1. 10/26/06Takao Sakaguchi, BNL1 Hadron Blind Detector for the PHENIX experiment at RHIC Takao Sakaguchi Brookhaven National Laboratory For the PHENIX Collaboration

2. 10/26/06Takao Sakaguchi, BNL2 Excellent QGP detector: Thermal dileptons Thermal dileptons are an excellent probe for investigating the property of the hot and dense medium produced at RHIC. Thermal dileptons are “brother” of “thermal photons” No additional strong interaction in the medium produced Provide information on temperature, dof, etc. Signal to (Combinatorial random) Background is very small Estimated to be ~1/200! Mostly from Dalitz decay of neutral pions and photon conversions Proven by the recent data from PHENIX (firstly shown at QM’05) Need to identify the origin of electrons to reduce combinatorial background We want to see S/B ratio of at least ~1/10 Recent data from CERES coll. PHENIX preliminary data Black: Foreground Red: Random Background Blue: Net signal

3. 10/26/06Takao Sakaguchi, BNL3 Solution: Hadron Blind Detector Tag background electron pairs via opening angle Veto electrons with partner in field free region PHENIX has two (inner and outer) coils to make such a region Electron pairs do not open up Hadron Blind Detector (HBD) : Proximity Focus Windowless Cherenkov detector 50cm radiator length, 2*135 , |y|<0.45 Radiator Gas=Working Gas Pure CF 4 radiator n CF4 =1.000620,  th =28 (~4GeV/c for  ) CsI photocathode + Triple GEM with pad readout Radiating tracks form “blobs” on the pad plane  max =cos -1 (1/n)~36 mrad  R BLOB ~3.6cm) Dalitz pairs & conversions make two blobs, single electrons make one signal electron Cherenkov blobs partner positron needed for rejection e+e+ e-e-  pair opening angle ~ 1 m Reduction by ~100!

4. 10/26/06Takao Sakaguchi, BNL4 How to Blind Hadrons Mesh CsI layer Triple GEM Readout Pads e-e- Primary ionization g EdEd Absolute Quantum efficiency measured as a function of WL 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 Primary ionization signal is greatly suppressed at slightly negative E d while photoelectron collection efficiency is mostly preserved Hadron Blindness as a function of E d Wave length [nm]

5. 10/26/06Takao Sakaguchi, BNL5 Detector Construction 24 Triple GEM Detectors (12 modules per side) Area = 23x27 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

6. 10/26/06Takao Sakaguchi, BNL6 Gas system Photon transmittance of the Gas is monitored at the input and output of the detector Water and oxygen level is also monitored Transmittance as a function of H 2 O contamination

7. 10/26/06Takao Sakaguchi, BNL7 heating elements 2 on each side, 2 on bottom (seen in next slide). 6 total on one hbd 38 x 25 cm 185cm 2 35um thick Traces (assume Cu) HBD before installation into PHENIX

8. 10/26/06Takao Sakaguchi, BNL8 HBD Installed in PHENIX HBD West (front side) Installed 9/4/06 HBD East (back side) Installed 10/19/06

9. 10/26/06Takao Sakaguchi, BNL9 GEM Performance 20% 5% All GEMs produced at CERN 133 produced (85 standard, 48 Au plated) 65 standard, 37 Au plated passed all tests Good GPA! (~75%) 48 standard, 24 Au plated installed 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 an entire sector Resulting gain variation is between 5-20 %

10. 10/26/06Takao Sakaguchi, BNL10 Gain Stability of GEMs This appears to be a charging effect that has typically been seen in GEMs before, but the magnitude is large ! 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. Gain increase has two components Charge up: ~30% increase Rate dep. Change: ~10% First Layer is coated by CsI Our HBD is operated at a very low rate (~ a few Hz)  Not a big problem

11. 10/26/06Takao Sakaguchi, BNL11 Hadron blindness of the detector Read 12 samples per trigger with 16 nsec interval for each channel (=200nsec, 2B.C.) MIP distribution nicely fitted with a Landau distribution for Forward Bias Derive detector gain from the mean of MIP distribution Reverse Bias rejects ionization electrons almost perfectly -> Blinding Hadrons! Hadron rejection power: ~15@90% elec. eff. Full scale prototype result Timing Sample (n-1, 16nsec step) Raw FADC dist. (sample”0” is subtracted from all other samples) electrons hadrons Pulse Height: B=0, Reverse BIAS 505 V Forward BIAS Reverse BIAS Landau Fit Detector gain: 2500 Pulse height MIP!

12. 10/26/06Takao Sakaguchi, BNL12 Summary PHENIX installed a Hadron Blind Detector to reject the random combinatorial background by electrons and the hadrons Identify electrons (single electron and photon converted electron pairs) in field free region GEMs are used as readout modules of photo/dEdX electrons Good GPA On-Beam Test of Full scale Prototype demonstrated the basic hadron blindness properties of the detector, and also provided information helpful for constructing the final detector Rejects primary ionization signals (dE/dx) of electrons and hadrons while keeping high photoelectron detection efficiency

13. 13 Principle Players 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, B.Jacak, J.Kamin, R.Hutter 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

14. 10/26/06Takao Sakaguchi, BNL14 Backup

15. 10/26/06Takao Sakaguchi, BNL15 The SB plant (I): CsI evaporation facility 4 photocathodes produced per shot together with chicklets for QE monitoring Excellent reproducibility. Excellent stability Cathode Stable

16. 10/26/06Takao Sakaguchi, BNL16 Detector Gain MPV, Mean and Gain derived from the mip distribution of the different runs  V GEM = 495 V up to run # 203145 505 V from run # 203146

17. 10/26/06Takao Sakaguchi, BNL17 heating elements 2 on each side 2 on bottom at the centers of each front panel (6 total) on one hbd 38 x 25 cm 185cm 2 35um thick Traces (assume Cu) 3.5m of 25mm copper tape 60um thick on one side and ½ length on the other Add ½ m for the faces Add 22gauge Cu wire twice the length (0.64mm in diam Cu +1.5mm Teflon) HBD before installation into PHENIX

18. 18 Present PHENIX Capabilities ~12 m e+e+ e+e+ e-e- e-e-

19. 19 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