  We attempt to understand the low-mass dielectron enhancement observed by
PHENIX Collaboration at Relativistic Heavy Ion Collider (RHIC) by transport
peak in the spectral function. On the basis of the second-order formalism of
relativistic dissipative hydrodynamics, we parameterize the spectral function
in low-frequency and long-wavelength region by two transport coefficients,
electric diffusion coefficient $D$ and relaxation time $\tau_{\rm J}$, and
compared our theoretical dielectron spectra with the experimental data. We
study 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 $D\geq 2/T$, with $T$ being temperature. Our analysis shows
that dielectrons emitted through transport process mainly come from
high-temperature QGP phase.

Nuclear Theory;High Energy Physics - Phenomenology;Nuclear Experiment