rich in the phenix experiment at rhic hideki hamagaki center for nuclear study graduate school of...
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RICH in the PHENIX Experimentat RHIC
Hideki HamagakiCenter for Nuclear Study
Graduate School of Science, University of Tokyo
2006/3/6 International CBM-RICH workshop at GSI
2RHIC
• Brookhaven National Laboratory, USA
• The first heavy-ion collider on the earth
• Two independent rings with circular length = 3.83 km
• Energy at CMS p+p 500 GeV Au+Au 200 A ・ GeV
• Luminosity– Au-Au: 2 x 1026 cm-2 s-1
– p-p : 2 x 1032 cm-2 s-1
-• Construction: 1991~1999 • Experimental runs since
2000
2006/3/6 International CBM-RICH workshop at GSI
3PHENIX Detector System
Central ArmsCoverage (E&W) -0.35< y < 0.35 30o <||< 120o
A complex apparatus to measure: Hadrons, Muons, Electrons, Photons
Muon ArmsCoverage (N&S) -1.2< |y| <2.3 - < <
2006/3/6 International CBM-RICH workshop at GSI
4Central Arms of the PHENIX experiment
• hadron, electron and photon measurement• detector components
– tracking chambers (DC + PC1,2,3 + TEC)– PID (TOF + RICH)– EM calorimeter (EMCAL)
2006/3/6 International CBM-RICH workshop at GSI
5Guiding Principles of PHENIX-RICH
• Primary purpose– electron identification under huge particle flux
environment
• Type of Cherenkov detector– gas radiator with relatively large index of refraction– ring imaging with a spherical mirror
• it measures incident direction of particles
• Small radiation length– low-Z radiator gas & materials
• Photon detectors should not face particle flux– protect them from the flux with the iron of central magnet
2006/3/6 International CBM-RICH workshop at GSI
6PHENIX-RICH overview
Acceptance coverage• || < 0.35 ; d = 90 degrees x
2
Three major components• Gas vessel
– C2H6 (th ~ 25) or CO2(th ~ 35)
– eID pt range : 0.2 ~ 4 GeV/c
• Gull-wing shaped spherical mirrors
• Photon detection by PMTs– 5,120 channels in 2 arms
Pixel size• 2-D angles (,) of electron
tracks– ~1 degree x ~1 degree
BNL, FSU, KEK, SUNY/SB, NIAS, ORNL, U.Tokyo, Waseda
Cerenkov photons are detected by array of PMTs
mirrorMost hadrons do not emit Cerenkov light
Electrons emit Cerenkov photons
Central Magnet
RICH
PMT arrayPMT array
2006/3/6 International CBM-RICH workshop at GSI
7RICH Specifications
• Vessel– Weight: 7250 kg/arm– Gas volume: 40 m3/arm– Radiator length: 0.9 - 1.5
m
• Mirror system – Radius : 403 cm– Surface area: 20 m2 / arm
• Photon detector– 2560 PMTs / arm
• Radiation length = 2.14%– Gas: 0.41 % (ethane)– Windows: 0.2%– Mirror panels: 0.53%– Mirror support: 1.0%
2006/3/6 International CBM-RICH workshop at GSI
8Gas Vessel
Dimensions• Width in Z
– 6000 mm
• Distance from top to bottom corner of vessel
– 5798.3 mm
• Entrance and Exit window– R(ent) = 2575 mm– R(exit) = 4100 mm– S(ent) = 8.9 m2
– S(exit) = 21.6 m2
– 125 m Kapton with supporting graphite-epoxy beams
– black vinyl coated polyester for light shield
2006/3/6 International CBM-RICH workshop at GSI
9RICH PMT
Hamamatsu H3171S• Cathode Diameter: 25 mm• Tube Diameter: 29 mm• Cathode: Bialkali• Gain: > 107
• Operation Voltage: - 1400 ~ -1800 V• Quantum efficiency: > 19% at 300 nm > 5 % at 200 nm• Rise Time: < 2.5n• Transit Time Spread: < 750ps
A Winstone cone shaped conical mirror• Entrance: 50 mm, Exit: 25 mm, Angular cut off = 30
Magnetic shielding case• FERROPERM (NKK); high susceptibility + large saturation
field
2006/3/6 International CBM-RICH workshop at GSI
10RICH PMT Arrays
• Supermodules– assembly of 32 PMTs
(2x16) – PMTs are grouped by its
gain• 8 tubes share the same HV
• Supermodules are installed in RICH vessel to form a tightly packed PMT array
