1. Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC Craig Woody Brookhaven National Lab For the PHENIX Collaboration N41-5 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference San Diego, CA November 2, 2006

2. C.Woody, NSS-N41-5, November 2, 2006 2 HBD Team n Weizmann Institute of Science A.Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D.Sharma, L.Shekhtman, I.Tserruya* n Stony Brook University W.Anderson, A. Drees, M. Durham, T.Hemmick, R.Hutter, B.Jacak, J.Kamin n Brookhaven National Lab 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) n Columbia University (Nevis Labs) C-Y. Chi * Project Leader

3. C.Woody, NSS-N41-5, November 2, 2006 3 Motivation - Measurement of Low Mass Electron Pairs in Relativistic Heavy Ion Collisions Low mass dilepton pairs are unique probes for studying chiral symmetry restoration in dense nuclear matter Chiral symmetry is the symmetry between light quark flavors, which is normally broken due to the finite value of the constituent quark masses. At high temperatures and/or high baryon densities, this symmetry may be at least partially restored 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) ρ (m = 770MeV t ~ 1.3 fm/c)  e + e - ω (m = 782MeV t ~ 20fm/c)  e + e - φ (m =1020MeV t ~ 40fm/c)  e + e - R. Rapp nucl-th/0204003 e- e+

4. C.Woody, NSS-N41-5, November 2, 2006 4 Experimental Challenges at RHIC Large combinatorial pair background due to copiously produced photon conversions and Dalitz decays Need rejection factor > 90% of  e + e - and    e + e -  e + e -    e + e - S/B ~ 1/500 “combinatorial pairs” total background Irreducible charm background all signal charm signal Would like to improve S/B by ~ 100-200 e + e - Pair Spectrum in PHENIIX

5. C.Woody, NSS-N41-5, November 2, 2006 5 The Hadron Blind Detector Cherenkov blobs e+e+ e-e-  pair opening angle ~ 1 m Radiator gas = Working gas Gas volume filled with pure CF 4 radiator ( n CF4 =1.000620, L RADIATOR = 50 cm) Proximity Focused Windowless Cherenkov Detector Electrons produce Cherenkov light, but hadrons with P < 4 GeV/c do not Radiating tracks form “blobs” on an image plane (  max = cos -1 (1/n)~36 mrad  Blob diameter ~ 3.6 cm) Tracks pass through the HBD in an essentially zero field region in PHENIX Electron pairs do not open up Dalitz pairs & conversions make two blobs, single electrons make one

6. C.Woody, NSS-N41-5, November 2, 2006 6 The Hardon Blind Concept Primary ionization is drifted away from GEM and collected by a mesh UV photons produce photoelectrons on a CsI photocathode and are collected in the holes of the top GEM Triple GEM stack provides gain ~ 10 4 Amplified signal is collected on pads and read out Mesh CsI layer Triple GEM Readout Pads e-e- Primary ionization g HV Primary ionization signal is greatly suppressed at slightly negative drift field while photoelectron collection efficiency is mostly preserved Test with UV photons and a particles Z.Frankel et.el., NIM A546 (2005) 466-480. A.Kozolov et.al. NIM A523 (2004) 345-354.

7. C.Woody, NSS-N41-5, November 2, 2006 7 Detector Construction 24 Triple GEM Detectors (12 modules per side) Area = 23 x 27 cm 2 Mesh electrode Top gold plated GEM for CsI Two standard GEMS Kapton foil readout plane One continuous sheet per side Hexagonal pads (a = 15.6 mm) Honeycomb panels Mylar entrance window HV panel Pad readout plane HV panelTriple GEM module with mesh grid Very low mass (< 3% X 0 including gas) Detector designed and built at the Weizmann Institute

8. C.Woody, NSS-N41-5, November 2, 2006 8 GEM Performance All GEMs produced at CERN 133 produced (85 standard, 48 Au plated) 65 standard, 37 Au plated passed all tests 48 standard, 24 Au plated installed The three GEMs in each stack are matched to minimize gain variation over the entire detector All GEMs pumped for many hours under high vacuum (~ 10 -6 Torr) prior to installation Gain of each module was mapped for all sectors Resulting gain variation is between 5-20 % 20% 5%

