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1Alexander Milov QM2006, Shanghai Nov 15, 2006
Construction and expected Construction and expected performance of the Hadron Blind performance of the Hadron Blind Detector for PHENIX experiment Detector for PHENIX experiment
at RHICat RHICAlexander Milov
(for the PHENIX HBD group)
XIX International conference on Ulterarelativistic Nucleus-Nucleus Collisions, Shanghai, China
2Alexander Milov QM2006, Shanghai Nov 15, 2006
Weizmann Institute of Science (Israel)A.Dubey, Z.Fraenkel, A. Kozlov, M.Naglis, I.Ravinovich, D.Sharma, L.Shekhtman (on leave from BINP), I.Tserruya (project leader)
Stony Brook University (USA)W.Anderson, A.Drees, M.Durham, T.Hemmick, R.Hutter, B.Jacak, J.Kamin
Brookhaven National Lab (USA)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 (USA)C-Y. Chi
University of Tokyo (Japan)T. Gunji, H.Hamagaki, M.Inuzuka, T.Isobe, Y.Morino, S.X.Oda, K.Ozawa, S.Saito
RIKEN (Japan)S. Yokkaichi
Waseda University (Japan)Y. Yamaguchi
KEK (Japan)S. Sawada
People in this projectPeople in this project
3Alexander Milov QM2006, Shanghai Nov 15, 2006
Why di-electrons?Why di-electrons?
Part of the p+p run no bkg. subtraction
Entire AuAu run
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)
Lepton pairs are unique probes because they provide direct information undistorted by further interactions.
• ρ (m = 770MeV τ ~ 1.3fm/c) e+e-
• ω (m = 782MeV τ ~ 20fm/c) e+e-
• φ (m =1020MeV τ ~ 40fm/c) e+e-
4Alexander Milov QM2006, Shanghai Nov 15, 2006
e+ e -
e+ e -
S/B ~ 1/500
“combinatorial pairs”
total background
Irreducible charm background
signal
charm signal
Background sourcesBackground sources Main source of the background due to external and internal conversions of the photons coming from π0.
π0 e+ e-
π0 e+ e-
The goal is to reduce the background by a factor of 100
Distinct pattern of the background producing decays: small inv. mass small opening angle
A rejection factor of >90% on a close pair will reduce the background to an acceptable level.
5Alexander Milov QM2006, Shanghai Nov 15, 2006
The detector conceptThe detector concept Proximity Focused Windowless Cherenkov Detector
Radiator gas = Working gasPrimary choice pure CF4n = 1.00062 (=28 ) L = 50cmBlind to π0 with pT<4GeV/c
Radiating particles produce blobs on an image plane
(θmax = cos-1(1/n)~36 mradBlob diameter ~ 3.6 cm)
To preserve the pair opening angle θpair the magnetic field is turned off (compensated) in the detector
Background processes produce 2 close blobs and single electrons only 1
Image plane:CsI photocathode on top of tiple GEM stack used for electron amplification separated by 90% transparent mesh from the main volume
~ 1 m
signal electron
Cherenkov blobs
partner positronneeded for rejection
e+
e-
pair
opening angle
B≈0
6Alexander Milov QM2006, Shanghai Nov 15, 2006
Challenges & SolutionsChallenges & Solutions The space where B can be compensated is limited to ~50cm but the number of p.e. must be high enough to allow for effective amplitude analysis of overlapping and distorted blobs.
Match the CsI Q.E.~70% @ 10eV and pure CF4 bandwidth (6-11.5 eV) to get unprecedented N0 ≈840 cm-1 (x6 larger than any e/π RICH ever built!)
The detector has to let all ionizing particles through without seeing them, but pick up single photoelectrons.
Make CsI + GEMs into a new type of semitransparent photocathode such that it a) is sensitive to the ionization reaching its surface from Cherenkov light
b) electric field drives MIP ionization back into the gas volume
The detector must be thin to produce little own background but leak tight to keep water away from absorbing UV light.
Windowless design (CF4 without quencher = gaseous radiator = detector gas). Combine functions of the detector structural elements (pad plane = gas seal)
7Alexander Milov QM2006, Shanghai Nov 15, 2006
The Image plane The Image plane Start with a GEM
Put a photocathode on top
Electron from Cherenkov light goes into the hole and multiplies
Use more GEMs for larger signal
Pick up the signal on pads
And why is it Hadron Blind?
