→η′η′ and ηη′. The decays χc2→η′η′, χc0→ηη′ and χc2→ηη′ are observed for the first time with statistical significances of 9.6σ, 13.4σ and 7.5σ, respectively. The branching fractions are determined to be B(χc0→η′η′)=(2.19±0.03±0.14)×10-3, B(χc2→η′η′)=(4.76±0.56±0.38)×10-5, B(χc0→ηη′)=(8.92±0.84±0.65)×10-5 and B(χc2→ηη′)=(2.27±0.43±0.25)×10-5, where the first uncertainties are statistical and the second are systematic. The precision for the measurement of B(χc0→η′η′) is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for χc0,2 decays into pseudoscalar meson pairs can be clarified.Using a sample of 447.9×106447.9\times 10^6 ψ(3686)\psi(3686) events collected with the BESIII detector in 2009 and 2012, we study the decays χc0,2\chi_{c0,2}\to ηη\eta'\eta' and ηη\eta\eta'. The decays χc2ηη\chi_{c2}\to\eta'\eta', χc0ηη\chi_{c0}\to\eta\eta' and χc2ηη\chi_{c2}\to\eta\eta' are observed for the first time with statistical significances of 9.6σ9.6\sigma, 13.4σ13.4\sigma and 7.5σ7.5\sigma, respectively. The branching fractions are determined to be B(χc0ηη)=(2.19±0.03±0.14)×103\mathcal{B}(\chi_{c0}\to\eta'\eta') =(2.19\pm0.03\pm0.14)\times10^{-3}, B(χc2ηη)=(4.76±0.56±0.38)×105\mathcal{B}(\chi_{c2}\to\eta'\eta') = (4.76\pm0.56\pm0.38)\times10^{-5}, B(χc0ηη)=(8.92±0.84±0.65)×105\mathcal{B}(\chi_{c0}\to\eta\eta') = (8.92\pm0.84\pm0.65)\times10^{-5} and B(χc2ηη)=(2.27±0.43±0.25)×105\mathcal{B}(\chi_{c2}\to\eta\eta') = (2.27\pm0.43\pm0.25)\times10^{-5}, where the first uncertainties are statistical and the second systematic. The precision for the measurement of B(χc0ηη)\mathcal{B}(\chi_{c0}\to\eta'\eta') is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for χc0,2\chi_{c0,2} decays into pseudoscalar meson pairs can be clarified

    Measurement of the phase between strong and electromagnetic amplitudes of J/ψ decays

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    Using 16 energy points of e+e− annihilation data collected in the vicinity of the J/ψ resonance with the BESIII detector and with a total integrated luminosity of around 100pb−1, we study the relative phase between the strong and electromagnetic amplitudes of J/ψ decays. The relative phase between J/ψ electromagnetic decay and the continuum process (e+e− annihilation without the J/ψ resonance) is confirmed to be zero by studying the cross section lineshape of μ+μ− production. The relative phase between J/ψ strong and electromagnetic decays is then measured to be (84.9±3.6)∘ or (−84.7±3.1)∘ for the 2(π+π−)π0 final state by investigating the interference pattern between the J/ψ decay and the continuum process. This is the first measurement of the relative phase between J/ψ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state ηπ+π− with η→π+π−π0, which provides additional information about the phase between the J/ψ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/ψ→2(π+π−)π0 is measured to be (4.73±0.44)% or (4.85±0.45)%, and the branching fraction of J/ψ→ηπ+π− is measured to be (3.78±0.68)×10−4. Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics. Keywords: Phase, Strong amplitude, Electromagnetic amplitude, J/ψ decay, BESII
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