Lepton Pair Production Through Photon-Photon Process In Relativistic Heavy Ion Collisions

The study of relativistic heavy ion collisions plays a crucial role in the investigation of the deconfinement phase transition of quantum chromodynamics.In relativistic heavy ion collisions,two charged heavy nuclei are accelerated to nearly the speed of light and collide with each other.The collisions can generate the strongest electromagnetic fields ever observed.It provides a platform for studying quantum matter under extremely strong electromagnetic fields.Strong electromagnetic fields can induce many novel quantum transport phenomena,such as chiral magnetic effect and chiral separation effect.These quantum effects have drawn lots of attentions in the field of relativistic heavy ion collision over the past decade.Recently,the strong electromagnetic fields generated in the relativistic heavy ion collisions have been utilized to investigate nonlinear quantum electrodynamic phenomena,such as lepton pair photoproduction,light by light scattering,photonuclear reactions,and vacuum birefringence.The lepton pair photoproduction has been systematically studied in ultraperipheral and peripheral collisions in Relativistic Heavy Ion Collider(RHIC)at Brookhaven National Laboratory.Several important physical phenomena,such as generating matter directly from lights and vacuum birefringence were explored.In Large Hadron Collider(LHC)at CERN,the light by light scattering has been observed in addition to the lepton pair photoproduction.In the past years,significant breakthroughs have been achieved in the study of photonuclear reactions in relativistic heavy ion collisions.Observations of entanglement in the final states of vector meson decays have been reported.The equivalent photon approximation(EPA)is a widely used approach to describe lepton pair photoproduction.However,several studies have shown that EPA fails to describe the broadening effect and the azimuthal angle modulation in experiments due to the lack of the information on the transverse momentum and polarization for initial photons.To provide a more accurate description of the data,the generalized equivalent photon approximation,quantum electrodynamics in background field approximation,transverse momentum dependent parton distribution function,and photon Wigner distribution function factorization framework have been introduced into the study of lepton pair photoproduction.In this thesis,we employ the quantum electrodynamics in wave packet approximation to investigate the lepton pair photoproduction in relativistic heavy ion collisions.The initial nuclei states are represented by wave packets,and the cross section of lepton pair photoproduction is derived using the standard method in quantum field theory.In our theoretical framework,the transverse momentum,position,and polarization of the initial photons are self-consistently encoded into the photon’s Wigner function.At ultra relativistic limits,the leading-order cross section agrees with that obtained from generalized equivalent photon approximation and factorization framework in the classical field approximation up to twist-2 order.Using our differential cross section,we calculate the transverse momentum and invariant mass spectra as well as the azimuthal angle distribution of lepton pairs produced in photoproduction.Our results agree with those obtained in RHIC experiments.Our studies demonstrate that accounting for the transverse momentum and polarization of the initial photon is essential for accurately describing the experimental data.Our theoretical framework also establishes connections between different models.We further computed several physical observables of lepton pair photoproduction in isobaric collisions.Our findings suggest that nuclear mass and charge distribution have a direct impact on the final cross section of lepton pair photoproduction.These results provide valuable insights for future studies on isobaric collisions and nuclear mass and charge distribution.