902 research outputs found

    A 10-3 drift velocity monitoring chamber

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    The MEG-II experiment searches for the lepton flavor violating decay: mu in electron and gamma. The reconstruction of the positron trajectory uses a cylindrical drift chamber operated with a mixture of He and iC4H10 gas. It is important to provide a stable performance of the detector in terms of its electron transport parameters, avalanche multiplication, composition and purity of the gas mixture. In order to have a continuous monitoring of the quality of gas, we plan to install a small drift chamber, with a simple geometry that allows to measure very precisely the electron drift velocity in a prompt way. This monitoring chamber will be supplied with gas coming from the inlet and the outlet of the detector to determine if gas contaminations originate inside the main chamber or in the gas supply system. The chamber is a small box with cathode walls, that define a highly uniform electric field inside two adjacent drift cells. Along the axis separating the two drift cells, four staggered sense wires alternated with five guard wires collect the drifting electrons. The trigger is provided by two 90Sr weak calibration radioactive sources placed on top of a two thin scintillator tiles telescope. The whole system is designed to give a prompt response (within a minute) about drift velocity variations at the 0.001 level

    Effects of the electronic threshold on the performance of the RPC system of the CMS experiment

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    Resistive Plate Chambers have a very important role for muon triggering both in the barrel and in the endcap regions of the CMS experiment at the Large Hadron Collider (LHC). In order to optimize their performance, it is of primary importance to tune the electronic threshold of the front-end boards reading the signals from these detectors. In this paper we present the results of a study aimed to evaluate the effects on the RPC efficiency, cluster size and detector intrinsic noise rate, of variations of the electronics threshold voltage

    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

    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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    Measurements of the differential cross sections of the production of Z + jets and Îł + jets and of Z boson emission collinear with a jet in pp collisions at s \sqrt{s} = 13 TeV

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    Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet

    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
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