arXiv 1209.04472012-09hep-exnucl-ex

使用ALICE探测器在LHC上进行的铅-铅碰撞中的带电粒子产生

Charged particle production in Pb--Pb collisions at the LHC with the ALICE detector

M. Floris

备注：: 4 pages, 2 figures. Proceedings of the 5th international conference on Hard and Electromagnetic Probes of High Energy Nuclear Collisions. Updated version after referee report (minor changes)
DOI：: 10.1016/j.nuclphysa.2012.12.031

摘要：

ALICE合作测量了LHC中$\sqrt{s_{NN}}=2.76$ TeV铅-铅碰撞中带电粒子的产生。我们报告带电粒子多重数和横动量谱的结果。所有的结果作为碰撞的中心性的函数，估计与Glauber Monte Carlo拟合在各种检测器中重建的多重性分布。详细讨论了Glauber模型在LHC能区的适用性、中心性确定的精度以及相关的系统不确定性。利用硅内跟踪系统（ITS）和时间投影室（TPC）在赝快度窗口$|η| \lesssim 0.9$ \中跟踪粒子，范围为$0.15 < \pt \lesssim 50$ GeV/ $c$。低$p_t$截止值在使用“tracklet”的多重性测量中进一步降低，在ITS的2个最内层中重建。在$|η| < 0.5$中测得的带电粒子多重性为$\mathrm{d}N_{ch}/\mathrm{d}η= 1601 \pm 60$，在5%最中心的铅-铅碰撞，表明能量密度比RHIC高$\sim 3$倍。它随中心性的演化显示出与RHIC测量的模式惊人相似的模式。中间（$5 \lesssim \pt \lesssim 15$ GeV/ $c$）的横向动量粒子被发现是最强烈的抑制相对于PP碰撞，符合一个大的能量损失的硬散射部分子在热和稠密的介质。结果以核修饰因子$R_{\mathrm{AA}}$表示，并与理论预期进行比较。

英文摘要：

The ALICE collaboration measured charged particle production in $\sqrt{s_{NN}}=2.76$ TeV Pb--Pb collisions at the LHC. We report on results on charged particle multiplicity and transverse momentum spectra. All the results are presented as a function of the centrality of the collision, estimated with a Glauber Monte Carlo fit to multiplicity distributions reconstructed in various detectors. The applicability of the Glauber model at LHC energies, the precision of the centrality determination and the related systematic uncertainties are discussed in detail. Particles are tracked in the pseudorapidity window $|η| \lesssim 0.9$\ with the silicon Inner Tracking System (ITS) and the Time Projection Chamber (TPC), over the range $0.15 < \pt \lesssim 50$ GeV/$c$. The low-$p_t$ cut-off is further reduced in the multiplicity measurement using "tracklets", reconstructed in the 2 innermost layers of the ITS. The charged particle multiplicity is measured in $|η| < 0.5$ to be $\mathrm{d}N_{ch}/\mathrm{d}η= 1601 \pm 60$ in 5% most central Pb--Pb collisions, indicating an energy density a factor $\sim 3$ higher than at RHIC. Its evolution with centrality shows a pattern strikingly similar to the one measured at RHIC. Intermediate ($5 \lesssim \pt \lesssim 15$ GeV/$c$) transverse momentum particles are found to be most strongly suppressed with respect to pp collisions, consistent with a large energy loss of hard-scattered partons in the hot and dense medium. The results are presented in terms of the nuclear modification factor $R_{\mathrm{AA}}$ and compared to theoretical expectations.

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