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Ring Image Cerenkov detector of PHENIX experiment at RHIC

The PHENIX-RHIC Cerenkov detector is used in the PHENIX experiment at RHIC to study high-energy density matter created in Au+Au collisions. It measures electrons, photons, hadrons, and muons in mid-rapidity and measures muons in forward and backward rapidity. This detector faces the challenge of handling a very high particle density.

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Ring Image Cerenkov detector of PHENIX experiment at RHIC

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  1. Ring Image Cerenkov detector of PHENIX experiment at RHIC PHENIX RICH group CNS, U.Tokyo (H.Hamagaki, S.Nishimura, K.Oyama) Florida State U. (R.Chappell, D.Crook, A.D.Frawley, M.Kennedy) KEK (Y.Akiba, K.Shigaki) Nagasaki IAS (K.Ebisu, H.Hara, Y.Nagasaka, Y.Tanaka) ORNL (M.S.Emery, G.G.moscone, J.W.Walker, A.L.Wintenberg, G.R.Young) SUNY at Stony Brook (R.Begay, J.Burward-Hoy, J.Ferriera, T.K.Hemmick, R.Hutter, S.Salomone) U.Tokyo (R.S.Hayano) Waseda U. (M.Hibino, J.Kikuchi, T.Matsumoto, T.Sakaguchi) Y. Akiba et. al. (PHENIX RICH)

  2. PHENIX Experiment at RHIC • One of two major experiment at RHIC • Study high energy density matter created in Au+Au collisions at RHIC (s1/2 = 200 A GeV) • Measure electrons, photons and hadrons in mid-rapidity and measure muons in forward and backward rapidity • A very high particle density (dNch/dy ~ 1000) is expected --- major experiemental challenge Y. Akiba et. al. (PHENIX RICH)

  3. Physics • Search for quark-gluon plasma (QGP) and other new physics in A+A collisions at RHIC • Measure as many signatures of QGP as possible • Electrons, photons, hadrons and muons • Electron and Electron pair measurement is of particular importance. • Little final state interaction • sensitive to early stage of collision • Interesting observations at SPS • J/Y suppression • Low mass pair enhancement Y. Akiba et. al. (PHENIX RICH)

  4. PHENIX Central Arm (1) • Two central arms measure electrons, photons and hadrons at mid-rapidity • Acceptance (one arm) -0.35 < h < 0.35 33.75 deg < f < 123.75 deg • Measure electrons, photons, and hadrons (p,p,K separated) • Good particle ID capability • Hadron PID • fine resolution TOF (s ~ 100ps) • EMCAL TOF (s ~ 300 ps) • Electron ID • RICH (the primary eID device) • EMCAL • TEC (dE/dx) Y. Akiba et. al. (PHENIX RICH)

  5. PHENIX Central Arm (2) • Charged particles are tracked by set of tracking systems • DC (Drift Chambers) • PC (PAD chambers) • TEC (Time Expansion Chambers) • RICH detector is sandwiched by tracking systems, and it provides electron identification of reconstructed tracks • EMCAL and TEC also provide electron ID • About 300 charged particles are expected in the acceptance of central arms in central Au+Au collisions Y. Akiba et. al. (PHENIX RICH)

  6. Electron Measurement in PHENIX • what to be measured • di-electron spectra • single electron spectra • “background” sources • Dalitz decay • heavy quarks • photon conversion • hadron mis-ID • requirements for eID • physics goal dependent • pt dependent • roughly 102 ~ 104 expected e/p ratio Y. Akiba et. al. (PHENIX RICH)

  7. Cerenkov photons from e+ or e- are detected by array of PMTs Most hadrons do not emit Cerenkov light mirror ＲＩＣＨ PMT array PMT array Electrons emit Cerenkov photons in RICH. Central Magnet PHENIX RICH • RICH is the primary electron ID device of PHENIX • hadron rejectionat 104 level for single track • full acceptance coverage for PHENIX central arms |y| < 0.35 ; df = 90 degrees x 2 • threshold gas Cherenkov C2H6 (gth ~ 25) or CO2( gth ~ 35) eID pt range : 0.2 ~ 4 GeV/c • PMT array readout 5,120 channels in 2 arms pixel size ~ 1 degree x 1 degree • 2-D angles (q,f) of electron tracks were determined from center of Cerenkov ring, and associated with the tracks reconstructed by DC+PC+TEC Y. Akiba et. al. (PHENIX RICH)

