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RICH in the PHENIX Experiment at RHIC

RICH in the PHENIX Experiment at RHIC. Hideki Hamagaki Center for Nuclear Study Graduate School of Science, University of Tokyo. RHIC. Brookhaven National Laboratory, USA The first heavy-ion collider on the earth Two independent rings with circular length = 3.83 km Energy at CMS

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RICH in the PHENIX Experiment at RHIC

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  1. RICH in the PHENIX Experimentat RHIC Hideki Hamagaki Center for Nuclear Study Graduate School of Science, University of Tokyo

  2. RHIC • 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 International CBM-RICH workshop at GSI

  3. PHENIX Detector System A complex apparatus to measure: Hadrons, Muons, Electrons, Photons Central Arms Coverage (E&W) -0.35< y < 0.35 30o <|f |< 120o Muon Arms Coverage (N&S) -1.2< |y| <2.3 -p < f < p International CBM-RICH workshop at GSI

  4. Central 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) International CBM-RICH workshop at GSI

  5. Guiding 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 International CBM-RICH workshop at GSI

  6. Cerenkov photons are detected by array of PMTs Most hadrons do not emit Cerenkov light mirror RICH PMT array PMT array Electrons emit Cerenkov photons Central Magnet PHENIX-RICH overview Acceptance coverage • |h| < 0.35 ; df = 90 degrees x 2 Three major components • Gas vessel • C2H6 (gth ~ 25) or CO2(gth ~ 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 (q,f) of electron tracks • ~1 degree x ~1 degree BNL, FSU, KEK, SUNY/SB, NIAS, ORNL, U.Tokyo, Waseda International CBM-RICH workshop at GSI

  7. RICH 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% International CBM-RICH workshop at GSI

  8. Gas 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 mm Kapton with supporting graphite-epoxy beams • black vinyl coated polyester for light shield International CBM-RICH workshop at GSI

  9. RICH 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 mmf, Exit: 25 mmf, Angular cut off = 30  Magnetic shielding case • FERROPERM (NKK); high susceptibility + large saturation field International CBM-RICH workshop at GSI

  10. RICH 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 International CBM-RICH workshop at GSI

  11. 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 (f) • 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 mm • 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 International CBM-RICH workshop at GSI

  12. Mirror Support Structure • Frame bars • graphite fiber • 1 % of radiation length (ave.) • Mirror panels are mounted by adjustable 3 point mounts on the frame bars International CBM-RICH workshop at GSI

  13. Mirror 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). International CBM-RICH workshop at GSI

  14. Front 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 International CBM-RICH workshop at GSI

  15. Controller Module Readout 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 • Transferring Data to PHENIX-DCM using • G-LINK at the maximum speed of 800 Mbps • G-LINK Transfer asynchronous to BUS Transfer inside RICH-FEE using four FIFOs (Depth: 9 events) G-Link Transmitter ROC Phase Shifter Readout FIFO DSU/ALM Analog Processing (AMU/ADC) Module K2 BTS • 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 AMU/ADC Chip Integrator+TAC (RICH) Chip AMU/ADC Burst Controller International CBM-RICH workshop at GSI

  16. Number of Photo-electrons • resolution for 1pe s/MPH(1pe) ~ 0.26 • number of photo-electrons per ring ~ 10.8 • N0 ~ 120 (Npe = N0 sin2qC) International CBM-RICH workshop at GSI

  17. Association 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 International CBM-RICH workshop at GSI

  18. Performance Limitation • Association is not seen well in high multiplicity events • Still works great to enrich electrons International CBM-RICH workshop at GSI

  19. Rejection 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 Central Blue: Real data for Au+Au Peripheral Red: Real data for Au+Au Central International CBM-RICH workshop at GSI

  20. E/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 International CBM-RICH workshop at GSI

  21. J/y in Au-Au collisions at RHIC • In Run-4, 240 mb-1 recorded with improved detector performance • ~100 times more J/y signals expected than in Run-2 • Outstanding J/y peak in e+e- invariant mass spectrum in 200 AGeV Au + Au central collisions International CBM-RICH workshop at GSI

  22. RdAu 1.2 1.0 |y|<0.35 0.8 0.6 0.4 0.2 Rapidity Some results on J/y • Nuclear modification factor of J/y yield for d + Au collisions • for Au + Au and Cu + Cu collisions International CBM-RICH workshop at GSI

  23. Thermal 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 International CBM-RICH workshop at GSI

  24. Real and Mixed e+e- Distribution Real - Mixed with systematic errors Run2 AuAu Minimum Bias 0 1 2 3 [GeV/c2] 0 1 2 3 [GeV/c2] Combinatorials 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 International CBM-RICH workshop at GSI

  25. “combinatorial pairs” total background S/B ~ 1/500 Irreducible charm background all signal charm signal How 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) International CBM-RICH workshop at GSI

  26. For 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 preferable for precise position determination International CBM-RICH workshop at GSI

  27. Experiment: PHENIX

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