5.02 TeV Pb+Pb和$pp$与ATLAS碰撞中光子喷注横向动量关联的测量
Measurement of photon-jet transverse momentum correlations in 5.02 TeV Pb+Pb and $pp$ collisions with ATLAS
摘要：
与光子相关的射流可以用作校准探针，以研究核碰撞中产生的介质中的能量损失。利用ATLAS探测器记录的$\sqrt{s_\mathrm{NN}}=5.02$ TeV的Pb+Pb碰撞数据的0.49 nb $^{-1}$和$\sqrt{s}=5.02$ TeV的$pp$碰撞数据的25 pb $^{-1}$的积分光度测量了孤立光子和包容喷流之间的横向动量平衡。具有$63.1 < p_\mathrm{T}^γ < 200$ GeV和$\left|η^γ\right| < 2.37$的横动量的光子与具有$p_\mathrm{T}^\mathrm{jet} > 31.6$ GeV和伪快度$\left|η^\mathrm{jet}\right| < 2.8$的事件中的所有喷流配对。横向动量平衡给出的射流光子$p_\mathrm{T}$比，$x_\mathrm{Jγ}$，测量与方位角开度角$Δϕ> 7π/8$对。作为$x_\mathrm{Jγ}$，$(1/N_γ)(\mathrm{d}N/\mathrm{d}x_\mathrm{Jγ})$的函数的每光子射流产率的分布，通过一个二维展开程序的检测器效应进行校正，并在粒子水平上报告。在$pp$碰撞中，分布很好地描述了蒙特卡罗事件发生器。在Pb+Pb碰撞中，$x_\mathrm{Jγ}$分布从$pp$碰撞中观察到的中心性增加而修改，与热核介质中部分子能量损失的图像一致。数据进行了比较，一套能源损失模型和计算。
英文摘要：
Jets created in association with a photon can be used as a calibrated probe to study energy loss in the medium created in nuclear collisions. Measurements of the transverse momentum balance between isolated photons and inclusive jets are presented using integrated luminosities of 0.49 nb$^{-1}$ of Pb+Pb collision data at $\sqrt{s_\mathrm{NN}}=5.02$ TeV and 25 pb$^{-1}$ of $pp$ collision data at $\sqrt{s}=5.02$ TeV recorded with the ATLAS detector at the LHC. Photons with transverse momentum $63.1 < p_\mathrm{T}^γ < 200$ GeV and $\left|η^γ\right| < 2.37$ are paired inclusively with all jets in the event that have $p_\mathrm{T}^\mathrm{jet} > 31.6$ GeV and pseudorapidity $\left|η^\mathrm{jet}\right| < 2.8$. The transverse momentum balance given by the jet-to-photon $p_\mathrm{T}$ ratio, $x_\mathrm{Jγ}$, is measured for pairs with azimuthal opening angle $Δϕ> 7π/8$. Distributions of the per-photon jet yield as a function of $x_\mathrm{Jγ}$, $(1/N_γ)(\mathrm{d}N/\mathrm{d}x_\mathrm{Jγ})$, are corrected for detector effects via a two-dimensional unfolding procedure and reported at the particle level. In $pp$ collisions, the distributions are well described by Monte Carlo event generators. In Pb+Pb collisions, the $x_\mathrm{Jγ}$ distribution is modified from that observed in $pp$ collisions with increasing centrality, consistent with the picture of parton energy loss in the hot nuclear medium. The data are compared with a suite of energy-loss models and calculations.
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