12/12/09 MPGD研究会@神戸大学
Yusuke KomatsuA
B. AzmounB, C. WoodyB, K. OzawaA
University of TokyoA ,Brook Haven National Lab.B 1
Outline
 HBD for PHENIX
 Results from the last year run
 Gain - gas fraction & VGEM 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- ≤ １GeV)
 Dalitz rejection with opening angle under “no” magnetic
field
 Improve S/B ratio ~2 orders(goal) in mass spectrum!
Signal: ex) φ→ e+ eBG: π0 → e+ e- γ
γ → e+ ePHENIX 200GeV
Au+Au Run4(before
install HBD)
arXiv:0706.3034
3
HBD Concept
e-(+)
Charged particle(γ<γth)
CF4 : UV Ecutoff =11.5eV
→λ=108nm
+
Mesh
CsI : limit from QE
→λ=200nm
CF4
e-
Cherenkov light
pe
Reverse bias
CsI
Sensitive region
of wave lengh is
108< λ[nm] <200
GEM
(as an electron
multiplication)
Readout pad
Forward bias
~40 photoelectrons /e-(+)
CsI photocathode is coated on the top GEM.
CF4 both for Cherenkov radiator and electron multiplication gas .
4
View & performance of HBD
Run9
few pe Hadron blind
e
+
e
-
55
cm
q
Pair
Opening
Angle
5
cm
22 pe
Single electron signal
Triple GEM detectors
(10 panels per side)
Gas & HV
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
Green Ar
Red CF4
7
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 VGEM
in ArCF4
 Measured triple GEM gain vs V across GEM(VGEM)
with Fe55 .
 Dependence of the ArCF4 ratio.
GEM made by CERN
Pitch : 120μm
Hole size(outer): 80μm
(Inner ): 50μm
Fe55
Mesh
DG
VGEM
GEM
Readout
Pad
TG
１
TG
２
IG
4.09 mm , 1 kV/cm
1.59 mm , 2.5 kV/cm
1.57 mm , 3 kV/cm
1.61 mm , 3.5 kV/cm
9
GEM CERN-segmented
Each resistor is 10MΩ.
One side is composed of 4 segments.
10
GEM chamber
H2O: <100ppm
Electrodes for GEM
11
ArCF4 gain vs VGEM
ArCF4 : gain vs Vgem(after p/T Normalization)
10000
60/40
gain
80/20
10/90
40/60
20/80
0/100
1000
50/50
70/30
30/70
15/85
5/95
100
320
340
360
380
400
420 440 460
Vgem[V]
480
500
520
540
Green line represents the effective voltage for mixed gas to obtain the
same signal strength as pure CF4. Results show ArCF4 has enough gain.
12
90/10
ArCO2 FWHM Res. vs gain
60.0
80/20
40.0
70/30
60/40
20.0
FWHM/mean[%]
FWHM/mean[%]
Energy Res. of ArCO2 and ArCF4
50/50
0.0
40/60
100
50.0
1000
10000
gain
ArCF4 FWHM Res. vs gain
40.0
30.0
20.0
10.0
0.0
100
1000 gain
10000
80:20
70:30
60:40
50:50
40:60
30:70
20:80
15:85
10:90
5:95
0:100
13
Gain vs time measurement:
ArCO270/30 (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]
DG
4.11
1
TG1
1.67
2.5
TG2
1.68
3
IG
1.65
3.5
14
Relative gainRelative gain vs time
4.00
3.50
relative gain
3.00
2.50
2.00
ArCO2 70/30
1.50
1.00
0.50
0.00
0:00:00
0:28:48
0:57:36
1:26:24
1:55:12
2:24:00
time
Gain of Tech-Etch GEM increased by ~3.5 times in 2.5 hrs.
15
Gain vs VGEM in plateau
ArCO2 70/30 gain vs Vgem (gain plateau)
gain norm.
100000
10000
ArCO2 70/30
Expon. (ArCO2 70/30)
1000
(exponential)
100
290
300
310
320
330
340
350
Vgem
Gain was extremely high compared to CERN-segmented(gain abs.=1342@340V,
ArCO2 70/30).
