arXiv 1601.044622016-01-18hep-exnucl-ex

在LHC与ALICE的pp，p-Pb和Pb-Pb碰撞中喷流测量

Jet measurements in pp, p--Pb and Pb--Pb collisions with ALICE at the LHC

S. K. Prasad

备注：: 6 pages, 5 figures, 7th International Conference on Physics and Astrophysics of Quark Gluon Plasma, 1-5 February, 2015, Kolkata, India

摘要：

本文介绍了在LHC上利用ALICE探测器对pp、p-Pb和Pb-Pb碰撞中喷流测量的系统研究。测量了$\sqrt{s}$ = 2.76和7 TeV的pp碰撞、$\sqrt{s_{\rm NN}}$ = 5.02 TeV的p-Pb碰撞和$\sqrt{s_{\rm NN}}$ = 2.76 TeV的Pb-Pb碰撞的喷流产生截面.在7~TeV的pp碰撞中测量了喷流形状观测值和碎裂分布。在宽的横向动量范围内，用连续重组喷流发现算法（$k_{\rm T}$、反$k_{\rm T}$和SISCone）在中等速度下重建喷流，喷流分辨率参数$R$的值在0.2 - 0.6之间。测量进行比较，下一个领先的顺序（NLO）微扰量子色动力学（pQCD）的计算和预测从蒙特卡罗（MC）事件发生器，如PYTHIA，PHOJET和HERWIG。在$\sqrt{s}$ = 2.76 TeV的pp碰撞中，用非线性光学pQCD方法很好地再现了喷流产生截面. MC模型不能解释在PP碰撞在$\sqrt{s}$ = 7 TeV的射流截面，而射流形状和碎片分布是相当好地再现这些模型。喷注核修改因子$R_{\rm pPb}$在p-Pb碰撞被发现是一致的，与统一的初始部分子分布或强烈的最终状态的影响喷注产生的情况下，没有大的修改，而大的喷注抑制观察到在Pb-Pb中心事件相对于外围事件，表明在中央Pb-Pb事件形成致密介质。

英文摘要：

We present a systematic study of jet measurements in pp, p--Pb and Pb--Pb collisions using the ALICE detector at the LHC. Jet production cross sections are measured in pp collisions at $\sqrt{s}$ = 2.76 and 7~TeV, in p--Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02~TeV and in Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76~TeV. Jet shape observables and fragmentation distributions are measured in pp collisions at 7~TeV. Jets are reconstructed at midrapidity in a wide range of transverse momentum using sequential recombination jet finding algorithms ($k_{\rm T}$, anti-$k_{\rm T}$, and SISCone) with several values of jet resolution parameter $R$ in the range 0.2 -- 0.6. Measurements are compared to Next-to-Leading Order (NLO) perturbative Quantum Chromodynamics (pQCD) calculations and predictions from Monte Carlo (MC) event generators such as PYTHIA, PHOJET and HERWIG. Jet production cross sections are well reproduced by NLO pQCD calculations in pp collisions at $\sqrt{s}$~=~2.76~TeV. MC models could not explain the jet cross sections in pp collisions at $\sqrt{s}$ = 7 TeV, whereas jet shapes and fragmentation distributions are rather well reproduced by these models. The jet nuclear modification factor $R_{\rm pPb}$ in p--Pb collisions is found to be consistent with unity indicating the absence of large modifications of the initial parton distribution or strong final state effects on jet production, whereas a large jet suppression is observed in Pb--Pb central events with respect to peripheral events indicating formation of a dense medium in central Pb--Pb events.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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英文摘要：

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