| In the Standard Model of particle physics,Quantum Chromodynamics(QCD)—the gauge theory that describes the strong interactions of quarks and gluons(partons),predicts that parton densities inside a hadron grow rapidly with increasing energy(or decreasing Bjorken x),and then a condensate state will be formed with high gluon densities,which is called Color Glass Condensate(CGC),at the same time,gluon recombination processes that tame the growth of gluon densities,eventually,gluons tends to be saturated,and a theory is developed in describing the dynamics of gluon in saturation regime is known as CGC effective field theory(EFT).In high energy limit(or small-xlimit),the research on the phenomenon of gluon saturation has always been one of the frontier in high-energy nuclear physics and particle physics,currently,the main goal of the experimental programs on proton(deuteron)-nucleus(p/d-A)collisions at Brookhaven National Laboratory(BNL)’s relativistic heavy-ion collider(RHIC)in United States and at CERN’s Large Hadron Collider(LHC)is to search the signal of gluon saturation.On the theory side,in high energy limit,CGC EFT provides a good description for gluon saturation phenomenon,and has been regarded as best candidate theory in describing the dynamics and the interaction of initial stage of heavy-ion collisions.So,the research on gluon saturation in high energy limit,plays a crucial role in understanding the dynamics of quark and gluon,as well as for searching and exploring properties of Quark Gluon Plasma(QGP)in heavy-ion collisions.In this thesis,gluon saturation has been considered and studied in the framework of CGC EFT,mainly includes the following:Two-gluon rapidity correlations in high energy collisions The experimental data of RHIC and LHC shows that the distribution of two-particles in the plane of relative azimuthal angle(△Φ)and relative(pseudo-)rapidity(△η)has a Ridge structure,this type correlation is known as two particle long-range rapidity correlation.In recent years,the reason and the origin of Ridge has been a interest topic in the field of high-energy collisions.According to causality,the correlation must be originated from the early stage in a collision if the two particles are correlated in final state.However,the detailed dynamical origin of these correlations is not completely clear.In this part,we studied the two-gluon rapidity correlations in the framework of CGC EFT,including the dependence of transverse momentum,rapidity and azimuthal angle,and studied the effects of saturation scale(Qs)and kinematic region of incident particles in the two-gluon rapidity correlations.Firstly,the strength of correlation is sensitive to the transverse momentum of two gluons,studied shows the correlation is peaked at the summation of two saturation momenta of incident particles QsA+ QsB and is more obviously in a certain kinetic window of transverse momenta,both below and above the kinematic window,the correlation becomes systematically weaker,and the width of the transverse momentum window are closely related to the distribution of UGD of colliding particles.Secondly,we studied the influence of the kinematic region of projectile and target in two-gluon rapidity correlation,results show that the Ridge structure will be emerged only if the dynamics involved of projectile and target in the small-x region.The relative azimuthal angular of two trigger gluon,which do not alter the trend of correlation in relative rapidity direction,only affect the strength of correlation.Furthermore,we find the ridge is more likely observed at higher incident energy and lower transverse momentum of trigger gluon if the small-x degree of freedom exists.Finally,the contribution of sub-leading order is mainly short range quantum correlations.It is much smaller than that of the leading one,but is not negligible.The dynamical evolution of Balitksy-Kovchegov equation and the solution In high energy limit(or small-x limit),the dynamical evolution of gluon towards energy(or small x)is captured by non-linear BK equation.In this part,we firstly introduce the basic idea and the theoretical framework of Color Glass Condensate Effective Field Theory,in the eikonal approximation,through the study of the a quark scattering off gluon gauge field and the first order correction of dipole scattering off gluon gauge field,the evolution of dipole scattering amplitude towards rapidity Y(or x)is obtained—LO BK equation,then the BK equation are numerically solved,and the problems of running coupling correction and the initial condition are discussed and analysed.For the initial condition of the BK equation,in the MV model,it is considered that the density of color charge is very large and has a local Gaussian distribution(the effect of high-order coupling is neglected),however,in practice,the density inside a hadron is finite,so the high-order coupling of color charge cannot be ignored simply,and then we get a new type initial condition of BK equation,named as Quartic action.By comparing with MV and AAMQS(MVγ),we studied the influence of the high-order coupling effect on the gluon gauge field.Results show that the effect of high-order coupling of color charges will suppress gluon emission,and when the density of color charges is larger,the suppression becomes weaker.The transverse momentum distribution of final particles at RHIC energy In p/d—A collision,the density of gluons inside nuclear A is very large,so the non-linear effect of gluons will be very important in the collision,through the study of the production of final-hadrons,will help us to understand the non-linear effects(gluon saturation)of nucleus A.Firstly,we focus on the transverse momentum distribution of final-state hadron in p/d—A collision at RHIC energy,in the calculation,we adopt two kinds of initial conditions:AAMQS(MVγ)and Quartic Action.Results obtained by using two initial conditions are quite well in agreement with experimental data,which further proves the reliability and accuracy of CGC EFT.By comparing the results of two initial conditions,we found that,for pp collisions,the difference of the results obtained by using two initial conditions is small,as for dAu,the difference is obvious,for specific,the results by using Quartic Action is larger than that of AAMQS(MVγ),which further indicates the effect of color charge on suppressing gluon emission for Au is no obvious than that of AAMQSMVγ.Furthermore,we calculated the transverse momentum distribution of proton,anti-proton and net-proton in AuAu collision at(?)＝ 200 and 62.4 GeV,results show that the failure of the formalism in larger rapidity at(?)= 62.4 GeV.This may be an indication that the net-proton are not produced by independent valence quark fragmentation. |
