891 research outputs found

    Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

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    The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ÏˆÎł, with the photons being measured through conversions to eâșe⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → ÎŒâșΌ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum

    Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)ÎŒâșΌ⁻ in proton-proton collisions at √s = 13 TeV

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    The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79±11(stat)±6(syst)±3(B) pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb⁻Âč. This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)ÎŒâșΌ⁻ in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks and two b antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass

    Observation of Two Excited B-c(+) States and Measurement of the B-c(+) (2S) Mass in pp Collisions at root s=13 TeV

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    Signals consistent with the B-c(+)(2S) and B-c*(+)(2S) states are observed in proton-proton collisions at root s = 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb(-1), collected by the CMS experiment during the 2015-2018 LHC running periods. These excited (b) over barc states are observed in the B-c(+)pi(+)pi(-) invariant mass spectrum, with the ground state B-c(+) reconstructed through its decay to J/psi pi(+). The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 +/- 1.5(stat) +/- 0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B-c(+)(2S) meson is measured to be 6871.0 +/- 1.2(stat) +/- 0.8(syst) +/- 0.8(B-c(+)) MeV, where the last term corresponds to the uncertainty in the world-average B-c(+) mass.Peer reviewe

    Observation of Two Excited Bâșc_{c} States and Measurement of the Bâșc_{c}(2S) Mass in pp Collisions at √s = 13 TeV

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    Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)ÎŒâșΌ⁻ in proton-proton collisions at √s = 13 TeV

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    The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79±11(stat)±6(syst)±3(B) pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb⁻Âč. This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)ÎŒâșΌ⁻ in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks and two b antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass

    Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)mu(+)mu(-) in proton-proton collisions at root s=13 TeV

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    The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13TeVin the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79 +/- 11 (stat) +/- 6 (syst) +/- 3 (B) pbassuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)mu(+)mu(-) in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two bquarks and two (b) over bar antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass. (C) 2020 The Author(s). Published by Elsevier B.V.Peer reviewe

    Search for W Boson Decays to Three Charged Pions

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    Search for a Narrow Resonance Lighter than 200 GeV Decaying to a Pair of Muons in Proton-Proton Collisions at root s=13 TeV

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    A search is presented for a narrow resonance decaying to a pair of oppositely charged muons using root s = 13 TeV proton-proton collision data recorded at the LHC. In the 45-75 and 110-200 GeV resonance mass ranges, the search is based on conventional triggering and event reconstruction techniques. In the 11.5-45 GeV mass range, the search uses data collected with dimuon triggers with low transverse momentum thresholds, recorded at high rate by storing a reduced amount of trigger-level information. The data correspond to integrated luminosities of 137 and 96.6 fb(-1) for conventional and high-rate triggering, respectively. No significant resonant peaks are observed in the probed mass ranges. The search sets the most stringent constraints to date on a dark photon in the similar to 30-75 and 110-200 GeV mass ranges.Peer reviewe
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