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D-meson production in p-Pb collisions at √sNN = 5.02 TeV and in pp collisions at √s = 7 TeV

机译：√sNN= 5.02 TeV时p-Pb碰撞中的D介子产生和√s= 7 TeV时pp碰撞中的D介子产生

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Background: In the context of the investigation of the quark gluon plasma produced in heavy-ion collisions, hadrons containing heavy (charm or beauty) quarks play a special role for the characterization of the hot and dense medium created in the interaction. The measurement of the production of charm and beauty hadrons in proton– proton collisions, besides providing the necessary reference for the studies in heavy-ion reactions, constitutes an important test of perturbative quantum chromodynamics (pQCD) calculations. Heavy-flavor production in proton–nucleus collisions is sensitive to the various effects related to the presence of nuclei in the colliding system, commonly denoted cold-nuclear-matter effects. Most of these effects are expected to modify open-charm production at low transverse momenta (pT) and, so far, no measurement of D-meson production down to zero transverse momentum was available at mid-rapidity at the energies attained at the CERN Large Hadron Collider (LHC).udPurpose: The measurements of the production cross sections of promptly produced charmed mesons in p-Pb collisions at the LHC down to pT = 0 and the comparison to the results from pp interactions are aimed at the assessment of cold-nuclear-matter effects on open-charm production, which is crucial for the interpretation of the results from Pb-Pb collisions.udMethods: The prompt charmed mesons D0, D+, D∗+, and Ds+ were measured at mid-rapidity in p-Pb collisions at a center-of-mass energy per nucleon pair √sNN = 5.02 TeV with the ALICE detector at the LHC.D mesons were reconstructed from their decays D0 → K−π+, D+ → K−π+π+, D∗+ → D0π+, Ds+ → φπ+ → K−K+π+, and their charge conjugates, using an analysis method based on the selection of decay topologies displaced from the interaction vertex. In addition, the prompt D0 production cross section was measured in pp collisions at √s = 7 TeV and p-Pb collisions at √sNN = 5.02 TeV down to pT = 0 using an analysis technique that is based on the estimation and subtraction of the combinatorial background, without reconstruction of the D0 decay vertex. Results: The production cross section in pp collisions is described within uncertainties by different implementations of pQCD calculations down to pT = 0. This allowed also a determination of the total cc ̄ production cross section in pp collisions, which is more precise than previous ALICE measurements because it is not affected by uncertainties owing to the extrapolation to pT = 0. The nuclear modification factor RpPb(pT), defined as the ratio of the pT-differential D meson cross section in p-Pb collisions and that in pp collisions scaled by the mass number of the Pb nucleus, was calculated for the four D-meson species and found to be compatible with unity within uncertainties. The results are compared to theoretical calculations that include cold-nuclear-matter effects and to transport model calculations incorporating the interactions of charm quarks with an expanding deconfined medium.udConclusions: These measurements add experimental evidence that the modification of the D-meson transverse momentum distributions observed in Pb–Pb collisions with respect to pp interactions is due to strong final-state effects induced by the interactions of the charm quarks with the hot and dense partonic medium created in ultrarelativistic heavy-ion collisions. The current precision of the measurement does not allow us to draw conclusions on the role of the different cold-nuclear-matter effects and on the possible presence of additional hot-medium effects in p-Pb collisions. However, the analysis technique without decay-vertex reconstruction, applied on future larger data samples, should provide access to the physics-rich range down to pT = 0
机译：背景：在对重离子碰撞中产生的夸克胶子等离子体进行研究的背景下，包含重（魅力或美感）夸克的强子在表征相互作用中产生的高温高密度介质方面起着特殊作用。质子-质子碰撞中魅力和美丽强子的产生的测量除为重离子反应研究提供必要的参考外，还构成了扰动量子色动力学（pQCD）计算的重要测试。质子-核碰撞中的重味产生对碰撞系统中与核的存在有关的各种效应敏感，通常称为冷核物质效应。预期这些效应中的大多数会在低横向动量（pT）时改变开式煤的生产，到目前为止，在CERN Large所达到的能量下，在中速时还无法测量D介子的生产直至零横向动量。 Hadron Collider（LHC）。 ud目的：测量LHC直至pT = 0时p-Pb碰撞中迅速产生的介子介子的生产截面，并将其与pp相互作用的结果进行比较以评估寒冷-核物质对开孔化学物质产生的影响，这对于解释Pb-Pb碰撞的结果至关重要。 ud方法：在中速时测量了迅速迷住的介子D0，D +，D ∗ +和Ds +在LHC上用ALICE检测器在每个核子对质心能量√pNN处碰撞sNS = 5.02 TeV.D介子是根据其衰变D0→K-π+，D +→K-π+π+重建的，D ∗ +→D0π+，Ds +→φπ+→K−K +π+及其电荷共轭物，使用分析方法库d关于从交互顶点位移的衰减拓扑的选择。此外，采用分析技术，基于√s= 7 TeV的pp碰撞和√sNN= 5.02 TeV直至pT = 0的p-Pb碰撞，测量了D0瞬变截面。组合背景，无需重建D0衰减顶点。结果：pp碰撞中的生产横截面在不确定性下通过pQCD计算的低至pT = 0的描述来描述。这也使得能够确定pp碰撞中的总cc̄生产横截面，这比以前的ALICE测量更精确因为它不受外推至pT = 0的不确定性的影响。核修饰因子RpPb（pT）定义为p-Pb碰撞中pT-D介子截面的比例与pp碰撞中的比例计算了四个D介子物种的Pb原子核的质量数，发现与不确定性内的单位相容。将结果与包括冷核物质效应的理论计算结果进行比较，并与结合了夸克夸克与扩展的受限介质的相互作用的传输模型计算结果进行比较。 ud结论：这些测量结果提供了实验证据，表明D介子横向动量的变化在Pb–Pb碰撞中观察到的与pp相互作用有关的分布是由于夸克夸克与超相对论重离子碰撞中产生的浓热的部分离子介质的相互作用引起的强烈的最终状态效应。当前的测量精度无法得出关于不同的冷核物质效应的作用以及在p-Pb碰撞中可能存在其他热介质效应的结论。但是，如果将分析技术应用于未来的较大数据样本，而无需进行衰减-顶点重建，则应可访问低pT = 0的丰富物理范围

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