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.

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.PACS numbers: 12.38. Mh, 25.75.+r, 24.85.+p, 25.75.Nq The main aim of ongoing ultra relativistic heavy ion collisions is to study the properties of nuclear or hadronic matter at extreme conditions. A particular goal lies in the identification of a new state of matter formed in such collisions, the quark-gluon plasma (QGP), where the quarks and gluons are deconfined from the nucleons and move freely over an extended space-time region. Various measurements taken at CERN Super Proton Synchrotron ( Some of the important features of the plasma produced in heavy ion collisions include energy loss and jet quenching of high energetic partons, viz., light and heavy quarks. The Gunion-Bertsch (GB) formula [10] for gluon emission from the processes qq → qqg has been widely used in different phenomenological studies of heavy ion collisions, in particular for radiative energy loss of high energy partons propagating through a thermalized QGP [11][12][13][14][15][16][17][18][19][20][21][22][23][24]. The energy loss is presently a field of high interest in view of jet quenching of high energy partons, viz., both light [22,[25][26][27] and heavy quarks [11-14, 16-18, 23-25, 28-32]. Generally, one expects that jet quenching for heavy quarks should be weaker than that of light quarks. In contrast the non-photonic data at RHIC [8] reveal a similar suppression for heavy flavored hadrons compared to that of light hadrons.An early attempt to calculate the heavy quark energy loss in a QGP medium was done in Ref. [12] by using the GB formula of gluon emission for light quark scattering [10] and just modifying the relevant kinematics for heavy quarks. Later the soft gluon emission formula for heavy quarks in the high energy approximation [14] was renewed in Ref.[13] for the small angle limit. Soft gluon emission from a heavy quark was found to be suppressed in the forward direction compared to that from a light quark due to the mass effect (dead cone effect). The corresponding suppression factor was obtained as [13],where θ 0 = M/E ≪ 1. E is the energy of the heavy quark with mass, M and θ, the angle between the heavy quark and the radiated gluon. Often in the literature [15,16] the expressionis used as the suppression factor to calculate heavy quark energy loss in heavy ion collisions. Here, k ⊥ denotes the transverse momentum of the emitted g...

We generalise the most extensively used Gunion-Bertsch formula for the soft gluon emission in a perturbative QCD. We show that the corrections arising due to this generalisation could be very important for the phenomenology of the hot and dense matter produced in the heavy-ion collisions. PACS numbers: 12.38.Mh, 25.75.+r, 24.85.+p, 25.75.Nq The prime intention for ultra relativistic heavy-ion collisions is to study the behaviour of nuclear or hadronic matter at extreme conditions like very high temperatures and energy densities. A particular goal lies in the identification of a new state of matter formed in such collisions, the quark-gluon plasma (QGP), where the quarks and gluons are deliberated from the nucleons and move freely over an extended space-time region. Various measurements taken in CERN-SPS [1] and BNL-RHIC [2-7] do lead to 'wealth of information' for the formation of QGP through the hadronic final states. In the upcoming experiments at the CERN LHC, one is hoping to produce QGP during the first several fm/c of the collisions and to substantiate those evidences already found in the past as well in the recent experiments.Some quantitative key features of the plasma produced in such collisions include equilibration and its time, initial temperature, energy-loss and jet quenching of high energetic partons, and elliptic flow of hadrons and its scaling with the number of valence quarks. The Gunion-Bertsch (GB) formula [8] for soft gluon emission has widely been used for various aspect of the heavy-ion phenomenology. To set the perspective we note that there are many papers in the literature based on the GB formula. We recall: the sequence of events in hot glue scenario [9][10][11][12], thermal equilibration [13,14], gluon chemical equilibration [13,15,16], parton matter viscosity [17,18], radiative energy-loss of high energy partons propagating through a thermalised QGP [19][20][21] etc., where the GB formula has extensively been used. The original GB formula was derived in Ref. [8] for gluon emission from quark-quark scattering and later it was explicitly used in Ref. [15,22] to derive the soft gluon emission from gluongluon scattering. Recently in Ref.[23] a correction to the GB formula for soft gluon emission was obtained. In present article we make an effort to generalise the GB formula for soft gluon emission from gluon-gluon scattering, i.e., gg → ggg and find a more important correction than it is found in Ref. [23]. We also show that in an appropriate limit the generalisation reduces to the GB formula. We further note that the results for similar inelastic processes can be obtained in a straightforward way by using our generalisation.For the process, gg → ggg, there are 25 different topologies. We note that k 1 and k 2 are momenta of the gluons in the entrance channel, k 3 and k 4 are those for exit channel gluons whereas k 5 is that of the emitted gluon. The invariant amplitude summed over all the final states and averaged over initial states for such process can elegantly be written [24] as:

The case of gluon bremsstrahlung off a heavy quark in extended nuclear matter is revisited within the higher twist formalism. In particular, the in-medium modification of "semi-hard" heavy quarks is studied, where the momentum of the heavy quark is larger but comparable to the mass of the heavy quark (p M ). In contrast to all prior calculations, where the gluon emission spectrum is entirely controlled by the transverse momentum diffusion parameter (q), both for light and heavy quarks, in this work, we demonstrate that the gluon emission spectrum for a heavy quark (unlike that for flavors) is also sensitive toê, which so far has been used to quantify the amount of light-cone drag experienced by a parton. This mass dependent effect, due to the non-light-like momentum of a semi-hard heavy-quark, leads to an additional energy loss term for heavy-quarks, while resulting in a negligible modification of light flavor (and high energy heavy flavor) loss. This result can be used to estimate the value of this sub-leading non-perturbative jet transport parameter (ê) from heavy flavor suppression in ultra-relativistic heavy-ion collisions.

Based on quantum statistical mechanics, we show that the SU (3) color singlet ensemble of a quark-gluon gas exhibits a Z(3) symmetry through the normalized character in fundamental representation and also becomes equivalent, within a stationary point approximation, to the ensemble given by Polyakov Loop. In addition, a Polyakov Loop gauge potential is obtained by considering spatial gluons along with the invariant Haar measure at each space point. The probability of the normalized character in SU (3) vis-a-vis a Polyakov Loop is found to be maximum at a particular value, exhibiting a strong color correlation. This clearly indicates a transition from a color correlated to an uncorrelated phase, or vice versa. When quarks are included in the gauge fields, a metastable state appears in the temperature range 145 T (MeV) 170 due to the explicit Z(3) symmetry breaking in the quark-gluon system. Beyond T 170 MeV, the metastable state disappears and stable domains appear. At low temperatures, a dynamical recombination of ionized Z(3) color charges to a color singlet Z(3) confined phase is evident, along with a confining background that originates due to the circulation of two virtual spatial gluons, but with conjugate Z(3) phases in a closed loop. We also discuss other possible consequences of the center domains in the color deconfined phase at high temperatures.