Collision-energy dependence of the Breit-Wheeler process in heavy-ion collisions and its application to nuclear charge radius measurements
Collision-energy dependence of the Breit-Wheeler process in heavy-ion collisions and its application to nuclear charge radius measurements
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DOI：
10.1103/physrevc.107.044906
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发表时间：
2022-07
影响因子：
3.1
通讯作者：
Xiaofeng Wang;J. Brandenburg;L. Ruan;Feng-lan Shao;Zhangbu Xu;Chi Yang;W. Zha
中科院分区：
文献类型：
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作者：
Xiaofeng Wang;J. Brandenburg;L. Ruan;Feng-lan Shao;Zhangbu Xu;Chi Yang;W. Zha
在最低阶QED下计算了重离子碰撞中Breit-Wheeler过程的双电子截面和横动量分布对碰撞能量的依赖关系，发现它们对核电荷分布和超Lorentz增强库仑场的红外发散角敏感.在给定的实验运动学接受范围内，发现横截面增加，而对横向动量（$\sqrt{\langle p_{T}^{2} \rangle}$）随着光束能量的增加而减小。我们证明了Weizsacker-Williams光子的横向动量分量是由于电荷源和电场分量在纵向上的有限范围。进一步阐明了核电荷分布与Breit-Wheeler过程产生的e^+e^-$运动学之间的联系，并提出了Breit-Wheeler过程在相对论重离子碰撞中有效性的判据.按照这种方法，我们证明了超相对论重离子碰撞中布赖特-惠勒过程的实验测量可以用来定量限制核电荷半径。提取的参数对碰撞参数的依赖性表现出敏感性，可以用来研究强子相互作用中的初态和末态效应。
The collision energy dependence of the cross section and the transverse momentum distribution of dielectrons from the Breit-Wheeler process in heavy-ion collisions are computed in the lowest-order QED and found to be sensitive to the nuclear charge distribution and the infrared-divergence of the ultra-Lorentz boosted Coulomb field. Within a given experimental kinematic acceptance, the cross section is found to increase while the pair transverse momentum ($\sqrt{\langle p_{T}^{2} \rangle}$) decreases with increasing beam energy. We demonstrate that the transverse-momentum component of Weizsacker-Williams photons is due to the finite extent of the charge source and electric field component in the longitudinal direction. We further clarify the connection between the nuclear charge distribution and the kinematics of produced $e^+e^-$ from the Breit-Wheeler process, and propose a criterion for the validity of the Breit-Wheeler process in relativistic heavy-ion collisions. Following this approach we demonstrate that the experimental measurements of the Breit-Wheeler process in ultra-relativistic heavy-ion collisions can be used to quantitatively constrain the nuclear charge radius. The extracted parameters show sensitivity to the impact parameter dependence, and can be used to study the initial-state and final-state effects in hadronic interactions.