Jet Production In Pp Collision Based On NLO Perturbative QCD

The Relativistic Heavy ion Collider(RHIC)at Brookhaven N ational Laboratory and the Large Hadron Collider(LHC)at CERN have conducted a series of high-energy heavy ion collisions in the past two decades.A large number of experimental data and theoretical analysis show that these high-energy heavy ion collisions pro-duce a new form of matter with high temperature and density-Quark-Gluon-Plasma(QGP).In the initial stage of collision,when the large transverse momentum parton passes through the high temperature and high density QGP medium,it will encounter the multiple scattering of the medium to cause the radiation gluon and lose energy.This phenomenon is called jet quenching.To study the high temperature and high density properties of QGP precisely by jet quenching,it is necessary to accurately understand and calculate the production of jet in the initial state.Jet is defined as a collection of parton concentrated in a certain cone Angle range in the rapidity-azimuth space.Theoretically,the production of jet in the initial state can be obtained indirectly through the information of the final hadrons based on a certain algorithm reconstruction,such as the Phenomenological model of AMPT,or through the analytical calculation of perturbative quantum chromodynamics(pQCD)based on a certain algorithm.The Hard Scattering(HS:Hard Scattering)process of high-energy nucleon-nucleon collision produces a large number of high-energy par-tons.The 2?2 process of the leading order pQCD gives two partons,each individually forming two jets.The 2?3 process of the next leading order pQCD gives three partons that either make three jets separately,or two partons make one jet based on a cer-tain algorithm,and the other parton makes one jet separately.And so on.This is the basic method for calculating jet based on pQCD(denoted as HS).The soft collinear effective theory(SCET)improves the above method to calculate jet.In this theory,it is believed that the parton production in the hard scattering process will further evolve,that is,the "jet function" is defined to consider the splitting process of soft or collinear gluon radiation,the high-order correction is calculated by resummation,and the jet is obtained by a certain algorithm.This is a relatively perfect method for calculating jet based on pQCD+SCET theory(denoted as SCET).In this paper,based on the theoretical framework of next leading order pertur-bative quantum chromodynamics,two methods,HS and SCET,are adopted to study the jet production in high-energy nucleon-nucleon collisions,respectively,in an at-tempt to theoretically "calibrate" the hard probe used to detect the thermal density properties of QGP.The numerical results show that the jet given by HS method of the next leading order is consistent with the jet given by SCET method which only calculates the splitting process of the next leading order and does not calculate the high-order correction by resummation,indicating that the two are equivalent.In the case of choosing the appropriate factorization scale and renormalization scale,the theoretical results of both accord with the experimental data.The numerical results in this paper also show that the dependence on scale of jet with different cone Angle sizes given by the next leading order is less than that given by the next leading order,indicating that the calculation of jet by the higher order perturbation theory is more perfect and reliable.Moreover,the smaller the cone Angle is,the stronger the scale dependence is.It is noted that with the SCET method of heavy summation and high order correction,the improvement of the results is more and more obvious as the cone Angle is smaller,and the dependence of small cone Angle jet on scale is expected to be reduced,which is a focus of our future research.Finally,we expect that in the future research,the production of jet in the initial state can be accurately adjusted through high-order correction,which can be used to analyze the jet quenching effect in high-energy nucleus-nucleus collision,so as to further demonstrate the thermal density properties of QGP accurately.