Collider Detectors for Heavy Ion Physics W A

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 15 -Nov-99 W. A. Zajc 1

Outline l 2 Heavy Ion Collider(s) Previous q RHIC q LHC q l RHIC Program PHOBOS q BRAHMS q STAR q PHENIX q l LHC (CMS) q ALICE q 15 -Nov-99 W. A. Zajc

RHIC l l l 3 RHIC = Relativistic Heavy Ion Collider Located at Brookhaven National Laboratory Schedule: q q 15 -Nov-99 Commissioning: Jul-Aug, 1999 First physics run: ~Feb-00 through Aug-00 W. A. Zajc

RHIC Specifications l l 3. 83 km circumference Two independent rings q q l l 120 bunches/ring 106 ns crossing time Capable of colliding ~any nuclear species on ~any other species 4 6 1’ 3 5 4 2 1 Energy: è 500 Ge. V for p-p è 200 Ge. V for Au-Au (per N-N collision) l Luminosity q q 15 -Nov-99 Au-Au: 2 x 1026 cm-2 s-1 p-p : 2 x 1032 cm-2 s-1 (polarized) W. A. Zajc

5 Making Something from Nothing l Explore non-perturbative “vacuum” by melting it Temperature scale è Particle production è Our ‘perturbative’ region is filled with q u gluons u quark-antiquark pairs è A Quark-Gluon Plasma (QGP) l Experimental method: Energetic collisions of heavy nuclei l Experimental measurements: Use probes that are q q Auto-generated Sensitive to all time/length scales 15 -Nov-99 W. A. Zajc

6 What’s Different from “Ordinary” Colliders? l Obviously: Multiplicities q (Cross sections) q l But also: Hermeticity requirements q Rates q Low p. T physics q High p. T physics q Signals q 15 -Nov-99 W. A. Zajc

Hermeticity l A key factor in “most” collider detectors q q q l 7 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 d. Nch/dy ~ 1000 è exclusive event reconstruction “unfeasible” q But q u Seeking to characterize a state of matter u Large numbers statistical sampling of phase space a valid approach 15 -Nov-99 W. A. Zajc

Low p. T matters l 8 l Heavy ion physics takes Search for a phase transition place in phase space in hadronic matter q q Characteristic scale LQCD ~ 200 Me. V Flavor dynamics crucial both to transition and to its signatures q Coordinate space as important as momentum space q Measure via identical particle correlations (aka HBT ) Low p. T Particle Identification (PID) is crucial to QGP Physics 15 -Nov-99 W. A. Zajc

PID Techniques 9 The usual textbook examples… l Time-of-flight BRAHMS, PHOBOS, PHENIX l d. E/dx (in 1/b 2 region) PHENIX, PHOBOS, STAR l Cerenkov q Threshold (PHENIX), BRAHMS q RICH BRAHMS, PHENIX, STAR 15 -Nov-99 W. A. Zajc

(PID) Acceptances PHOBOS Acceptance 10 BRAHMS Acceptance STAR Acceptance 15 -Nov-99 W. A. Zajc

Tracking l l 11 Occupancies are typically 2 -15% More importantly, large number of tracks per event è Maximal projective ambiguities è Space points are essential q BRAHMS TPC q PHOBOS Si Pixels q PHENIX Pad Chambers q STAR TPC, Si Drift 15 -Nov-99 W. A. Zajc

Jet Physics at RHIC l Tremendous interest in hard scattering (and subsequent energy loss in QGP) at RHIC q q l 12 Predictions that d. E/dx ~ (amount of matter to be traversed) Due to non-Abelian nature of medium But: q q “Traditional” jet methodology fails at RHIC Dominated by the soft background: u For a typical jet cone R = 0. 33 (R 2 = DF 2 + Dh 2) have u l <n. SOFT> ~ 64 <ET> ~ 25 Ge. V Fluctuations in this soft background swamp any jet signal for p. T < ~ 40 Ge. V: Solution: q q Let R ~0 (PHENIX Dh x Df = 0. 01 x 0. 01) Then use high p. T leading particles 15 -Nov-99 W. A. Zajc

RHIC Luminosity l l l 13 It’s high! It’s an equal opportunity parton collider: Can accelerate essentially all species q q q Designed for p-p to Au-Au Asymmetric collisions (esp. p-A) allowed Good news / bad news: u u Permits many handles on systematics Permits in situ measurements of “background” p-p and p-A physics èDetectors must handle unparalleled dynamic range in rates and track densities 15 -Nov-99 W. A. Zajc

Other Differences l Event characterization q q q l 14 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 b Models q HEP has SM èReliable predictions of baseline phenomena q HI has only Sub-SM’s… u Even the baseline physics at RHIC and beyond is intrinsically unknown 15 -Nov-99 W. A. Zajc

15 Design Guidelines for QGP Detection Question: How to proceed with experimental design when (Partial) answers: l The QGP phase transition will not be “seen” at RHIC Instead it will emerge as a consistent framework for describing the observed phenomena ê Avoid single-signal detectors q l There are no* cross sections at RHIC Except s. GEOM ~ few barns s. CENTRAL ~ (1 -10)% s. GEOM but s. QGP ~ s. CENTRAL ? ? ê Preserve high-rate and triggering capabilities l Expect the unexpected High gluon density production of exotics? q Color topology high anti-baryon production? q New vacuum large isospin fluctuations? ê Maintain flexibility as long as $’s allow q 15 -Nov-99 W. A. Zajc

