Currently time resolution of TOF is some 120 ps. The key requirement for the best resolution is flowing: (1) number of photo-electrons, determined dominantly by the thickness of scintillator and shape of light guide. (2) optics of electron avalance among the cathodes in the PMT (cost of PMT), and (3) relative stability of the clocks in the front end readout electronics (FEE) between a start counter (the Beam-Beam counter) and a stop counter (the TOF counter). The FEE's are located in some 50 meters of distance in terms of cable length used for connection (either electrically or optically). There is EMcal-time-of-flight as well, and the time resolution is some 420ps in average. With 2 sigma cut on the mass squared distribution, K/pi separation up to 2 GeV/c and p/K separation up to 4 GeV/c are achieved. The Fig. 7 shows PHENIX hadron particle identification capability as a scatter plot in momentum versus mass squared (note that momentum is multiplied by -1 for the negative particle).
With this PID capability, PHENIX has succeeded to measure inclusive pion, kaon, proton and anti-proton specrta shown in Fig. 8 [shown at QM2002].