jason kamin may 17 th, 2006 1 title slide!! hbd. jason kamin may 17 th, 2006 2 di-lepton physics...
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Jason KaminMay 17th, 2006
1
Title Slide!!
HBD
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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→
Jason KaminMay 17th, 2006
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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???
Jason KaminMay 17th, 2006
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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)
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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)
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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.
16
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
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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)
Jason KaminMay 17th, 2006
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AC
Jason KaminMay 17th, 2006
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Jason KaminMay 17th, 2006
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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
Jason KaminMay 17th, 2006
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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!!
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