1. 1 STAR TOF Calibration

2. 2 Detectors TPC(TPX) - tracking MRPC TOF (TOFr) – stop time measurement pVPD/upVPD - start time measurement Particle momentum; dE/dx ~8% resolution  /K separation to ~0.6GeV/c k/p separation to ~1.0GeV/c Aim at 100ps time resolution TOF system  /K separation to ~1.6GeV/c & k/p separation to ~3.0GeV/c

3. 3 TOF system pVPD/VPD consists of plastic scintillators + fast PMTs, 5.4~5.7m from TPC geometry center along the beam line 3 channels each side (runV and before) to 19 channels each side (after runV) Full barrel TOF consists of 120 trays, 32 MRPC modules per tray, 6 channels per module Only one tray in run V, 5 trays in run VIII, 94 trays in run IX and all 120 trays in runX

4. 4 TOF Electronics 2 THUB per side, 4 total 1 TCPU per tray/VPD, 122 total 1 TPMT/TDIS per VPD, 2 total 8 TINO/TDIG per tray, 960 total 24 channel per TINO/TDIG, 23040 total

5. 5 HPTDC INL Correction Integral Non-Lineraity Diffrential Non- Lineraity

6. 6 update Calibration results Related software

7. 7 TOF Calibration – runV (and later on) Leading-edge timing signal, trailing-edge signal width (TOT) time Amp. T 1l T 2l T 2t T 1t Thre. Time stamp Leading-edge trigger, signal charge (ADC) is measured for correction time Amp. T1 T2T1 T2 Thre. Q1Q1 Q2Q2

8. 8 VPD Collision Point VPD PMTs All hits in the same event arrived at the same time As reference for each other

9. 9 VPD calibration procedure

10. 10 TDC-TOT correlation Use spline fit (3rd polynomials TSplineFit based on ROOT, developed by François-Xavier Gentit)TSplineFit Run VIII, 200 GeV pp Run V, 62.4 GeV CuCu TDC 1 – (TDC 2 +TDC 3 )/2 (ns) TOT (ns)

11. 11 Resolution before/after calibration ~6 ns~0.16 ns Before calibration After calibration TDC 1 – (TDC 2 +TDC 3 )/2 (ns) Run VIII 200 GeV pp

12. 12 Global offset tune Slewing effect correction was done on east/west side separately Absolute time from east/west side are floating Tune the global offset between east/west side to match Vz(VPD) with Vz(TPC) Beam line Vertex Z z T 0 +(L/2-V z )/c T 0 +(L/2+V z )/c West East upVPD CP

13. 13 Choose  sample by limiting dE/dx and momentum range (or pre-calibrated TOF) T0 correction, different cable length and signal transition time TOFr TOT and Z position calibration, using charged pion sample. Iteration several times (if needed) TOFr Calibration procedure Try channel-by-channel first Not enough statistics? Then try module-by-module, or board-by-board

14. 14 T0 correction TOF measured – TOF expected (ns) Comts Channel-by-Channel Simple Gaussian function Fit Shift the mean of TOF measured – TOF expected to 0 Run VIII 200 GeV pp

15. 15 TOFr TOT slewing correction Run V 200 GeV CuCu Signal ringing effect Run VIII 200 GeV pp Better signal termination achieved TOT (ns) TOF measured – TOF expected (ns)

16. 16 Hit position (Z) corrction TOF measured – TOF expected (ns) Hit Position Z (cm) Run V 200 GeV CuCu Run VIII 200 GeV pp MRPC strip Readout Finite signal propagation speed vs. hit position

17. 17 TOF Time Resolution Run V CuCu 62.4GeV Run V CuCu 200GeV Run VIII pp 200GeV

18. 18 TOF resolution summary Operation condition Time Resolution (ps) pVPD TOFr (overall) TOFr (stop time) Run III 200GeV d+Au ~85~120~85 200GeV p+p ~140~160~80 Run IV 62GeV (Au+Au) ~55~105~89 200GeV (Au+Au) FF/RFF ~27~74~70 HF ~20~74~71 Run V 200GeV Cu+Cu (TOT) ~ 50~92~75 62GeV Cu+Cu (TOT) ~ 82~125~94 Run VIII 200 GeV d+Au NA 200 GeV p+p (TOT) ~83~112~75

19. 19 Expectation (ideal) TOF calibration w/o start detector Fast simulation TOF mean time resolution: 90ps Time-TOT/Z correlation taken from run V CuCu data T0 obtained by direct average of T i Several iteration of calibration

20. 20 T0 w/o start detector – from data Run V 62.4 GeV CuCu After 6-round calibration iteration

21. 21 Summary VPD Calibration  INL correction  Slewing correction TOF tray Calibration  INL correction  T0 correction  Slewing correction  Hit position correction Calibration database  INL table  T0 table  T-TOT table  T-Z table Calibration w/o VPD  Fast simulation  Data results

22. 22 Backup Slides

23. 23 Output calibration parameter Inconvinient to retrieve and use the parameters of all of the Splines Upload each TOT bin boundaries and the corresponding corrections Interpolate in each TOT bin Bin boundary Same statistics in each bin

24. 24 #Events needed for calibration Collisions arXiv: 0808.2041 ×1/4(pure pion) ×80% (match) ×2 (  ) Useable hits per channel #Events for channel- by- channel #Events for module- by- module #Events for board- by- board #Event s for T0 (500/ch annel) p+p (MB)2.40.964.2e-5240 M40 M10 M12 M d+Au(MB)10.24.11.8e-456 M9.3 M2.3 M2.8 M Au+Au(MB)200803.5e-32.9 M0.5 M0.12 M0.15 M Au+Au (0-10%) 5152068.9e-31.2 M0.2 M0.05 M0.06 M 10 K for slewing correction Note in pp collisions, the upVPD efficiency is only ~40% if requiring >=2 hits on both sides

25. 25 VPD fired channels ~35% events have >=3 hits on either side (useable for calibration) ~40% events have >=2 hits on both sides (better start time or ~15% events have >=3 hits on both sides Vz resolution) Run VIII 200 GeV pp Zebo Tang

26. 26 Track projection and Vz correlation 2D DCA Beam line uncalibrated, fix to (0.5,0) cm Should be different between fills Unnecessary to parallel to z direction Vertex from track projection ( No vertex from TPX ): project tracks matched to TOF hits, get the closest position to beam line.

27. 27 Calibration Procedure – before run V Leading-edge trigger, signal charge (ADC) is measured for correction time Amp. T1 T2T1 T2 Thre. Q1Q1 Q2Q2

28. 28 pVPD Calibration – start time

29. 29 TOFr Calibration – MRPC TA & TZ TA slewing correction Hit position (TZ) correction 7th-order polynomial

30. 30 Time resolution determination Increase with n (assume equal time resolution for each channel)

31. 31 Calibrated time resolution

32. 32 Hadron PID

33. 33 Electron PID

34. 34 Muon PID 200 GeV CuCu

35. 35 Run-VIII PID 1.2<p<1.4 GeV/c