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Title Slide!!. HBD. 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. Invariant Mass Spectrum from e + e -. relativistic electrons.

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title slide
Title Slide!!


Jason Kamin

May 17th, 2006

di lepton physics
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 Kamin

May 17th, 2006


Invariant Mass Spectrum from e+e-

relativistic electrons



photoelectron blob

All Pairs

Combinatorial Pairs

Signal Pairs


  • 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)

Field can be canceled in a small region around beampipe.

Lighter particles have smaller opening angles!!

Jason Kamin

May 17th, 2006

unfocused cherenkov blobs
Unfocused Cherenkov “Blobs”
  • 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.

Cherekov Radiation


  • Can YOU design this detector???

(r,phi) – bins grow with radius

(x,y) – uniform bins

Jason Kamin

May 17th, 2006


Gas Electron Multiplier (GEM)

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


  • 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 shine back onto photocathode

Jason Kamin

May 17th, 2006


The concept


~150 μm

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

Jason Kamin

May 17th, 2006

hadron blindness uv photons vs charged particles
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

Jason Kamin

May 17th, 2006


The HBD Detector

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

Windowless Cherenkov Detector

Radiator gas = Avalanche Gas

Cherenkov light forms “blobs” on an image plane





Pair Opening


55 cm

Pcb pad readout (~ 2x2 cm2)

5 cm

Electrons radiate, but hadrons with

P < 4 GeV/c do not

CsI photocathode covering GEMs

Triple GEM detectors

(12 panels per side)

Space allocated for services

Dilepton pair

Beam Pipe

Jason Kamin

May 17th, 2006

the clean tent at usb


glove box

laminar flow hood


storage vessel

The Clean Tent at USB

Level of Clean Room

Entrance Foyer

Jason Kamin

May 17th, 2006

the evaporator
The Evaporator

on loan from INFN Roma

Magnetically coupled driver for moving the GEMs inside the vacuum.

Quantum Efficiency Station

Evaporation Chamber

Jason Kamin

May 17th, 2006

the evaporation chamber

Harpoon for moving mounting box

GEM mounting box w/ wheels on track



The Evaporation Chamber

Molybdenum boats

  • 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
  • ~24 hrs to pump down vessel
  • vacuum ~10-8 mbar
    • no water!!
  • Evaporate 4 GEMs simultaneously


Jason Kamin

May 17th, 2006

the quantum efficiency station

GEM w/ CsI




~ 100 V

~ 2mm

Xe lamp

MgF2 window

(λ=160,185,200 nm)


(e- collection)



reference PMT

The Quantum Efficiency Station

Harpoon for moving mounting box

GEM mounting box w/ wheels on track

GEM with CsI

Molybinum boats


Jason Kamin

May 17th, 2006

quantum efficiency


Relative QE (%)


x-coordinate across GEM

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

Jason Kamin

May 17th, 2006



Jason Kamin

May 17th, 2006






  • 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.

Jason Kamin

May 17th, 2006

the phenix hbd collaboration
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.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. Ozawa

University of Tokyo

L.Baksay, M.Hohlmann, S.Rembeczki

Florida Institute of Technology

D. Kawall


M. Grosse-Purdekamp

University of Ilinois

conclusions not mine stolen needs work
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 Kamin

May 17th, 2006

final hbd
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:


  • 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

Jason Kamin

May 17th, 2006

hbd response simulation
HBD Response Simulation

Includes 20 cm absorption length in CF4, lamp shadowing, realistic losses and conservative N0 = 840 cm-1

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

Total signal: 62 e = 29 dE/dx + 33 Cherenkov

Blob size: single pad 12%, more than one pad 88%

Jason Kamin

May 17th, 2006

aging tests
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 < 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 ?)

Jason Kamin

May 17th, 2006

clean room survey
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!!!)


Laminar Table



Jason Kamin

May 17th, 2006

Jason Kamin

May 17th, 2006



Jason Kamin

May 17th, 2006

Jason Kamin

May 17th, 2006

hadron blindness response to electrons detector response vs e d at fixed gain


ED (+)











ED = 0

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

Jason Kamin

May 17th, 2006

pad dimensions
Pad Dimensions

photoelectron blob

3.36 cm

2.74 cm

3.16 cm


Jason Kamin

May 17th, 2006