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Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC

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. HBD Team.

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Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC

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

  3. Motivation - Measurement of Low Mass Electron Pairs in Relativistic Heavy Ion Collisions R. Rapp nucl-th/0204003 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) e- e+ • 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- C.Woody, NSS-N41-5, November 2, 2006

  4. Experimental Challenges at RHIC  e+ e - po   e+ e- “combinatorial pairs” total background S/B ~ 1/500 Irreducible charm background all signal charm signal e+e- Pair Spectrum in PHENIIX Large combinatorial pair background due to copiously produced photon conversions and Dalitz decays Need rejection factor > 90% of  e+ e - andp0   e+ e - Would like to improve S/B by ~ 100-200 C.Woody, NSS-N41-5, November 2, 2006

  5. The Hadron Blind Detector Proximity Focused Windowless Cherenkov Detector Cherenkov blobs Electrons produce Cherenkov light, but hadrons with P < 4 GeV/c do not e- e+ qpair opening angle Radiating tracks form “blobs” on an image plane (Qmax = cos-1(1/n)~36 mrad Blob diameter ~ 3.6 cm) ~ 1 m 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 Radiator gas = Working gas Gas volume filled with pure CF4 radiator (nCF4=1.000620, LRADIATOR = 50 cm) C.Woody, NSS-N41-5, November 2, 2006

  6. The Hardon Blind Concept Mesh g Primary ionization HV e- CsI layer Triple GEM Readout Pads 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 • 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 ~ 104 • Amplified signal is collected on pads • and read out Z.Frankel et.el., NIM A546 (2005) 466-480. A.Kozolov et.al. NIM A523 (2004) 345-354. C.Woody, NSS-N41-5, November 2, 2006

  7. Detector Construction HV panel Triple GEM module with mesh grid Pad readout plane Mylar entrance window Honeycomb panels HV panel Detector designed and built at the Weizmann Institute • 24 Triple GEM Detectors • (12 modules per side) • Area = 23 x 27 cm2 • 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) Very low mass (< 3% X0 including gas) C.Woody, NSS-N41-5, November 2, 2006

  8. GEM Performance 20% 5% • 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 % 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 55Fe 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%) Secondary rise 1.5 Initial Rise • Not a fundamental problem in PHENIX • GEMs will reach operating • plateau in a few hours • Rates are low Effect seen in other GEMs See talk by B.Azmoun, Workshop on Micropattern Gas Detectors, 10/29 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 Laminar Flow Hood High Vacuum GEM Storage Container Large glove box O2 < 5 ppm H2O < 10 ppm Class 10-100 ( N < 0.5 mm particles/m3) 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 Virtually no water ! Small “chicklets” evaporated at same time for full QE measurement (120-200 nm) • Measures photocathode quantum efficiency in situ • from 165-200 nm over entire area • Photocathodes transported to glove box without • exposure to air C.Woody, NSS-N41-5, November 2, 2006

  12. Photocathode Quality 72 36 Number of photoelectrons Photocathodes are produced with consistently good quantum efficiencies Large bandwidth of CF4 (6-11.5 eV), windowless construction and high QE of CsI in deep VUV gives very large N0 (840 cm-1) Expect ~ 36 p.e. per blob Gives good separation between single and double electrons Flat position dependence 27 cm Need to monitor photocathode performance over the lifetime of the experiment C.Woody, NSS-N41-5, November 2, 2006

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

  14. Gas Transmission Monitor Scanning Monochrometer (120-200 nm) Movable mirror Oxygen and water must be kept at the few ppm level to avoid absorption in the gas D2 lamp Turbopump Lamp Monitor Gas Cell Monitor Measure photocathode current of CsI PMTs Heaters are installed on each detector to drive out water from GEMs and sides of detector vessel C.Woody, NSS-N41-5, November 2, 2006

  15. Test of a Full Scale Prototype Detector in PHENIX Cluster Size Pulse height electrons hadrons electrons hadrons Reverse Bias, B=0 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 CF4 gas system Hadron rejection ~ 85% at ee ~ 90 % MIP Forward Bias Reverse Bias Landau fit C.Woody, NSS-N41-5, November 2, 2006

  16. Both Halves of the HBD Installed in PHENIX HBD East (back side) Installed 10/19/06 HBD West (front side) Installed 9/4/06 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 CF4 with a windowless design) to achieve unprecedented performance in photon detection (N0 ~ 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 C.Woody, NSS-N41-5, November 2, 2006

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

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

  20. HBD Detector Parameters Acceptance nominal location (r=5cm) || ≤0.45, =135o retracted location (r=22 cm) || ≤0.36, =110o GEM size (,z) 23 x 27 cm2 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 C.Woody, NSS-N41-5, November 2, 2006

  21. Readout Electronics 15 mm 19 mm Preamp (BNL IO-1195) 2304 channels total Differential output Noise on the bench looks very good Gaussian w/o long tails 3s cut  < 1% hit probability 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 sNN = 200 GeV • 10 weeks data taking with Au x Au at sNN = 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 sNN = 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 C.Woody, NSS-N41-5, November 2, 2006

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