– 40 super-modules (1280 PMTs) per one side of a RICH vessel
2006/3/6 International CBM-RICH workshop at GSI
11
Rohacell foam core (1.25 cm thick)
Gel-coat (0.05 mm thick)
4 ply graphite-epoxy (0.7 mm thick)
Mirror• Segmented spherical mirror
– R = 403 cm, L = 81.2 cm, W = 43.2 ~ 50.5 cm
– 48 panels/arm; 2 (side) x 2 (z) x 12 ()
• Structure of panel panels– substrates (by ARDCO)
• steel master• 1.25 cm Rohacell foam + 4 layers of graphite
epoxy (~0.7 mm) at each side• gel coat layer (0.05 mm)
– reflection surface (by OPTICON)• replication of aluminum surface using a glass
master (surface roughness rms ~ 2.5 nm)• epoxy thickness = ~150 m
• Performance– weight: 1.2 ~ 1.3 kg– reflectivity = 83% at 200 nm; 90% at 250
nm– R = 401.1 cm, with variation of 2.2 cm– surface roughness = ~+-1.5 mrad
2006/3/6 International CBM-RICH workshop at GSI
12Mirror Support Structure
• Frame bars– graphite fiber– 1 % of radiation length
(ave.)• Mirror panels are mounted by
adjustable 3 point mounts on the frame bars
2006/3/6 International CBM-RICH workshop at GSI
13Mirror Alignment
• After mirror installation, the RICH vessel is rotated up in the same orientation as on PHENIX carriage
• Positions of optical targets placed on mirror surface were surveyed with a computerized theodolite system (MANCAT).
2006/3/6 International CBM-RICH workshop at GSI
14Front End Electronics (FEE)
• Readout Signals from 5120 PMTs:– 0 ~ 10 Photon; max = 160 pC (with x10 Pre-Amp)– Time resolution = ~200 ps (for background rejection)
• Very fast operation– 9.6 MHz RHIC beam clock– Average Trigger Frequency 25 KHz
• Transfer to Data Collection Module (DCM) using G-LINK• Compactness -> 640 PMT signals per crate
2006/3/6 International CBM-RICH workshop at GSI
15Readout ModuleController Module
• Heap Management of AMU• Controls FEE synchronous to Master Timing System• Controls Burst Transfer• Generate AMU Write / TAC Stop Timing• Slow Serial Control using ARCNET
DSU/ALM
BTSK2
Readout FIFO
G-LinkTransmitter
ROC
PhaseShifter
• Transferring Data to PHENIX-DCM usingG-LINK at the maximum speed of 800 Mbps• G-LINK Transfer asynchronous to BUS Transfer inside RICH-FEE using four FIFOs (Depth: 9 events)
Analog Processing (AMU/ADC) Module
Inte
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C (
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Chi
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U/A
DC
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DC
Bur
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ontr
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• 64 Inputs, 64 Charge and TAC Outputs/Board• Trigger Sum: 16 Trigger Sum Outputs/Board (4 PMT Signal Sum)• Burst Transfer to Readout Module in 20-40MHz• Serial Controllable ASICs on Board
• 8 RICH Chips (Integrator+VGA+LED+CFD+TAC+Trigger Sum)• 8 Inputs, 8 CHARGE and TAC outputs/Chip, and 4 TriggerSum/Chip
• 4 AMU/ADC Chips (Analog Memory Unit and ADC); 32 Inputs/Chip
2006/3/6 International CBM-RICH workshop at GSI
16Number of Photo-electrons
• resolution for 1pe/MPH(1pe) ~ 0.26
• number of photo-electrons per ring ~ 10.8
– N0 ~ 120 (Npe = N0 sin2C)
2006/3/6 International CBM-RICH workshop at GSI
17Association of RICH Hits to Tracks
• reconstruction of rings is difficult– due to coarse segmentation of photon detectors
• association method– associate the photon hits to a charged track
2006/3/6 International CBM-RICH workshop at GSI
18Performance Limitation
• Association is not seen well in high multiplicity events
• Still works great to enrich electrons
2006/3/6 International CBM-RICH workshop at GSI
19Rejection Power of RICH (CO2 Gas)
• Data– Class defined by PC1 Hit:
• Peripheral: (PC1 Hit) < 150• Central: (PC1 Hit) > 400
– e+ e- and + - identified with TOF in the momentum range from 0.3 GeV to 0.4 GeV
– Number of PMTs are counted for hits with 3.4cm < r < 8.4cm
– Ring shape cut is applied– Errors are statistical only
• Simulation– additional shielding materials in
• effect of a factor of ~2
– the shielding materials are in after this run
Black: Simulation for Au+Au CentralBlue: Real data for Au+Au PeripheralRed: Real data for Au+Au Central
2006/3/6 International CBM-RICH workshop at GSI
20E/p Plot
• Pion rejection factor with RICH only
– ~100 for high multiplicity events
– 10000 for single pions
• With RICH + EMCAL– another factor of ...,
depending on the momentum
2006/3/6 International CBM-RICH workshop at GSI
21J/ in Au-Au collisions at RHIC
• In Run-4, 240 b-1 recorded with improved detector performance
– ~ 100 times more J/signals expected than in Run-2
• Outstanding J/ peak in e+e- invariant mass spectrum in 200 AGeV Au + Au central collisions
2006/3/6 International CBM-RICH workshop at GSI
22Some results on J/
• Nuclear modification factor of J/ yield for d + Au collisions
• for Au + Au and Cu + Cu collisions
|y|<0.350.2
0.4
0.6
0.8
1.0
1.2
RdAu
Rapidity
2006/3/6 International CBM-RICH workshop at GSI
23Thermal radiation and low-mass vector mesons
• Still missing at RHIC
• Experimentally, combinatorial background is very large and must be subtracted properly
• Large physics background comes from charm.
– Charm production is measured with ~15% accuracy by single electron measurements.
A prediction
R. Rapp, nucl-ex 0204003
2006/3/6 International CBM-RICH workshop at GSI
24Combinatorials is overwhelming
• Combinatorial background is determined with ~1% accuracy in Run3 and Run2 using a mixed event method
• Higher statistics from Run4 data should help, but it may not be enough for low-mass vector mesons
Real and Mixed e+e- Distribution
Run2 AuAuMinimum Bias
0
Real - Mixed with systematic errors
1 2 3 [GeV/c2] 0 1 2 3 [GeV/c2]
2006/3/6 International CBM-RICH workshop at GSI
25How to measure low-mass pairs
• Efforts are on-going to develop a Dalitz rejecter, based on HBD (hadron Blind Detector).
– UV photon detector• with CsI cathode• CF4 gas radiator• Ne(Cherenkov) > Ne(ionization)
S/B ~ 1/500
“combinatorial pairs”
total background
Irreducible charm backgroundall signal
charm signal
2006/3/6 International CBM-RICH workshop at GSI
26For Better Performance
• PHENIX-RICH– coarse segmentation of photon detector
• difficult to reconstruct Cherenkov rings• angular resolution is not great
-> false electron candidates from miss-association
• Recommendations– fine segmentation of photon detector– large number of photo-electrons preferablefor precise position determination
Experiment: PHENIX
detector part requirements solution advantages disadvantages
mirror •Lrad ~ 0.5%•precise R < 1/200•small surface roughness (< 3 nm)
•segmented structure
•Rohacell + graphite-epoxy
•steel master• replication
• light weight~1300 g per mirror segment
• fine adjustment is needed; once for all
photodetector •sensitive to ~200 nm
•reasonable segmentation
•adoption of PMT + light collection funnel
•high stability -> easy operation
•small concern to gas quality
•high cost: ~400$ per PMT
• low segmentation
radiator •> 10 PE for ~1 particles
• low scintillation
• CO2–original choice was C2H6, and its use is pended due to safety reason
• non-flammable• small Lrad
• small N(PE)• small ring radius
optical layout, adjustment, monitoring
• spherical mirror + photon detector
• gain monitor
• photon detector behind the magnet iron
• LED + fiber for gain monitoring
• low flux in the detectors