Medium-induced Radiative Energy Loss Research Articles

Jet quenching in expanding medium

Comprehensive understanding of medium-induced radiative energy loss is of a paramount importance in describing observed jet quenching in heavy-ion collisions. In this work, we have calculated the medium-modified gluon splitting rates for different profiles of the expanding partonic medium, namely profiles for static, exponential, and Bjorken expanding medium. Here in this study, we have used the Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPSZ) formalism is used for multiple soft scatterings with a time-dependent transport coefficient for characterizing the expanding medium. Using the kinetic rate equation, we have numerically evaluated the distribution of the medium evolved gluon spectra for different medium profiles. We have presented a calculation of the jet QAA which quantifies a sensitivity of the inclusive jet suppression on the way how the medium expands. Comparisons of predicted jet QAA with experimental data from the LHC are also presented.

Collisional vs. Radiative Energy Loss of Heavy Quark in a Hot and Dense Nuclear Matter

We study the heavy quark evolution in a quark-gluon plasma medium within the framework of Langevin equation coupled to a (2+1)-dimensional viscous hydrodynamic model. We modify the current Langevin algorithm such that apart from quasi-elastic scattering, medium-induced radiative energy loss is incorporated as well by treating gluon radiation as an extra force term. We find a significant effect of gluon radiation on heavy quark energy loss at LHC energies. Our calculation provides a good description of the D meson suppression measured by ALICE experiment, and makes a prediction for B meson suppression and flow.

Gluon radiation outside a finite cone

The medium-induced gluon radiation angular distributions of light quarks and heavy quarks outside a finite jet cone are studied. We find the effect of destructive interference between the vacuum and medium-induced radiation plays an important role in gluon radiation for very small value of path length L, which leads to the negative value of medium-induced energy loss. The medium-induced radiative energy loss outside an angle for heavy quarks is found to have a minimum and a maximum at small angle for small path length, which are caused by dead cone effect and Brownian k⊥-broadening effect, respectively. However for large path length the minimum and maximum disappear.

Jet shapes in opaque media

We present general arguments, based on the medium-induced radiative energy loss, to explain the presence of nontrivial angular structures within this perturbative mechanism. Simple analytical estimates of this effect are provided which are relevant to the current discussion on the interpretation of the data on two- and three-particle correlations of semihard particles at BNL's Relativistic Heavy Ion Collider.

Heavy quarks as a test of medium-induced energy loss at RHIC and at the LHC

We present our recent studies of the medium-induced radiative energy loss of heavy quarks and its experimental signatures in heavy ion collisions. In particular, we discuss the ratio of nuclear modification factors of high-pT heavy-flavoured mesons to light-flavoured hadrons (heavy-to-light ratio). Depending on the transverse momentum of the heavy quark, this ratio turns out to be sensitive either to the mass-dependence or to the colour charge dependence expected for radiative parton energy loss. Based on this observation, we show how the simultaneous analysis of D and B mesons at the LHC in the region 10 < pT < 20 GeV allows one to disentangle the dependence of parton energy loss on parton identity. We then discuss to what extent high-pT electron spectra, expected to be dominated by heavy quark decay contributions, can give access to the microscopic mechanism underlying parton energy loss.

From leading hadron suppression to jet quenching at RHIC and at the LHC

In nucleus-nucleus collisions at the Relativistic Heavy Ion Collider (RHIC), one generically observes a strong medium-induced suppression of high-pT hadron production. This suppression is accounted for in models which assume a significant medium-induced radiative energy loss of high-pT parent partons produced in the collision. How can we further test the microscopic dynamics conjectured to underly this abundant high-pT phenomenon? What can we learn about the dynamics of parton fragmentation, and what can we learn about the properties of the medium which modifies it ? Given that inelastic parton scattering is expected to be the dominant source of partonic equilibration processes, can we use hard processes as an experimentally well-controlled window into QCD non-equilibrium dynamics ? Here I review what has been achieved so far, and which novel opportunities open up with higher luminosity at RHIC, and with the wider kinematical range accessible soon at the LHC.

Jet quenching versus jet enhancement: a quantitative study of the BDMPS-Z gluon radiation spectrum

We study the gluon radiation spectrum off a hard in-medium produced quark in the multiple soft-rescattering formalism of Baier–Dokshitzer–Mueller–Peigné–Schiff and of Zakharov (BDMPS-Z). Its dependence on the quark and gluon energy, on the gluon transverse momentum, on the in-medium pathlength and on the rescattering properties of the nuclear medium is analyzed quantitatively. The two components of gluon radiation, the hard vacuum radiation associated to the quark production vertex, and the medium-induced rescattering contribution interfere destructively. For small spatial extensions of the medium, this destructive interference overcompensates the hard vacuum radiation, and the total medium-induced radiative energy loss decreases as ΔE∝− L 3 . Medium-induced gluon production dominates only above a finite critical length L>L crit which varies between 3 and more than 6 fm depending on the rescattering properties of the medium. Deviations from the BDMPS- L 2 -behaviour persist above L crit . The medium-dependence of the angular gluon distribution is dominated by transverse brownian k ⊥ -broadening. This results in a depletion of the low transverse momentum part of both the hard and the medium-induced contribution. As a consequence, the medium-induced energy loss outside a finite angular cone size Θ can be more than a factor two larger than the total medium-induced radiative energy loss. We discuss implications of these results for the jet quenching signal in relativistic heavy-ion collisions at RHIC and LHC.

Medium-induced radiative energy loss; equivalence between the BDMPS and Zakharov formalisms

We extend the BDMPS formalism for calculating radiative energy loss to the case when the radiated gluon carries a finite fraction of the quark momentum. Some virtual terms, previously overlooked, are now included. The equivalence between the formalism of BDMPS and that of B. Zakharov is explicitly demonstrated.