Soft-hard factorization of heavy-quark transport in QCD matter at finite chemical potential

Abstract

We calculate the collisional energy loss and momentum diffusion coefficients of heavy quarks traversing a hot and dense QCD medium at finite quark chemical potential, $\mu \ne 0$. The analysis is performed within an extended soft-hard factorization model (SHFM) that consistently incorporates the $\mu$-dependence of the Debye screening mass $M_D(\mu )$ and of the fermionic thermal distribution functions. Both the energy loss and the diffusion coefficients are found to increase with $\mu$, with the enhancement being most pronounced at low temperatures where the chemical potential effects dominate the medium response. To elucidate the origin of this dependence, we derive analytic high-energy approximations in which the leading $\mu$-corrections appear as logarithmic terms: a soft logarithm $\sim {\mu }^2\ln (|t^{\ast }|/M_D^2)$ from $t$-channel scattering off thermal gluonic excitations, and a hard logarithm $\sim {\mu }^2\ln (E_{1}T/|t^{\ast }|)$ from scattering off thermal quarks. In the complete result the dependence on the intermediate separation scale $t^{\ast }$ cancels, as required. We also confirm the expected mass hierarchy $-dE/dz(charm)<-dE/dz(bottom)$ at fixed velocity. Our findings demonstrate that finite chemical potential plays a significant role in heavy-quark transport and must be included in theoretical descriptions of heavy-flavor dynamics in baryon-rich environments, such as those probed in the RHIC Beam Energy Scan, and at FAIR and NICA.

16 pages, 7 figures

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