A measurement of J / ψ and ψ ( 2 S ) production is presented. It is based on a data sample from Pb+Pb collisions at s NN = 5.02 TeV and pp collisions at s = 5.02 TeV recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of 0.42 nb - 1 and 25 pb - 1 in Pb+Pb and pp, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for 9 < p T μ μ < 40 GeV in dimuon transverse momentum, and - 2 < y μ μ < 2 in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt J / ψ , increasing with event centrality. The suppression of prompt ψ ( 2 S ) is observed to be stronger than that of J / ψ , while the suppression of non-prompt ψ ( 2 S ) is equal to that of the non-prompt J / ψ within uncertainties, consistent with the expectation that both arise from b-quarks propagating through the medium. Despite prompt and non-prompt J / ψ arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.

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• časopisecké články MeSH

We present results on transverse momentum ([Formula: see text]) and rapidity ([Formula: see text]) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive [Formula: see text] and [Formula: see text] at forward rapidity ([Formula: see text]) as well as [Formula: see text]-to-[Formula: see text] cross section ratios. These quantities are measured in pp collisions at center of mass energies [Formula: see text] and 13 TeV with the ALICE detector. Both charmonium states are reconstructed in the dimuon decay channel, using the muon spectrometer. A comprehensive comparison to inclusive charmonium cross sections measured at [Formula: see text], 7 and 8 TeV is performed. A comparison to non-relativistic quantum chromodynamics and fixed-order next-to-leading logarithm calculations, which describe prompt and non-prompt charmonium production respectively, is also presented. A good description of the data is obtained over the full [Formula: see text] range, provided that both contributions are summed. In particular, it is found that for [Formula: see text] GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield.

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• časopisecké články MeSH

The nuclear modification factor [Formula: see text] and the azimuthal anisotropy coefficient [Formula: see text] of prompt and nonprompt (i.e. those from decays of b hadrons) [Formula: see text] mesons, measured from PbPb and pp collisions at [Formula: see text] [Formula: see text] at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta [Formula: see text] [Formula: see text] and rapidity [Formula: see text], extending down to [Formula: see text] [Formula: see text] in the [Formula: see text] range. The [Formula: see text] of prompt [Formula: see text] is found to be nonzero, but with no strong dependence on centrality, rapidity, or [Formula: see text] over the full kinematic range studied. The measured [Formula: see text] of nonprompt [Formula: see text] is consistent with zero. The [Formula: see text] of prompt [Formula: see text] exhibits a suppression that increases from peripheral to central collisions but does not vary strongly as a function of either y or [Formula: see text] in the fiducial range. The nonprompt [Formula: see text] [Formula: see text] shows a suppression which becomes stronger as rapidity or [Formula: see text] increases. The [Formula: see text] and [Formula: see text] of open and hidden charm, and of open charm and beauty, are compared.

• Publikační typ
• časopisecké články MeSH

The production of two prompt [Formula: see text] mesons, each with transverse momenta [Formula: see text] GeV and rapidity [Formula: see text], is studied using a sample of proton-proton collisions at [Formula: see text] TeV, corresponding to an integrated luminosity of 11.4 fb[Formula: see text] collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised [Formula: see text] production, is measured as a function of the transverse momentum of the lower-[Formula: see text] [Formula: see text] meson, di-[Formula: see text] [Formula: see text] and mass, the difference in rapidity between the two [Formula: see text] mesons, and the azimuthal angle between the two [Formula: see text] mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two [Formula: see text] mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be [Formula: see text] mb.

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• časopisecké články MeSH

We report on the inclusive production cross sections of [Formula: see text], [Formula: see text], [Formula: see text](1S), [Formula: see text](2S) and [Formula: see text](3S), measured at forward rapidity with the ALICE detector in [Formula: see text] collisions at a center-of-mass energy [Formula: see text] TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb[Formula: see text]. Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum [Formula: see text] and rapidity y, over the [Formula: see text] ranges [Formula: see text] GeV/c for [Formula: see text], [Formula: see text] GeV/c for all other resonances, and for [Formula: see text]. The cross sections, integrated over [Formula: see text] and y, and assuming unpolarized quarkonia, are [Formula: see text] [Formula: see text]b, [Formula: see text] [Formula: see text]b, [Formula: see text] nb, [Formula: see text] nb and [Formula: see text] nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most [Formula: see text], with measurements performed by the LHCb collaboration in the same rapidity range.

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• časopisecké články MeSH