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Collider Detectors for Heavy Ion Physics

Collider Detectors for Heavy Ion Physics. W.A. Zajc Columbia University. Thanks to: Y. Akiba, M. Baker, D. Cebra, J. Dodd, Y. Fisyak, T. Hallman, M. Lisa, D. Lynn, J. Schukraft, J. Thomas, F. Videbaek, S. White. Outline. Heavy Ion Collider(s) Previous RHIC LHC RHIC Program PHOBOS

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Collider Detectors for Heavy Ion Physics

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  1. Collider Detectors for Heavy Ion Physics W.A. ZajcColumbia University • Thanks to: • Y. Akiba, M. Baker, D. Cebra, J. Dodd, Y. Fisyak, T. Hallman, M. Lisa, D. Lynn, J. Schukraft, J. Thomas, F. Videbaek, S. White W.A. Zajc

  2. Outline • Heavy Ion Collider(s) • Previous • RHIC • LHC • RHIC Program • PHOBOS • BRAHMS • STAR • PHENIX • LHC • (CMS) • ALICE W.A. Zajc

  3. RHIC • RHIC = Relativistic Heavy Ion Collider • Located at Brookhaven National Laboratory • Schedule: • Commissioning: Jul-Aug, 1999 • First physics run: ~Feb-00 through Aug-00 W.A. Zajc

  4. RHIC Specifications • 3.83 km circumference • Two independent rings • 120 bunches/ring • 106 ns crossing time • Capable of colliding ~any nuclear species on ~any other species • Energy: • 500 GeV for p-p • 200 GeV for Au-Au(per N-N collision) • Luminosity • Au-Au: 2 x 1026 cm-2 s-1 • p-p : 2 x 1032 cm-2 s-1(polarized) 6 3 5 1’ 4 1 2 W.A. Zajc

  5. Making Something from Nothing • Explore non-perturbative “vacuum” by melting it • Temperature scale • Particle production • Our ‘perturbative’ region is filled with • gluons • quark-antiquark pairs • A Quark-Gluon Plasma (QGP) • Experimental method: Energetic collisions of heavy nuclei • Experimental measurements:Use probes that are • Auto-generated • Sensitive to all time/length scales W.A. Zajc

  6. What’s Different from “Ordinary” Colliders? • Obviously: • Multiplicities • (Cross sections) • But also: • Hermeticity requirements • Rates • Low pT physics • High pT physics • Signals W.A. Zajc

  7. Hermeticity • A key factor in “most” collider detectors • Goal of essentially complete event reconstruction • Discovery potential of missing momentum/energy now well established • Of course this due to manifestation of new physics via electroweak decays • In heavy ion physics • dNch/dy ~ 1000 • exclusive event reconstruction “unfeasible” • But • Seeking to characterize a state of matter • Large numbers  statistical sampling of phase space a valid approach W.A. Zajc

  8. Low pT matters • Heavy ion physics takes place in phase space • Coordinate space as important as momentum space • Measure via identical particle correlations(aka HBT ) • Search for a phase transition in hadronic matter • Characteristic scale LQCD ~ 200 MeV • Flavor dynamics crucial both to transition and to its signatures Low pT Particle Identification (PID) is crucial to QGP Physics W.A. Zajc

  9. PID Techniques The usual textbook examples… • Time-of-flight BRAHMS, PHOBOS, PHENIX • dE/dx (in 1/b2 region) PHENIX, PHOBOS, STAR • Cerenkov • Threshold (PHENIX), BRAHMS • RICH BRAHMS, PHENIX, STAR W.A. Zajc

  10. BRAHMS Acceptance (PID) Acceptances PHOBOS Acceptance STAR Acceptance W.A. Zajc

  11. Tracking • Occupancies are typically 2-15% • More importantly, large number of tracks per event • Maximal projective ambiguities • Space points are essential • BRAHMS TPC • PHOBOS Si Pixels • PHENIX Pad Chambers • STAR TPC, Si Drift W.A. Zajc

  12. Jet Physics at RHIC • Tremendous interest in hard scattering(and subsequent energy loss in QGP) at RHIC • Predictions that dE/dx ~ (amount of matter to be traversed) • Due to non-Abelian nature of medium • But: • “Traditional” jet methodology fails at RHIC • Dominated by the soft background: • For a typical jet cone R = 0.33 (R2 = DF2 + Dh2) have <nSOFT> ~ 64 <ET> ~ 25 GeV • Fluctuations in this soft background swamp any jet signal for pT < ~ 40 GeV: • Solution: • Let R ~0 (PHENIX Dh x Df = 0.01 x 0.01) • Then use high pT leading particles • Investigate by (systematics of) high-pT single particles W.A. Zajc

  13. RHIC Luminosity • It’s high! • It’s an equal opportunity parton collider: • Can accelerate essentially all species • Designed for p-p to Au-Au • Asymmetric collisions (esp. p-A) allowed • Good news / bad news: • Permits many handles on systematics • Permits in situmeasurements of “background” p-p and p-A physics • Detectors must handle unparalleled dynamic range in rates and track densities W.A. Zajc

