[en] The effect of detailed balance in induced gluon radiation for an energetic parton propagating inside a quark-gluon plasma is discussed. The stimulated thermal gluon emission reduces while absorption increases the parton's energy. The net contribution results in a reduction of the effective parton energy loss. The relative reduction of the parton energy loss is found to be important for intermediate parton energies and negligible for very high energies. This will increase the energy dependence of the parton energy loss and will affect the shape of suppression of moderately high p_T hadron spectra

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[en] Stimulated gluon emission and thermal absorption, in addition to induced radiation, are considered for an energetic parton propagating inside a quark-gluon plasma. In the presence of thermal gluons, stimulated emission reduces, while absorption increases, the parton's energy. The net effect is a reduction of the parton energy loss. Though decreasing asymptotically as T/E with the parton energy, the relative reduction is found to be important for intermediate energies. The modified energy dependence of the energy loss will affect the shape of suppression of moderately high p_T hadrons due to jet quenching in high-energy heavy-ion collisions

[en] Motivated by a schematic model of multiple parton scattering within the Glauber formalism, the transverse momentum spectra in pA and AA collisions are analyzed in terms of a nuclear modification factor with respect to pp collisions. The existing data at the CERN Super Proton Synchrotron energies are shown to be consistent with the picture of Glauber multiple scattering in which the interplay between soft and hard processes and the effect of absorptive processes lead to nontrivial nuclear modification of the particle spectra. Relative to the additive model of incoherent hard scattering, the spectra are enhanced at large p_T (hard) by multiple scattering while suppressed at low p_T (soft) by absorptive correction with the transition occurring at around a scale p₀∼1-2 GeV/c that separates soft and hard processes. Around the same scale, the p_T spectra in pp collisions also change from an exponential form at low p_T to a power-law behavior at high p_T. At very large p_T>>p₀, the nuclear enhancement is shown to decrease as 1/p_T². Implications of these nuclear effects on the study of jet quenching, parton thermalization, and collective radial flow in high-energy AA collisions are discussed

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[en] The first order correction to the parton fragmentation functions in a thermal medium is derived in the leading logarithmic approximation in the framework of thermal field theory. The medium-modified evolution equations of the parton fragmentation functions are also derived. It is shown that all infrared divergences, both linear and logarithmic, in the real processes are canceled among themselves and by corresponding virtual corrections. The evolution of the quark number and the energy loss (or gain) induced by the thermal medium are investigated

[en] Within the framework of the constituent quark model, it is shown that the single hadron fragmentation function of a parton can be expressed as a convolution of shower diquark or triquark distribution function and quark recombination probability, if the interference between amplitudes of quark recombination with different momenta is neglected. The recombination probability is determined by the hadron's wave function in the constituent quark model. The shower diquark or triquark distribution functions of a fragmenting jet are defined in terms of overlapping matrices of constituent quarks and parton field operators. They are similar in form to dihadron or trihadron fragmentation functions in terms of parton operator and hadron states. Extending the formalism to the field theory at finite temperature, we automatically derive contributions to the effective single hadron fragmentation function from the recombination of shower and thermal constituent quarks. Such contributions involve single or diquark distribution functions which in turn can be related to diquark or triquark distribution functions via sum rules. We also derive QCD evolution equations for quark distribution functions that in turn determine the evolution of the effective jet fragmentation functions in a thermal medium

[en] Multiple scattering, modified fragmentation functions and radiative energy loss of a heavy quark propagating in a nuclear medium are investigated in perturbative QCD. Because of the quark mass dependence of the gluon formation time, the medium size dependence of heavy quark energy loss is found to change from a linear to a quadratic form when the initial energy and momentum scale are increased relative to the quark mass. The radiative energy loss is also significantly suppressed relative to a light quark due to the suppression of collinear gluon emission by a heavy quark

No abstract available