1. 1 Alexander Milov QM2006, Shanghai Nov 15, 2006 Construction and expected performance of the Hadron Blind Detector for PHENIX experiment at RHIC Alexander Milov (for the PHENIX HBD group) XIX International conference on Ulterarelativistic Nucleus-Nucleus Collisions, Shanghai, China

2. 2 Alexander Milov QM2006, Shanghai Nov 15, 2006  Weizmann Institute of Science (Israel) A.Dubey, Z.Fraenkel, A. Kozlov, M.Naglis, I.Ravinovich, D.Sharma, L.Shekhtman (on leave from BINP), I.Tserruya (project leader)  Stony Brook University (USA) W.Anderson, A.Drees, M.Durham, T.Hemmick, R.Hutter, B.Jacak, J.Kamin  Brookhaven National Lab (USA) B.Azmoun, A.Milov, R.Pisani, T.Sakaguchi, A.Sickles, S.Stoll, C.Woody (Physics) J.Harder, P.O’Connor, V.Radeka, B.Yu (Instrumentation Division)  Columbia University, Nevis Labs (USA) C-Y. Chi  University of Tokyo (Japan) T. Gunji, H.Hamagaki, M.Inuzuka, T.Isobe, Y.Morino, S.X.Oda, K.Ozawa, S.Saito  RIKEN (Japan) S. Yokkaichi  Waseda University (Japan) Y. Yamaguchi  KEK (Japan) S. Sawada People in this project

3. 3 Alexander Milov QM2006, Shanghai Nov 15, 2006 Why di-electrons? Part of the p+p run no bkg. subtraction Entire AuAu run  Effects of chiral symmetry restoration manifest themselves in terms of in-medium modifications of the line shapes of low mass vector mesons (e.g., mass shifts, spectral broadening)  Lepton pairs are unique probes because they provide direct information undistorted by further interactions. ρ (m = 770MeV τ ~ 1.3fm/c)  e + e - ω (m = 782MeV τ ~ 20fm/c)  e + e - φ (m =1020MeV τ ~ 40fm/c)  e + e -

4. 4 Alexander Milov QM2006, Shanghai Nov 15, 2006  e + e -    e + e - S/B ~ 1/500 “combinatorial pairs” total background Irreducible charm background signal charm signal Background sources  Main source of the background due to external and internal conversions of the photons coming from π 0. π 0      e + e - π 0   e + e -  The goal is to reduce the background by a factor of 100  Distinct pattern of the background producing decays: small inv. mass  small opening angle  A rejection factor of >90% on a close pair will reduce the background to an acceptable level.

5. 5 Alexander Milov QM2006, Shanghai Nov 15, 2006 The detector concept  Proximity Focused Windowless Cherenkov Detector  Radiator gas = Working gas Primary choice pure CF4 n = 1.00062 (  =28 ) L = 50cm Blind to π 0 with p T <4GeV/c  Radiating particles produce blobs on an image plane (θ max = cos -1 (1/n)~36 mrad Blob diameter ~ 3.6 cm)  To preserve the pair opening angle θ pair the magnetic field is turned off (compensated) in the detector  Background processes produce 2 close blobs and single electrons only 1  Image plane: CsI photocathode on top of tiple GEM stack used for electron amplification separated by 90% transparent mesh from the main volume ~ 1 m signal electron Cherenkov blobs partner positron needed for rejection e+e+ e-e-  p air opening angle B≈0

6. 6 Alexander Milov QM2006, Shanghai Nov 15, 2006 Challenges & Solutions  The space where B can be compensated is limited to ~50cm but the number of p.e. must be high enough to allow for effective amplitude analysis of overlapping and distorted blobs. Match the CsI Q.E.~70% @ 10eV and pure CF 4 bandwidth (6-11.5 eV) to get unprecedented N 0 ≈840 cm -1 (x6 larger than any e/π RICH ever built!)  The detector has to let all ionizing particles through without seeing them, but pick up single photoelectrons. Make CsI + GEMs into a new type of semitransparent photocathode such that it a) is sensitive to the ionization reaching its surface from Cherenkov light b) electric field drives MIP ionization back into the gas volume  The detector must be thin to produce little own background but leak tight to keep water away from absorbing UV light. Windowless design (CF 4 without quencher = gaseous radiator = detector gas). Combine functions of the detector structural elements (pad plane = gas seal)

