Lusaka Bhattacharya, Pradip k Roy
We calculate photons from jet plasma interaction in a collisional energy loss scenario. It is shown that the PHENIX photon data is well reproduced when photons from initial hard collisions are taken into account.
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We estimate the energy loss distribution and investigate the quenching of hadron spectra in ultrarelativistic heavy-ion collisions due to the collisional energy loss of energetic partons from hard parton collisions in the initial stage.
It was argued recently that loop corrections to tree-level amplitudes are essential in the discussion of the collisional energy loss of energetic partons in the hot quark gluon plasma: Instead of $dE_{\rm coll}^B/dx \sim α^2 T^2 \ln(ET/m_D^2)$, as first derived by Bjorken (assuming a constant $α$), the mean energy loss actually behaves as $dE_{\rm coll}/dx \sim α(m_D^2)T^2$. Here we calculate, within this resummation-improved framework, the probability distribution functions (`quenching weights') of the collisional energy loss. First results from a Monte Carlo implementation of this probabilis…
Within the framework of Boltzmann transport equation with a Bhatnagar-Gross-Krook (BGK) collisional kernel, we study the wake potential induced by fast partons traveling through the high-temperature QCD plasma which is anisotropic in momentum-space. We calculate the dielectric response function of a collisional anisotropic quark-gluon plasma (AQGP) for small $ξ$ (anisotropic parameter) limit. Using this, the wake potential for various combinations of the anisotropy parameter ($ξ$) and the collision rate ($ν$) is evaluated both for parallel and perpendicular directions of motion of the fast par…
We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a quark-gluon plasma. Our treatment of both processes is complete at leading order in the coupling and accounts for the probabilistic nature of the jet energy loss. We find that the nuclear modification factor $R_{AA}$ for neutral $π^0$ production in heavy ion collisions is sensitive to the inclusion of collisional and radiative energy loss contributions while the averaged energy loss only slightly increases if collisional energy loss is included for parent parton energies $E\gg T$. These results are…
Cone-Dependent Jet Collisional Energy Loss in Finite QCD Medium
研究了有限QCD介质中喷注碰撞能量损失的锥度依赖性，推导了紧凑的HTL重正化表达式，揭示了弹性部分与辐射部分的非线性依赖关系及介质响应贡献。
Wakes created by a parton moving through a static and infinitely extended quark-gluon plasma are considered. In contrast to former investigations collisions within the quark-gluon plasma are taken into account using a transport theoretical approach (Boltzmann equation) with a Bhatnagar-Gross-Krook collision term. Within this model it is shown that the wake structure changes significantly compared to the collisionless case.
In this paper, we calculate the soft-collisional energy loss of heavy quarks traversing the viscous quark-gluon plasma including the effects of a finite relaxation time $τ_π$ on the energy loss. We find that the collisional energy loss depends appreciably on $τ_π$ . In particular, for typical values of the viscosity-to-entropy ratio, we show that the energy loss obtained using $τ_π$ = 0 can be $\sim$ 10$\%$ larger than the one obtained using $τ_π$ = 0. Moreover, we find that the energy loss obtained using the kinetic theory expression for $τ_π$ is much larger that the one obtained with the $τ_…
We calculate radiative and collisional energy loss of hard partons traversing the quark-gluon plasma created at RHIC and compare the respective size of these contributions. We employ the AMY formalism for radiative energy loss and include additionally energy loss by elastic collisions. Our treatment of both processes is complete at leading order in the coupling, and accounts for the probabilistic nature of jet energy loss. We find that a solution of the Fokker-Planck equation for the probability density distributions of partons is necessary for a complete calculation of the nuclear modificatio…
Collisional processes in ultrarelativistic N=1 SUSY QED plasma are studied and compared to those in an electromagnetic plasma of electrons, positrons and photons. Cross sections of all binary interactions which occur in the supersymmetric plasma at the order of e^4 are computed. Some processes, in particular the Compton scattering on selectrons, appear to be independent of momentum transfer and thus they are qualitatively different from processes in an electromagnetic plasma. It suggests that transport properties of the SUSY plasma are different than those of its non-supersymmetric counterpart…
Following an argument by Kirzhnits we rederive an exact expression for the energy loss of a fast charged particle in a relativistic plasma using the quantum field theoretical language. We compare this result to perturbative calculations of the collisional energy loss of an energetic electron or muon in an electron-positron plasma and of an energetic parton in the quark-gluon plasma.