  14. Other Differences • Event characterization • Impact parameter b is well-defined in heavy ion collisions • Event multiplicity predominantly determined by collision geometry • Characterize this by global measures of multiplicit and/or transverse energy • Models • HEP has SM • Reliable predictions of baseline phenomena • HI has only Sub-SM’s… • Even the baseline physics at RHIC and beyond is intrinsically unknown b W.A. Zajc

  15. Design Guidelines for QGP Detection Question: How to proceed with experimental design when (Partial) answers: • The QGP phase transition will not be “seen” at RHIC • Instead it will emerge as a consistent framework for describing the observed phenomena • Avoid single-signal detectors • There are no* cross sections at RHIC • Except • sGEOM ~ few barns • sCENTRAL ~ (1-10)% sGEOM • but sQGP ~ sCENTRAL ?? • Preserve high-rate and triggering capabilities • Expect the unexpected • High gluon density  production of exotics? • Color topology  high anti-baryon production? • New vacuum  large isospin fluctuations? • Maintain flexibility as long as $’s allow W.A. Zajc

  16. Approaches to QGP Detection 1. Deconfinement R(U) ~ 0.13 fm < R(J/Y) ~ 0.3 fm < R(Y ’ ) ~ 0.6 fm • Electrons, Muons 2. Chiral Symmetry Restoration Mass, width, branching ratio of F to e+e-, K+K- with dM < 5 Mev: • Electrons, Muons, Charged Hadrons Baryon susceptibility, color fluctuations, anti-baryon production: • Charged hadrons DCC’s, Isospin fluctuations: • Photons, Charged Hadrons 3. Thermal Radiation of Hot Gas Prompt g, Prompt g * toe+e-, m+m - : • Photons, Electrons, Muons 4. Strangeness and Charm Production Production of K+, K- mesons: • Hadrons Production of F, J/Y, D mesons: • Electrons, Muons 5. Jet Quenching High pT jet via leading particle spectra: • Hadrons, Photons 6. Space-Time Evolution HBT Correlations of p±p±, K± K± : • Hadrons Summary: Electrons, Muons, Photons, Charged Hadrons W.A. Zajc

  17. Screening by the QGP In pictures: W.A. Zajc

  18. PHOBOS An experiment with a philosophy: • Global phenomena • large spatial sizes • small momenta • Minimize the number of technologies: • All Si-strip tracking • Si multiplicity detection • PMT-based TOF • Unbiased global look at very large number of collisions (~109) W.A. Zajc

  19. PHOBOS Design W.A. Zajc

  20. PHOBOS Details • Si tracking elements • 15 planes/arm • Front: “Pixels” (1mm x 1mm) • Rear: “Strips”(0.67mm x 19mm) • 56K channels/arm • Si multiplicity detector • 22K channels • |h| < 5.3 W.A. Zajc

  21. PHOBOS “Results” W.A. Zajc

  22. BRAHMS An experiment with an emphasis: • Quality PID spectra over a broad range of rapidity and pT • Special emphasis: • Where do the baryons go? • How is directed energy transferred to the reaction products? • Two magnetic dipole spectrometers in “classic” fixed-target configuration W.A. Zajc

  23. BRAHMS Acceptance BRAHMS Acceptance • Combination of • Tracking • Time-of-Flight • Cerenkov provides broad PID in y-pT • Small dipole apertures • narrow in f W.A. Zajc

  24. BRAHMS Details TOF Module TPC in situ RICH • C4F10 • Multi-anode PMT readout W.A. Zajc

  25. BRAHMS “Results” W.A. Zajc

  26. Time Projection Chamber Magnet Coils Silicon Vertex Tracker TPC Endcap & MWPC FTPCs ZCal ZCal Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter Central Trigger Barrel or TOF RICH STAR • An experiment with a challenge: • Track ~ 2000 charged particles in |h| < 1 W.A. Zajc

  27. STAR Challenge W.A. Zajc

  28. STAR Design W.A. Zajc

  29. STAR Reality W.A. Zajc

  30. 60 cm 190 cm STAR TPC Readout • 12 sectors/side • Large pads for good dE/dx resolution in the Outer sector • Small pads for good two-trackresolution in the inner sector • ~137K channels W.A. Zajc

  31. STAR SVT One ladder installed for next running period W.A. Zajc

  32. STAR EMC Four modules installed for next running period W.A. Zajc

  33. STAR TPC Data From RHIC commissioning run Looks like collisions! But not beam-beam collisions W.A. Zajc

  34. STAR “Results” Demonstrate large hadronic rates from: Large acceptance coupled with Large multiplicities (Assuming centraltriggers ) ~ 1 count per hour limit F yield from ~12 minutes of running W.A. Zajc

  35. PHENIX GlobalMVD/BB/ZDC • An experiment with something for everybody • A complex apparatus to measure • Hadrons • Muons • Electrons • Photons Executive summary: • High resolution • High granularity Muon Arms Coverage (N&S) -1.2< |y| <2.3 -p < f < p DM(J/y )=105MeV DM(g) =180MeV 3 station CSC 5 layer MuID (10X0) p(m)>3GeV/c WestArm East Arm South muon Arm North muon Arm Central Arms Coverage (E&W) -0.35< y < 0.35 30o <|f |< 120o DM(J/y )= 20MeV DM(g) =160MeV W.A. Zajc

