Mutual boosting of the saturation scales in colliding nuclei

Strangeness Saturation: Energy- and System-Size Dependence

Relativistic heavy-ion collisions lead to a final state which has a higher degree of strangeness saturation than those of elementary collisions. A systematic analysis of this phenomenon, based on the strangeness saturation factor, is made for C+C, Si+Si and Pb+Pb collisions at the CERN SPS collider and for Au+Au collisions at RHIC energies. Strangeness saturation is shown to increase with the number of participants within a colliding system, at both CERN SPS and RHIC energies. The saturation observed in central collisions of lighter nuclei deviates from that seen in peripheral collisions of he…

Gluon saturation effects on J/Psi production in heavy ion collisions

We consider a novel mechanism for J/Psi production in nuclear collisions arising due to the high density of gluons. We calculate the resulting J/Psi production cross section as a function of rapidity and centrality. We evaluate the nuclear modification factor and show that the rapidity distribution of the produced J/Psi's is significantly more narrow in AA collisions due to the gluon saturation effects. Our results indicate that gluon saturation in the colliding nuclei is a significant source of J/Psi suppression that can be disentangled from the quark-gluon plasma effects.

Has saturation physics been observed in deuteron-gold collisions at RHIC?

We have addressed the question of whether saturation (CGC) has been observed in deuteron-gold collisions at RHIC. We have made a detailed analysis of the Cronin peak characteristic of the nuclear modification factor measured for d-Au collisions at mid-rapidity. The Cronin peak which is obtained around $p_t\simeq 3$ GeV may be reproduced at the proper height only by boosting the saturation momentum by a huge non-perturbative additional component. At forward rapidity, we get a quantitative agreement with data, reproducing hadron production spectra and the $R_{CP}$ ratio using a recently develope…

J/Psi production in nuclear collisions: measuring the transport coefficient

The observed pT-dependence of nuclear effects for J/Psi produced in heavy ion collisions at RHIC might look puzzling, since the nuclear suppression seems to fade at large pT. We explain this by the interplay of three mechanisms: (i) attenuation of J/Psi in the hot medium created in the nuclear collision; (ii) initial state shadowing of charmed quarks and attenuation of a c-cbar dipole propagating through the colliding nuclei; (iii) a strong Cronin effect for J/Psi caused by saturation of gluons in the colliding nuclei. All three effects are well under control and calculated in a parameter free…

High Gluon Densities in Heavy Ions Collisions

The early stages of heavy ion collisions are dominated by high density systems of gluons that carry each a small fraction $x$ of the momenta of the colliding nucleons. A distinguishing feature of such systems is the phenomenon of "saturation" which tames the expected growth of the gluon density as the energy of the collision increases. The onset of saturation occurs at a particular transverse momentum scale, the "saturation momentum", that emerges dynamically and that marks the onset of non-linear gluon interactions. At high energy, and for large nuclei, the saturation momentum is large compar…

Has saturation physics been observed in deuteron-gold collisions at RHIC?

In the framework of the recently proposed saturation picture, we examine in a systematic way whether the nuclear modification factor measured for d-Au collisions at RHIC may be simply explained. The Cronin peak which is obtained at mid-rapidity around $k_{\bot}\simeq 3$ GeV may be reproduced at the proper height only by boosting the saturation momentum by an additional nuclear component as already shown in the literature. In this respect, mid-rapidity RHIC data cannot necessarily be seen as a probe of the saturation picture. The large rapidity ($η\simeq 3$) region allows us to test the shape o…

Inclusive Gluon Production in DIS at High Parton Density

We calculate the cross section of a single inclusive gluon production in deep inelastic scattering at very high energies in the saturation regime, where the parton densities inside hadrons and nuclei are large and the evolution of structure functions with energy is nonlinear. The expression we obtain for the inclusive gluon production cross section is generated by this nonlinear evolution. We analyze the rapidity distribution of the produced gluons as well as their transverse momentum spectrum given by the derived expression for the inclusive cross section. We propose an ansatz for the multipl…

Long-Range Rapidity Correlations in Heavy-Light Ion Collisions

We study two-particle long-range rapidity correlations arising in the early stages of heavy ion collisions in the saturation/Color Glass Condensate framework, assuming for simplicity that one colliding nucleus is much larger than the other. We calculate the two-gluon production cross section while including all-order saturation effects in the heavy nucleus with the lowest-order rescattering in the lighter nucleus. We find four types of correlations in the two-gluon production cross section: (i) geometric correlations, (ii) HBT correlations accompanied by a back-to-back maximum, (iii) away-side…

Classical Initial Conditions for Ultrarelativistic Heavy Ion Collisions

We construct an analytical expression for the distribution of gluons in the state immediately following a heavy ion collision in the quasi-classical limit of QCD given by McLerran-Venugopalan model. The resulting gluon number distribution function includes the effects of all multiple rescatterings of gluons with the nucleons of both colliding nuclei. The typical transverse momentum k of the produced gluons is shown to be of the order of the saturation scale of the nuclei Qs, as predicted by Mueller. We analyze the properties of the obtained distribution and demonstrate that due to multiple res…

From Color Glass Condensate to Quark Gluon Plasma through the event horizon

We propose a new thermalization scenario for heavy ion collisions which at sufficiently high energies implies the phase transition to the quark--gluon plasma. The key ingredient of our approach is the Hawking--Unruh effect: an observer moving with an acceleration $a$ experiences the influence of a thermal bath with an effective temperature $T = a / 2π$, similar to the one present in the vicinity of a black hole horizon. For electric charges moving in external electromagnetic fields of realistic strength, the resulting temperature appears too small to be detected. However for partons in strong …

Chemical equilibrium study in nucleus-nucleus collisions at relativistic energies

We present a detailed study of chemical freeze-out in nucleus-nucleus collisions at beam energies of 11.6, 30, 40, 80 and 158A GeV. By analyzing hadronic multiplicities within the statistical hadronization approach, we have studied the strangeness production as a function of centre of mass energy and of the parameters of the source. We have tested and compared different versions of the statistical model, with special emphasis on possible explanations of the observed strangeness hadronic phase space under-saturation. We show that, in this energy range, the use of hadron yields at midrapidity in…

LHC高亮度质子-原子核碰撞的物理研究

Physics with high-luminosity proton-nucleus collisions at the LHC

本文综述了LHC第三、四运行期高亮度质子-铅碰撞的物理潜力，涵盖核子部分子分布、低x QCD、强子谱学、夸克-胶子等离子体基线及超出标准模型新物理等方向，并总结了加速器运行与实验测量需求。

基于广义Fokker-Planck分布研究sqrt(sNN)=200 GeV小系统非对称碰撞中的动力学冻结与扩散动力学

Kinetic freeze-out and diffusion dynamics in small-system asymmetric collisions at sqrt(sNN)=200 GeV in light of a generalized Fokker-Planck distribution

利用广义Fokker-Planck解分析小系统非对称碰撞中π^0的横动量谱，提取热-硬过程转变能标、有效温度和幂律指数，揭示系统大小和中心度对冻结温度及扩散过程的影响。