TOF $\beta$ distribution for tracks with momentum 0.95 GeV/$c$ < $p$ < 1.05 GeV/$c$. The Pb-Pb histogram is normalized to the p-Pb one at the pion peak ($\beta=0.99$). While the resolution (width of the mass peaks) is the same, the background of mismatched tracks increases in the high-multiplicity environment of Pb-Pb collisions. Both samples are minimum bias.