Low-mass dilepton production through transport processes in a quark-gluon plasma

We attempt to understand the low-mass dielectron enhancement observed by the PHENIX Collaboration at the Relativistic Heavy Ion Collider by transport peak in the spectral function. On the basis of the second-order formalism of relativistic dissipative hydrodynamics, we parametrize the spectral function in low-frequency and long-wavelength regions by two transport coefficients, electric diffusion coefficient D and relaxation time tau(J), and compare our theoretical dielectron spectra with the experimental data. We study the spectrum of dielectrons produced in relativistic heavy-ion collisions by using the profile of matter evolution under full ( 3 + 1)-dimensional hydrodynamics. We find that the experimental data require the diffusion coefficient to be D >= 2/T, with T being temperature. Our analysis shows that dielectrons emitted through the transport process mainly come from the high-temperature quark-gluon plasma phase.