9. C.Woody, NSS-N41-5, November 2, 2006 9 Gain Stability of GEMs During gain mapping, a single pad is irradiated with a 8 KHz 55 Fe source for ~ 20 min. Then all other pads are measured, and the source is returned to the starting pad. Gain is observed to initially rise and then reach a plateau. Rise can be ~ few % to almost a factor of 2. Gain increase is somewhat rate dependent (10-30%) Not a fundamental problem in PHENIX GEMs will reach operating plateau in a few hours Rates are low 1.5 Initial Rise Effect seen in other GEMs See talk by B.Azmoun, Workshop on Micropattern Gas Detectors, 10/29 Secondary rise

10. C.Woody, NSS-N41-5, November 2, 2006 10 Photocathode Production and Detector Assembly “Clean Tent” at Stony Brook CsI Evaporator and quantum efficiency measurement Large glove box O 2 < 5 ppm H 2 O < 10 ppm Laminar Flow Hood High Vacuum GEM Storage Container Class 10-100 ( N < 0.5 m m particles/m 3 )

11. C.Woody, NSS-N41-5, November 2, 2006 11 Evaporator and QE Measurement Complete CsI evaporation station was given on loan to Stony Brook from INFN/ISS Rome (Thank you Franco Garibaldi !) Produces 4 photocathodes per evaporation Deposit 2400 – 4500 Å CsI @ 2 nm /sec Vacuum ~ 10 -7 Torr Contaminants measured with RGA Measures photocathode quantum efficiency in situ from 165-200 nm over entire area Photocathodes transported to glove box without exposure to air Virtually no water ! Small “chicklets” evaporated at same time for full QE measurement (120-200 nm )

12. C.Woody, NSS-N41-5, November 2, 2006 12 Photocathode Quality Large bandwidth of CF 4 (6-11.5 eV), windowless construction and high QE of CsI in deep VUV gives very large N 0 (840 cm-1) Expect ~ 36 p.e. per blob Photocathodes are produced with consistently good quantum efficiencies Need to monitor photocathode performance over the lifetime of the experiment Number of photoelectrons 36 72 Gives good separation between single and double electrons Flat position dependence 27 cm

13. C.Woody, NSS-N41-5, November 2, 2006 13 Construction of the Actual Detector All twelve modules installed in HBD West

14. C.Woody, NSS-N41-5, November 2, 2006 14 Gas Transmission Monitor Oxygen and water 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 Scanning Monochrometer (120-200 nm) Movable mirror Turbopump

15. C.Woody, NSS-N41-5, November 2, 2006 15 Test of a Full Scale Prototype Detector in PHENIX electrons hadrons Cluster Size Tested in PHENIX with p-p collisions at RHIC April-June ‘06 Full scale detector with one GEM module 68 readout channels Full readout chain Operated with full pure CF 4 gas system electrons hadrons Pulse height Forward Bias Reverse Bias Landau fit MIP Reverse Bias, B=0 Hadron rejection ~ 85% at  e ~ 90 %

16. C.Woody, NSS-N41-5, November 2, 2006 16 Both Halves of the HBD Installed in PHENIX HBD West (front side) Installed 9/4/06 HBD East (back side) Installed 10/19/06

17. C.Woody, NSS-N41-5, November 2, 2006 17 Summary  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 with a 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

18. C.Woody, NSS-N41-5, November 2, 2006 18 Backup Slides

19. C.Woody, NSS-N41-5, November 2, 2006 19 Present PHENIX Capabilities ~12 m e+e+ e+e+ e-e- e-e-

20. C.Woody, NSS-N41-5, November 2, 2006 20 HBD Detector Parameters 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 5 mm wide, 0.3mm cross Hexagonal pad size a = 15.6 mm Number of pads per arm 1152 Dead area within central arm acceptance 6% Radiation length within central arm acceptance box: 0.92%, gas: 0.54% Weight per arm (including accessories) <10 kg

21. C.Woody, NSS-N41-5, November 2, 2006 21 Readout Electronics 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

22. C.Woody, NSS-N41-5, November 2, 2006 22 Run Plan for the HBD at RHIC  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