Study of prompt D 0 meson production in pPb collisions at s N N = 5 $$ \sqrt{s_{\mathrm{N}\;\mathrm{N}}}=5 $$ TeV

Abstract

Production of prompt D 0 mesons is studied in proton-lead and lead-proton collisions recorded at the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58±0.02 nb −1 recorded at a nucleon-nucleon centre-of-mass energy of √ s NN = 5 TeV. Measurements of the differential cross-section, the forward-backward production ratio and the nuclear modification factor are reported using D 0 candidates with transverse momenta less than 10 GeV/c and rapidities in the ranges 1.5 < y * < 4.0 and −5.0 < y * < −2.5 in the nucleon-nucleon centre-of-mass system. Keywords: Charm physics, Heavy Ion Experiments, Heavy-ion collision, Particle and resonance productionArXiv ePrint: 1707.02750Open Access, Copyright CERN, for the benefit of the LHCb Collaboration. Article funded by SCOAP 3 .https://doi.org/10.1007/JHEP10(2017)090 JHEP10(2017)090 Conclusion 17The LHCb collaboration 23 IntroductionCharm hadrons produced in hadronic and nuclear collisions are excellent probes to study nuclear matter in extreme conditions. The differential cross-sections of c-quark production in pp or pp collisions have been calculated based on perturbative quantum chromodynamics (QCD) and collinear or k T factorisation [1][2][3][4][5][6]. These phenomenological models [7] are also able to predict the differential cross-section of c-quark production including most of the commonly assumed "cold nuclear matter" (CNM) effects in nuclear collisions, where CNM effects related to the parton flux differences and other effects come into play. Since heavy quarks are produced in hard scattering (with momentum transfer squared Q 2 2m c ) typically at a short time scale, they are ideal to examine hot nuclear matter, the so-called "quark-gluon plasma" (QGP), by studying how they traverse this medium and interact with it right after their formation.These studies require a thorough understanding of the CNM effects, which can be investigated in systems where the formation of QGP is not expected. In addition, a precise quantification of CNM effects would significantly improve the understanding of charmonium and open-charm production by confirming or discarding the possibility that the suppression pattern in the production of quarkonium states, like J/ψ , at the SPS, RHIC and LHC is due to QGP formation [7].The study of CNM effects is best performed in collisions of protons with heavy nuclei like lead, where the most relevant CNM effects, such as nuclear modification of the parton densities [8,9] and in-medium energy loss [10] in initial-and final-state radiation [11,12], -1 - JHEP10(2017)090are more evident. Phenomenologically, collinear parton distributions are often used to describe the nuclear modification of the parton flux in the nucleus. The modification with respect to the free nucleon depends on the parton fractional longitudinal momentum x, Q 2 and the atomic mass number of the nucleus A [13,14]. In the low-x region, down to x ≈ 10 −5 −10 −6 , which is accessible at LHC energies at forward rapidity, a possible onset of gl...

Cathode tube effect: Heavy quarks probing the glasma in p -Pb collisions

“…In particular, we are interested to the nuclear modification factor, R pPb , for D−mesons that has been measured recently [54,55]. In fact, we find that the propagation in gluon fields leads to R pPb that reminds at least qualitatively the one measured for D−mesons in p-Pb collisions.…”

“…The result is shown for two values of g 2 µ Pb for the Pb nucleus at √ s = 5.02 TeV, namely g 2 µ Pb = 3.4 GeV (dashed blue line) and g 2 µ Pb = 5.2 GeV (solid green line) as discussed in the previous section. Experimental data correspond to the backward rapidity region (namely to the proton side) obtained by the LHCb collaboration [55]. We remark that although we show experimental data here, we do not aim to a precise fit of these by our calculation because we miss the longitudinal expansion: data are shown only to quantify the order of magnitude of our result, while a closer comparison with data will be the subject of a forthcoming study.…”

Saturation and forward jets in proton-lead collisions at the LHC

“…Particle production at the LHC in the forward direction will probe much smaller values of x in the nucleus than what is achievable at RHIC. Currently, the most decisive small-x data are arguably the D-and B-meson measurements by the LHCb collaboration [28,29] which both show that the p-Pb cross sections at y 0 are clearly suppressed with respect to the p-p baseline. Out of these two the D-meson production should be the most sensitive to the non-linear dynamics due to the low interaction scale involved.…”

Forward rapidity isolated photon production in proton-nucleus collisions

“…Nuclear modifiction factor for D-mesons [7] (left) and double ratio of nuclear modification factor for J/ψ divided by the one for Drell-Yan-dileptons [8] (right). Note that the LHCb data in this plot is preliminary and the normalization in the finalized data [9] is somewhat lower.…”