12/12/09 MPGD 神戸大学 1 Yusuke Komatsu A B. Azmoun B, C. Woody B, K. Ozawa A University of Tokyo A,Brook Haven National Lab. B

Outline HBD for PHENIX Results from the last year run Gain - gas fraction & V GEM dependence (ArCF4) Gain - Time dependence with Tech-Etch GEM Comparison between Tech Etch and CERN Time dependence as a function of the amount of water 2

Hadron Blind Detector for PHENIX Windowless Cherenkov light detector Dalitz rejector for measurements of low–mass e + e - pairs.(m e+ e- ≤ １ GeV) Dalitz rejection with opening angle under “no” magnetic field Improve S/B ratio ~2 orders(goal) in mass spectrum! Signal: ex) φ → e + e - BG: π 0 → e + e - γ γ → e + e - arXiv: PHENIX 200GeV Au+Au Run4(before install HBD) 3

HBD Concept Mesh GEM CsI Readout pad Reverse bias e-(+) Cherenkov light Charged particle(γ<γ th ) Forward bias pe e- CF4 4 CsI photocathode is coated on the top GEM. CF4 both for Cherenkov radiator and electron multiplication gas. (as an electron multiplication) CF4 : UV E cutoff =11.5eV → λ=108nm + CsI : limit from QE → λ=200nm Sensitive region of wave lengh is 108< λ[nm] <200 ~40 photoelectrons /e -(+)

View & performance of HBD Run9 5 cm 55 cm e-e- e+e+  Pair Opening Angle Triple GEM detectors (10 panels per side) Gas & HV 22 pe few pe Hadron blind Single electron signal

Installed HBD for Run10. 6

Objective ◎ Base measurements of GEM for further upgrades  Improved gas mixture Ar & CF4 have all most 100% transmittance in the sensitive wave lengh region. Ar mixed gas can reduce the operation voltage. -gain measurement in ArCF4 7 Green Ar Red CF4

Objective  Time dependence of gain and H2O contamination Used Tech-Etch GEM. They are said to have different property from CERN GEM in time dependence of gain. And H2O ppm effects gain. -gain vs time (Tech-Etch) -gain vs time changing H2O ppm (Tech-Etch) 8

Measurements of gain vs V GEM in ArCF 4 Measured triple GEM gain vs V across GEM(V GEM ) with Fe 55. Dependence of the ArCF4 ratio. Mesh GEM Readout Pad DG4.09 mm, 1 kV/cm TG １ 1.59 mm, 2.5 kV/cm IG 1.57 mm, 3 kV/cmTG ２ 1.61 mm, 3.5 kV/cm GEM made by CERN Pitch : 120μm Hole size(outer): 80μm (Inner ): 50μm V GEM 9 Fe 55

GEM CERN-segmented 10 Each resistor is 10MΩ. One side is composed of 4 segments.

GEM chamber 11 Electrodes for GEM H2O: <100ppm

ArCF 4 gain vs V GEM 12 20/80 Green line represents the effective voltage for mixed gas to obtain the same signal strength as pure CF4. Results show ArCF4 has enough gain.

Energy Res. of ArCO 2 and ArCF 4 13

Gain vs time measurement: ArCO 2 70/30 (Tech-Etch) Measured time dependency of gain in ArCO2 70/30. Used another GEM series. They were made by Tech- Etch. Insulator CERN: apical TE:E-type Kapton Pitch : 120μm Hole size(outer): 80μm (Inner ): 50μm Double conical gap[mm]electric field[kV/cm] DG4.111 TG TG IG

Relative gain 15 Gain of Tech-Etch GEM increased by ~3.5 times in 2.5 hrs.

Gain vs V GEM in plateau Gain was extremely high compared to CERN-segmented(gain ArCO2 70/30). 16

Gain curve :TE changing H 2 O & CERN 17 TE ~50 ppm 36%increase TE ~250ppm 31.1% TE ~1100ppm 1100ppm 38.1% C-C-TE 330~140ppm 23% C-C-C 330~130 ppm 28.4% When reset charge up, flow Ar+H2O at ~2 l/min for 10 min. Tech-Etch GEM need longer time to reach gain saturation than CERN GEM. H2O can decrease a saturation time,however could not see such effects.

Summary Measured gain vs V GEM in ArCF4. Energy resolution did not depend on gain but a kind of gas mixture. Gain changed according to time ~3.5times eventually when used Tech-Etch GEM. About Tech-Etch GEM, water content in the chamber changed the gain, but did not the time to reach a saturated point of gain. 18

Backup 19

Requirements for HBD Very high e -(+) efficiency Double hit resolution at least 90% when opening angle is small. Hadron blindness and high sesitivity to a small number of photoelectrons as signal. ~10 4 multiplication factor Use GEM and CsI photocathode. Use analog information about charge. Need photo electrons as many as possible. Respond to a large bandwidth of Cherenkov light. pure CF4 bandwidth:6~11.5eV 20

GEM chamber (closed) 21

ArCO 2 gain vs V GEM 60/40 22

Gain value ArCO2 Ar_CO2 Vgem[V]90_1080_2070_30(abs gain)60_4050_5040_

Ar_CF4 Vgem[V]80_2070_3060_4050_5040_6030_7020_8015_ Vgem[V]10_ Gain value ArCF4 24

Results: ArCO 2 Energy resolution 25 Consistent with a reference thesys NIM A523(2004) ~22%.

Results: ArCF 4 Energy resolution 26

ArCO 2 90/10 CERN-segmented Left)V GEM =320V, Right)310V 27

28 ArCO 2 CERN-segmented Left)70/30 400V, Right)80/20 400V

Gain was saturated after 45hours. 29

Gain curve changing H 2 O ppm (TE GEM) % increase 31.1% Tech-Etch GEM need longer time to reach gain saturation than CERN GEM. H2O can decrease a saturation time,however could not see such effects. 36.0% ~1100 ppm ~250ppm ~50 ppm

QE of CsI photocathode 31 From Craig’s slide.

But GEM had tripped on the way. “11/12 9:36 all GEM tripped.Ramped up 350V again. There seems no damage.” Kept on measurement. Gain still increased. 32

Results: Time dependency of gain ArCO2 70/30,V GEM =350V 33

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35 I.Ravinovich Electron pairs – Central Arms (200 GeV pp)