Research On A Novel EA Generator And Assessing The Capabilities For The Coherent Diffractive J/ψ Measurements At The EIC

Understanding various fundamental properties of nucleons and nuclei are among the most important scientific goals of nuclear physics.To date,a series of experimental facilities,such as SLAC,EMC,HERA,and etchave been built to explore the partonic structure of nucleons and the nucleus,and the origin of their mass and spin,among others.It is generally agreed that the nucleons are composed of more microscopic particles called quarks in modern physics.With the impact of strong force which is mediated by gluons,the quarks are bound together into hadrons,such as protons and neutrons.The theory of Quantum Chromodynamics(QCD)is developed to describe the underlying mechanism of the interactions among quarks and gluons.However,despite the successes of QCD,many fundamental questions remain largely unexplored.The upcoming U.S.-based Electron Ion Collider(EIC)might provide definitive answers to many standing puzzles and open questions in modern nuclear physics.With a wide range of center of mass energies from 20 to 140 GeV,polarized beams,and beam species,as well as high luminosity,EIC will enable to precisely image the distributions of quarks and gluons and to study their interactions,and to explore the new QCD frontier of strong color fields in nuclei,in short,to understand how matter at its most fundamental level is made.In order to achieve the scientific goals of the EIC,it will require not only cuttingedge technologies in hadron and electron acceleration and detectors to perform highprecision measurements,but also theoretical models to interpret the data.This thesis presents a general-purpose eA Monte Carlo model-BeAGLE.We will provide a general description of the BeAGLE model,applications of the model in eA physics,implications for detector requirements at the EIC,and the tuning of the physics model based on available experimental data.Specifically,we focus on a selection of model and data comparisons in particle production in both ep and eA collisions,where baseline particle distributions provide essential information to describe the event topology.Based on BeAGLE event generator,we investigate the collision geometry determination in eA collisions,which can be used as an experimental handle for controlling the underlying nuclear effects.In addition,we investigate one of the golden measurements proposed at the EIC,which is to obtain the spatial gluon density distribution within a lead(Pb)nucleus.The proposed experimental process is the exclusive J/ψ vector-meson production off the Pb nucleus:e+Pb→e’+J/ψ+Pb’.The Fourier transformation of the momentum transfer|t| distribution of the coherent diffraction is the transverse gluon spatial distribution.In order to measure it,the experiment has to overcome an overwhelmingly large background arising from the incoherent diffractive production,where the nucleus Pb’ mostly breaks up into fragments of particles in the far-forward direction close to the hadron-going beam rapidity.We study systematically the rejection of incoherent J/ψ production by vetoing products from these nuclear breakups,such as protons,neutrons and photons.The study is based on the BeAGLE event generator and the most up-to-date EIC Farforward Interaction Region design.The achieved vetoing efficiency,the ratio between number of vetoed events and total incoherent events,ranges from about 80%-99%depending on |t|.Assuming a 5%smearing applied to the reconstructed |t| resolution in the Sartre model,this vetoing efficiency can suppress the incoherent background at least to the first minimum of the coherent |t| distribution.Experimental and accelerator machine challenges as well as potential improvements are also discussed.