1. STAR MRPC TOF: Project Overview BNL January 26, 2006 Geary Eppley Rice University

2. Design considerations The integration space available for TOF in STAR is that currently occupied by the CTB. The space is about 2.2m from the beam line: requires precision time measurement. The clearance between the TPC and EMC is about 10 cm. The space has a uniform 0.5T magnetic field parallel to the beam. There is limited space for “nearby” electronics outside the magnet steel.

3. MRPC development Multigap glass RPCs developed in the late 1990s at CERN, C. Williams, et.al. STAR TOF group designed STAR-specific MRPC modules that would fit existing CTB trays and tested them at CERN in 2000 & 2001.

4. MRPC prototypes in STAR One tray of MRPC modules has been installed in STAR for Runs 3, 4, & 5. An improved tray design each year but some modules have been installed for all 3 years. Runs 3 & 4 used CAMAC electronics. Prototype HPTDC based electronics used in Run 5 and Run 6

5. Electronics integral to tray 95% of the electronics resides on the tray inside the cover 4 external electronics boxes located on the magnet steel connect the 23k-channel system to STAR trigger and DAQ

6. Tray specifications There are 32, 6-channel modules per tray. The active area covers about 87% of -0.9<eta<0.9 Occupancy in central AuAu is ~12%. HV provides +-7 kV. Gas mixture: 95% r134a, 5% isobutane. Average noise rates are ~15 Hz/channel with greater than 100% correlation. Detection efficiency is ~95%.

7. Time measuring Absolute times are recorded and buffered by the HPTDC for all hits above threshold. A single 40 MHz oscillator provides the clock for the 2882 HPTDCs in the system. Both start and stop detectors use the HPTDC to record times eliminating systematic uncertainty from the choice of counter. Each HPTDC has a 21 bit clock counter providing a 51 us clock period. The HPTDCs are reset by a signal with a common origin at the beginning of each run giving each HPTDC a different phase that may be learned from the data. Since this phase is always the same, the phase becomes a powerful tool to monitor the integrity of the data through buffering, trigger matching, event building, transmission to DAQ, and global event building.

8. Total time resolution from Run 5: 200GeV CuCu, 105ps 62GeV CuCu, 124ps

9. Time resolution by channel

10. Timing results, Runs 3, 4, &5:

11. STAR TOF publications: Physics –Open charm yields in d+Au collisions: STAR Collaboration, Phys.Rev.Lett. 94 (2005) 062301. –Cronin effect of identified particle at RHIC: STAR Collaboration, Phys.Lett.B 616 (2005) 8. Technical –B. Bonner et al., Nucl.Instr.Meth.A 478 (2002) 176. –M. Shao et al., Nucl.Instr.Meth.A 492 (2002) 344. –W.J. Llope et al., Nucl.Instr.Meth.A 522 (2004) 252. –F. Geurts et al., Nucl.Instr.Meth.A 533 (2004) 60. –J. Wu et al., Nucl.Instr.Meth.A 538 (2005) 243. –Y. Wang et al., Nucl.Instr.Meth.A 538 (2005) 425. –Y.E. Zhao et al., Nucl.Instr.Meth.A 547 (2005) 334.

12. Organization chart

13. Manufacturing overview Module production and test, electronics production and test, and tray assembly and test each have a duration of ~2.2 years. Module production begins ~3 months before the start of tray assembly and electronics production ~1.5 months before the start of tray assembly. Modules are thoroughly tested in China with integral HV wire and signal cables. Electronics cards are tested in groups of 17, 1 tray, with their integral cables and sent to the tray assembly site as a set. Modules are assembled into trays, the electronics added, and tested for 2-4 weeks as a complete detector unit. Tested trays are shipped to BNL as complete detector units ready for insertion into STAR. Trays are re-tested at BNL: HV current, noise rates, gas leak test Test beam at BNL for selected trays?

14. Gantt chart

15. TOF system functional requirements

16. Current project status: Cosmic ray testing of the TINO front-end board is ongoing. Automated TINO board production has been achieved. Upgraded 38-channel start detector under construction. Based on a recommendation from the review, the China TOF project built a few new modules with highly resistive electrodes. Due to difficulties involved with the manufacturing process, the China groups decided to stick with the graphite-tape electrodes. Layout of the first prototype THUB is underway. The project started officially January 1. We hope to get the university accounts open before the end of February.

17. TOF Gas system The TOF system will operate on a gas mixture of 90 parts r134a and 5 parts isobutane. The system will vent ~12 pounds r134a per day during STAR operations The system will be sealed but not operate during shutdown periods. The isobutane/r134a ratio is set by the factory calibration of the mass flow meters. It will also be monitored by an isobutane analyzer. The aggregate gas circulation rate through the trays is ~450 l/h. The gas is re-circulated and dried maintaining H2O<20 ppm, O2<30 ppm. The system is interfaced to STAR slow controls through a shared disk. Isobutane content is alarmed to insure non-flammable gas. Gas flow is alarmed to maintain safe operation of the trays.

18. TOF gas system schematic

19. DOE review recommendation Investigate using SF6 or C4F10: Improves MRPC operational characteristics. Our reply: Our AGS 11-week test run data confirms this: SF6 greatly extends the HV plateau from 1000v. Using SF6 will allow running at a higher voltage and improve timing resolution. We will investigate: –Developing standards for gas-tight integrity –Adding gas leak SF6 detectors –Adding positive air flow in the TOF tray area