Response of charged hadrons to a Coulomb potential in heavy-ion collisions at the RHIC

We have analyzed the charged hadron spectra at the Relativistic Heavy Ion Collider (RHIC) in terms of the Coulomb interaction between the hadrons and the thermally expanding fireball. Fitting the pion, kaon, and proton spectra simultaneously by using the boost-invariant thermal blast wave formula gives a common kinetic freeze-out temperature of 130 MeV and an expansion velocity of 0.67c, which are quite different from the previous estimates. Considering the Coulomb interaction, the yield ratios of negative to positive hadrons are expected to increase significantly in the low-momentum region. For the published hadron spectra at the RHIC, we determine the upper limit of the magnitude for the Coulomb potential as 10 MeV. Such a relatively small value of the Coulomb potential is consistent with the large nuclear transparency observed at the RHIC.