Color-glass condensate

About: Color-glass condensate is a research topic. Over the lifetime, 885 publications have been published within this topic receiving 35169 citations.

Bulk quantities in nuclear collisions from running-coupling k(T) factorization and hybrid simulations

Abstract: Starting from a Color Glass Condensate (CGC) framework, based on a running-coupling improved $k_T$-factorized formula, we calculate bulk observables in several heavy-ion collision systems. This is done in two ways: first we calculate the particle distribution directly implied from the CGC model, and we compare this to the case where it is instead used as initial conditions for a hybrid hydrodynamic simulation. In this way, we can assess the effects of hydrodynamic and hadronic evolution by quantifying how much they change the results from a pure initial state approach and, therefore, to what extent initial condition models can be directly compared to experimental data. We find that entropy production in subsequent hydrodynamic evolution can increase multiplicity by as much as 50\%. However, disregarding a single overall normalization factor, the centrality, energy, and system size dependence of charged hadron multiplicity is only affected at the $\sim$5\% level. Because of this, the parameter-free prediction for these dependencies gives reasonable agreement with experimental data whether or not hydrodynamic evolution is included. On the other hand, our model results are not compatible with the hypothesis that hydrodynamic evolution is present in large systems, but not small systems like p-Pb, in which case the dependence of multiplicity on system size would be stronger than seen experimentally. Moreover, we find that hydrodynamic evolution significantly changes the distribution of momentum, so that observables such as mean transverse momentum are very different from the initial particle production, and much closer to measured data. Finally, we find that a good agreement to anisotropic flow data cannot be achieved due to the large eccentricity generated by this model.

Correlations in the Initial Conditions of Heavy-Ion Collisions

Abstract: Ultracentral collisions of heavy nuclei, in which the impact parameter is nearly zero, are especially sensitive to the details of the initial state model and the microscopic mechanism for collective flow In a hydrodynamic “flow” picture, the final state momentum correlations are a direct response to the fluctuating initial geometry, although models of the initial geometry differ widely Alternatively, dynamical mechanisms based in the color glass condensate (CGC) formalism can naturally lead to many-body correlations with very different systematics Here we present a calculation of event-by-event elliptic flow in both the hydrodynamic and CGC paradigms and show that they can be qualitatively distinguished in ultracentral collisions of deformed nuclei Specifically, the multiplicity dependence in such collisions is qualitatively opposite, with the CGC correlations increasing with multiplicity while the hydrodynamic correlations decrease The consistency of the latter with experimental data on UU collisions appears to rule out a CGC-mediated explanation We find that these qualitative features also persist in small deformed systems and can therefore be a valuable test of the microscopic physics in that regimeThe authors acknowledge support from the US-DOE Nuclear Science Grant No DE-SC0019175, and the Alfred P Sloan Foundation, and the Zuckerman STEM Leadership Program

Hadron Multiplicity in Pb+Pb Collisions at √s = 2.76 TeV from Color Glass Condensate

Abstract: The pseudo-rapidity distribution of charged hadron multiplicity in Pb+Pb collisions at √s = 2.76 TeV is studied by using Color Glass Condensate dynamics in the fixed coupling case. We fit the HERA experimental data with heavy parton mass effect to obtain saturation exponent λ = 0.22. It is found that the charged hadron multiplicity can only describe after including heavy parton mass effect due to a large amount of heavy partons produced at large hadron collider (LHC) energy. The pomeron loop effect contribution to hadron production is also investigated. It shows that charged hadron multiplicity is underestimated by including the pomeron loop effect, which indicates that the pomeron loop effect may not exist at LHC energy.

Multi-messenger heavy-ion physics

Abstract: This work studies the production of direct photons in relativistic nuclear collisions, along with the production of hadrons. Radiation from the very first instants to the final moments of the evolution is included. The hybrid model used here describes all stages of relativistic heavy-ion collisions. Chronologically, those are an initial state reflecting the collision of nuclei described within the Color Glass Condensate effective theory; a pre-equilibrium phase based on non-equilibrium linear response; relativistic viscous hydrodynamics, and a hadronic afterburner. The effect of the pre-equilibrium phase on both photonic and hadronic observables is highlighted for the first time. The potential of photon observables -- spectrum, differential elliptic and triangular flow -- to reveal the chemical equilibration time is studied. Finally, we consider "small collision systems", including proton+nucleus collisions and collisions of light nuclei, as probed by hadronic and electromagnetic observables. We demonstrate how photon production can signal the formation of quark-gluon plasma in such small systems.