Quenching of high-pThadrons: Energy loss versus color transparency

Abstract

High-pT hadrons produced in hard collisions and detected inclusively bear peculiar features: (i) they originate from jets whose initial virtuality and energy are of the same order; (ii) such jets are rare and have a very biased energy sharing among the particles, namely, the detected hadron carries the main fraction of the jet energy. The former feature leads to an extremely intensive gluon radiation and energy dissipation at the early stage of hadronization, either in vacuum or in a medium. As a result, a leading hadron must be produced on a short length scale. Evaluation within a model of perturbative fragmentation confirms the shortness of the production length. This result is at variance with the unjustified assumption of long production length, made within the popular energy loss scenario. Thus we conclude that the main reason of suppression of high-pT hadrons in heavy ion collisions is the controlled by color transparency attenuation of a high-pT dipole propagating through the hot medium. Adjusting a single parameter, the transport coefficient, we describe quite well the data from LHC and RHIC for the suppression factor RAA as function of pT , collision energy and centrality. We observe that the complementary effect of initial state interaction causes a flattening and even fall of RAA at large pT . The azimuthal anisotropy of hadron production, calculated with no further adjustment, also agrees well with data at different energies and centralities.

Cronin effect at different energies: from RHIC to LHC

“…This supports a manifestation of another mechanism proposed in [7] and applied for description of various processes in p(d) + A interactions [8] and in heavy ion collisions [9]. Such a mechanism is valid at any energy and is responsible for a significant suppression of particle production at ξ → 1, where ξ = [7] leads to breakdown of the QCD factorization at large ξ and we rely on the factorization formula, Eq.…”

Charmonium propagation through a dense medium

“…3-4(left) on one plot Fig. 4(right) for the selected value of q 0 = 2 GeV/fm, extracted from the analysis [26] of data for high-p T hadron suppression in lead-lead collisions at LHC. We see that the magnitude of suppression caused by the two mechanisms is similar at transverse J/ψ momenta around the mean value.…”

Survival of charmonia in a hot environment

“…As a result, the mean dipole separation rises with path length as ∝ √ l, rather than linearly. If acc dipole is produced and moving with momentum p ψ , its transverse (relative to its momentum) separation rises as [26,27],…”

“…The falling time dependence 1/t is due to longitudinal expansion. It is also assumed that the medium takes time t 0 to reach equilibrium, and in (27) is assumed that the medium "appears" at this moment. Of course such a treatment of the medium development is grossly oversimplified, and the time scale t 0 is poorly defined.…”