16
Gain curve :TE changing H2O & CERN
C-C-C 330~130 ppm 28.4%
TE ~1100ppm 1100ppm 38.1%
C-C-TE 330~140ppm 23%
TE ~250ppm 31.1%
TE ~50 ppm 36%increase
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 .
17
Summary
 Measured gain vs VGEM 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
Hadron blindness and high sesitivity to a small number
of photoelectrons as signal.
~104 multiplication factor
Use GEM and CsI photocathode.
 Double hit resolution at least 90% when opening
angle is small.
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
ArCO2 gain vs VGEM
ArCO2 : gain vs Vgem (after p/T Normalization,p=760Torr,T=298K)
100000
70/30(abs.)
80/20
90/10
10000
gain
60/40
50/50
1000
40/60
100
250
300
350
Vgem[V]
400
450
22
Gain value
ArCO2
Ar_CO2
Vgem[V]
90_10
80_20
70_30(abs gain) 60_40
270
450
280
945
290
1972
300
4312
649
310
9593
2613
320
8093
5116
50_50
40_60
330
10462
340
21795
1342
379
350
16402
2676
641
360
4962
1136
263
370
9771
1955
418
380
18728
3571
670
390
32352
1105
294
400
17267
1857
439
410
660
420
1016
23
Gain value ArCF4
Ar_CF4
Vgem[V]
80_20
70_30
60_40
50_50
40_60
30_70
20_80
15_85
Vgem[V] 10_90
475
709
485 1130
495 1776
505 3051
350
416
360
756
364
370
1455
658
380
2738
1159
472
390
5396
2125
826
3932
1447
556
410
2539
965
403
420
4679
1673
679
430
2898
1159
460
440
5083
1993
745
3375
1280
553
460
2076
894
634
470
3469
1479
931
480
2484
1504
490
4094
2519
400
450
500
4034
510
520
24
Results: ArCO2 Energy resolution
ArCO2 FWHM Res. vs gain
60.0
FWHM/mean[%]
50.0
90/10
40.0
80/20
30.0
70/30
60/40
20.0
50/50
40/60
10.0
0.0
100
1000
gain
10000
Consistent with a reference thesys NIM A523(2004)345-354.
~22%.
25
Results: ArCF4 Energy resolution
ArCF4 FWHM Res. vs gain
FWHM/mean[%]
45.0
40.0
80:20
35.0
70:30
30.0
60:40
50:50
25.0
40:60
20.0
30:70
15.0
20:80
10.0
15:85
10:90
5.0
5:95
0.0
0
2000
4000
gain
6000
8000
0:100
26
ArCO2 90/10 CERN-segmented
Left)VGEM=320V, Right)310V
27
ArCO2 CERN-segmented
Left)70/30 400V, Right)80/20 400V
28
Gain was saturated after 45hours.
ArCO2 70/30 gain vs time,Vgem=320V
5000
4800
4600
gain abs.
4400
4200
4000
3800
ArCO2 70/30,Vgem=320V
3600
3400
3200
3000
44:38:24 45:07:12 45:36:00 46:04:48 46:33:36 47:02:24 47:31:12
time
29
Gain curve changing H2O ppm (TE GEM)
38.1% increase
~1100 ppm
31.1%
36.0%
~250ppm
~50 ppm
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 .
30
QE of CsI photocathode
From Craig’s slide.
31
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.
ArCO2 70/30 gain vs time Vgem=350V
35000
Output of preamp
was saturated
gain norm.
30000
25000
20000
15000
ArCO2 70/30
10000
5000
0
42:28:48 42:43:12 42:57:36 43:12:00 43:26:24 43:40:48 43:55:12 44:09:36 44:24:00
time
32
Results: Time dependency of gain
ArCO2 70/30,VGEM =350V
ArCO2 70/30 gain vs time (Tech-Etch GEMs)
gain norm. to 760Torr, 298K
16000
14000
12000
10000
8000
ArCO2…
6000
4000
2000
0
0:00:00
0:28:48
0:57:36
1:26:24
1:55:12
2:24:00
Time[h:m:s]
33
34
Electron pairs – Central Arms (200 GeV pp)
I.Ravinovich
35

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