  8. Gas vessel Two RICH detectors one for each arm - 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 lenghth Gas: 0.41 % (ethane) Windows: 0.2% Mirror panels: 0.53% Mirror support: 1.0% Total: 2.14% The vessels are designed and fabricated at FSU Y. Akiba et. al. (PHENIX RICH)

  9. RICH PMT Hamamatsu H3171S • Cathode Diameter: 25 mm • Tube Diameter: 29 mm • Cathode: Bialkali • Gain: > 107 • Operation Voltage: - 1400 ~ -1800 V • Dark current: < 100 nA at Gain=107 • Cathode Luminous: >70 (mA/lm) • Blue Sensitivity: > 9(mA/lm) • Quantum efficiency: >19% at 300 nm >5 % at 200 nm • Rise Time: < 2.5n • Transit Time Spread: < 750ps Total number of PMTs in RICH: 5120 Y. Akiba et. al. (PHENIX RICH)

  10. Relative Output Magnetic filed (Gauss) RICH PMT(2) • Each PMT is housed in a magnetic shielding case • First 900 PMTs • Soft iron and mu-metal • Other 4220 PMTs: • FERROPERM (NKK) • A Winstone cone shaped conical mirror is attached to each PMT to collect Cerenkov light • Entrance: 50 mm • Exit: 25 mm • Angular cut off: 30 deg Magnetic Shielding Case design Effect of magnetc shielding case Y. Akiba et. al. (PHENIX RICH)

  11. PMT super module • 32 PMTs are assembled into 2x16 sub-assembly called “super module” • PMTs are grouped by its gain so that 8 tubes can share the same HV • Supermodules are assembled and tested at StonyBrook, and sent to BNL • At BNL, winston cones are installed in PMTs, and the completed supermodules are installed in the RICH vessel Y. Akiba et. al. (PHENIX RICH)

  12. PMT QA • All PMTs are tested at Tokyo, and sent to StonyBrook. Gain and operating voltage is measured at manufacturer • At StonyBrook, PMTs are assembled to supermodules • The gain of each PMT in a supermodule is measured from the single photo-electron peak • After the gain measurement, supermoduels are “burn-in” for 3 weeks in a dark room. The tubes failed in burn-in period are replaced. • After the burn-in, the gain of the tubes are measured again, and shipped to BNL for installation. Y. Akiba et. al. (PHENIX RICH)

  13. RICH PMT array • Supermodule are installed in RICH vessel to form a tightly packed PMT array • 40 super-modules per one side of a RICH vessel, forming a 16x80 array • Two arrays per RICH vessel, 4 arrays in two arms. Total number of PMTs: 5120 Completed PMT array of the first RICH detector. There is an identical PMT array in the opposite side of the RICH Y. Akiba et. al. (PHENIX RICH)

  14. Mirror(1) • Segmented spherical mirror • Radius: 403 cm • 48 panels / arm • 2 (side) x 2 (z) x 12 (f) • Reflection surface • Aluminum • Total area: 20 m2 / arm • Substrate • graphite fiber epoxy • only 0.53 % of radiation length • Mirror support structure • graphite fiber, Delrin, • 1 % of radiation length (ave.) Structure of the mirror Y. Akiba et. al. (PHENIX RICH)

  15. Mirror(2) • Mirror pales are mounted by adjustable 3 point mounts on the frame bars • 2 x 12 miror panels forms a spherical surface for one side of a RICH vessel • 2 spherical surfaces in a vessel, total of 48 panels Design of 3 points mirror mounts Completed mirror array of the first RICH Y. Akiba et. al. (PHENIX RICH)

  16. RICH (mirror alignment) • After mirrors are installed, 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). • Mirror mounts are adjusted so that all optical targets are within 0.25 mm of the designed sperical surface. BNL survey crew were measuring the optical targets on the mirror during the mirror alignment. Y. Akiba et. al. (PHENIX RICH)

