Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC...
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Transcript of Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment at RHIC...
Prototype Tests and Construction of the Hadron Blind
Detector for the PHENIX Experiment at RHIC
Prototype Tests and Construction of the Hadron Blind
Detector for the PHENIX Experiment at RHIC
Craig WoodyBrookhaven National Lab
For the PHENIX Collaboration
N41-5
2006 IEEE Nuclear Science Symposium and Medical Imaging ConferenceSan Diego, CA
November 2, 2006
C.Woody, NSS-N41-5, November 2, 2006 2
HBD TeamHBD Team
Weizmann Institute of Science• A.Dubey, Z. Fraenkel, A. Kozlov, M. Naglis, I. Ravinovich, D.Sharma, L.Shekhtman, I.Tserruya*
Stony Brook University• W.Anderson, A. Drees, M. Durham, T.Hemmick,
R.Hutter, B.Jacak, J.Kamin
Brookhaven National Lab• B.Azmoun, A.Milov, R.Pisani, T.Sakaguchi, A.Sickles, S.Stoll, C.Woody (Physics)• J.Harder, P.O’Connor, V.Radeka, B.Yu
(Instrumentation Division)
Columbia University (Nevis Labs)• C-Y. Chi
* Project Leader
C.Woody, NSS-N41-5, November 2, 2006 3
Motivation - Measurement of Low Mass Electron Pairs in Relativistic Heavy Ion Collisions
Motivation - Measurement of Low Mass Electron Pairs in Relativistic Heavy Ion Collisions
Low mass dilepton pairs are unique probes for studying chiral symmetry restoration in dense nuclear matter
Chiral symmetry is the symmetry between light quark flavors, which is normally broken due to the finite value of the constituent quark masses. At high temperatures and/or high baryon densities,
this symmetry may be at least partially restored
Effects of chiral symmetry restoration manifest themselves in terms of in-medium modifications of the line shapes of low mass vector mesons (e.g., mass shifts, spectral broadening)
• ρ (m = 770MeV t ~ 1.3 fm/c) e+e-
• ω (m = 782MeV t ~ 20fm/c) e+e-
• φ (m =1020MeV t ~ 40fm/c) e+e-
R. Rapp nucl-th/0204003
e-e+
C.Woody, NSS-N41-5, November 2, 2006 4
Experimental Challenges at RHIC Experimental Challenges at RHIC
Large combinatorial pair background due to copiously produced photon conversions and Dalitz decays
Need rejection factor > 90% of e+ e - and e+ e -
e+ e -
e+ e -
S/B ~ 1/500
“combinatorial pairs”
total background
Irreducible charm background
all signal
charm signal
Would like to improve S/B by ~ 100-200
e+e- Pair Spectrum in PHENIIX
C.Woody, NSS-N41-5, November 2, 2006 5
The Hadron Blind DetectorThe Hadron Blind Detector
Cherenkov blobs
e+
e-
pair opening angle
~ 1 m
Radiator gas = Working gasGas volume filled with pure CF4 radiator
(nCF4=1.000620, LRADIATOR = 50 cm)
Proximity Focused Windowless Cherenkov Detector
Electrons produce Cherenkov light, but hadrons with P < 4
GeV/c do not
Radiating tracks form “blobs” on an image plane
(max = cos-1(1/n)~36 mrad Blob diameter ~ 3.6 cm)
Tracks pass through the HBD in an essentially zero field region in PHENIX
Electron pairs do not open up
Dalitz pairs & conversions maketwo blobs, single electrons make one
C.Woody, NSS-N41-5, November 2, 2006 6
The Hardon Blind ConceptThe Hardon Blind Concept
• Primary ionization is drifted away from GEM and collected by a mesh
• UV photons produce photoelectrons on a CsI photocathode and are collected in the holes of the top GEM
• Triple GEM stack provides gain ~ 104
• Amplified signal is collected on pads and read out
Mesh
CsI layer
Triple GEM
Readout Pads
e-Primary ionizationg
HVPrimary ionization signal is
greatly suppressed at slightly negative drift field while photoelectron collection
efficiency is mostly preserved
Test with UV photons and a particles
Z.Frankel et.el., NIM A546 (2005) 466-480.A.Kozolov et.al. NIM A523 (2004) 345-354.