7. 7 Alexander Milov QM2006, Shanghai Nov 15, 2006 The Image plane  Start with a GEM  Put a photocathode on top  Electron from Cherenkov light goes into the hole and multiplies  Use more GEMs for larger signal  Pick up the signal on pads  And why is it Hadron Blind?  Mesh with a reverse bias drifts ionization away from multiplication area HV  Sensitive to UV and blind to traversing ionizing particles

8. 8 Alexander Milov QM2006, Shanghai Nov 15, 2006 Honeycomb panels Mylar window Readout plane Service panel Triple GEM module with mesh grid The Detector  The detector fits under 3%X 0 and it is leak tight to keep water out 0.12cc/min (~1 volume per year)! Side panel Sealing frame HV terminals Detector is designed and built at the Weizmann Institute FEEs  Readout plane with 1152 hex. pads is made of Kapton in a single sheet to serve as a gas seal  Each side has 12 (23x27cm 2 ) triple GEM Detectors stacks: Mesh electrode  Top gold plated GEM for CsI  Two standard GEMs  pads

9. 9 Alexander Milov QM2006, Shanghai Nov 15, 2006 Detector elements  GEM positioning elements are produced with 0.5mm mechanical tolerance.  Dead areas are minimized by stretching GEM foils on a 5mm frames and a support in the middle.  Detector construction involves ~350 gluing operations per box

10. 10 Alexander Milov QM2006, Shanghai Nov 15, 2006 “Clean Tent” a.k.a. “The Battle Field of Stony Brook” CsI Evaporator and quantum efficiency measurement (on loan from INFN) 6 men-post glove box, continuous gas recirculation & heating O 2 < 5 ppm H 2 O < 10 ppm Laminar Flow Table for GEM assembly High Vacuum GEM storage Class 10-100 ( N < 0.5 mm particles/m 3 ) Detector assembly

11. 11 Alexander Milov QM2006, Shanghai Nov 15, 2006  CsI evaporation station was given on loan to Stony Brook from INFN/ISS Rome Thank you Franco Garibaldi & Italian team!  Produces 4 photocathodes per shot 240 – 450nm of CsI @ 2 nm/sec Vacuum drops to 10 -5 Torr and then to 10 -7 Torr (water out of the structure). Contaminants measured with RGA  Photocathode Q.E. is measured “in situ” from in 165-200 nm wavelength range over entire area  Photocathodes transported to glove box without exposure to air  4 small “chicklets” evaporated at same time for full QE control (120-200 nm) Photocathode production

12. 12 Alexander Milov QM2006, Shanghai Nov 15, 2006 First module installed in HBD West Some of the production steps GEMs pre-installed for evaporation Photocathode installation chain: removal from transfer box, gain test, installation into the HBD.

13. 13 Alexander Milov QM2006, Shanghai Nov 15, 2006  GEMs produced at CERN Tested for 500V in air @ CERN Framed & tested @ WIS for gain uniformity Tested at SUNYSB prior to installation Gain uniformity between 5% and 20%  GEM statistics 133 produced (85 standard, 48 Au plated) 65 standard, 37 Au plated passed all tests 48 standard, 24 Au plated installed GEMs combined into stacks are matched to minimize gain variation over the entire detector  All GEMs pumped for many days under 10 -6 Torr prior to installation into detector 20% 5% The GEM stacks

