Performance of Prototype MRPC Detector for STAR Frank Geurts (Rice Univ.) for the STAR TOF collaboration

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 2 Outline STAR Time of Flight MRPC Prototype: TOFr TOFr at AGS test results TOFr at RHIC (STAR) physics results Summary

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 3 Solenoidal Tracker At RHIC Great interest in large acceptance PID over an extended pT range full TOF replaces the existing Central Trigger Barrel. covers the TPC tracking detector based on Multi-gap Resistive Plate Chambers (MRPC) prototype detector: TOFr

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 4 STAR Time of Flight STOP detector: future: barrel of MRPCs prototype single tray of MRPCs: TOFr START detector dedicated detector, close to the beam line run II – IV: pseudo-Vertex Position Detectors particle trajectories and momentum: TPC tracker σ(p)/p ~ 1-2%, σ(s)/s~0.2% Requirements: total time resolution σ(t)~100ps MRPC resolution ~80ps detector segmentation to limit occupancy to 10-15% fit into integration envelope for present CTB operate in 0.5T magnetic field operate at particle fluxes ~200Hz/cm 2 inexpensive safe not impair performance of other subsystems (interaction material, gas containment)

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 5 STAR MRPC Tests at BNL AGS test near E949 exp. STAR detector Brookhaven National Lab Upton, NY

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 6 MRPC Module dimensions: 21.8 x 8.4 cm 2 sensitive area: 20.0 x 6.1 cm 2 6 gas gaps spacing 220 micron outer glass thickness: 1.1 mm inner glass thickness: 0.54 mm 6 Copper pick-up pads 6.1 x 3.4 cm cm spacing

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 7 Tray Layout form factor: Central Trigger Barrel tray 241 x 21.6 x 8.9 cm 3 TOFr single tray 28 modules installed 168 channels two HV busses full TOF 120 trays in two barrels different tray design φ-coverage: 60 x 6˚ z-coverage: 2 x (Δη=1) 32 modules/tray 192 channels η=1 sideη=0 side

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 8 TOFr Tray Construction FEEs installed η~1 side η~0 side all MRPC modules installed February 2002 Rice Univ., Houston TX

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 9 TOFr at the AGS close to E949 experiment no test beam, but radiation area significant non-relativistic momentum spread significant radiation during the spills in-spill (2s) dark current: 60nA out-spill (3s): 30nA no AGS operation: 10nA measurements Optimal FEE threshold voltages Optimal high voltage gas mixtures

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 10 8 PMTs’ coincident signal as TDC start and ADC gate. AGS Trigger Set-up in-beam view 4 x 19 cm 2 covered area by scintillators along-beam view tray FEE beam direction tray

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 11 AGS TOFr Analysis strict cuts on all PMT trigger pedals strict cuts on single MRPC pad signals no neighboring hits ADC signal < (μ ped + 1.5*σ ped ) effectively select on central hits eliminate edge effects (5ps effect) T-A (slewing) corrections reference PMTs MRPCs (Shao Ming et al.) CERN T10 data AGS – MRPC slewing

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 12 AGS TOFr Analysis (cont’d) Time resolution for one MRPC pad  (t) ~70 ps after PMT T-A correction no accurate position information: remaining position smearing 45 ps/cm propagation time < 4 cm wide raw MRPC timing (incl. start timing) start timing (based on 8 PMTs) 0 -18˚~30˚ σ(t) distributions for different incident angles 12 modules at η = ˚ 4 modules at η =1 ~30 ˚

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 13 AGS: HV & FEE Threshold 90% Freon + 5% iso-butane + 5% SF 6 FEE threshold voltages: 1.2, 2.2 and 2.7 V High voltages: – 16 kV typical noise rates (mod.#2) V thres =1.2V, HV=14.5kV: 7 - 8Hz caveat: no control over the beam quality possible time dependent spread

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 14 AGS: Gas Mixtures module #2 tested at various HVs all other modules at fixed HVs (table) V thres = 1.2 V start time corrected σ(t) SF 6 : stronger quenching, higher HV larger primary ionization for iso-butane similar efficiencies for A and B mixtures HV [kV] efficiency [%] σ(t) [ps] A. freon + iso-butane + SF B. freon + iso-butane C. freon

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 15 TOFr in STAR run II (2001/2): Au+Au, p+p start: pVPD stop: TOFp (PMT+scintillators) run III (2003): d+Au, p+p start: pVPD stop: TOFp + TOFr TOFr tray East-TPC TOFpTOFr x y 54˚

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 16 TOFr Operations in STAR High voltage at 14kV V thres = 1.2V gas mixture: 95% freon + 5% iso-butane 72 digitized out of 168 available channels 2 dead channels noise rate for 70 channels: ~240 Hz Δφ=6°, Δη~0.4 only ~0.3% TPC coverage large data sets, dedicated TOFr trigger 25M STAR minimum bias events 6.6M pVPD events 0.7M TOFr hits 0.1 hits per pVPD physics event 2.5M STAR TOFr trigger events 2.0M pVPD events 2.4M TOFr hits 1.22 hits per pVPD physics event.

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 17 start time: pVPD coincidence 3 detector elements per pVPD coverage 19% solid angle 4.43 < η < 4.94 start timing resolution is multiplicity dependent Au+Au (run II): σ(t) ~ 24ps d+Au (run III): σ(t) ~ 80ps p+p: σ(t) ~ 120ps path length and momentum TPC track extrapolation to TOFr tray primary tracks only, i.e. must originate from the primary collision vertex at least 15 out of maximum 45 hits in the TPC tracker match tracks to TOFr hits calibration T0 correction T-A slewing correction local z-position correction MRPC stop timing resolution ~80ps consistent for d+Au and p+p data STAR: TOFr Analysis TPC pVPD east pVPD west Au d TOFx STAR TOFr p+p σ(total)~162ps STAR TOFr p+p σ(start)~139ps (Lijuan Ruan et al.)

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 18 STAR: TOFr Analysis (cont’d) 1/β vs. momentum for π ±, K ± and p(pbar) from 200 GeV d+Au collisions. insert shows m 2 =p 2 (1/β 2 -1) for 1.2 < p T <1.4 GeV/c

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 19 STAR: TPC tracking and TOFr matching efficiencies TPC tracking efficiency for pbar TPC-TOFr matching efficiency for pbar

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 20 STAR: TOFr Results other corrections: particle feed-down and contamination trigger background and biases energy loss invariant cross sections for π ±, K ± and p(pbar) in 200GeV/c d+Au and p+p collision (p+pbar)/h ratios measured by TOFr compared with other measurements similar for d+Au at 200GeV/c, and p+pbar at 1.8TeV/c and p+p at 23.8GeV/c ratio for Au+Au at 130GeV/c twice that of d+Au Final state rescattering, Cronin effect can not explain this.

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 21 STAR: TOFr Physics! nucl/ex , submitted to PRL

RPC Oct. 20, 2003F.Geurts -- Performance of Prototype MRPC Detector for STAR 22 Summary prototype TOF detector build in Feb.2002 tested at the AGS for various V thres, HVs and gas settings optimal running conditions for STAR HV=14kV V thres =1.2V gas mixture: 95% Freon + 5% Iso-butane STAR d+Au and p+p run very successful large data set dedicated trigger very stable operations fast and relevant physics results important push for full MRPC-based STAR TOF proposal