Top: minimum bias, centrality, and muon triggers as a function of time during Pb-Pb data taking (run 169721). The B mask selects the LHC bunch slots where collisions between bunches of Beam 1 and Beam 2 are expected at IP2, while the ACE mask selects slots where no beam-beam collision is expected. Bottom: ZDC-A trigger rate as a function of time in the same run.