14. 14 Alexander Milov QM2006, Shanghai Nov 15, 2006  During gain mapping, a single pad is irradiated with a 8kHz 55 Fe source for ~20 min. Then all other pads are measured (~1.5h) and the source is returned to the starting pad.  Gain is observed to initially rise and then reach a plateau. Rise can be from few % to almost a factor of 2.  Further study show that the gain increase is rate dependent (10-30%)  This does not impose a problem for GEM operation at PHENIX GEMs will reach operating plateau in a few hours Rates are lower then during mapping 1.5 Initial Rise Secondary rise GEM gain stability

15. 15 Alexander Milov QM2006, Shanghai Nov 15, 2006 Flat position dependence 27 cm Photocathode quality Number of photoelectrons 36 72  Q.E. needs to distinguish a single electron from a pair.  Absolute Q.E. must be continuously controlled and preserved. At the production stage During transportation and installation During physics data taking  At the production stage the Q.E. is as high as measured in R&D stage and uniform

16. 16 Alexander Milov QM2006, Shanghai Nov 15, 2006 H 2 O & O 2 must be kept at the few ppm level to avoid absorption in the gas Heaters are installed on each detector to drive out water from GEMs and sides of detector vessel Lamp MonitorGas Cell Monitor Measure photocathode current of CsI PMTs D 2 lamp Monochromator (120-200 nm) is a part of the HBD gas system Movable mirror Turbopump Gas transparency

17. 17 Alexander Milov QM2006, Shanghai Nov 15, 2006 electrons hadrons Cluster size, reverse bias Tested in PHENIX with p-p collisions at RHIC April-June ‘06  Full scale detector prototype: 1 GEM + CsI stack module installed in the volume 68 readout channels full readout chain  Pure CF 4 gas system  LVL2 triggers to enrich e-sample electrons hadrons Pulse height, reverse bias Forward Bias+Landau Reverse Bias MIP e/ π rejection ~85% at ε e ~90 % Full scale prototype test

18. 18 Alexander Milov QM2006, Shanghai Nov 15, 2006 HBD West (front side) Installed 9/4/06 HBD East (back side) Installed 10/19/06 Now

19. 19 Alexander Milov QM2006, Shanghai Nov 15, 2006  The HBD will provide a unique capability for PHENIX to measure low mass electron pairs in heavy ion collisions at RHIC  This detector incorporates several new technologies (GEMs, CsI photocathodes, operation in pure CF 4, windowless design) to achieve unprecedented performance in photon detection N 0 ~840 cm -1  The operating requirements are very demanding in terms of leak tightness and gas purity, but we feel they can be achieved  Tests with the full scale prototype were very encouraging and demonstrated the hadron blindness properties of the detector.  The final detector is now installed in PHENIX and ready for commissioning and data taking during the upcoming run at RHIC Summary

20. 20 Alexander Milov QM2006, Shanghai Nov 15, 2006 BACKUPS

21. 21 Alexander Milov QM2006, Shanghai Nov 15, 2006 Challenges & Solutions  The space where B can be compensated is limited to ~50cm but the number of p.e. must be high enough to allow for effective amplitude analysis of overlapping and distorted blobs. Match the CsI Q.E.~70% @ 10eV and pure CF 4 bandwidth (6-11.5 eV) to get unprecedented N 0 ≈840 cm -1 (x6 larger than any e/π RICH ever built!)  The detector has to let all ionizing particles through without seeing them, but pick up single photoelectrons. Make CsI + GEMs into a new type of semitransparent photocathode, which a) does not have usual losses for such type of photocathode b) allows multi-stage multiplication to follow it.  The detector must be thin to produce little own background but leak tight to keep water away from absorbing UV light. Go to windowless design by using CF 4 without quenching gas both as a radiator and working gas due to the fact that GEMs have no photon feedback

22. 22 Alexander Milov QM2006, Shanghai Nov 15, 2006 ~12 m e+e+ e+e+ e-e- e-e- PHENIX now

