Medium-induced radiation with vacuum propagation in the pre-hydrodynamics phase

Abstract

The recent discovery of the potential of jet quenching observables to constrain the initial stages after a heavy-ion collision makes imperative to have a better understanding of the process of medium-induced radiation before the formation of the quark-gluon plasma (QGP) and its impact on observables at high-pT. In this work, we generalize the BDMPS-Z framework for medium-induced radiation to account for additional emissions occurring before the creation of the QGP. For simplicity, we assume that during the pre-hydrodynamics phase the hard parton propagates as in vacuum. This set-up, allows us to isolate the contribution from the additional initial radiation by comparing with the usual scenarios in which the emitter is created inside the medium but with different starting points. Using both a numerical implementation of the fully resummed emission spectrum and the usual analytical approximations, we find that replacing an initial slab of the medium by vacuum yields to a significant reduction of the emission spectrum for low radiated gluon energies, while the high-energy tails remain largely unmodified. Finally, we assess the effect of replacing the initial medium by vacuum propagation on the single-inclusive particle suppression RAA and high-pT azimuthal asymmetry v2. Our findings indicate that considering vacuum propagation prior to hydrodynamization leads to an increase in the v2, thus corroborating the importance of the treatment of jet quenching in the initial stages for the correct description of both observables.

Early time dynamics and constraints on medium evolution

“…with transverse momenta 𝑞 ⊥,𝑖 with 𝑖 = 𝑦 or 𝑧. It has been pointed out recently that pre-equilibrium dynamics may have sizable effects on heavy-quark diffusion and jet quenching [42,[47][48][49][50][51][52]. More specifically, the transport coefficients 𝜅 and q have been recently computed during the Glasma phase [41,42,48,50,[53][54][55] using force-force correlations or, alternatively, Wong's equations in classical-statistical simulations.…”

Jet medium modifications

“…However, most of jet quenching phenomenological studies typically neglect any quenching effects prior to the hydrodynamization phase. Recent studies have shown that certain energy loss observables are indeed sensitive to these early stages [44][45][46]. Nevertheless a comprehensive understanding of the impact of these initial stages on jet quenching observables in heavy-ion collisions is still lacking.…”

Momentum Broadening of Heavy Quarks and Jets in the Glasma from Classical Colored Particle Simulations

“…The Glasma fields are obtained in the proper time expansion and the transport of the hard probes is treated using the Fokker-Planck equations adapted to the Glasma. Complementary, it was shown that the initial stage, implemented in different frameworks, has an effect on jet quenching [38,39]. Even though these approaches vary with respect to the approximations which are used, they all converge to the same key result: the Glasma phase has a considerable effect on the transport of hard probes.…”