The Hadron Photo-production In High Energy Heavy Ion Collisions

Quantum Chromodynamics?QCD?predicts that the high energy heavy ion collisions will produce a high temperature and high density environment which induces the normal hadronic matter transition to a new state called quark gluon plasma?QGP?.The studies of the formation and evolution of QGP are a hot subject in high energy nuclear physics.In order to study QGP,scientists set up many models based on different principles,such as perturbative QCD model?pQCD?and color glass condensate?CGC?model.All these models can well describe the experimental data under some uncertainties,so that scientists are still not clear about the formation and evolution mechanism of QGP.To further understand QGP,we investigate the hadron photo-production by using pQCD factorization model,non-relativistic quantum chromodynamics?NRQCD?model and CGC model.Firstly,based on the pQCD factorization model,we calculate the hadron photo-production cross section.According to the pQCD factorization model,there are three ingredients for calculating the hadron production cross section.The first part is parton distribution functions,the second is partonic cross section,and the third is fragmentation functions.For the parton distribution functions,one usually considers only the initial parton?quark and gluon?and neglect the photon contributions in the literature,we calculate the hadron photo-production by taking into account the photon contribution in this study.Usually,the photo-production processes include semi-hard direct photo-production processes,semi-hard resolved photo-production processes,deep inelastic direct photo-production processes and deep inelastic resolved photo-production processes.The numerical results of four kinds of photo-production processes indicate that?1?the contri-bution of photo-production processes play a key role in the hadron production at relativistic heavy ion collisions;?2?although the initial parton-parton production processes are prominent in hadron production,the photo-production processes have contributed to over 10%,therefore we can not neglect this contribution.By taking into account the contribution of photo-production processes,the pQCD factorization theorem could give a good description of K_s⁰,?,K and?produc-tions and strangeness enhancement.The strangeness enhancement becomes more evident once the photo-production processes are taken into account.Secondly,based on the factorization model of non-relativistic QCD,we cal-culate the production cross section of the heavy quarkonium at Large Hadron Collider?LHC?energies.We consider the contribution of photo-production pro-cesses and the fragmentation processes to the production of charmonium(J/?,??2S?,?_cJ,?_c,h_c)and the bottomonium(??nS?,?_bJ,?_b,h_b).The numerical re-sults indicate that?1?the contribution of fragmentation processes is comparable to the direct production processes because of the high gluon densities at high ener-gy;?2?the photo-production and fragmentation processes are same important in proton-proton and lead-lead collisions at LHC energies,thus the photo-production process cannot be neglected.Finally,based on color glass condensate model,we calculate the vector mesons photo-production cross section.In the framework of color glass condensate,the vector meson production process can be viewed as the virtual photo fluctuates into quark and antiquark pair?a dipole?,then the dipole scattering with anoth-er nucleus?nucleon?,finally the quark and antiquark recombining into a vector meson.To obtain a precision description of the vector meson production,we in-troduce a vector meson mass dependent skewness correction factor on top of the original CGC vector meson production model.The factor effectively complement the dependence of production cross section on the species of the vector meson.By using this factor,we compute the vector meson production at LHC energies.Our numerical results show that the mass dependent factor plays a important role in the vector meson production process.In addition,in order to enhance the preci-sion of the model,we extend the leading order CGC model to the next-to-leading order level.We first use numerical method to solve the rcBK equation and get the cross-section of color dipole,then we introduce the numerical cross-section into the CGC vector meson production model,which can improve the precision of the model.By comparing the theoretical model with experimental data,the?²/d.o.f resulting from next-to-leading order calculation are smaller than leading order re-sults,which indicate that the next-to-leading order effect cannot be neglected in the calculation of vector meson production.