23. 23 Alexander Milov QM2006, Shanghai Nov 15, 2006 Acceptance nominal location (r=5cm) |  | ≤0.45,  =135 o retracted location (r=22 cm) |  | ≤0.36,  =110 o GEM size ( ,z) 23 x 27 cm 2 Number of detector modules per arm 12 Frame W:5mm T:0.3mm Hexagonal pad size a = 15.6 mm Number of pads per arm 1152 Dead area within central arm acceptance 6% Radiation length (central arm acceptance)box: 0.92%, gas: 0.54% Weight per arm (including accessories) <10 kg HBD parameters

24. 24 Alexander Milov QM2006, Shanghai Nov 15, 2006 Preamp (BNL IO-1195) 2304 channels total 19 mm 15 mm Differential output Noise on the bench looks very good Gaussian w/o long tails 3 s cut  < 1% hit probability Readout chain

25. 25 Alexander Milov QM2006, Shanghai Nov 15, 2006  Run 7 (Dec ‘06 – June ’07)  ~ 4 weeks commissioning with Au x Au beams at  s NN = 200 GeV  10 weeks data taking with Au x Au at  s NN = 200 GeV  10 weeks data taking with polarized p-p beams at  s = 200 GeV  Run 8 (Fall ’07 – Summer ’08) 15 weeks d-Au at  s NN = 200 GeV 10 weeks polarized p-p at  s = 200 GeV  Run 9 (Fall ’08 – Summer ’09) 10-15 weeks heavy ions (different energies and possibly species) 15-10 weeks polarized p-p at  s = 500 GeV (including commissioning)  Run 10 (Fall ’09 – Summer ’09) HBD is removed in order to install new silicon vertex detector in PHENIX Run Plan

26. 26 Alexander Milov QM2006, Shanghai Nov 15, 2006 Photocathode and gas.  Photocathode: CsI is an obvious choice. We are using INFN built evaporator, currently at Stony Brook to do this project.  High area,  High vacuum,  In-situ Q.E. control,  Zero exposure to open air.  Gas CF 4 (was not really known): Has high electron extraction probability Has avalanche self quenching mechanism  Gas CF 4 (well known): Transparent up to 11.5 eV, makes perfect match to CsI Is a good detector gas.

27. 27 Alexander Milov QM2006, Shanghai Nov 15, 2006 Made of 2 units with R~60cm, the volume is filled with CF 4 magnetic field is turned off Electrons emit Cherenkov light Cherenkov light is registered by 12 photo-detectors in each unit Signal is read out by 94 pads in each unit, pad size ~ size of a circle Accumulating ~36 photoelectrons from each primary electron, while most other operational RICHes have ~15 or less. High statistics allows to separate 2 close electrons even if their signals overlay! Number of photoelectrons 36 72 The design.

28. 28 Alexander Milov QM2006, Shanghai Nov 15, 2006 Event display (simulation).

29. 29 Alexander Milov QM2006, Shanghai Nov 15, 2006 Background sources? ~12 m  In the decays contributing to the background: π 0  e + e - γ π 0  γ γ  e + e - γ  Only one electron is detected in PHENIX and another is lost  To cut the background we need a new detector such that: It sees only electrons Located at the origin It does not produce its own background (is thin) …

30. 30 Alexander Milov QM2006, Shanghai Nov 15, 2006 All raw materials (FR4 sheets, honeycomb, HV resistors, HV connectors) ordered and most of them in house Detector box design fully completed Jig design underway Small parts (insert, pins, screws, HV holders..) in the shops Detector construction to start Nov. 1st PCB design almost complete Detailed construction schedule foresees shipment of boxes to SUNY in January 2006. What does it look like

31. 31 Alexander Milov QM2006, Shanghai Nov 15, 2006 Mechanical parts and PCB. PCB final design. Quick MC shows no difference with standard cells Entrance window frames are ready, the window itself to be tight between them