Strong Field QED And Nucleon Structure Study

It is an important frontier subject and task of particle physics and nuclear physics to study nucleon structure in the theoretical framework of quantum chromodynamics.Quantum chromodynamics and quantum electrodynamics,both of which belong to gauge field theory,are powerful theoretical tools developed in the last century to describe the microscopic world.The good convergence of the quantum electrodynamics perturbation series expansion makes the theoretical results agree with the experimental results surprisingly.In contrast,the color confinement and non-perturbation properties of quantum chromodynamics in the low energy region make it difficult to understand the structure of nucleons.At present,there are lattice field theory,low energy efficient theory,phenomenological model and sum rule to deal with non-perturbative energy region.The parton model within high energy scattering has achieved great success from the very beginning of its development.The separability of the high energy perturbation region and the low energy non-perturbative region in the scattering process proved by the factorization theorem and the universality of the parton distribution function parameterized in the low energy region are one of the important reasons for people to believe in the correctness of the quantum chromodynamics theory.At present,there are many advances in the study of nucleon structure,such as the spin structure of nucleon,the three-dimensional parton distribution function,and the mass decomposition of nucleon.Many methods and techniques have been developed to solve these problems under the framework of quantum chromodynamics.However,due to the non-perturbative nature of quantum chromodynamics,these methods ultimately depend on the understanding of the low energy region.We believe that these methods in quantum chromodynamics should be naturally extended to quantum electrodynamics.Such a generalization,in addition to being able to accurately explain and predict some experimental phenomena of quantum electrodynamics,is also of great significance in itself.This can be a good validation and development of quantum chromodynamics theoretical tools from the consistency.On the other hand,there are some strange phenomena in strong electric fields,and the related research is called strong field quantum electrodynamics.For example,in the vicinity of heavy ions,the electromagnetic coupling constant Zα approaches or even exceeds 1 because the nucleus has Z charges,which is more similar to quantum chromodynamics.This makes it possible to develop and test theoretical tools for quantum chromodynamics using simple quantum electrodynamics.Therefore,this thesis is devoted to the above aspects,on the part of the three-dimensional parton distribution function and bound state mass decomposition of the relevant content,complete the calculation and research about quantum electrodynamics,and compare it with quantum chromodynamics.This has helped us to further understand the structure of the nucleus.Specifically,this thesis has done the following aspects of work:First,we review the transverse momentum dependent parton distribution function of gluons in the small x region of quantum chromodynamics.In the color glass condensate framework,the transverse momentum dependent parton distribution function of gluons can be divided into WW type distribution and dipole distribution according to the structure of their gauge link.It is generally believed that these two types of unpolarized gluon distribution are equivalent to linearly polarized gluon distribution in a certain transverse momentum region,but it has not been verified experimentally.Therefore,we return to the framework of quantum electrodynamics and propose that these two types of photon distribution functions also exist in the photon distribution around charged particles.This was previously known as the Coulomb correction in strong field quantum electrodynamics.We find that by parameterizing the matrix element of the photon distribution,the photon distribution with Coulomb correction is of dipole type,and the photon distribution without Coulomb correction is of WW type.Although the effect of Coulomb correction has not been found in the present experiments,our analytical and numerical calculations show that Coulomb correction has a significant effect on photon distribution.We propose that the existence of these two photon distributions can be verified by the ratio of the electron-proton collision cross section to the electron-ion collision cross section at future electron ion colliders.We further numerically calculate the polarization dependent observable measurement,i.e.,Cos 2φ azimuthal asymmetry,at the electron ion Collider.This work is not only of great significance to our study of the quantum electrodynamics process of photon-photon scattering in ultraperipheral collisions of heavy ions,but also helpful to our understanding of the effect of gauge link generated by multiple gluon exchanges on gluon distribution functions in quantum chromodynamics.Secondly,in the problem of nucleon mass decomposition we are concerned with trace anomaly caused by quantum corrections in quantum field theory.We first review the expression of the virial theorem in the framework of quantum field theory and how to derive the trace anomaly from the quantum electrodynamics.Then several different nucleon mass rules based on the energy momentum tensor and trace anomaly are introduced.According Ji sum rule,nucleon mass can be divided into quark mass term,quark kinetic and potential term,gluon kinetic and potential term and trace anomaly term.According to Lorce sum rule,nucleon mass can only be divided into quark contribution and gluon contribution physically,and nucleon must obey stability condition.The other view is that the mass decomposition of nucleons depends on the renormalization scheme.In a particular renormalization scheme,particle masses can be resolved in classical terms,namely,the kinetic and potential energy of quarks,the mass of quarks,and the kinetic and potential energy of gluons.The different understandings of nucleon mass decomposition need to be further clarified,and this is the motivation for our subsequent work.Finally,in an attempt to understand the role of trace anomaly in the nucleon mass problem and the source of the contradiction between the different sum rules,we return to quantum electrodynamics and study the trace anomaly contribution to the simplest bound state,the hydrogen atom.We first show that the leading order of the energy momentum tensor,the mass operator,in the hydrogen state will give the familiar ionization energy of the hydrogen atom;Secondly,in the sub-leading-order,our calculations show that the trace anomaly will give the Uhling effect in hydrogen energy level splitting.This is the first perturbative and model independent calculation of the trace anomaly contribution to mass of a real world bound states.Finally,we calculate the sub-leading-order self-energy correction of the mass operator in the bound state electrons,which will give the remaining logarithmic partial contribution to the Lamb shift,which well verifies the consistency of our bound state mass decomposition scheme.It is of great significance to help people understand the nucleon mass decomposition and the origin of mass.