Jason Kamin

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• A Hadron Blind Detector for the PHENIX Experiment

Jason Kamin Stony Brook University
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Outline

• Motivation for a Hadron Blind Detector
• Principles of HBD operation
• CsI Evaporation Techniques

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Di-lepton Physics

• Diverse Physics
• Vector Mesons
• Dalitz
• Correlated semi-leptonic decays.
• Chiral Restoration??
• Very difficult measurement in Heavy Ion Physics
• (see Alberica Toias talk 5/18/06, 1030am)

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Invariant Mass Spectrum from ee-
All Pairs Combinatorial Pairs Signal Pairs

• Major problem Huge combinatorial background
  mostly due to
• ?-conversions p0 Dalitz decays.
• We need a new detector to identify the above by
  supplying
• eID
• momentum direction
• thus reducing background by a factor of 10-100.
  

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Why so much background?

• Typically only 1 electron from the pair falls in
  the acceptance.
• The magnetic field bends the pair in opposite
  directions.
• Some curl up in the magnetic field and never
  come out.

• The new detector needs
• gt90 electron ID
• sit near the collision
• sit in zero B-field
• catch e/- before they get lost

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Is it a p or a f?
A lot of particles have ee- decay channels. How
can we tell the Dalitz decays and photon
conversions apart from the decays that were
interested in??
Back to the basics (briefly)
relativistic electrons
pads
f
p
Given the same initial momentum, more massive
particles have lower velocities than lighter
ones. Therefore, the opening angle of the decay
is bigger.
Lighter particles have smaller opening angles!!
How about a Cherenkov Detector???

• ID electrons
• give directional information.

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Looking Closer

• Inner coil can cancel B-field at r lt 60 cm

• Not enough room for traditional optics mirrors
  wont work.

• Just put the detector right in the middle of
  things!

• Has potential, but
• must be thin
• must detect a single UV photon and still be
  blind to all ionizing particles passing through
  it!!!

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Unfocused Cherenkov Blobs

• Windowless Radiator Gas Avalanche Gas
• CF4 (n1.000620)
• Blind to hadrons w/ lt4 GeV
• Some challenges
• No room for traditional optics (ie. focusing
  mirror).
• Cherenkov light collected as an unfocused blob.
• 1.5 m2 photosensitive region
• Low radiation length
• minimize photon conversions.
• Charged particles from collision will pass
  through
• ionization must not interfere with photoelectron
  detection.

Cherekov Radiation
e-

• Can YOU design this detector???

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Gas Electron Multiplier (GEM)

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

150µ
80µ

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

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

• Just add the photocathode

• By the way no photon feedback onto photocathode

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Watch the Magic

• Start with 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!!!

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

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Hadron Blindness UV photons vs charged
particles

• At slightly negative Ed, photoelectron detection
  efficiency is preserved whereas charge collection
  is largely suppressed.
• Charge collected from 150µ layer above top GEM

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The HBD Detector
HBD Gas Volume Filled with CF4 Radiator
(nCF41.000620, LRAD50 cm)
Windowless Cherenkov Detector Radiator gas
Avalanche Gas
Cherenkov light forms blobs on an image
plane (rBLOB3.36cm)
e
e-
55 cm
q Pair Opening Angle
Pcb pad readout ( 2x2 cm2)
5 cm
Electrons radiate, but hadrons with P lt 4 GeV/c
do not
CsI photocathode covering GEMs
Triple GEM detectors (12 panels per side)
Space allocated for services
Dilepton pair
Beam Pipe
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• Photocathode Production

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The Clean Tent at USB
(Class number of 0.5 µm particles/m3)
Class of Clean Room
Entrance Foyer
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The Evaporator
on loan from INFN Roma
Magnetically coupled driver for moving the GEMs
inside the vacuum.
Evaporation Chamber
Quantum Efficiency Station
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The Evaporation Chamber
Molybdenum boats

• 24 hrs to pump down vessel
• vacuum 10-7 mbar
• no water!!
• Evaporate 4 GEMs simultaneously

• 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

AC
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The Quantum Efficiency Station
Harpoon for moving mounting box
GEM mounting box w/ wheels on track
GEM with CsI
Molybinum boats
AC
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Quantum Efficiency

• Excellent QE.
• Comparable to other research institutes
  throughout the world.
• QE constant across GEM.
• Its crucial to maintain high QE after production.

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Summary

• Hadron Blind Detector is crucial to the low-mass
  dielectron spectrum (est. to reduce bkgrd by a
  factor of 10-100)
• 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!! (its
  working).
• Final HBD is scheduled to be installed in late
  Aug 2006.

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Summary

• 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!! (its
  working).
• Final HBD is scheduled to be installed in late
  Aug 2006.

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The PHENIX HBD Collaboration

• A.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.OConnor, 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. Ozawa
• University of Tokyo
• L.Baksay, M.Hohlmann, S.Rembeczki

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Final HBD
Exploded view

• 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

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HBD Response Simulation
Normal case, no absorption in CF4, no lamp
shadowing, realistic losses and conservative N0
840 cm-1
Includes 20 cm absorption length in CF4, 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
Total signal 62 e 29 dE/dx 33 Cherenkov
Blob size single pad 12, more than one pad 88
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Aging Tests
Test both GEM and CsI photocathode

• Illuminate photocathode with UV lamp,
• measure DC current to mesh
• Measure gain with 55Fe source
• Keep Imesh lt 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 mC/cm2 ( 10 years at
  RHIC)
• Gain was found to increase with exposure time
• (Possible charging effect in GEM foils ?)

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Clean Room Survey

• Laminar 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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Pad Dimensions
photoelectron blob
2.74 cm
3.36 cm
3.16 cm
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Hadron Blindness Response to Electronsdetector
response vs ED at fixed gain

• Charge collected from 150µ layer above GEM

Efficient detection of photoelectrons even at
negative drift fields