1. P HOTON Y IELD DUE TO S CINTILLATION IN CF4 Bob Azmoun, Craig Woody ( BNL ) Nikolai Smirnov ( Yale University )

2. Motivation CF4 good radiator for Cherenkon light production (high refraction index, low chromatic dispersion, high transmission properties in the far UV). In a combination with CsI-based UV-photons detectors GEM detectors allows to realize these ideas (windowless). { A. Breskin group pioneer job }. But CF4 has been known as a good scintillation gas ( UV peak around 160 nm) {A.Pansky, A.Breskin, A.Busulutskov, R.Chechik, V.Elkind, J.Va ’ vra mesurements } Detector simulations and proposals for future (and today) set-ups have to include scintillation light production. So, we decided to use triple GEM with CsI to measure CF4 scintillation production once more.

3. The PHENIX Hadron Blind Detector (HBD) Proximity Focused Windowless Cherenkov Detector Radiator gas = Working gas Gas volume filled with pure CF 4 radiator 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) Cherenkov blobs e+e+ e-e-  pair opening angle ~ 1 m

4. ALICE VHMPID variant, GEANT Simulation Y Z X 50 cm AeroGel, 10cm UV Mirror, spherical shape in ZY Double sided Read-out plane Triple GEM foils with CsI CaF2 Window C4F10 gas CF4 gas Particle track & UV photons R position: ~450 cm. Bz: 0.5 T Detector response: GEANT hits (π+, Pt~10. GeV/c; local coordinate system, cm) UV photoelectrons from “CF4 + Mirror” side UV photoelectrons from “C4F10 + Window” side MIP

5. Pb+Pb “ central ” HIJING event, one VHMPI Detector response ( “ slow ” simulator and reconstruction) X - MIP position - Track “reflection” from mirror; “circle center” - Photo-electrons from “bottom” gas UV light + window. Red circle – track has hits in TPC - Photo-electrons from “top” gas UV light + mirror green means Sc. Light from CF4

6. CF4 scintillation data, from NIM 354, (1995), 262; Pansky, Breskin, … Va ’ vra. E , ev N of UV photons / MeV / 4π Two approximations were used (MIN, MAX) in simulation for the variant with spherical mirror.

7. S ET -U P : “S CINTILLATION C UBE ” Signal: SBD  -trigger Signal: GEM pulse HV: Mesh/GEM HV: SBD CF4 Flow control SS Cubical Vessel Gas Analyzer Scintillation Light Collimated  -source (Am-241) Surface Barrier Det. (SBD) (  -trigger) Bubbler 3x3 cm Mesh &Triple GEM Stack/ 7 electrode volt. divider Plunger (y) Plunger (x) Fe55 (GEM abs. gain) Pressure Gauge CsI Photocathode

8. Absolute Quantum Efficiency of CsI photocathodes CsI PMT Comparison of our CsI photocathodes with a calibrated CsI PMT Good quality CsI photocathodes are now being made at Stony Brook Stack with Au coated GEM foil for depositing CsI photocathode VUV Spectrometer Scint. peak  160nm QE=27.5%

9. MAXIMIZING PE COLL. EFF. +0.1kV/cm

10. Gas Amplification Of GEM Detector Monitored gain of GEM through-out measurement, every hour or so. Gain ~ 7860

11. MC simulation Alpha Path Length

12. dE/dX for Alpha particles in CF4. -- SBD measurements in vacuum and gas -- Energy v Range published data

13. Preliminary result for CF4

14. STILL TO DO … Study ( measure ) systematic errors Measure abs. pe coll. Efficiency. Results with gases of know scintillation photon yield (Ar, CH4, mixtures) Try interesting mixtures such as Ar-CF4. More data in the report for IEEE meeting (November) Preliminary result – 180 +/- 20(?) UV photons / MeV / 4π