Download ppt - Title Slide!!

Jason KaminMay 17th, 2006

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Title Slide!!

HBD


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Di-lepton Physics

• Diverse Physics:– Vector Mesons– Dalitz– Correlated semi-

leptonic decays.– Chiral Restoration??

• Staple in High Energy Physics.

• Arguably the most difficult measurement in Heavy Ion Physics


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Invariant Mass Spectrum from e+e-

• Major problem: Huge combinatorial background mostly due to:•γ-conversions & π0 Dalitz decays.

•We need a new detector, that can ID e’s from these two sources. •Full ID of background: eID & chargeID & (minv < mπ)•Good enough: eID & P-hat (two e’s with small opening angle)

•Hadron-Blind Detector:•Cherenkov for eID.•Field free region of PHENIX (p-hat)

All Pairs

Combinatorial Pairs

Signal Pairs

Lighter particles have smaller opening angles!!

Field can be canceled in a small region around beampipe.

>100x

photoelectron blob

relativistic electrons

φ π

p→


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Unfocused Cherenkov “Blobs”

(r,phi) – bins grow with radius (x,y) – uniform bins

Cherekov Radiation

e-

• No room for traditional optics (ie. focusing mirror).• Cherenkov light collected as an unfocused blob.• 1.5 m^2 photosensitive region• Low radiation length:

• minimize photon conversions.• Charged particles from collision will pass through:

• ionization must not interfere with photoelectron detection.

• Can YOU design this detector???


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Gas Electron Multiplier (GEM)

• Two copper layers separated by insulating film with regular pitch of holes

• Just add the photocathode

• HV creates very strong field such that the avalanche develops inside the holes

• By the way: no photon shine back onto photocathode

150μ• The original idea by F.Sauli (mid 90s) US Patent 6,011,265• Traditionally CHARGED PARTICLE detectors (not photons)


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The concept

• Get a GEM

• Put a photocathode (CsI) on top

• photoelectron from Cherenkov light avalanches in the high density E-field

• Use more GEMs for larger signal

• Pick up the signal on pads

• What about ionizing particles (hadrons)?

• We need a mesh with a reverse voltage on it to blow electrons away!!!

HV

• We have a detector sensitive to UV and blind to ionizing particles!

~1

50

μ

m


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• At slightly negative Ed, photoelectron detection efficiency is preserved whereas charge collection is largely suppressed.

• Charge collected from ~150μ layer above top GEM

Hadron Blindness: UV photons vs charged particles


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Dilepton pair

Beam Pipe

HBD Gas Volume: Filled with CF4 Radiator (nCF4=1.000620, LRAD=50 cm)

Cherenkov light forms “blobs” on an image plane(rBLOB~3.36cm)

Triple GEM detectors(12 panels per side) Space allocated

for services

Windowless Cherenkov DetectorRadiator gas = Avalanche Gas

Electrons radiate, but hadrons with P < 4 GeV/c do not

Pcb pad readout (~ 2x2 cm2)

5 cm

55 cme-

e+

Pair Opening

Angle

The HBD Detector

CsI photocathode covering GEMs


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The Clean Tent at USB

Entrance Foyer

Level of Clean Roomevaporator

glove box

GEMstorage vessel

laminar flow hood


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The Evaporator

Evaporation Chamber Quantum Efficiency Station

Magnetically coupled driver for moving the GEMs inside the vacuum.

on loan from INFN Roma


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The Evaporation Chamber

• ~24 hrs to pump down vessel

• vacuum ~10-8 mbar

• no water!!

•Evaporate 4 GEMs simultaneously

Molybdenum boats

GEM

GEM mounting box w/ wheels on track

Harpoon for moving mounting box

CsI

AC

• Boats are in series so they must be brought up to temperature slowly (~10 min)

• 250 – 450 nm layer of CsI at rate of ~2 nm/sec


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The Quantum Efficiency Station

GEM with CsI

Molybinum boats

GEM mounting box w/ wheels on track

Harpoon for moving mounting box

ACγ

e-e-

~ 100 V~ 2mm

ampmeter

GEM w/ CsI

mirror

reference PMT

mesh(e- collection)

Xe lampMgF2 window

(λ=160,185,200 nm)


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Quantum Efficiency

• Excellent QE. • Comparable to best in the world. • QE constant across GEM. • It’s crucial to maintain high QE after production.

x-coordinate across GEM

Rel

ativ

e Q

E

(%)

40

0


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55Fe


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SummaryJason Tom

Bill Liz

• Hadron Blind Detector is crucial to the low-mass dielectron spectrum.

• Excellent QE is achieved at the Stony Brook production facility.

