Thermal radiation and direct photon production in Pb-Pb and pp collisions with dielectrons in ALICE
Thermal radiation and direct photon production in Pb-Pb and pp collisions with dielectrons in ALICE
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DOI：
10.22323/1.414.0452
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发表时间：
2022-11
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影响因子：
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通讯作者：
D. Sekihata
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文献类型：
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作者：
D. Sekihata
介电子是研究在超相对论重离子碰撞中产生的热而致密的QCD物质的时空演化的独特工具。它们在碰撞的各个阶段由各种过程产生，末态相互作用可以忽略不计。来自强子相的热辐射有助于低不变质量（𝑚ee）的光谱，而来自较大𝑚ee的夸克-胶子等离子体（QGP）的热辐射携带有关介质早期温度的信息。后者主要是受部分子能量损失和介质流动影响的相关重味强子半光子衰变的大背景。在𝑚ee≪𝑝T， ee的准实虚光子区，可以从𝑚ee光谱中提取出作为横向动量函数的直接光子分数（𝑝T, ee）。在pp碰撞中，这种测量可以作为微扰QCD计算的基本测试，也可以作为重离子碰撞研究的基线。我们讨论了在√𝑠NN = 5.02 TeV和√𝑠= 13 TeV下Pb-Pb和pp碰撞中产生介电子的最新ALICE结果。结果与已知强子源的预期介电子产率和介质热辐射的预测进行了比较。本文还报道了在不同的碰撞系统中直接光子的产生，包括高多重pp碰撞
Dielectrons are unique tools to study the space-time evolution of the hot and dense QCD matter created in ultra-relativistic heavy-ion collisions. They are produced by a variety of processes during all stages of the collision with negligible final-state interactions. Thermal radiation from the hadronic phase contributes to the spectrum at low invariant mass ( 𝑚 ee ), while thermal radiation from the quark-gluon plasma (QGP) at larger 𝑚 ee carries information about the early temperature of the medium. The latter is dominated by a large background from semileptonic decays of correlated heavy-flavor hadrons affected by parton energy loss and flow in the medium. In the quasi-real virtual photon region where 𝑚 ee ≪ 𝑝 T , ee , the direct photon fraction can be extracted from the 𝑚 ee spectrum as a function of transverse momentum ( 𝑝 T , ee ). In pp collisions, such measurement serves as a fundamental test for perturbative QCD calculations and as a baseline for the studies in heavy-ion collisions. We discuss the latest ALICE results on dielectron production in Pb–Pb and pp collisions at √ 𝑠 NN = 5.02 TeV and √ 𝑠 = 13 TeV, respectively. The results are compared with the expected dielectron yield from known hadronic sources and predictions for thermal radiation from the medium. The production of direct photons in the different colliding systems including high-multiplicity pp collisions is also reported