Suppression Effect Of Single Hadron Spectra On System Size Dependence Of Energy Loss In High Energy Heavy Ion Collision

Quantum Chromo-Dynamics (QCD), the theory of strong interaction, predicts that nuclear matter undergoes a phase transition to a deconfined state of quark and gluon at extreme densities and temperatures. The condition of extreme high energy density and temperature could be created in high energy heavy-ion collision experiment, then the study of the new matter state-Quark-Gluon Plasma (QGP) the goal that high energy and nuclear physics scientists all over the world have been searching for collaborative since several past decades.In high energy heavy ion collisions, the suppression of the yield of final state high transverse momentum hadrons is considered to be a important signal of exiting Quark-Gluon Plasma. In the process of nuclear-nuclear(AA) collisions, hard scattering is on the initial stage. High transverse momentum partons which come from hard scattering will propagate in the strong interaction medium and interact with matter. These partons are expected to lose their energy in medium by gluon bremsstrahlung, which is called jet quenching.In RHIC, through comparing the yield of leading particle in nuclear-nuclear collisions with that in nucleon-nucleon collision it shows that hadron spectrum of neutral pions are suppressed because of jet quenching or jet energy loss. Furthermore, the affect of the jet quenching or energy loss is more obvious through computing the nuclear modified factor. After studying the central and the peripheral collisions, we find that the hot and dense matter or QGP matter is formed in central AA collisions, but not in the peripheral AA collisions.Based on parton model in QCD, at the leading-order approximation we study theÏ€⁰ spectra and nuclear modification factor R_AA in Au + Au and Cu + Cu collisions with different centralities. Because of parton jet energy loss in heavy ion collision, large transverse momentum hadrons spectra are suppressed as compared to p + p collisions at the same energy. It is shown that the suppression has strong dependence on the system size which determines the amount of the jet energy loss. The bigger the system is, the larger parton energy loss is. It results in the much more suppression of the spectra and also the much less R_AA.