e+e− Pair Production at Very Low Transverse Mometum in Au+Au Collisions at s NN = 200 GeV and U+U Collisions at sNN = 193 GeV at STAR

We present the first measurements of [Formula: see text] pair production at very low transverse momentum ([Formula: see text] 0.15 GeV/[Formula: see text]) in Au + Au collisions at [Formula: see text] = 200 GeV and U + U collisions at [Formula: see text] = 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 [Formula: see text] range. Remarkably, the excess almost entirely happens below [Formula: see text] 0.15 GeV/[Formula: see text], and can not be explained by a theoretical model calculation incorporating in-medium broadened [Formula: see text] spectral function. Moreover, the observed excess yield has no significant centrality dependence. In addition, the steepness of [Formula: see text] distribution exhibits mild invariant mass and collision species dependence.