C.Woody, NSS-N41-5, November 2, 2006 7
Detector ConstructionDetector Construction
24 Triple GEM Detectors (12 modules per side)
Area = 23 x 27 cm2
• Mesh electrode• Top gold plated GEM for CsI• Two standard GEMS• Kapton foil readout plane One continuous sheet per side Hexagonal pads (a = 15.6 mm)
Honeycomb panels
Mylar entrance window
HV panel
Pad readout plane
HV panel Triple GEM module with mesh grid
Very low mass (< 3% X0 including gas)
Detector designed and built at the Weizmann Institute
C.Woody, NSS-N41-5, November 2, 2006 8
GEM PerformanceGEM Performance
• All GEMs produced at CERN• 133 produced (85 standard, 48 Au plated)• 65 standard, 37 Au plated passed all tests• 48 standard, 24 Au plated installed • The three GEMs in each stack are matched to minimize gain variation over the entire detector
• All GEMs pumped for many hours under high vacuum (~ 10-6 Torr) prior to installation
• Gain of each module was mapped for all sectors
• Resulting gain variation is between 5-20 %
20%
5%
C.Woody, NSS-N41-5, November 2, 2006 9
Gain Stability of GEMsGain Stability of GEMs• During gain mapping, a single pad is irradiated with a 8 KHz 55Fe source for ~ 20 min. Then all other pads are measured, and the source is returned to the starting pad.
• Gain is observed to initially rise and then reach a plateau. Rise can be ~ few % to almost a factor of 2.
• Gain increase is somewhat rate dependent (10-30%)
Not a fundamental problem in PHENIX• GEMs will reach operating plateau in a few hours• Rates are low
1.5 Initial Rise
Effect seen in other GEMsSee talk by B.Azmoun, Workshop on Micropattern Gas Detectors, 10/29
Secondary rise
C.Woody, NSS-N41-5, November 2, 2006 10
Photocathode Production and Detector AssemblyPhotocathode Production and Detector Assembly
“Clean Tent” at Stony Brook
CsI Evaporator and quantum
efficiency measurement
Large glove boxO2 < 5 ppm
H2O < 10 ppm
Laminar Flow Hood
High Vacuum
GEMStorage
Container
Class 10-100 ( N < 0.5 mm particles/m3)
C.Woody, NSS-N41-5, November 2, 2006 11
Evaporator and QE MeasurementEvaporator and QE MeasurementComplete CsI evaporation station was given on
loan to Stony Brook from INFN/ISS Rome (Thank you Franco Garibaldi !)
Produces 4 photocathodes per evaporation• Deposit 2400 – 4500 Å CsI @ 2 nm /sec• Vacuum ~ 10-7 Torr• Contaminants measured with RGA
• Measures photocathode quantum efficiency in situ from 165-200 nm over entire area
• Photocathodes transported to glove box without exposure to air
Virtually no water !
