System size in relativistic heavy ion collisions

System size is more than a geometrical quantity in relativistic heavy ion collisions; it is closely related to evolution process,i.e.a different system size corresponds to a different evolution process,and whether QGP is produced depends on the system size.We propose that the system size should be under the same level when comparing the measurements from different colliding nuclei.The equivalence of the peripheral collisions of Au-Au and the central collisions of smaller nuclei is studied using the Monte Carlo method.Comparing the transverse overlapping area of the colliding nuclei,the number of participant nucleons and the number of nucleon-nucleon binary collisions in various colliding nuclei,we give an estimate of the correspondence in system size.This is helpful in the experimental comparison of the measurements from different colliding nuclei.     

High energy heavy ion collisions: Lessons from relativistic heavy ion collider

In this talk, I review the recent results from RHIC and discuss their significance.     

System size in relativistic heavy ion collisions

System size is more than a geometrical quantity in relativistic heavy ion collisions; it is closely related to evolution process, i.e. a different system size corresponds to a different evolution process, and whether QGP is produced depends on the system size. We propose that the system size should be under the same level when comparing the measurements from different colliding nuclei. The equivalence of the peripheral collisions of Au-Au and the central collisions of smaller nuclei is studied using the Monte Carlo method. Comparing the transverse overlapping area of the colliding nuclei, the number of participant nucleons and the number of nucleon-nucleon binary collisions in various colliding nuclei, we give an estimate of the correspondence in system size. This is helpful in the experimental comparison of the measurements from different colliding nuclei.     

Photon production in relativistic heavy ion collisions with equilibrium and non-equilibrium QGP

We consider the production sources of prompt and thermal photons which include the contribution of gluons in relativistic heavy ion collisions. Considering in our calculation the shadowing and iso-spin effects of the nucleus we can properly estimate the prompt photon production. We develop a new thermal jet-photon conversion mechanism which plays a vital role in the low transverse momentum region. The effect of the non-equilibrium quark-gluon plasma enhances the contribution of thermal photons.     

Two-pion interferometry at small relative momentum for pion sources with transverse and longitudinal expansions in relativistic heavy ion collisions

A two-pion correlation function at small relative momentum for pion sources with transverse and longitudinal expansions in relativistic heavy ion collisions is obtained using two-pion interferometry at small relative momentum, and the relations between the real and apparent parameters of the pion source are given. The relations can be used to extract both the temperature and the transverse and longitudinal expansion velocities of pion sources and to verify the correctness of relativistic transformation T′=T\sqrt {1-v^2} of temperature in relativistic statistical mechanics and thermodynamics.     

Photon production in relativistic heavy ion collisions with equilibrium and non-equilibrium QGP

We consider the production sources of prompt and thermal photons which include the contribution of gluons in relativistic heavy ion collisions. Considering in our calculation the shadowing and iso-spin effects of the nucleus we can properly estimate the prompt photon production. We develop a new thermal jet-photon conversion mechanism which plays a vital role in the low transverse momentum region. The effect of the non-equilibrium quark-gluon plasma enhances the contribution of thermal photons.     

Recent relativistic heavy ion collider results on photon,dilepton and heavy quark

We present here a review of the recent results obtained by the RHIC experiments in the framework of QCD under extreme conditions of high temperature or large baryon density, the so-called quark gluon plasma. We focus on a specific category of observables: the electromagnetic probes which cover a large spectrum of experimental studies.      

Critical phenomena in a disc-percolation model and their application to relativistic heavy ion collisions

By studying the critical phenomena in continuum-percolation of discs, we find a new approach to locate the critical point, i.e.using the inflection point of P_∞ as an evaluation of the percolation threshold.The susceptibility, defined as the derivative of P_∞, possesses a finite-size scaling property, where the scaling exponent is the reciprocal of ν, the critical exponent of the correlation length.A possible application of this approach to the study of the critical phenomena in relativistic heavy ion collisions is discussed.The critical point for deconfinement can be extracted by the inflection point of P_(QGP)-the probability for the event with QGP formation.The finite-size scaling of its derivative can give the critical exponent ν, which is a rare case that can provide an experimental measure of a critical exponent in heavy ion collisions.     

Critical phenomena in a disc-percolation model and their application to relativistic heavy ion collisions

By studying the critical phenomena in continuum-percolation of discs, we find a new approach to locate the critical point, i.e. using the inflection point of P∞ as an evaluation of the percolation threshold. The susceptibility, defined as the derivative of P∞, possesses a finite-size scaling property, where the scaling exponent is the reciprocal of v, the critical exponent of the correlation length. A possible application of this approach to the study of the critical phenomena in relativistic heavy ion collisions is discussed. The critical point for deconfinement can be extracted by the inflection point of PQGP -- the probability for the event with QGP formation. The finite-size scaling of its derivative can give the critical exponent v, which is a rare case that can provide an experimental measure of a critical exponent in heavy ion collisions.     

Study of neutron generation from relativistic heavy ion interactions

Study has been carried out on neutron generation in the interactions of 44 and 18 GeV ¹²C with Cu-and Pb-targets. The properties studied include, (1) Relative yields of secondary neutrons generated in 44 GeV versus in 18 GeV ¹²C bombardment to Cu target and also to Pb target. The ratios of these are 2.12±0.19 and 2.04±0.15, respectively, which is nearly in consistence with but somewhat larger than the values of theoretical calculations for Cu target. (2) Relative yields of secondary neutrons produced in Pb target versus in Cu target. The ratios obtained are 2.54±0.20 and 2.56±0.20 for 44 GeV and 18 GeV, respectively. More neutrons are generated in Pb target than in Cu target.     