  17. RICH (after mirror alignment) Y. Akiba et. al. (PHENIX RICH)

  18. RICH FEE Chain The front end electronics (FEE) for the RICH(Ring Imaging Cherenkov counter) subsystem for the PHENIX experiment at RHIC,BNL is being developed. RICH is a major device for electron identification at PHENIX. Individual Cherenkov photons are detected by total of 5120 PMT’s. The RICH FEE has to record timing and charge information of photons for selected events. As shown in figure below, the signal from PMT will be amplified by Pre Amplifier and sent to Integrator and CFD. Integrator integrates charge from PMT and it will be amplified by VGA, then will go to AMU(Analog Memory Unit). On the other hand, CFD and TAC convert timing information of PMT signal to voltage data, then also timing data will be accumulated in AMU. Furthermore, integrated charge information after Integrator will be sent to LVL-1 Sum which is trigger information. And the data only specified by Level-1 Trigger will be AD converted by ADC. Integrator, VGA, CFD and TAC will be constructed in one chip. And AMU and ADC are also in one chip. Y. Akiba et. al. (PHENIX RICH)

  19. Pre-amplifiers A Preamplifier Card consists of 16 Preamplifiers. This custom Preamplifier Card has special shape (it has diagonal input connector), and use surface mount parts. INPUT RICH VESSEL OUTPUT to FEE The gain of Preamplifier is 10. The dynamic range is 0 to 200mV The first RICH detector with pre-amplifiers installed on the signal feed-through Y. Akiba et. al. (PHENIX RICH)

  20. RICH FEE The figure in this page shows how PMT’s will be connected to the FEE and data flow from PMT’s to PHENIX Data Collection System (DCM) via our FEE We use 9U VME crate and one crate has 10 AMU/ADC cards (only half of the crate can be seen in the figure). One AMU/ADC board has 64 channels. Then one crate can read 640 channels of PMT outputs. RICH has 5120 channels of PMT’s, then we fabricate 8 crates in total. RHIC Bunch Crossing timing (around 9.6MHz) comes from PHENIX Master timing system via G-LINK. Also trigger code and other control (Stop or Run, etc.) will go into Control Board placed in the center of FEE crate. Control Board distributes timing data and control data transfer from each AMU/ADC Board to Readout Board. Readout board collects data from AMU/ADC Boards and format and send to PHENIX D.C.M. Also AMU/ADC Boards make Level-1 trigger sum and it will be sent to PHENIX LVL-1 system by the Level-1 Trigger Board. Y. Akiba et. al. (PHENIX RICH)

  21. Trigger Sum Current Generator • Integrator • Variable Gain Amp． • CFD • TAC • 2 ways of 4ch Trigger Sum • Programmable Integrator, VGA, etc.. • ８Ｃｈ． Integrator/TAC ASIC INT/TAC ASCI is developed at ORNL Y. Akiba et. al. (PHENIX RICH)

  22. Capacitor AMU/ADC ASIC • Developed at ORNL for PHENIX • 64 Cells AMU x 32 Channels • 10,11,12bit variable bits ADC Y. Akiba et. al. (PHENIX RICH)

  23. RICH performace (test beam) • A small prototype RICH was tested at KEK PS and BNL AGS • e/p separation better than 104 with electron efficiency >99% was achieved by counting number of PMT hits alone • Time resolution of ~ 250 ps per PMT hits achieved. Consistent with transit time spread. • N0 ~ 120 /cm obtained pion electron Number of PMT hits PMT timing Y. Akiba et. al. (PHENIX RICH)

  24. RICH performance (1) • A very high particle density is expected in Au+Au collisions at RHIC. dN/dy ~ 1000 is expected in central Au+Au collisions. • Photon conversions in PHENIX detector causes many background electrons within PHEINX acceptance. Those electrons produces hits in the RICH • Background hits and high particle density reduces the e/p rejection power of RICH in Au+Au collisions. This effect was studied by a detailed GEANT simulation PMT hits pattern in central Au+Au collisions simulated by HIJING event generator and PISA GEANT program Y. Akiba et. al. (PHENIX RICH)

  25. RICH performance (2) • simulated w/ • various eID cuts • different radiator gases • possible shielding • rejection poweree/eh • function of occupancy • 200 ~ 1500 in central Au+Au events by Y.Akiba w/ shield Y. Akiba et. al. (PHENIX RICH)

  26. Summary and Outlook • PHENIX RICH is the primary electron ID device of the experiment • Construction is well underway for the detector and the FEE • e/p rejection 200-1500 expected in Au+Au collisions • The first RICH detector of PHENIX was completed, and was installed on West Arm of PHENIX in October 1998 • The construction of the second RICH is in progress. It will be completed by June 1999, to be ready for the first year run of RHIC starting at November 1999. Y. Akiba et. al. (PHENIX RICH)

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