Di-lepton PhysicsDiverse Physics:Vector MesonsDalitzCorrelated 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- Major problem: Huge combinatorial background mostly due to:-conversions & 0 Dalitz decays. We need a new detector, that can ID es from these two sources. Full ID of background: eID & chargeID & (minv < m)Good enough: eID & P-hat (two es with small opening angle)Hadron-Blind Detector:Cherenkov for eID.Field free region of PHENIX (p-hat)All PairsCombinatorial PairsSignal PairsLighter particles have smaller opening angles!!Field can be canceled in a small region around beampipe. >100x
Unfocused Cherenkov Blobs(r,phi) bins grow with radius(x,y) uniform binsCherekov Radiatione- 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???
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 photocathode150 The original idea by F.Sauli (mid 90s) US Patent 6,011,265 Traditionally CHARGED PARTICLE detectors (not photons)
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!!! We have a detector sensitive to UV and blind to ionizing 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 ~150 layer above top GEM
Dilepton pairBeam PipeHBD 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 servicesWindowless Cherenkov DetectorRadiator gas = Avalanche GasElectrons radiate, but hadrons with P < 4 GeV/c do not
Pcb pad readout (~ 2x2 cm2)5 cm55 cme-e+qPair Opening AngleThe HBD DetectorCsI photocathode covering GEMs
The Clean Tent at USBEntrance FoyerLevel of Clean Room
The EvaporatorEvaporation ChamberQuantum Efficiency StationMagnetically coupled driver for moving the GEMs inside the vacuum.on loan from INFN Roma
The Evaporation Chamber ~24 hrs to pump down vessel vacuum ~10-8 mbar no water!!Evaporate 4 GEMs simultaneously Molybdenum boatsAC 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
The Quantum Efficiency StationGEM with CsIMolybinum boatsGEM mounting box w/ wheels on trackHarpoon for moving mounting boxAC
Quantum EfficiencyExcellent QE. Comparable to best in the world. QE constant across GEM. Its crucial to maintain high QE after production.
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.
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.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.ToiaStony 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
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
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:
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 dataIncludes 20 cm absorption length in CF4, lamp shadowing, realistic losses and conservative N0 = 840 cm-1
Aging Tests 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 ?)Test both GEM and CsI photocathode
Clean Room SurveyLaminar Table Better than Class 1Foyer could be better (improve seal to main tent)Dirty spot in the back (Air Conditioner filters!!!)FoyerLaminar Table???Outside
Hadron Blindness: Response to Electronsdetector response vs ED at fixed gainEfficient detection of photoelectrons even at negative drift fieldsCharge collected from 150 layer above GEM
RICH 2004, Playa del Carmen
Pad Dimensions3.16 cm2.74 cm3.36 cmphotoelectron blobWHAT ABOUT A PICTURE OF A GEM HERE TOO!!