论文标题
在$ \ sqrt {s _ {\ rm nn}} = 5.02 $ tev
Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV
论文作者
论文摘要
$ {\ rm e}^{+} {\ rm e}^{ - } $ pair Production的第一个测量$ \ sqrt {s _ {\ rm nn}} = 5.02 $ tev在LHC上显示。在中期（$ |η_{\ rm e} | <0.8 $）中研究了Dielectron的生产，作为不变质量的函数（$ 0.4 \ leq m _ {\ rm ee} <2.7 $ gev/$ c^2 $）在50美元t，ee} <0.1 $ gev/$ c $，作为$ p _ {\ rm t，ee} $的函数，在三$ m _ {\ rm ee} $间隔中，最外围pb $ - $ $ pb碰撞。在0.1 Gev/$ c $的$ p _ {\ rm t，ee} $中，明显过剩的$ {\ rm e}^{+} {+} {\ rm e}^{ - } $ pairs是与已知的耐知的辐射辐射源的预期相比，发现的预期。 $ m _ {\ rm ee} $多余的光谱在不确定性内复制了对电介质的光子$ - $光子产生的不同预测，其中光子来自高度Lorentz Contarts Contarts Contracted PB核产生的极强的电磁场。最低阶量子电动力学（QED）计算以及一个考虑到光子平均横向动量的冲击参数依赖性的模型，还提供了$ p _ {\ rm t，ee} $光谱的良好描述。测得的$ \ sqrt {\ langle p _ {\ rm t，ee}^{2}^{2} \ rangle} $的多余$ p _ {\ rm t，ee} $ propsrum在外围pb $ - $ pb碰撞中与以前在rhic at a rhic a in a phace相似的值相似。
The first measurement of the ${\rm e}^{+}{\rm e}^{-}$ pair production at low lepton pair transverse momentum ($p_{\rm T,ee}$) and low invariant mass ($m_{\rm ee}$) in non-central Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity ($|η_{\rm e}| < 0.8$) as a function of invariant mass ($0.4 \leq m_{\rm ee} < 2.7$ GeV/$c^2$) in the 50$-$70% and 70$-$90% centrality classes for $p_{\rm T,ee} < 0.1$ GeV/$c$, and as a function of $p_{\rm T,ee}$ in three $m_{\rm ee}$ intervals in the most peripheral Pb$-$Pb collisions. Below a $p_{\rm T,ee}$ of 0.1 GeV/$c$, a clear excess of ${\rm e}^{+}{\rm e}^{-}$ pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The $m_{\rm ee}$ excess spectra are reproduced, within uncertainties, by different predictions of the photon$-$photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the $p_{\rm T,ee}$ spectra. The measured $\sqrt{\langle p_{\rm T,ee}^{2} \rangle}$ of the excess $p_{\rm T,ee}$ spectrum in peripheral Pb$-$Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region.
