Recent jet quenching measurements in Pb+Pb collisions at the LHC report a significant energy imbalance of di-jets. The imbalance is found to be compensated by a large amount of soft particles produced at large angles with respect to the di-jet axis. This observation questions the conventional picture of parton energy loss models, established at RHIC, which typically expect that the radiated gluons are emitted at moderate angles close to the outgoing parton. In this letter, we qualitatively discuss two possible contributions of the underlying heavy-ion background that may have to be taken into account when interpreting the recent data. We show that a large jet v_3, potentially caused by a pathlength dependent energy loss in the presence of fluctuating initial conditions, could contribute to the observed excess of soft particles apparently originating from large angle in-medium radiation. In addition, the observed excess could also be induced by multiple jets produced in the vicinity of the leading jet, caused by a potential selection bias imposed on the di-jet momentum imbalance.
本文综述了大型强子对撞机ALICE、ATLAS和CMS三个主要实验对重离子碰撞中高PT粒子和喷流的最新研究结果。讨论了2010年和2011年$\sqrt{s_{NN}} = 2.76$ TeV Pb+Pb数据的分析结果。我们主要集中在完全重建射流的结果，并讨论实验之间的测量的相似性和重要差异。我们指出了从夸克引发喷注和胶子引发喷注之间的差异的角度理解这些结果的重要性
Recent experiments have observed large anisotropic collective flows in high multiplicity proton-lead collisions at the Large Hadron Collider (LHC), which indicates the possible formation of mini quark-gluon plasma (QGP) in small collision systems. However, no jet quenching has been confirmed in such small systems so far. To understand this intriguing result, the system size scan experiments have been proposed to bridge the gap between large and small systems. In this work, we perform a systematic study on both heavy and light flavor jet quenching in different collision systems at the LHC energ…
This article presents the motivation for developing a comprehensive modeling framework in which different models and parameter inputs can be compared and evaluated for a large range of jet-quenching observables measured in relativistic heavy-ion collisions at RHIC and the LHC. The concept of a framework us discussed within the context of recent efforts by the JET Collaboration, the authors of JEWEL, and the JETSCAPE collaborations. The framework ingredients for each of these approaches is presented with a sample of important results from each. The role of advanced statistical tools in comparin…
Jet quenching has been one of the most important indicators that ultra-relativistic heavy-ion collisions produce a deconfined state of quarks and gluons, known as the Quark-Gluon Plasma. While the quenching of jets traditionally refers to the energy loss of high-momentum partons, the study of jet quenching has grown into a multi-pronged field where the measurement of jets and their modification in heavy-ion collisions is used as an important tool to study many aspects of QCD deconfinement. This contribution reviews the current experimental status of jets at the LHC and RHIC, and reports recent…
Quenching of Leading Jets and Particles: the p_t Dependent Landau-Pomeranchuk-Migdal effect from Nonlinear k_t Factorization
本文首次推导了RHIC（Relativistic Heavy Ion Collider）到LHC（Large Hadron Collider）强子-核碰撞中，在束流碎裂区中，横向动量p_t固定时，引导喷流的Landau-Pomeranchuk-Migdal效应。这项工作的主要新颖之处是这些过程中缺少的虚辐射pQCD校正的推导-实际发射辐射校正已经在文献中提供。我们显然实现了么正关系，它以最简单的形式要求，在虚发射修正和实发射修正相加时，散射夸克的总数必须正好等于1。对于自由核子靶，我们证明了前导喷流谱满足Balitsky-Fadin-Kuraev-Lipatov前导log（1/x）（LL-1/x）线性演化。对于核靶，超前喷流谱的LL-1/x演化的非线性k_t-因子分解与集体核胶的非线性LL-1/x演化完全匹配--在两个非线性演化的核观测量之间出现了唯一的线性k_t-因子分解关系。我们认为，在从RHIC到LHC的有限能量范围内，在重核的标准稀释非关联核子气体处理中，主导喷流谱可以在LL-1/x Balitsky-Kovchegov近似下演化。我们评论这些结果的扩展，和他们可能reggeon场论解释，在LHC中快射流。
We extend our POWLANG transport setup for the modelling of heavy-flavour production in heavy-ion collisions to the case of full 3+1 simulations, dropping the approximation of longitudinal boost-invariance of the background medium. This enables us to provide predictions for observables for which the rapidity dependence is essential in order to obtain a non-vanishing signal, like the directed flow $v_1$, and to get reliable results also for kinematic distributions of heavy-flavour particles at forward rapidity. We compare our predictions with experimental data obtained in Au-Au and Pb-Pb collisi…
The ALICE Collaboration reports the measurement of semi-inclusive distributions of charged-particle jets recoiling from a high-transverse momentum trigger hadron in p-Pb collisions at $\sqrt{s_{\rm NN}} =5.02$ TeV. Jets are reconstructed from charged-particle tracks using the anti-$k_{\rm T}$ algorithm with resolution parameter $R=0.2$ and $0.4$. A data-driven statistical approach is used to correct the uncorrelated background jet yield. Recoil jet distributions are reported for jet transverse momentum $15<p_{\rm T,jet}^{\rm ch} <50$ GeV/$c$ and are compared in various intervals of p-Pb event …
Background subtraction and jet quenching on jet reconstruction
为了评估喷流观测量约束在LHC重离子碰撞中产生的介质特性的能力，我们研究了背景扣除和喷流淬灭对喷注重建的影响，重点是目前由ATLAS和CMS研究的双喷流不对称性。使用一个玩具模型，我们研究了不同的背景扣除方法对双射流动量不平衡和方位角分布的影响。我们比较了通常的喷气面积为基础的背景减除技术和CMS使用的噪声基座减法的一个变体。这项工作的目的是了解这两种技术之间的差异，给定相同的事件配置。我们使用Q-PYTHIA Monte Carlo分析了淬灭效应对先前观测值的影响，以及Q-PYTHIA能够在多大程度上重现CMS数据的平均缺失横向动量，这似乎表明存在大角度发射的软粒子。
Bayesian Constraints on Pre-Equilibrium Jet Quenching and Predictions for Oxygen Collisions
IGFAE, Universidade de Santiago de Compostela（圣地亚哥-德孔波斯特拉大学）；Departamento de Física, Universidad de Oviedo（奥维耶多大学）；Instituto Universitario de Ciencias y Tecnologías Espaciales de Asturias (ICTEA)（阿斯图里亚斯太空科学与技术大学研究所）；Institute for Theoretical Physics, Heidelberg University（海德堡大学理论物理研究所）
We construct a measure of transverse momentum loss of jets in nuclear collisions at LHC directly using measurements of jet cross sections in PbPb and pp collisions. The proposal is shown to be equivalent to R_AA and is equally straightforward to construct. Using data from the ATLAS collaboration at two different collision energies, we show that the proposed measure has small statistical uncertainties. We argue that systematic errors can be easily improved over our estimates by the experimental collaboration to such an extent that it directly probes whether the jet-medium interaction is due to …
