1. TOF detector in PHENIX experiment PHENIX time-of-flight counter The PHENIX time-of-flight (TOF) counter serves as a particle identification device for hadrons. The TOF system, located 5.0 m away from the vertex, consists of 1000 elements of plastic scintillation counters with photomultiplier tube readouts. The time resolution of the TOF system is designed to be less than 80 ps, which corresponds to the pion and kaon separation up to 2.4 GeV/c in the experiment. The highly segmented high resolution TOF system has been developed and being constructed at Tsukuba.  960 plastic scintillators with 1920 PMT ’ s  Locate at 5m from the vertex  Acceptance : driven by HBT and  meson  = 40 o,  = 45 o,  ~1/3 Sr Panel: 96 slats Slat: Plastic scintillator w. 2 PMT’s

2. TOF performance at PHENIX We have studied PID cut criteria for charged hadrons by the Time-of-Flight (TOF) counter, based on the measured width of squared mass distributions as a function of momentum. By the parameterization of width of squared mass, the momentum resolution and PID boundaries have been determined. Using the PID cut boundaries, the uncorrected raw transverse mass spectra for pions, kaons, protons and anti- protons are shown. Figure 1 shows the contour plot of inverse momentum * charge vs. TOF after PID cut. By using this parameterization, PID boundaries for each particle species have been determined as a function of momentum. Fig. 2 shows the squared mass vs. charge * momentum scatter plot with PID boundaries. We introduced additional PID cut in both low and high momentum region to reduce contamination from other particle species. We set these momentum cutoff in 0.2 GeV/c and 2.0 GeV/c for pions, 0.2 GeV/c and 1.5 GeV/c for kaons, 0.3 GeV/c and 2.0 GeV for protons (anti-protons), respectively. As seen in Fig. 5, there is a known problem for measured anti-proton's mass, shifted about -0.1 GeV/c2 compared to expected mass. By using the PID cut described above, we have checked the TOF resolution by selecting positively charged pions in limited momentum region. Fig. 4 shows the TOF resolution, estimated by taking the difference between (TOF - BBC time zero) and expected timing of pions in 0.6 < p < 0.8 GeV/c momentum range. In this momentum region, TOF resolution is estimated about 178.2 +- 12.2 ps. Recently we can estimate about 110 ps Figure. 2  < 110ps Fig. 3. Squared mass distribution for positively (left) and negatively (right) charged particles. In each figure, the hatched areas represent identified particles. Figure. 4

3. TOF on-line monitoring for the shifter This side is showed hit slat. The deep color button is more hit than the thin one. So we can discriminate between hit slat and no hit slat. We can also simultaneously see some histograms. (charge, time, and so on) The shifts which take the real data want to know that all slats working well and to see some histograms. So we have developed on-line monitoring program with using GUI, pmonitoring (multi-threaded root). Using the GUI, we can easily use the program. And we can do(see hit information, see some histograms) while taking data. This program was used by shifters until last run. TOF total event display TOF main display TOF histogram display

4. Summary  For particle identification, PHENIX time-of-flight (TOF) detector has been developed.  Analysis of the first PHENIX data shows the TOF detector is functioning properly.  We have developed the TOF on-line monitoring software.  TOF monitoring program has been used during data taking to check TOF data quality.  TOF data analysis is under progress