Scaling Behavior Of The Transverse Momentum Spectra Of Pions, K Mesons And Protons Under The Collision Of Pb-Pb 2.76 TeV

High energy heavy ion collision is an important research area in theoretical physics.The high temperature and high density environment produced by the collision process is similar to the environment at the early stage of the cosmic explosion.Therefore,high energy heavy ion collisions play an important role in the exploration of the origin of matter and its evolution.At extremely high temperatures and densities,Quantum Chromodynsmics(QCD)predicts a new form of matter that is called Quark Gluon Plasma(QGP).One of the most important observations in high energy heavy ion collisions is the transverse momentum(PT)spectrum of the final state particles.It is greatly important for understanding the evolution of high energy heavy ion collision from hadron to QGP and the particles production mechanisms.Several approaches are utilized to search for regularities in the particle production both in the experiment and in theory,one of them being the search for a scaling behaviour of some quantities versus suitable variables.In recent years,the scaling behavior of transverse momentum spectrum of some final particles has been observed in nucleus-nucleus collisions.For example,the transverse momentum spectra of the pions,protons and anti-protons at midrapidity in gold-gold(Au-Au)at a center-of-mass energy per nucleon pair(SNN)200 GeV collisions at RHIC(Relativistic Heavy Ion Collider,RHIC)exhibit a scaling behavior that does not depend on the centrality classes.With the experimental data collected by the ALICE collaboration in Pb-Pb collisions at a center-of-mass energy per nucleon pair 2.76 TeV for six different centrality classes(0-5%,5-10%,10-20%,20-40%,40-60%and 60-80%),we investigate the scaling property of the pion,kaon and proton transverse momentum spectra at these centrality classes.We show that in the lowPT region,pT<2.75,3.10 and 2.35 GeV/c,the pion.kaon and protonPT-spectra exhibit a scaling behaviour independent of the centrality of the collisions.This scaling behaviour arises when the pT spectra are presented in terms of a suitable variable,z = pT/K.The scaling parameter K is determined by the quality factor method and is parameterized by a<Npart>b,where<Npart>is the average value of the number of participating nucleons,a and b are free parameters,b characterizes the rate at which 1nK changes with In<Npaert>.For these three particle,the values of b are greater than 0,which means that the scale parameter K changes with the centrality and the more central the collisions are,the larger the value of K is.The values of b for pions and kaons are consistent within uncertainties,while they are smaller than that for protons.In the high pT region,due to the suppression of the spectra,a violation of the proposed scaling is observed going from central to peripheral collisions.The more peripheral the collisions are,the more clearly violated the proposed scaling becomes.We argue that the pions,kaons and protons originate from the fragmentation of clusters which are formed by strings overlapping and the cluster's fragmentation functions are different for different hadrons.The scaling behaviour of the pion,kaon and proton pT spectra in the low pT region can be simultaneously explained by the colour string percolation model in a quantitative way.