Study Of Light Nuclei Production In Pb-Pb Collisions At The LH

In ultra-relativistic heavy ion collisions,light nuclei such as deuterons（d）,helions（³He）and tritons（t）,are a special group of observables.On one hand,as they are mostly formed at the late stage of the system evolution,light nuclei are regarded as sensitive probes of the fireball freeze-out properties.On the other hand,light nuclei are composite clusters and their production mechanisms are still under debate so far.The study of the production of light nuclei can help understand many fundamental issues in relativistic heavy ion collision physics,e.g.,the hadronization mechanism,the structure of the quantum chromodynamics phase diagram and the search for dibaryons or other molecular states.In recent decades,the production of light nuclei in ultra-relativistic heavy ion collisions has always attracted much attention both in experiment and in theory.The STAR experiment at the BNL Relativistic Heavy Ion Collider（RHIC）and the ALICE experiment at the CERN Large Hadron Collider（LHC）have collected a wealth of data on light nuclei production.These data exhibit some fascinating features,especially their non-trivial energy-dependent behaviors in a wide collision energy range from Ge V to TeV magnitude.Theoretical studies have also made significant progress.Two production mechanisms,the thermal production mechanisms and the coalescence mechanism,have proved to be successful in describing light nuclei formation.In addition,transport scenario is employed to study how light nuclei evolve and survive during the hadronic system evolution.The coalescence mechanism,in which light nuclei are assumed to be produced by the coalescence of the jacent nucleons in the phase space,possesses its unique characteristics.In order to see whether,if so,to what extent,these characteristics depend on the particular coalescence model used in obtaining these characteristics,we in our previous works developed an analytic description for the production of different species of light nuclei in the coalescence picture with the assumption of the coordinate-momentum factorization.The obtained analytic formulas clearly show the relationship of light nuclei with primordial hadronic bodies and effects of different factors on light nuclei production such as the whole hadronic system scale as well as the sizes of the formed light nuclei.In previous work,we applied the coordinate momentum factorization’s coalescence model to Au-Au collisions at RHIC energies to successfully explain the transverse momentum spectra,rapidity yield densities,averaged transverse momenta and yield ratios of different light nuclei.We also applied it to p-p,p-Pb and Pb-Pb collisions at LHC to study the coalescence factor B_A.We found it can naturally explain the relatively weak p _T dependence of B_A in pp and p-Pb collisions.It also qualitatively gave growth of B_A against p _Tfor all centralities in Pb-Pb collisions,but quantificationally explanations are urgently necessary.Does this mean that there are other factors causing B_A to grow with p _T that are not taken into account?It is well known that strong collective flows are formed in the Pb-Pb collisions with so high collision energies.So is it still suitable to adopt the assumption of the coordinate momentum factorization?In order to solve these issues,the coordinate momentum correlation in nucleon joint distribution is included in this paper.The formation of various light nuclei in the Pb-Pb collisions at LHC is studied with the improved nucleon coalescence model.The specific influences of coordinate momentum correlation on the production of light nuclei are studied.The main work of this paper is as follows:In Sec.2,considering the coordinate momentum correlation,the momentum distributions of different light nuclei are derived analytically,and the analytical results of coalescence factor B_A are given.In Sec.3,the production of d,³He,t in the mid-rapidity in different centralities at （?）=5.02TeV is systematically studied.Firstly,the Blast-Wave Model is employed to fit the transverse momentum spectra of protons and anti-protons.Then,we use the nucleon coalescence model to calculate the transverse momentum spectra of d,³He,t and rapidity yield densities in the mid-rapidity as well as averaged transverse momenta.Finally,we calculate the coalescence factor B₂ and B₃as well as the yield ratios of d,³He and t.In Sec.4,to further detect whether the dependence of the light nuclei radius on transverse momentum of light nuclei is universal,we study the production of d,³He and t in the mid-rapidity in different centralities at （?）=2.76TeV.Firstly,the Blast-Wave Model is used to fit the transverse momentum spectra of protons and anti-protons.Then,the nucleon coalescence model is used to calculate and analyze the transverse momentum spectra of d,3He,t and rapidity yield densities in the mid-rapidity as well as averaged transverse momenta.Finally,we calculate and analyze the coalescence factor B₂ and B₃ as well as the yield ratios of d,³He and t.