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Raktim Abir

Publications and source records attributed to Raktim Abir.

25 records · Page 2Linked to original sources
arXiv2014

Multiple scattering of heavy-quarks in dense matter and the parametric prominence of drag

The case of heavy quark propagation in dense extended matter is studied in the multiple scattering formalism of the higher twist energy loss scheme. We consider the case of deep inelastic scattering off a large nucleus. The hard lepton scatters off a heavy quark fluctuation within one of the nucleons. This heavy quark then propagates through the dense medium, multiply scattering off the gluon field of the remaining nucleons in its path. We consider the fictitious process where a heavy quark propagates through the nucleus without radiation. Invoking Soft-Collinear Effective Theory power counting arguments, we consider the case of a "semi-hard" heavy-quark where the mass is of the order of the out-going momentum and larger than the transverse momentum imparted per unit length due to scattering. In this limit, it is found that longitudinal momentum exchanges (quantified by the transport coefficient $\hat{e}$) have a comparable effect on the off-shellness of the propagating quark, as the transverse momentum exchanges (quantified by $\hat{q}$) which constitute the leading cause of off-shellness for propagating light quarks or gluons. Consequences of this new hierarchy for the propagation of the heavy quark in dense matter are discussed.

nucl-th↗
arXiv2013

Jet-parton inelastic interaction beyond eikonal approximation

Most of the models of jet quenching generally assumes that a jet always travels in a straight eikonal path, which is indeed true for sufficiently hard jet but may not be a good one for moderate and low momentum jet. In this article an attempt has been made to relax part of this approximation for 2 --> 3 processes and found a (15-20)% suppression in the differential cross-section for moderately hard jets because of the noneikonal effects. In particular, for the process qq' --> qq'g in the centre of momentum frame the scattering with an angle wider than \pm 0.52π, is literally forbidden unlike the process gg --> ggg that allows an angular range \pm π. This may have consequence on the suppression of hadronic spectra at low transverse momenta.

hep-ph↗
arXiv2012

Heavy quark energy loss and D-Mesons at RHIC and LHC energies

We obtain the radiative energy loss of a heavy quark in a deconfined medium due to radiation of gluons off them using a recently derived generalised gluon emission spectrum. We find that the heavy flavour loses energy almost in a similar fashion like light quarks through this process. With this, we further analyse the nuclear modification factor for D-meson at LHC and RHIC energies. In particular, the obtained result is found to be in close agreement with the most recent data from ALICE collaboration at 2.76 ATeV Pb-Pb collisions. We also discuss the nuclear modification factor due to the collisional energy loss. Furthermore, the result of non-photonic single electron from the decay of both D and B mesons is compared with the RHIC data at 200 AGeV Au-Au collisions, which is also in close agreement.

hep-ph↗
arXiv2012

Soft gluon emission off a heavy quark revisited

An improved generalized suppression factor for gluon emission off a heavy quark is derived within perturbative QCD, which is valid for the full range of rapidity of the radiated gluon and also has no restriction on the scaled mass of the quark with its energy. In the appropriate limit it correctly reproduces the usual dead cone factor in the forward rapidity region. On the other hand, this improved suppression factor becomes close to unity in the backward direction. This indicates a small suppression of gluon emission in the backward region, which should have an impact on the phenomenology of heavy quark energy loss in the hot and dense matter produced in ultra-relativistic heavy-ion collisions.

hep-ph↗
arXiv2010

On the critical exponent of η/s and a new exponent-less measure of fluidity

We discuss on the critical exponent of $η/s$ for a fluid, and propose a new exponent-less measure of fluidity based on a mode-mode coupling theory. This exhibits a remarkable universality for fluids obeying a liquid-gas phase transition both in hydrodynamic as well as in nonhydrodynamic region. We show that this result is independent of the choice of the fluid dynamics, {\em viz.}, relativistic or nonrelativistic. Quark-Gluon Plasma, being a hot relativistic and a nearly perfect fluid produced in relativistic heavy-ion collisions, is expected to obey the same universality constrained by both the viscous and the thermal flow modes in it. We also show that if the elliptic flow data in RHIC puts a constraint on $η/s$ then the new fluidity measure for Quark-Gluon Plasma in turn also restricts the other transport coefficient, {\it viz.}, the thermal conductivity.

hep-ph↗
arXiv2009

Colour-singlet clustering of partons and recombination model for hadronization of quark-gluon plasma

$SU(N_c)$ colour-singlet restriction, along with flavour and spin symmetry, on thermal partonic ensemble is shown to recombine the partons with internal colour structure into colour-singlet multi-quark clusters which can be identified with various hadronic modes at a given temperature. This provides a possible basis for recombination model for hadronization of quark-gluon plasma. This also leads to a natural explanation for the ratio of (anti)protons to pions and the quark number scaling of the elliptic flow coefficient in relativistic heavy-ion collisions.

hep-ph↗