Invariant mass distribution of top quark pairs near threshold

We investigate the invariant mass distribution of top quark pairs near the $2m_t$ threshold, where current theoretical predictions are incompatible with experimental measurements at the LHC. We show that higher-order non-relativistic Coulomb corrections lead to large corrections, which cannot be incorporated at fixed orders due to the divergent behavior. We derive a factorization formula to resum such corrections to all orders in the strong coupling, and calculate necessary ingredients to perform the resummation at next-to-leading power. We combine the resummation with fixed-order results and present phenomenologically relevant numeric results. We find that the resummation effect significantly enhances the differential cross section in the threshold region, and makes the theoretical prediction more compatible with experimental data.