Considering the collisional energy loss rates of heavy quarks from hard light parton interactions the total energy loss of a charm quark for a static medium has been computed. For the energy range $E\sim (5-10)$ GeV of charm quark, it is found to be almost same order as that of radiative ones estimated to a first order opacity expansion. The collisional energy loss will become much more important for lower energy charm quarks and this feature could be very interesting for phenomenology of hadrons spectra. Using such collisional energy loss rates we estimate the momentum loss distribution emplo…
Energy loss of a heavy fermion in a collisional QED plasma
本文利用BGK碰撞核修正硬热圈重求和传播子，自洽计算QED等离子体中重费米子的碰撞能量损失，无需引入硬软动量分离标度，并发现碰撞效应会增大能量损失。
We perform a comparison of the radiative and collisional parton energy losses in an expanding quark-gluon plasma. The radiative energy loss is calculated within the light-cone path integral approach. The collisional energy loss is calculated using the Bjorken method with an accurate treatment of the binary collision kinematics. Our numerical results demonstrate that for RHIC and LHC conditions the collisional energy loss is relatively small in comparison to the radiative one. We find an enhancement of the heavy quark radiative energy loss as compared to that of the light quarks at high energie…
We suggest a new mechanism for the energy loss of fast heavy quarks in quark-gluon plasma. This mechanism is based on pion production caused by the anomalous chromomagnetic quark-gluon-pion interaction induced by strong topological fluctuations of the gluon fields represented by instantons. We found that this mechanism gives a considerable contribution to the collisional energy loss of a heavy quark in quark-gluon plasma, which shows a nontrivial role of nonperturbative phenomena in strongly interacting quark-gluon plasma.
Collisional energy loss of a heavy quark in a semiquark-gluon plasma
本研究利用背景场有效理论计算半夸克-胶子等离子体中重夸克的碰撞能量损失，发现背景场会显著抑制该能量损失，且抑制程度与温度强相关，其近似因子仅由背景场决定，可用于重味物理唯象研究。
Energy-loss studies of hard particle probes produced in heavy ion collisions have often been used to get information on the interactions within the medium of a quark-gluon plasma (QGP). However, with the study of in-medium energy-loss of individual particles alone, it remains still ambiguous, whether the occured decrease in particle energy is caused by predominantly radiative or collisional energy-loss mechanisms. Focusing on the in-medium energy-loss of hard jet-partons, we propose additional studies of the angular jet-structure as a means to further constrain the energy-loss mechanisms.
We present an operator definition of the collisional energy and momentum loss suffered by an energetic charged particle in the presence of a medium. Our approach uses the energy-momentum tensor of the medium to evaluate the energy and momentum transfer rates. We apply this formalism to an energetic lepton or quark propagating in thermal electron-positron or quark-gluon plasmas, respectively. By using two different approaches to describe the energetic charged particle, an external current approach and a diagrammatic approach, we show explicitly that the operator method reproduces the known resu…
Plasma Effects Suppress Mixing-Induced Collisional Freeze-In
本文利用Kadanoff-Baym方程证明等离子体效应同样抑制碰撞冻结入，以等离子体修正混合角替代真空混合角，并据此排除惰性中微子作为keV-MeV质量范围暗物质的可能性。
We calculate the nuclear modification factor for RHIC and LHC conditions accounting for the radiative and collisional parton energy loss with the running coupling constant.We find that the RHIC data can be explained both in the scenario with the chemically equilibrium quark-gluon plasma and purely gluonic plasma with slightly different thermal suppression of the coupling constant. The role of the parton energy gain due to gluon absorption is also investigated. Our results show that the energy gain gives negligible effect.
We supply recently obtained results from lattice EQCD with the correct UV limit to construct the collisional broadening kernel $C(b_\perp)$ in a QCD plasma. We discuss the limiting behavior of $C(b_\perp)$ at small and large impact parameters $b_\perp$, and illustrate how the results can be used to compute medium-induced radiation rates.
We compute the leading-order collisional energy loss of a heavy quark propagating through a quark-gluon plasma in which the quark and gluon distributions are anisotropic in momentum space. Following the calculation outlined for QED in an earlier work we indicate the differences encountered in QCD and their effect on the collisional energy loss results. For a 20 GeV bottom quark we show that momentum space anisotropies can result in the collisional heavy quark energy loss varying with the angle of propagation by up to 50%. For low velocity quarks we show that anisotropies result in energy gain …
In the article by M. G. Mustafa published in Phys. Rev. C {\bf 72}, 014905 (2005) the author has estimated the total energy loss of a charm quark and quenching of hadron spectra due to the collisional energy loss of energetic partons in an expanding quark-gluon plasma employing Fokker-Planck equation. We wish to point out through this Comment that some of conceptual and numerical results of the said paper are unreliable. For the sake of clarity our discussion will focus on the massless case (although a few remarks on the $m\neq 0$ case are also made).
