5.02 TeV中心p + Pb碰撞中的介子干涉测量研究

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"中心p + Pb碰撞中的干涉测量相关性" 这篇公开访问的论文(Eur.Phys.J.C(2018)78:53, https://doi.org/10.1140/epjc/s10052-017-5482-5)详细探讨了在5.02TeV中心p + Pb碰撞中，通过3+1维粘性流体力学模型分析的介子干涉测量相关性。作者Piotr Bo˙zeka和Sebastian Bysiak来自波兰克拉科夫AGH科技大学物理与应用计算机科学学院。干涉测量是一种利用粒子对之间的相关性来研究其发射源特性的技术，通常用于理解高能物理实验中产生的热辐射。在核碰撞中，这种测量可以揭示系统的行为，如膨胀、冷却和集体流动。在本研究中，初始条件由Glauber Monte Carlo模型提供，该模型是模拟高能碰撞中核相互作用的常用工具，能够计算出参与碰撞的核子密度分布。研究者计算了介子对的关联函数，这是作为它们的相对快速度的函数。他们提取的干涉法半径揭示了一个较弱的快速度依赖性，这表明介子分布缺乏提升不变性。提升不变性是理论物理中一个重要的概念，它表示物理定律在不同参考系中保持不变。在这种情况下，缺乏提升不变性意味着介子的发射特性在不同速度下有所不同。文章还发现，出方向（transverse direction）和长方向（longitudinal direction）间的交叉项不为零，这是一个有趣的结果，因为它暗示了在这些碰撞中存在非零的空间时间结构，可能与系统的集体动态有关。出方向通常指的是与碰撞平面垂直的方向，而长方向则沿着两核的对撞方向。这些在3+1维粘性流体力学模型中得出的结果与ATLAS合作组最近的数据有较好的一致性。ATLAS是大型强子对撞机(LHC)上的一个实验，它专注于探索基本粒子和宇宙学的奥秘。流体力学模型的成功应用支持了将高能核碰撞系统视为近乎理想的液体的观点，其中粘性（或阻力）效应是次要的。总结起来，这项工作提供了对p + Pb碰撞中粒子产生过程的深入见解，特别是通过干涉测量揭示了介子对的发射特征和系统的动态行为。这些研究结果对于理解核物质在极端条件下的性质以及QCD（量子色动力学）的集体效应至关重要，同时也有助于我们更好地理解早期宇宙的条件。

Eur. Phys. J. C (2018) 78:53

https://doi.org/10.1140/epjc/s10052-017-5482-5

Regular Article - Theoretical Physics

Interferometry correlations in central p+Pb collisions

Piotr Bo˙zek

, Sebastian Bysiak

AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków, Poland

Received: 5 September 2017 / Accepted: 19 December 2017 / Published online: 21 January 2018

Abstract We present results on interferometry correlations

for pions emitted in central p+Pb collisions at

√

5.02 TeV in a 3 + 1-dimensional viscous hydrodynamic

model with initial conditions from the Glauber Monte Carlo

model. The correlation function is calculated as a function

of the pion pair rapidity. The extracted interferometry radii

show a weak rapidity dependence, reﬂecting the lack of boost

invariance of the pion distribution. A cross term between the

out and long directions is found to be nonzero. The results

obtained in the hydrodynamic model are in fair agreement

with recent data of the ATLAS Collaboration.

1 Introduction

In relativistic p+Pb collisions at the CERN Large Hadron

Collider (LHC) a small region of large density matter is

formed, which makes possible the generation of a collec-

tive ﬂow in the expansion [1]. A number of signatures of

collectivity due to ﬁnal state interactions have been observed

experimentally in small collision systems at relativistic ener-

gies (see e.g. [2]). We use the viscous hydrodynamic model to

describe the dynamics in p+Pb interactions. We note that the

initial state effect can also explain the observed two-particle

correlations [3].

Quantum interferometry correlations for identical parti-

cles can serve as a measure of space-time correlations in

the source [4,5]. These interferometry (also named Hanbury

Brown–Twiss (HBT)) correlations have been studied in both

elementary and nuclear collisions. An estimate of the size

of the emission region, in the form of the HBT radii, can be

extracted from a ﬁt to the interferometry correlations. HBT

radii have been measured in p+Pb collisions [6,7] and can

be reproduced fairly well in hydrodynamic models posing

e-mail: piotr.bozek@ﬁs.agh.edu.pl

Glauber model or color glass condensate initial conditions

[8–10].

In collisions of symmetric systems the correlation func-

tion in relative momentum of the pair is usually parametrized

using three HBT radii [11,12]. For a source without forward–

backward symmetry, e.g. for pairs at forward/backward

rapidity, an additional cross term can appear in the correla-

tions function [13]. Such a term is predicted to be signiﬁcant

in the case of asymmetric collisions, d+Au or p+Pb [14].

Recently the ATLAS Collaboration has presented results

on the interferometry correlations in p+Pb collisions for dif-

ferent rapidities of the pion pair [15]. The HBT radii show

a rapidity dependence. The size of the emission region is

larger on the Pb going side. The cross term is also found to

be nonzero, reﬂecting the rapidity dependence of the charged

particle density.

In this paper we present results for the interferometry

radii in p+Pb collisions with 0–1% centrality calculated in

a wide range of rapidities corresponding to the pioneering

measurements of the ATLAS Collaboration. As in the exper-

iment, an exponential ansatz is used that better reproduces the

simulated correlation function. We show that the hydrody-

namic model with Glauber model initial conditions can semi-

quantitatively reproduce the experimental observations. For

the ﬁrst time, the presented model calculations allow one to

compare quantitatively the predicted magnitude of the new

cross term in the correlation function with experiment. Good

agreement is found. It means that the space-momentum cor-

relations built in during the hydrodynamic expansion, includ-

ing the predicted forward–backward asymmetry, are consis-

tent with experiment.

2 Hydrodynamic model and HBT correlations

We describe the evolution of the matter created in p+Pb col-

lisions using the viscous hydrodynamic model, with initial

entropy density given by the nucleon Glauber Monte Carlo

123

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