  36. PHENIX Design W.A. Zajc

  37. PHENIX Reality January, 1999 W.A. Zajc

  38. PHENIX Technologies • Event Characterization • Si strips and pads (MVD) • Cerenkov (Beam-Beam) • Tracking • Central Arms • Drift Chambers • Pad Chambers • Time Expansion Chamber (TEC) • Muon Arms • Cathode Strip Chambers (muTr) • Iarocci Tubes (muID) • Particle Identification • Time-of-Flight scintillators • dE/dx (TEC) • RICH • TOF in EmCal • Calorimetry • Lead-scintillator (PbSc) • Pb-glass (PbGl) See Friday’s talk by A. Frawley W.A. Zajc

  39. PHENIX PID Rely on a variety of techniques to • Perform p/K/p… separation over a broad range • Time-of-flight in Beam-Beam/TOF-wall combination • Time-of-flight in Beam-Beam/EmCal combination • Use RICH above pion threshold ~ 4 GeV/c • Achieve e/p rejection in excess of 103 • RICH • TEC dE/dx • EmCal shower shape, E/p match W.A. Zajc

  40. PHENIX PID via TOF • Superb Particle Identification for hadrons: • Measure time difference between Beam-Beam (START) counters and “TOF” wall or EmCal elements. • Beam-Beam: • 2 x 64 Cerenkov radiators + PMT’s • s ~ 50 ps • Time-of-Flight (TOF) wall: • ~ 2000 PMT’s reading out ~1000 “slats” • s ~ 80 ps • EmCal: • Both PbSc and PbGl have timing capability(greatly extends coverage) • s(PbSc) ~ 300 ps • s(PbGl) ~ 400 ps W.A. Zajc

  41. Most hadrons do not emit Cerenkov light mirror Cerenkov photons from e+,e- are detected by an array of PMTs ＲＩＣＨ PMT array PMT array Electrons emit Cerenkov light in RICH gas volume Central Magnet PHENIX PID via Cerenkov Key Features: • Ring imaging Cherenkov with gaseous radiator • Radiator gas:ethane (n = 1.00082) or methane (n = 1.00044) • Electron identification efficiency: Close to 100% for a single electron with momentum less than ~ 4 GeV/c • Pion rejection factor: > 103 for a single charged pion with momentum less than ~ 4 GeV/c • Ring angular resolution: ~ 1 degree in both q andf • Two ring separation: ~ few degrees in both q andf W.A. Zajc

  42. PHENIX PID via dE/dx • Additional quality PID information, especially for electron/hadron rejection, from energy loss measurements in Time Expansion Chamber: • Key parameters: • Total of 29,312 channels on day 1. 42,944 channels after upgrade. • Determines particle speciesusing dE/dx informatione / p < 2% at 500 MeV/c with Xe gas e/ p ~ 5% at 500 MeV/c with P10 gas. i W.A. Zajc

  43. PHENIX “Results” High pT hadrons: • Very fine segmentation • High rate capability Vector mesons: • Superb e/p rejection • Excellent momentum resolution W.A. Zajc

  44. Di-Muon Physics • Much larger acceptance for vector mesons in either of the PHENIX muon arms • Physics rates compare well to existing fixed-target ``standards'': Compilation by M. Leitch W.A. Zajc

  45. RHIC ZDC’s • ZDC  Zero Degree Calorimeter • Goals: • Uniform luminosity monitoring at all 4 intersections • Uniform event characterization by all 4 experiments • Process: • Correlated Forward-Backward Dissociation • stot = 11.0 Barns (+/- few %) W.A. Zajc

  46. A polarized hadron collider is uniquely suited to some spin measurements: DG via Direct photons Hign pT pions J/Y production via W+/W- production Polarized Drell-Yan RHIC has been equipped To provide polarized beams of protons To make spin measurementsof same in (at least)PHENIX and STAR RHIC Spin Physics W.A. Zajc

  47. LHC • Heavy ion capabilities • Pb+Pb at 5.5 TeV / nucleon (~ 25 times RHIC energy) • Conditions • ~ 1027 cm-2 s-1 • 125 ns crossing time • dNch/dy ~ 8000 • Two experiments • CMS • ALICE (dedicated) W.A. Zajc

  48. ALICE • A large heavy ion experiment • Both hadronic and muon capabilities • Based onL3 infrastructure W.A. Zajc

  49. ALICE Design TOF RICH Muon Tracker TPC Inner Tracking System PHOS W.A. Zajc

  50. ALICE Technologies Inner Tracking System 6 layers of Si drift, pixel, strip TPC |n| < 0.9 (field cage prototype) TOF 160k PPC (150 m2) RICH CsI photocathode (prototype in STAR) PHOS Pb-W04 crystals Muon Tracking Cathode pad chambers See Friday’s talk by M. Spegel W.A. Zajc

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