Collisional broadening in QCD plasmas leads to the emission of medium induced radiation, which governs the energy loss of highly energetic particles or jets. While recent studies have obtained non-perturbative contributions to the collisional broadening kernel $C(b_\bot)$ using lattice simulation of the dimensionally reduced long-distance effective theory of QCD, Electrostatic QCD (EQCD), so far all phenomenological calculations of jet quenching rely on perturbative determinations of the collisional broadening kernel. By matching the short-distance behavior of the lattice extracted EQCD broade…
We calculate the collisional energy loss of a muon of high energy $E$ in a hot QED plasma beyond logarithmic accuracy, i.e., we determine the constant terms of order O(1) in $-dE/dx \propto \ln{E}+ O(1)$. Considering first the $t$-channel contribution to $-dE/dx$, we show that the terms $\sim O(1)$ are sensitive to the full kinematic region for the momentum exchange $q$ in elastic scattering, including large values $q \sim O(E)$. We thus redress a previous calculation by Braaten and Thoma, which assumed $q << E$ and could not find the correct constant (in the large $E$ limit). The relevance of…
The suppression of single jets at high transverse momenta in a quark-gluon plasma is studied at RHIC energies, and the additional information provided by a photon tag is included. The energy loss of hard jets traversing through the medium is evaluated in the AMY formalism, by consistently taking into account the contributions from radiative events and from elastic collisions at leading order in the coupling. The strongly-interacting medium in these collisions is modelled with (3+1)-dimensional ideal relativistic hydrodynamics. Putting these ingredients together with a complete set of photon-pr…
Angular structure of radiative and collisional energy losses of a hard parton jet propagating through dense QCD-matter is investigated. For small angular jet cone sizes, $θ_0 < 5^0$, the radiative energy loss is shown to dominate over the collisional energy loss due to final state elastic rescattering of the hard projectile on thermal particles in the medium. Due to coherent effects, the radiative energy loss decreases with increasing the angular size the jet. It becomes comparable with the collisional energy loss for $θ_0 > 5^0-10^0$.
The comments raised in Ref. [1] by Mishra et al aim at two papers contained in Ref. [2]. We show that those comments on Ref. [2] pointed out by Mishra et al in Ref.[1] are not relevant and the concept used in Ref.[2] is consistent and in compliance with the classical approximation of the transport coefficients [3]. We would also like to note that most of the comments in Ref. [1] were meant for light quarks, but are not even appropriate for heavy quarks.
We discuss the average collisional energy loss dE/dx of a heavy quark crossing a quark-gluon plasma, in the limit of high quark energy E >> M^2/T, where M is the quark mass and T >> M is the plasma temperature. In the fixed coupling approximation, at leading order dE/dx \propto α_s^2, with a coefficient which is logarithmically enhanced. The soft logarithm arising from t-channel scattering off thermal partons is well-known, but a collinear logarithm from u-channel exchange had previously been overlooked. We also determine the constant beyond those leading logarithms. We then generalize our cal…
Surface waves propagating in the semi-bounded collisional hot QCD medium (quark-gluon plasma) are considered. To investigate the effect of collisions as damping and non-ideality factor, the longitudinal and transverse dielectric functions of the quark-gluon plasma are used within the Bhatnagar-Gross-Krook (BGK) approach. The results were obtained both analytically and numerically in the long wavelength limit. First of all, collisions lead to smaller values of surface wave frequency and their stronger damping. Secondly, the results show that non-ideality leads to the appearance of a new branch …
Collective modes of a collisional anisotropic quark-gluon plasma
本文研究碰撞对各向异性夸克-胶子等离子体集体模式的影响，发现足够大的碰撞率可消除不稳定模式，且增长率在沿各向异性方向最大。
We study the effect of including a BGK collisional kernel on the collective modes of a QCD plasma which has a hard-particle distribution function which is anisotropic in momentum space. We calculate dispersion relations for both the stable and unstable modes and show that the addition of hard particle collisions slows the rate of growth of QCD plasma unstable modes. We also show that for any anisotropy there is an upper limit on the collisional frequency beyond which no instabilities exist. Estimating a realistic value for the collisional frequency for alpha_s ~ 0.2 - 0.4 we find that for the …
We investigate the response of a relativistic plasma to electromagnetic fields in the framework of the Boltzmann equation incorporating a collision term in the relaxation rate approximation selected in a form assuring current conservation. We obtain an explicit solution for the linearized perturbation of the Fermi-Dirac equilibrium distribution in terms of the average relaxation rate $κ$. We study the resulting covariant, gauge invariant, and current conserving form of the polarization tensor in the ultrarelativistic and non-relativistic limits. We evaluate the susceptibility in the ultrarelat…
Collisional parton energy loss is revisited within a simple model assuming incoherent elastic scattering of on-shell projectile partons on partonic constituents of the QGP with HTL screening. The thermal motion of plasma particles is carefully taken into account. Results on $dE/dx$ are found to be consistent with other authors. There is a significant discrepancy in the energy loss pattern for the cases with thermal motion on and off, which illustrates the importance of taking the kinematics into account exactly. The dependence on the mass of the partons forming the plasma is included in the ca…
We systematically compare the N=1 SUSY QED plasma to its non-supersymmetric counterpart which is QED plasma of electrons, positrons and photons. Collective excitations and collisional processes in the two systems are confronted to each other in a regime of small coupling. The collective and collisional characteristics of supersymmetric plasma are both very similar to those of QED plasma.
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