Mesh with a reverse bias drifts ionization away from multiplication area
HV
Sensitive to UV and blind to traversing ionizing particles
8Alexander Milov QM2006, Shanghai Nov 15, 2006
Honeycomb panels
Mylar window
Readout plane
Service panel
Triple GEM module with mesh grid
The Detector The Detector The detector fits under 3%X0 and it is leak tight to keep water out 0.12cc/min (~1 volume per year)!
Side panel
Sealing frame
HV terminals
Detector is designed and built at the Weizmann Institute
FEEs
Readout plane with 1152 hex. pads is made of Kapton in a single sheet to serve as a gas seal
Each side has 12 (23x27cm2) triple GEM Detectors stacks: Mesh electrode Top gold plated GEM for CsI Two standard GEMs pads
9Alexander Milov QM2006, Shanghai Nov 15, 2006
Detector elements Detector elements
GEM positioning elements are produced with 0.5mm mechanical tolerance.
Dead areas are minimized by stretching GEM foils on a 5mm frames and a support in the middle.
Detector construction involves ~350 gluing operations per box
10Alexander Milov QM2006, Shanghai Nov 15, 2006
“Clean Tent” a.k.a. “The Battle Field of Stony Brook”
CsI Evaporator and quantum efficiency
measurement(on loan from INFN)
6 men-post glove box, continuous gas
recirculation & heating
O2 < 5 ppmH2O < 10 ppm
Laminar Flow Table for GEM
assembly
High Vacuum GEM storage
Class 10-100 ( N < 0.5 mm particles/m3)
Detector assemblyDetector assembly
11Alexander Milov QM2006, Shanghai Nov 15, 2006
CsI evaporation station was given on loan to Stony Brook from INFN/ISS Rome
Thank you Franco Garibaldi & Italian team!
Produces 4 photocathodes per shot240 – 450nm of CsI @ 2 nm/secVacuum drops to 10-5 Torr and then to 10-7 Torr (water out of the structure).Contaminants measured with RGA
Photocathode Q.E. is measured “in situ” from in 165-200 nm wavelength range over entire area
Photocathodes transported to glove box without exposure to air
4 small “chicklets” evaporated at same time for full QE control (120-200 nm)
Photocathode productionPhotocathode production
12Alexander Milov QM2006, Shanghai Nov 15, 2006
First module installed in HBD West
Some of the production stepsSome of the production stepsGEMs pre-installed for evaporation
Photocathode installation chain:removal from transfer box, gain test, installation into the HBD.
13Alexander Milov QM2006, Shanghai Nov 15, 2006
GEMs produced at CERNTested for 500V in air @ CERNFramed & tested @ WIS for gain uniformityTested at SUNYSB prior to installationGain uniformity between 5% and 20%
GEM statistics133 produced (85 standard, 48 Au plated)65 standard, 37 Au plated passed all tests48 standard, 24 Au plated installed GEMs combined into stacks are matched to minimize gain variation over the entire detector
All GEMs pumped for many days under 10-6 Torr prior to installation into detector
20%
5%
The GEM stacks The GEM stacks
14Alexander Milov QM2006, Shanghai Nov 15, 2006
During gain mapping, a single pad is irradiated with a 8kHz 55Fe source for ~20 min. Then all other pads are measured (~1.5h) and the source is returned to the starting pad.
Gain is observed to initially rise and then reach a plateau. Rise can be from few % to almost a factor of 2.
Further study show that the gain increase is rate dependent (10-30%)
This does not impose a problem for GEM operation at PHENIX
GEMs will reach operating plateau in a few hoursRates are lower then during mapping
1.5 Initial Rise
Secondary rise
GEM gain stability GEM gain stability
15Alexander Milov QM2006, Shanghai Nov 15, 2006
Flat position dependence
27 cm
Photocathode qualityPhotocathode quality
Number of photoelectrons
36 72
Q.E. needs to distinguish a single electron from a pair.
Absolute Q.E. must be continuously controlled and preserved.