Small “chicklets” evaporated at
same time for full QE measurement
(120-200 nm)
C.Woody, NSS-N41-5, November 2, 2006 12
Photocathode QualityPhotocathode Quality
Large bandwidth of CF4 (6-11.5 eV), windowless construction and high QE of CsI in deep VUV gives very large
N0 (840 cm-1)
Expect ~ 36 p.e. per blob
Photocathodes are produced with consistently good quantum
efficiencies
Need to monitor photocathode performance over the lifetime of the experimentNumber of photoelectrons
36 72
Gives good separation between single and double
electrons
Flat position dependence
27 cm
C.Woody, NSS-N41-5, November 2, 2006 13
Construction of the Actual DetectorConstruction of the Actual Detector
All twelve modules installed in HBD West
C.Woody, NSS-N41-5, November 2, 2006 14
Gas Transmission MonitorGas Transmission Monitor
Oxygen and water must be kept at the few ppm level to avoid absorption in the gas
Heaters are installed on each detector to drive out water from GEMs and
sides of detector vessel
Lamp Monitor Gas Cell Monitor
Measure photocathode current of CsI PMTs
D2 lamp
Scanning Monochrometer (120-200 nm)
Movable mirror
Turbopump
Transmittance in 36cm of Ar Vs PPM's of H2O
0
10
20
30
40
50
60
70
80
90
100
110
1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Wavelength [Angstroms]
% T
rans
mitt
ance
[%] ~10ppm H2O
~40ppm H2O
~200ppm H2O
C.Woody, NSS-N41-5, November 2, 2006 15
Test of a Full Scale Prototype Detector in PHENIXTest of a Full Scale Prototype Detector in PHENIX
electronshadrons
Cluster Size
Tested in PHENIX with p-p collisions at RHIC April-June ‘06
• Full scale detector with one GEM module • 68 readout channels• Full readout chain• Operated with full pure CF4 gas system
electronshadrons
Pulse height
Forward BiasReverse Bias
Landau fit
MIP
Reverse Bias, B=0
Hadron rejection ~ 85% at e ~ 90 %
C.Woody, NSS-N41-5, November 2, 2006 16
Both Halves of the HBD Installed in PHENIXBoth Halves of the HBD Installed in PHENIX
HBD West (front side)Installed 9/4/06
HBD East (back side)Installed 10/19/06
C.Woody, NSS-N41-5, November 2, 2006 17
SummarySummary
The HBD will provide a unique capability for PHENIX to measure low mass electron pairs in heavy ion collisions at RHIC This detector incorporates several new technologies (GEMs, CsI photocathodes, operation in pure CF4 with a windowless design) to achieve unprecedented performance in photon detection (N0 ~ 840 cm-1)
The operating requirements are very demanding in terms of leak tightness and gas purity, but we feel they can be achieved Tests with the full scale prototype were very encouraging and demonstrated the hadron blindness properties of the detector. The final detector is now installed in PHENIX and ready for commissioning and data taking during the upcoming run at RHIC
C.Woody, NSS-N41-5, November 2, 2006 18
Backup SlidesBackup Slides
C.Woody, NSS-N41-5, November 2, 2006 19
Present PHENIX Capabilities Present PHENIX Capabilities
~12 m
e+
e+
e-e-
C.Woody, NSS-N41-5, November 2, 2006 20
HBD Detector ParametersHBD Detector Parameters
Acceptance nominal location (r=5cm) || ≤0.45, =135o
retracted location (r=22 cm) || ≤0.36, =110o
GEM size (,z) 23 x 27 cm2
Number of detector modules per arm 12Frame 5 mm wide, 0.3mm crossHexagonal pad size a = 15.6 mmNumber of pads per arm 1152Dead area within central arm acceptance 6%Radiation length within central arm acceptance box: 0.92%, gas: 0.54%Weight per arm (including accessories) <10 kg
C.Woody, NSS-N41-5, November 2, 2006 21
Readout ElectronicsReadout Electronics
Preamp (BNL IO-1195)2304 channels total
19 mm
15 mmDifferential
output
Noise on the bench looks very goodGaussian w/o long tails
3s cut < 1% hit probability
C.Woody, NSS-N41-5, November 2, 2006 22
Run Plan for the HBD at RHICRun Plan for the HBD at RHIC Run 7 (Dec ‘06 – June ’07)
• ~ 4 weeks commissioning with Au x Au beams at sNN = 200 GeV • 10 weeks data taking with Au x Au at sNN = 200 GeV • 10 weeks data taking with polarized p-p beams at s = 200 GeV
Run 8 (Fall ’07 – Summer ’08)• 15 weeks d-Au at sNN = 200 GeV• 10 weeks polarized p-p at s = 200 GeV
Run 9 (Fall ’08 – Summer ’09)• 10-15 weeks heavy ions (different energies and possibly species)• 15-10 weeks polarized p-p at s = 500 GeV (including commissioning)
Run 10 (Fall ’09 – Summer ’09)• HBD is removed in order to install new silicon vertex detector in PHENIX