ブルックヘブンにおけるＨＢＤ開発とＧＥＭ基礎特性について

12/12/09 MPGD研究会@神戸大学

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Yusuke KomatsuA B. AzmounB, C. WoodyB, K. OzawaA

University of TokyoA ,Brook Haven National Lab.B

OutlineHBD for PHENIX

Results from the last year runGain - gas fraction & VGEM dependence (ArCF4)

Gain - Time dependence with Tech-Etch GEMComparison between Tech Etch and CERNTime dependence as a function of the amount of water

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Hadron Blind Detector for PHENIXWindowless Cherenkov light detectorDalitz rejector for measurements of low–mass

e+ e- pairs.(m e+ e- ≤ １ GeV)Dalitz rejection with opening angle under “no”

magnetic fieldImprove S/B ratio ~2 orders(goal) in mass

spectrum!Signal: ex) φ→ e+ e-

　　 BG: π0 → e+ e- γ　　　　　 γ → e+ e-

arXiv:0706.3034

PHENIX 200GeV Au+Au Run4(before install HBD)

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HBD ConceptMesh

GEM

CsI

Readout pad

Reverse bias

e-(+)

Cherenkov light

Charged particle(γ<γth)

Forward bias

pe

e-

CF4

4CsI photocathode is coated on the top GEM. CF4 both for Cherenkov radiator and electron multiplication gas .

(as an electron multiplication)

CF4 : UV Ecutoff =11.5eV→λ=108nm

+CsI : limit from QE →λ=200nm

Sensitive region of wave lengh is108< λ[nm] <200

~40 photoelectrons /e-(+)

View & performance of HBD Run9

5 cm

55 cm

e-

e+

qPair

Opening Angle

Triple GEM detectors(10 panels per side)

Gas & HV

22 pe

few pe Hadron blind

Single electron signal

Installed HBD for Run10.

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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

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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)

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Measurements of gain vs VGEM

in ArCF4

Measured triple GEM gain vs V across GEM(VGEM) with Fe55 .

Dependence of the ArCF4 ratio.

Mesh

GEM

Readout Pad

DG 4.09 mm , 1 kV/cm

TG１

1.59 mm , 2.5 kV/cm

IG

1.57 mm , 3 kV/cmTG２

1.61 mm , 3.5 kV/cm

GEM made by CERNPitch : 120μmHole size(outer): 80μm (Inner ): 50μm

VGEM

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Fe55

GEM CERN-segmented

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Each resistor is 10MΩ.One side is composed of 4 segments.

GEM chamber

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Electrodes for GEM

H2O: <100ppm

ArCF4 gain vs VGEM

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320 340 360 380 400 420 440 460 480 500 520 540100

1000

10000 ArCF4 : gain vs Vgem(after p/T Normalization)

Vgem[V]

gain

80/20

70/30

60/40

50/50

40/60

30/7015/85

10/90

5/95

0/100

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 ArCO2 and ArCF4

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100 1000 10000 0.0

10.0

20.0

30.0

40.0

50.0 ArCF4 FWHM Res. vs gain 80:2070:3060:4050:5040:6030:7020:8015:8510:905:95gain

FW

HM

/mean

[%]

100 1000 10000 0.0

20.0

40.0

60.0 ArCO2 FWHM Res. vs gain 90/10

80/20

70/30

60/40

50/50

40/60

gainFW

HM

/mean

[%]

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.InsulatorCERN: apicalTE:E-type Kapton

Pitch : 120μmHole size(outer): 80μm (Inner ): 50μmDouble 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

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Relative gain

0:00:00 0:28:48 0:57:36 1:26:24 1:55:12 2:24:000.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00Relative gain vs time

ArCO2 70/30

time

rela

tive

gain

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

Gain vs VGEM in plateau

290 300 310 320 330 340 350 360100

1000

ArCO2 70/30 gain vs Vgem (gain plateau)

ArCO2 70/30Exponential (ArCO2 70/30)

Vgem

gain

n

orm

.

(exponential)

Gain was extremely high compared to CERN-segmented(gain abs.=1342@340V, ArCO2 70/30).

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Gain curve :TE changing H2O & CERN

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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 .

SummaryMeasured 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.

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Backup

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Requirements for HBDVery 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.

~104 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 CF4bandwidth:6~11.5eV 20

GEM chamber (closed)

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ArCO2 gain vs VGEM

250 270 290 310 330 350 370 390 410 430 450100

1000

10000

100000 ArCO2 : gain vs Vgem (after p/T

Normalization,p=760Torr,T=298K)

Vgem[V]

gain

90/10

80/2070/30(abs.)

50/50

40/60

60/40

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Gain value ArCO2Ar_CO2

Vgem[V] 90_10 80_20 70_30(abs gain) 60_40 50_50 40_60 　

270 450 280 945 290 1972 300 4312 649 310 9593 2613 320 8093 5116 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

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Ar_CF4

Vgem[V] 80_20 70_30 60_40 50_50 40_60 30_70 20_80 15_85

350 416

360 756 364

370 1455 658

380 2738 1159 472

390 5396 2125 826

400 3932 1447 556

410 2539 965 403

420 4679 1673 679

430 2898 1159 460

440 5083 1993 745

450 3375 1280 553

460 2076 894 634

470 3469 1479 931

480 2484 1504

490 4094 2519

500 4034

510

520

Vgem[V] 10_90

475 709 485 1130 495 1776 505 3051

Gain value ArCF4

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Results: ArCO2 Energy resolution

100 1000 10000 0.0

10.0

20.0

30.0

40.0

50.0

60.0 ArCO2 FWHM Res. vs gain

90/1080/2070/3060/4050/5040/60

gain

FW

HM

/mean

[%]

25Consistent with a reference thesys NIM A523(2004)345-354.

~22%.

Results: ArCF4 Energy resolution

0 1000 2000 3000 4000 5000 6000 7000 0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0 ArCF4 FWHM Res. vs gain

80:2070:3060:4050:5040:6030:7020:8015:8510:905:950:100

gain

FW

HM

/mean

[%]

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ArCO2 90/10 CERN-segmentedLeft)VGEM=320V, Right)310V

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ArCO2 CERN-segmentedLeft)70/30 400V, Right)80/20 400V

Gain was saturated after 45hours.

44:3

8:24

45:0

7:12

45:3

6:00

46:0

4:48

46:3

3:36

47:0

2:24

47:3

1:12

3000

3200

3400

3600

3800

4000

4200

4400

4600

4800

5000ArCO2 70/30 gain vs time,Vgem=320V

ArCO2 70/30,Vgem=320V

time

gain

ab

s.

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Gain curve changing H2O ppm (TE GEM)

30

38.1% 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

31From 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.

42:14:24 42:43:12 43:12:00 43:40:48 44:09:36 44:38:240

5000

10000

15000

20000

25000

30000

35000

ArCO2 70/30 gain vs time Vgem=350V

ArCO2 70/30

time

gain

norm

.

Output of preamp was saturated

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Results: Time dependency of gainArCO2 70/30,VGEM =350V

0:00:00 0:28:48 0:57:36 1:26:24 1:55:12 2:24:000

2000

4000

6000

8000

10000

12000

14000

16000ArCO2 70/30 gain vs time (Tech-Etch GEMs)

ArCO2 70...

Time[h:m:s]

gain

no

rm.

to

760T

orr,

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8K

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I.Ravinovich

Electron pairs – Central Arms (200 GeV pp)