The angular distributions of elastic scattering of 12,13C+Zr

To obtain the neutron spectroscopic amplitudes for \begin{document}${}^{90-96}$\end{document}Zr overlaps, experimental data of elastic scattering with small experimental errors and precise optical potentials were analyzed. In this study, the elastic scattering angular distributions of \begin{document}${}^{12,13}$\end{document}C + \begin{document}${}^{A} {\rm{Zr}}$\end{document} (A = 90, 91, 92, 94, 96) were measured using the high-precision Q3D magnetic spectrometer in the Tandem accelerator. The S?o Paulo potential was used for the optical potential. The optical model and coupled channel calculations were compared with the experimental data. The theoretical results were found to be very close to the experimental data. In addition, the possible effects of the couplings to the inelastic channels of the \begin{document}${}^A {\rm{Zr}}$\end{document} targets and \begin{document}${}^{12, 13}$\end{document}C projectiles on the elastic scattering were studied. It was observed that the couplings to the inelastic channels of the \begin{document}${}^{12,13}$\end{document}C projectiles could improve the agreement with the experimental data, while the inelastic couplings to the target states are of minor importance. The effect of the one-neutron stripping in the \begin{document}${}^{13}$\end{document}C+\begin{document}${}^A {\rm{Zr}}$\end{document} elastic scattering was also studied. The one-neutron stripping channel in \begin{document}${}^{13}$\end{document}C + \begin{document}${}^A {\rm{Zr}}$\end{document} was found to be not relevant and did not affect the elastic scattering angular distributions. Our results also show that in the reactions with the considered zirconium isotopes, the presence of the extra neutron in \begin{document}${}^{13}$\end{document}C does not influence the reaction mechanism, which is governed by the collective excitation of the \begin{document}${}^{12}$\end{document}C core.     

Quark-gluon plasma: Status of heavy ion physics

Lattice quantum chromodynamics (QCD), defined on a discrete space-time lattice, leads to a spectacular non-perturbative prediction of a new state of matter, called quark-gluon plasma (QGP), at sufficiently high temperatures or equivalently large energy densities. The experimental programs of CERN, Geneva and BNL, New York of relativistic heavy ion collisions are expected to produce such energy densities, thereby providing us a chance to test the above prediction. After a brief introduction of the necessary theoretical concepts, I will present a critical review of the experimental results already obtained by the various experiments in order to examine whether QGP has already been observed by them.     

Algebraic expressions for effective potential characteristic parameters in heavy ion scattering

In this paper, we obtain reliable expressions to calculate the barrier and pocket positions of the real part of the effective phenomenological optical potential having Woods-Saxon form factor, for different partial waves. The comparison of the results obtained from these formulae, when compared with the numerical results obtained using Newton-Raphson iterative procedure are found to be quite accurate, with error less than 1%. We also obtain algebraic expressions for estimatingl _poc, the angular momentum at which the potential pocket vanishes, the accuracy of which is tested with the exact calculations, using self-consistent iterative procedures. These and other expressions deduced in this paper provide simple and useful methods for calculating critical parameters of heavy ion effective potentials like barrier and pocket positions, curvatures at the barrier and pocket positions,l _poc and the grazing angular momentuml _g to carry out the analysis of heavy ion scattering.     

Large transverse momentum dilepton Production in heavy ion collisions with two-photon processes

The cold component of large transverse momentum dilepton production via semi-coherent two-photon interaction is calculated.The cold contribution is essential to the dilepton spectra in the soft region for different mass bins.The results are compared with the PHENIX experimental data at RHIC,and we find that the modification of semi-coherent two-photon processes is more evident with the rising dilepton mass bins.     

Calculation of energy density in the colour tube model of relativistic heavy ion collisions

The energy density produced in a relativistic heavy ion collision is calculated within the framework of the colour tube model. The chromoelectric field generated in the collision produces quark-antiquark pairs. The motion of these particles is described by Boltzmann equation. The interaction between the quarks and antiquarks is approximated by introducing a relaxation time.     

Large transverse momentum dilepton production in heavy ion collisions with two-photon processes

The cold component of large transverse momentum dilepton production via semi-coherent two-photon interaction is calculated. The cold contribution is essential to the dilepton spectra in the soft region for different mass bins. The results are compared with the PHENIX experimental data at RHIC, and we find that the modification of semi-coherent two-photon processes is more evident with the rising dilepton mass bins.     

Experimental study of the elastic scattering of ~(10)Be on ~(208)Pb at the energy of around three times the Coulomb barrier

Elastic scattering of 10Be on a 208Pb target was measured at ELab=127 MeV,which corresponds to three times the Coulomb barrier.The secondary 10Be beam was produced at the Radioactive Ion Beam Line in Lanzhou of the Heavy-Ion Research Facility in Lanzhou.The angular distribution of elastic scattering in the 10 Be+208Pb system shows a typical Fresnel diffraction peak.Optical model analysis of the angular distribution was performed using the Woods-Saxon,double-folding and global potentials.With the global potential,different density distributions were used.The results indicate that different density distributions for the projectile induce distinct effects in the angular distribution.     

Jet-photon conversion with energy loss in heavy ion collisions

The rate of high energy photons produced from energetic jets during their propagation through the QGP at RHIC and LHC is studied by taking into account the contribution of jet quenching in the medium. It is shown that the jet quenching effect reduces the rate of jet-photon conversion at large transverse momemtum by about 40% at RHIC with √S＝ 200 AGeV, and by about 80% at LHC with √S = 5500 AGeV.     

Pion-proton elastic scattering at 200 GeV/c

Recent measurements of differential and elastic cross-sections, slope parameters and ratios of the real and imaginary parts of the forward scattering amplitudes for pion-proton elastic scattering at 200 GeV/c have been fitted by using a simple Regge pole model with phenomenological residue functions. The computed results for total cross-sections have also been compared with the experimental data.