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IEEE 2007, October 29, 2007, Hawaii

Construction, Commissioning and Performance of a Hadron Blind Detector for the PHENIX Experiment at RHIC. IEEE 2007, October 29, 2007, Hawaii. Itzhak Tserruya Weizmann Institute of Science, Rehovot, Israel for the HBD group:

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IEEE 2007, October 29, 2007, Hawaii

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  1. Construction, Commissioning and Performance of a Hadron Blind Detector for the PHENIX Experiment at RHIC IEEE 2007, October 29, 2007, Hawaii Itzhak Tserruya Weizmann Institute of Science, Rehovot, Israel for the HBD group: BNL (Physics): B.Azmoun, A.Milov, R.Pisani, T.Sakaguchi, A.Sickles, S.Stoll, C.Woody BNL (Instrumentation): J.Harder, P.O’Connor, V.Radeka, B.Yu Columbia Univ :C-Y. Chi SUNY: W.Anderson, A.Drees, Z. Citron, M.Durham, T.Hemmick, R.Hutter, B.Jacak, J.Kamin Weizmann: A.Dubey, Z.Fraenkel, A. Kozlov, M.Naglis, I.Ravinovich, D.Sharma, I.Tserruya

  2. Outline • Motivation • Concept • Construction • Performance IEEE-NSS, Hawaii, October 29, 2007

  3.  e+ e - po   e+ e - Motivation • Electron pairs (or dileptons in general) are unique probes to study the matter formed in relativistic heavy ion collisions at RHIC: • best probe for chiral symmetry restoration and in-medium modifications of light vector mesons , ω and  • sensitive probe for thermal radiation: QGP qqbar  *  e+e- HG +-   *  e+e- • Experimental challenge: huge combinatorial background arising from e+e- pairs from copiously produced from 0 Dalitz decay and  conversions. • Both members of the pair are needed to reconstruct a Dalitz decay or a  conversion. • Pair reconstruction limited by: • Low pT acceptance of outer PHENIX detector: ( p > 200MeV) • Limited geometrical acceptanceof present PHENIX configuration

  4. Upgrade Concept • Strategy • Create a field free region close to the vertex to preserve • opening angle of close pairs. • Identify electrons in the field free region • reject close pairs. Hardware * HBD in inner region * Inner coil (foreseen in original design)  B0 for r  60cm Software * Identify electrons with p>200 MeV in PHENIX central arm detectors * Match to HBD * Reject if another electron is found in the HBD within opening angle < 200 mrad.

  5. UV-photon hadron E ~1 cm detector element 50 cm CF4 radiator 5 cm beam axis HBD Concept HBD concept: ♣ windowless Cherenkov detector (L=50cm) ♣ CF4 as radiator and detector gas ♣ Proximity focus: detect circular blob not ring Detector element: ♣CsI reflective photocathode ♣ Triple GEM with pad readout • Why is it Hadron Blind? reverse bias between mesh and top GEM repels ionization charge away from multiplication area Sensitive to UV and blind to traversing ionizing particles

  6. The Detector Detector designed and built at the Weizmann Institute • The detector fits under 3%X0 (vessel 0.92%, gas 0.54%, electronics ~1.5%) and it is leak tight to keep water out 0.12cc/min (~1 volume per year)! Two identical arms All panels made of honeycomb & FR4 structure • Readout plane with 1152 hexagonal pads is made of Kapton in a single sheet to serve as gas seal FEEs • Each side has 12 (23x27cm2) triple GEM detectors stacks: Mesh electrode Top gold plated GEM for CsI  Two standard GEMs  pads Side panel Readout plane Mylar window HV terminals Triple GEM module with mesh grid Service panel Sealing frame

  7. Detector elements Jig for box assembly • Detector construction involves ~350 gluing operations per box • Dead areas are minimized by stretching GEM foils on a 5mm frames and a support in the middle. • GEM positioning elements are produced with 0.5mm mechanical tolerance.

  8. Detector assembly CsI evaporation and detector assembly in clean tent at Stony Brook” CsI Evaporator and quantum efficiency measurement (on loan from INFN) Can make up to 4 photocathodes in one shot Laminar Flow Table for GEM assembly High Vacuum GEM storage 6 men-post glove box, continuous gas recirculation & heating O2 < 5 ppm H2O < 10 ppm Class 10-100 ( N < 0.5 mm particles/m3) IEEE-NSS, Hawaii, October 29, 2007

  9. HBD Engineering Run • The HBD was commissioned during the 2007 RHIC run. • After overcoming an initial HV problem, the detector operated smoothly at a gas gain of 3000-6000 for several months. • The CF4 recirculation gas system worked very smoothly. The oxygen and water content of the gas were monitored at the input as well as at the output of each vessel. In addition the gas transparency was monitored with a monochromator system. A reasonable transmittance of ~80% was achieved at a gas flow of 4 lpm. Typical noise performance • The entire readout chain (both analog and digital) worked smoothly. • The excellent noise performance of the device (pedestal rms corresponding to 0.15 fC or 0.2 p.e. at a gain of 5000) allowed online implementation of a simple zero suppression algorithm to reduce the data volume. • A few billion minimum bias Au+Au collisions at √sNN = 200 GeV were collected and are presently being analyzed.

  10. Tracking & position resolution Run 226502 ES4 at 3600V FB • Hadrons selected in central arm: • Vertex +/- 20 cm • < 50 tracks • 3 matching to PC3 and EMCal • n0 < 0 • EMC energy < 0.5 • Projected onto HBD: • Z in HBD +/- 2 cm •  in HBD +/- 25 mrad Position resolution: z ≈  ≈ 1 cm Dictated by pad size: hexagon a = 1.55 cm (2a/√12 = 0.9 cm) IEEE-NSS, Hawaii, October 29, 2007

  11. Hadron suppression illustrated by comparing hadron spectra in FB and RB (same number of central tracks) Electron - hadron separation (RB) Pulse height Hadron rejection factor Pulse height Hadron Blindness & e-h separation Strong suppression of hadron signal while keeping efficient detection of photoelectrons at reverse drift field IEEE-NSS, Hawaii, October 29, 2007

  12. Electron detection efficiency • Identify e in central arm using RICH and EMCal • Project central arm track to HBD • Relative e-detection efficiency in HBD obtained by varying the charge threshold of the closest (matched) pad EN3 G ≈ 3300 (several runs at “nominal” voltage) All modules <G> ≈ 6600 (Run 237092 “nominal” voltage + 100V) ~4 p.e. ~4 p.e. • Efficiency drop at pad threshold larger than about 4p.e. probably due to electrons converted in the gas near the GEMs. Needs further study.

  13. Summary • Low-mass e+e- pairs is a significant observable to diagnose the matter formed at RHIC. • A novel HBD detector has been constructed and installed in the PHENIX set-up • A commissioning run took place in spring 2007 • Preliminary analysis of data show: • Clear separation between e and h • Hadron rejection factor • Good electron detection efficiency IEEE-NSS, Hawaii, October 29, 2007

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