We derive an analytical form for flow-background to jet-like azimuthal correlation in a cluster approach. We argue that the elliptic flow parameter to use in jet-correlation background is that from two-particle method excluding non-flow correlation unrelated to the reaction plane, but including cross-terms between cluster correlation and cluster flow. We verify our result with Monte Carlo simulations. We discuss implications of our finding in the context of jet-like correlations from STAR and PHENIX.
Measurements of two-particle azimuthal angle correlations are a useful tool to study the distribution of jet energy loss, however, they are complicated because of the significant anisotropic flow background. We devise a data-driven method for subtracting anisotropic flow background in jet-like correlation analysis. We first require a large recoil momentum ($P_x$) within a given pseudo-rapidity ($η$) range from a high-transverse momentum particle to enhance in-acceptance population of away-side jet-like correlations. Then we take the difference of two-particle correlations in the close-region a…
We present a measurement of azimuthal correlations between inclusive J/$ψ$ and charged hadrons in p-Pb collisions recorded with the ALICE detector at the CERN LHC. The J/$ψ$ are reconstructed at forward (p-going, 2.03 $<$ y $<$ 3.53) and backward (Pb-going, $-$4.46 $<$ y $<$ $-$2.96) rapidity via their $μ^+μ^-$ decay channel, while the charged hadrons are reconstructed at mid-rapidity ($|η|$ $<$ 1.8). The correlations are expressed in terms of associated charged-hadron yields per J/$ψ$ trigger. A rapidity gap of at least 1.5 units is required between the trigger J/$ψ$ and the associated charge…
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。
A collision system scan involving $α$-clustered $^{12}$C and $^{16}$O is studied by using a multiphase transport model for central collisions at $\sqrt{s_{NN}} = 6.37$ TeV. Background subtracted away-side dihadron azimuthal correlation is performed via the zero yield at minimum (ZYAM) method from raw signals, and the quantitative parameters, such as RMS width and Kurtosis, seem nicely follow the $A^{-1/3}$ law of the system size if the nucleus has the normal Woods-Saxon nucleon distribution. However, for $α$-clustering light nuclei, specifically for $^{12}$C and $^{16}$O, the RMS width and Kur…
Angular correlations between heavy-flavour decay electrons and charged particles at mid-rapidity ($|η| < 0.8$) are measured in p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The analysis is carried out for the 0-20% (high) and 60-100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavour hadrons. …
Two-particle long-range azimuthal correlations are measured in photonuclear collisions using 1.7 nb$^{-1}$ of 5.02 TeV Pb+Pb collision data collected by the ATLAS experiment at the LHC. Candidate events are selected using a dedicated high-multiplicity photonuclear event trigger, a combination of information from the zero-degree calorimeters and forward calorimeters, and from pseudorapidity gaps constructed using calorimeter energy clusters and charged-particle tracks. Distributions of event properties are compared between data and Monte Carlo simulations of photonuclear processes. Two-particle…
How transverse momentum conservation breaks azimuthal correlation factorization
Fudan University（复旦大学）；Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University（上海理论物理中心，NSFC与复旦大学）；AGH University of Krakow（克拉科夫AGH科技大学）
Two-particle correlations in pPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV are studied as a function of the pseudorapidity separation (Delta eta) of the particle pair at small relative azimuthal angle (abs(Delta phi) < pi/3). The correlations are decomposed into a jet component that dominates the short-range correlations (abs(Delta eta) < 1), and a component that persists at large Delta eta and may originate from collective behavior of the produced system. The events are classified in terms of the multiplicity of the produced particles. Finite azimuthal anisotropies are…
Measurement of the azimuthal anisotropy of charged particles in $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV $^{16}$O$+^{16}$O and $^{20}$Ne$+^{20}$Ne collisions with the ATLAS detector
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)（欧洲核子研究中心）
We employ a data-driven method to subtract the flow background of all harmonics by calculating the difference of the two-particle correlations between the close-region and far-region, determined depending on the pseudo-rapidity ($η$) distance from the region where an enhanced recoil transverse momentum ($P_x$) from a high-$p_T$ trigger particle is selected. We analyze the correlation shape as a function of the trigger particle azimuthal angle relative to the event-plane (EP) reconstructed from the beam-beam counters (BBCs) which are displaced by several units in $η$ from the mid-rapidity regio…
Non-flow correlations and elliptic flow fluctuations in gold-gold collisions at sqrt(s_NN)= 200 GeV
本文给出了在sqrt（sNN）= 200 Gev的Au+Au碰撞中的逐事件椭圆流涨落的结果，其中扣除了非流关联的贡献。引入了一种分析方法来测量非流动相关性，该方法依赖于非流动相关性在短范围内（Δ eta < 2）最突出的假设。假设非流动相关性是在p+p碰撞中观察到的长程相关性（Δ eta > 2）的量级，则观察到约30-40%的相对椭圆流动波动。这些结果与基于初始核重叠区参与核子空间涨落的预测是一致的。据发现，在Au+Au碰撞中的长程非流动相关性将不得不比p+p数据强一个数量级以上，以导致观察到的方位角各向异性波动，没有内在的椭圆流波动。
The hot, dense and strongly interacting medium known as the Quark Gluon Plasma (QGP) is produced in relativistic heavy-ion collisions at the Large Hadron Collider (LHC). Early in the collisions, quarks and gluons from the incoming nuclei collide to produce high momentum partons which fragment into collimated sprays of hadrons called "jets". In pp collisions, jet production is well understood within the framework of perturbative QCD and acts as a rigorous baseline measurement for jet quenching measurements. Using pp as a reference, we can compare to heavy-ion collision systems, and study the mo…
