2,963 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/ψγ, with the photons being measured through conversions to e⁺e⁻, 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 → μ⁺μ⁻ 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 quarkonium production cross sections in pp collisions at root s=13 TeV

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    Differential production cross sections of prompt J/psi and psi(2S) charmonium and Upsilon(nS) (n = 1, 2, 3) bottomonium states are measured in proton-proton collisions at root s = 13 TeV, with data collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 2.3 fb(-1) for the J/psi and 2.7 fb(-1) for the other mesons. The five quarkonium states are reconstructed in the dimuon decay channel, for dimuon rapidity vertical bar y vertical bar <1.2. The double-differential cross sections for each state are measured as a function of y and transverse momentum, and compared to theoretical expectations. In addition, ratios are presented of cross sections for prompt psi(2S) to J/psi, Upsilon(2S) to Upsilon(1S), and Upsilon(3S) to Upsilon(1S) production. (C) 2018 The Author(s). Published by Elsevier B.V.Peer reviewe
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