• The HBD prototype is installed in PHENIX and being tested. We have seen the light!! (it’s working).

• Final HBD is scheduled to be installed in late Aug 2006.

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The PHENIX HBD CollaborationA.Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D.Sharma, I.Tserruya

Weizmann Institute of Science

B.Azmoun, D.Lynch, R.Pisani, C.Woody Physics Dept., Brookhaven National Lab

J.Harder, P.O’Connor, V.Radeka, B.Yu Instrumentation Division, Brookhaven National Lab

W. Anderson, A. Drees, J. Franz,T. Hemmick, R. Hutter, B. Jacak, J. Kamin, M.McCumber, A. Milov, A. Sickles, A.Toia

Stony Brook University

C.-Y. Chi Nevis Labs, Columbia University

H. Hamagaki, S. Oda, K. OzawaUniversity of Tokyo

L.Baksay, M.Hohlmann, S.Rembeczki Florida Institute of Technology

D. Kawall Riken

M. Grosse-Purdekamp University of Ilinois


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Conclusions (not mine, stolen. Needs work. )

Strong hadron rejection can be achieved with good photoelectron efficiency

High gain/stable GEM operation can be obtained in pure CF4

A windowless Cherenkov detector can in principle achieve a very high N0 when used in conjunction with a with deep VUV transmitting gas such as CF4

However, impurities such as O2 and H2O can cause a significant loss of Cherenkov light (O2 and H2O must be kept at the few ppm level)

GEM detectors work in the high multiplicity environment at RHIC No significant aging effects are observed in either GEMs or CsI photocathodes for intergated charges well in excess of what is expected to be reached at RHIC

Need to meaure N0 in a realistic detector and test a fully functional prototype in the PHENIX


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Final HBD Design parameters:

• Acceptance at nominal position: || ≤0.45, =1350

• Acceptance at retracted position: || ≤0.36, =1100

• GEM size: 22 x 27 cm2

• # of detector modules per arm: 12 • GEM frame:

5 mm wide, 0.3mm cross

• Hexagonal pad size: a = 15.6 mm

• Number of pads per arm: 1152

• Dead area within acceptance: 6%

• Rad. length within acceptance: box: 0.92%, gas: 0.54%

• Weight per arm: <10 kg

Exploded view


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HBD Response Simulation

Total signal: 62 e = 29 dE/dx + 33 Cherenkov Blob size: single pad 12%, more than one pad 88%

Normal case, no absorption in CF4, no lamp shadowing, realistic losses

and conservative N0 = 840 cm-1

Total signal: 38 e = 29 (dE/dx) + 9 (Cherenkov )Blob size: single pad response =78%

very similar to data

Includes 20 cm absorption length in CF4, lamp shadowing, realistic

losses and conservative N0 = 840 cm-1


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0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 1000

2000

4000

6000

8000

10000

120000 20 40 60 80 100 120 140 160

Gain with UV Gain with x-rays

Gain

Time, h

1 PHENIX year ~ 16 μC/cm2

Corrected for P/T variations

Acc.charge, μC/cm2

• Illuminate photocathode with UV lamp, measure DC current to mesh

• Measure gain with 55Fe source

• Keep Imesh < 1 nA/cm2, gain ~ 5-10 x 103

• Continuously irradiate photocathode, measure gain periodically• No significant aging effects of either the GEM or CsI photocathode were observed up to ~ 150 μC/cm2 (~ 10 years at RHIC)

• Gain was found to increase with exposure time (Possible charging effect in GEM foils ?)

Aging TestsTest both GEM and CsI photocathodeTest both GEM and CsI photocathode


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Clean Room Survey• Laminar Table Better than Class 1Laminar Table Better than Class 1• Foyer could be better (improve seal to main tent)• Dirty spot in the back (Air Conditioner filters!!!)

Foyer Laminar Table ???

Outside


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0 2 4 6 8 10 12 14 16 18 20 220.9998

1

1.0002

1.0004

1.0006

1.0008

Cherenkov Thresholdpionmuonkaonetarho

Cherenkov Thresholdpionmuonkaonetarho

Cherenkov Thresholds in CF4

Energy (GeV)

cos(theta_cherenkov)


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AC


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Hadron Blindness: Response to Electronsdetector response vs ED at fixed gain

Efficient detection of photoelectrons even at negative drift fields

ED = 0

pA

ET

ED (+)

ET

EI

G

G

G

T

T

I

D

•Charge collected from 150μ layer above GEM


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Pad Dimensions

3.16 cm 2.74 cm3.36 cm

photoelectron blob

WHAT ABOUT A PICTURE OF A GEM HERE TOO!!