  High transverse momentum ($p_T$) single non-photonic electrons which have
been measured in the RHIC experiments come dominantly from heavy meson decay.
The ratio of their $p_T$ spectra in pp and AA collisions ($R_{AA}(p_T)$)
reveals the energy loss of heavy quarks in the environment created by AA
collisions. Using a fixed coupling constant and the Debye mass ($m_D\approx
gT$) as infrared regulator perturbative QCD (pQCD) calculations are not able to
reproduce the data, neither the energy loss nor the azimuthal $(v_2)$
distribution. Employing a running coupling constant and replacing the Debye
mass by a more realistic hard thermal loop (HTL) calculation we find a
substantial increase of the collisional energy loss which brings the $v_2(p_T)$
distribution as well as $R_{AA}(p_T)$ to values close to the experimental ones
without excluding a contribution from radiative energy loss.
