[论文解读] Measurement of D$^{+}$ meson production in p-Pb collisions with the ALICE detector

Riccardo Russo|arXiv (Cornell University)|Oct 20, 2015

High-Energy Particle Collisions Research参考文献 46被引用 11

一句话总结

本论文利用LHC上的ALICE探测器，在√sNN = 5.02 TeV的p-Pb碰撞中测量了D⁺介子的产生。通过分析D⁺ → K⁻π⁺π⁺衰变道，该研究在不同横动量和快度范围内提取了核子修改因子R_pPb，为质子-铅系统中部分子能量损失和冷核物质效应提供了新见解。

ABSTRACT

The main goal of the experimental programs on ultra-relativistic heavy ion collisions at the LHC is the production and characterization of the Quark Gluon Plasma (QGP), a phase of nuclear matter in which strongly interacting constituents (quarks and gluons) are deconfined. Heavy quarks are considered effective probes of the properties of the QGP as they are created on a short time scale, with respect to that of the QGP, and subsequently interact with it. Moreover, for a proper assessment of the characteristics of the matter produced in heavy-ion collisions, it is important to disentangle the final state effects due to the formation of a QGP from the initial state effects due to the fact that nuclei are present in the colliding system. Both initial and final state effects may lead to qualitatively similar phenomena in the observables of interest. The measurement of charmed meson production in proton-nucleus collisions allows to assess initial state effects present in nuclear collisions, under the assumption that an extended deconfined medium is not created in this kind of interactions. The nuclear modification factor of $D$ mesons in p-Pb collisions ($R_{ m pPb}$) is essential for a complete understanding of the modification of $D$ mesons momentum distributions observed in Pb-Pb collisions at $\sqrt{s_{ m NN}}$= 2.76 TeV, which is interpreted as due to the $c$-quark energy loss in the medium. In addition, some of the results obtained from high-multiplicity p-Pb collisions at LHC, such as the ridge structure in the two-particle correlation function, turned out to be unexpected, and have been interpreted in terms of final state effects such as hydrodynamic flow. These aspects make a study of charmed meson production in p-Pb collisions as a function of the event multiplicity of great interest.

研究动机与目标

• 测量在√sNN = 5.02 TeV下的p-Pb碰撞中D⁺介子的产生产额。
• 测定核子修改因子R_pPb随横动量和快度的变化关系。
• 研究质子-铅碰撞中部分子能量损失和核阴影效应等冷核物质效应。
• 为重夸克在核环境中产生理论模型提供精确的实验数据以供比较。

提出的方法

• 利用LHC上的ALICE探测器收集在√sNN = 5.02 TeV下p-Pb碰撞的数据。
• 通过D⁺ → K⁻π⁺π⁺衰变道，利用顶点重建和粒子识别方法重建D⁺介子。
• 应用运动学和拓扑选择条件以抑制组合背景和非D⁺背景贡献。
• 在横动量（p_T）和快度（y）的分箱中测量微分产生截面。
• 通过公式R_pPb = (1/N_coll) × (dσ_pPb/dp_T)/(dσ_pp/dp_T)计算核子修改因子，以量化核效应。
• 对效率、背景和探测器响应进行系统不确定性评估。

实验结果

研究问题

• RQ1 在相同质心系能量下，p-Pb碰撞中D⁺介子的产生率与pp碰撞相比如何？
• RQ2 核子修改因子R_pPb随横动量和快度的变化行为如何？
• RQ3 R_pPb是否存在显著偏离1的情况，表明存在部分子能量损失或其他冷核物质效应？
• RQ4 所测得的D⁺产生率在多大程度上支持或挑战重夸克在核物质中产生的理论模型？

主要发现

• 测量得到的p-Pb碰撞中D⁺介子产生截面显示出明显的横动量依赖性，低p_T区域呈现峰值。
• 在大多数p_T和y区间内，核子修改因子R_pPb与1一致，不确定性范围内，表明无显著抑制或增强。
• 在特定运动学区域观察到与1的小幅偏离，但均在系统不确定性范围内，未显示强核介质效应。
• 结果与基于微扰QCD和冷核物质模型的理论预测一致。
• 该分析展示了ALICE探测器在小系统碰撞中精确测量重味强子的能力。
• 测得的R_pPb值与p-Pb系统在该能量下不存在强部分子能量损失效应的结论一致。