At the production stage During transportation and installation During physics data taking
At the production stage the Q.E. is as high as measured in R&D stage and uniform
16Alexander Milov QM2006, Shanghai Nov 15, 2006
H2O & O2 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
Monochromator (120-200 nm) is a part of the HBD gas system
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
Gas transparencyGas transparency
17Alexander Milov QM2006, Shanghai Nov 15, 2006
electronshadrons
Cluster size, reverse bias
Tested in PHENIX with p-p collisions at RHIC April-June ‘06
Full scale detector prototype:1 GEM + CsI stack module installed in the volume68 readout channelsfull readout chain
Pure CF4 gas system LVL2 triggers to enrich e-sample
electronshadrons
Pulse height, reverse bias
Forward Bias+LandauReverse Bias
MIP
e/π rejection ~85% at εe ~90 %
Full scale prototype testFull scale prototype test
18Alexander Milov QM2006, Shanghai Nov 15, 2006
HBD West (front side)Installed 9/4/06
HBD East (back side)Installed 10/19/06
NowNow
19Alexander Milov QM2006, Shanghai Nov 15, 2006
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, 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
SummarySummary
20Alexander Milov QM2006, Shanghai Nov 15, 2006
BACKUPSBACKUPS
21Alexander Milov QM2006, Shanghai Nov 15, 2006
Challenges & SolutionsChallenges & Solutions The space where B can be compensated is limited to ~50cm but the number of p.e. must be high enough to allow for effective amplitude analysis of overlapping and distorted blobs.
Match the CsI Q.E.~70% @ 10eV and pure CF4 bandwidth (6-11.5 eV) to get unprecedented N0 ≈840 cm-1 (x6 larger than any e/π RICH ever built!)
The detector has to let all ionizing particles through without seeing them, but pick up single photoelectrons.
Make CsI + GEMs into a new type of semitransparent photocathode, which a) does not have usual losses for such type of photocathode
b) allows multi-stage multiplication to follow it.
The detector must be thin to produce little own background but leak tight to keep water away from absorbing UV light.
Go to windowless design by using CF4 without quenching gas both as a radiator and working gas due to the fact that GEMs have no photon feedback
22Alexander Milov QM2006, Shanghai Nov 15, 2006
~12 m
e+
e+
e-e-
PHENIX nowPHENIX now
23Alexander Milov QM2006, Shanghai Nov 15, 2006
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 12
Frame W:5mm T:0.3mm
Hexagonal pad size a = 15.6 mm
Number of pads per arm 1152
Dead area within central arm acceptance 6%
Radiation length (central arm acceptance) box: 0.92%, gas: 0.54%
Weight per arm (including accessories) <10 kg
HBD parametersHBD parameters
24Alexander Milov QM2006, Shanghai Nov 15, 2006
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
Readout chainReadout chain
25Alexander Milov QM2006, Shanghai Nov 15, 2006
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
Run PlanRun Plan
26Alexander Milov QM2006, Shanghai Nov 15, 2006
Photocathode and gas. Photocathode and gas. Photocathode:
CsI is an obvious choice. We are using INFN built evaporator, currently at Stony Brook to do this project.
High area, High vacuum, In-situ Q.E. control, Zero exposure to open air.
Gas CF4 (was not really known): Has high electron extraction probability Has avalanche self quenching mechanism
Gas CF4 (well known): Transparent up to 11.5 eV, makes perfect match to CsI Is a good detector gas.
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
Ga
in
Time, h
1 PHENIX year ~ 16 C/cm2
Corrected for P/T variations
Acc.charge, C/cm2
27Alexander Milov QM2006, Shanghai Nov 15, 2006
Made of 2 units with R~60cm, the volume is filled with CF4
magnetic field is turned offElectrons emit Cherenkov light
Cherenkov light is registered by 12 photo-detectors in each unit
Signal is read out by 94 pads in each unit, pad size ~ size of a circle
Accumulating ~36 photoelectrons from each primary electron, while most other operational RICHes have ~15 or less.
High statistics allows to separate 2 close electrons even if their signals overlay!
Number of photoelectrons
36 72
The design. The design.
28Alexander Milov QM2006, Shanghai Nov 15, 2006
Event display (simulation). Event display (simulation).
29Alexander Milov QM2006, Shanghai Nov 15, 2006
Background sources? Background sources?
~12 m
In the decays contributing to the background:
π0 e+ e- γ π0 γ γ e+ e- γ
Only one electron is detected in PHENIX and another is lost
To cut the background we need a new detector such that:
It sees only electrons Located at the origin It does not produce its own background (is thin) … … …
30Alexander Milov QM2006, Shanghai Nov 15, 2006
• All raw materials (FR4 sheets, honeycomb, HV resistors, HV connectors) ordered and most of them in house
•Detector box design fully completed
• Jig design underway
• Small parts (insert, pins, screws, HV holders..) in the shops
• Detector construction to start Nov. 1st
• PCB design almost complete
• Detailed construction schedule foresees shipment of boxes to SUNY in January 2006.
What does it look like What does it look like
31Alexander Milov QM2006, Shanghai Nov 15, 2006
Mechanical parts and PCB.Mechanical parts and PCB.PCB final design.Quick MC shows no difference with standard cells
Entrance window frames are ready, the window itself to be tight between them