e(+)e(-) Pair Production at Very Low Transverse Mometum in Au plus Au Collisions at root s(NN)=200 GeV and U+U Collisions at root s(NN)=193 GeV at STAR

We present the first measurements of e(+)e(-) pair production at very low transverse momentum (p(T) < 0.15 GeV/c) in Au + Au collisions at root s(NN) = 200 GeV and U + U collisions at root s(NN) = 193 GeV using the STAR detector at the Relativistic Heavy Ion Collider. A significant excess, with respect to known hadronic contributions, is observed in 60-80% central heavy-ion collisions over the whole M-ee range. Remarkably, the excess almost entirely happens below p(T) approximate to 0.15 GeV/c, and can not be explained by a theoretical model calculation incorporating in-medium broadened rho spectral function. Moreover, the observed excess yield has no significant centrality dependence. In addition, the steepness of p(T)(2) distribution exhibits mild invariant mass and collision species dependence.