Approaches to QGP Detection 1. Deconfinement 4. Strangeness and Charm Production R(U) ~ 0. 13 fm < R(J/Y) ~ 0. 3 fm < R(Y ’ ) ~ 0. 6 fm Production of K+, K- mesons: ê Electrons, Muons ê 2. Chiral Symmetry Restoration Mass, width, branching ratio of F to e+e-, K+K- with d. M < 5 Mev: ê Electrons, Muons, Charged Hadrons Baryon susceptibility, color fluctuations, antibaryon production: ê Charged hadrons DCC’s, Isospin fluctuations: ê Photons, Charged Hadrons 3. Thermal Radiation of Hot Gas Prompt g, Prompt g * to e+e-, m+m - : ê Photons, Electrons, Muons 15 -Nov-99 16 Hadrons Production of F, J/Y, D mesons: ê Electrons, Muons 5. Jet Quenching High p. T jet via leading particle spectra: ê Hadrons, Photons 6. Space-Time Evolution HBT Correlations of p± p±, K± K± : ê Hadrons Summary: Electrons, Muons, Photons, Charged Hadrons W. A. Zajc

Screening by the QGP 17 In pictures: 15 -Nov-99 W. A. Zajc

PHOBOS 18 An experiment with a philosophy: q Global phenomena èlarge spatial sizes èsmall momenta q Minimize the number of technologies: u All Si-strip tracking u Si multiplicity detection u PMT-based TOF q 15 -Nov-99 Unbiased global look at very large number of collisions (~109) W. A. Zajc

PHOBOS Design 15 -Nov-99 19 W. A. Zajc

PHOBOS Details l Si tracking elements q q l 15 -Nov-99 20 15 planes/arm Front: “Pixels” (1 mm x 1 mm) Rear: “Strips” (0. 67 mm x 19 mm) 56 K channels/arm Si multiplicity detector q 22 K channels q |h| < 5. 3 W. A. Zajc

PHOBOS “Results” 15 -Nov-99 21 W. A. Zajc

BRAHMS 22 An experiment with an emphasis: q q Quality PID spectra over a broad range of rapidity and p. T Special emphasis: u Where do the baryons go? u How is directed energy transferred to the reaction products? q 15 -Nov-99 Two magnetic dipole spectrometers in “classic” fixed-target configuration W. A. Zajc

BRAHMS Acceptance l 23 Combination of q q q Tracking Time-of-Flight Cerenkov provides broad PID in y-p. T l Small dipole apertures è narrow in f BRAHMS Acceptance 15 -Nov-99 W. A. Zajc

BRAHMS Details 24 TOF Module situ RICH q q 15 -Nov-99 TPC in C 4 F 10 Multi-anode PMT readout W. A. Zajc

BRAHMS “Results” 15 -Nov-99 25 W. A. Zajc

STAR l An experiment with a challenge: q Magnet Coils TPC Endcap & MWPC 26 Track ~ 2000 charged particles in |h| < 1 Time Projection Chamber Silicon Vertex Tracker FTPCs ZCal Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter Central Trigger Barrel or TOF RICH 15 -Nov-99 W. A. Zajc

STAR Challenge 15 -Nov-99 27 W. A. Zajc

STAR Design 15 -Nov-99 28 W. A. Zajc

STAR Reality 15 -Nov-99 29 W. A. Zajc

STAR TPC Readout l l 30 12 sectors/side Large pads for good d. E/dx resolution in the Outer sector Small pads for good two-track resolution in the inner sector ~137 K channels 60 cm 190 cm 15 -Nov-99 W. A. Zajc

STAR SVT 31 One ladder installed for next running period 15 -Nov-99 W. A. Zajc

STAR EMC 32 Four modules installed for next running period 15 -Nov-99 W. A. Zajc

STAR TPC Data 33 From RHIC commissioning run Looks like collisions! But not beam-beam collisions 15 -Nov-99 W. A. Zajc

STAR “Results” 34 Demonstrate large hadronic rates from: F yield from ~12 minutes of running Large acceptance ~ 1 count per hour limit coupled with Large multiplicities (Assuming central triggers ) 15 -Nov-99 W. A. Zajc

35 PHENIX l l An experiment with something for everybody A complex apparatus to measure q q q Muon Arms West Arm Hadrons Muons Electrons Photons Executive summary: q Global MVD/BB/ZDC 3 station CSC 5 layer Mu. ID (10 X 0) p(m)>3 Ge. V/c South muon Arm High resolution High granularity 15 -Nov-99 Coverage (N&S) -1. 2< |y| <2. 3 -p < f < p DM(J/y )=105 Me. V DM(g) =180 Me. V East Arm Central Arms Coverage (E&W) -0. 35< y < 0. 35 30 o <|f |< 120 o DM(J/y )= 20 Me. V DM(g) =160 Me. V North muon Arm W. A. Zajc

PHENIX Design 15 -Nov-99 36 W. A. Zajc

PHENIX Reality 37 January, 1999 15 -Nov-99 W. A. Zajc

PHENIX Technologies l Event Characterization q q l Si strips and pads (MVD) Cerenkov (Beam-Beam) Tracking q Central Arms u u u q q q Time-of-Flight scintillators d. E/dx (TEC) See Friday’s talk by A. Frawley RICH TOF in Em. Calorimetry q q 15 -Nov-99 Cathode Strip Chambers (mu. Tr) Iarocci Tubes (mu. ID) Particle Identification q l Drift Chambers Pad Chambers Time Expansion Chamber (TEC) Muon Arms u l 38 Lead-scintillator (Pb. Sc) Pb-glass (Pb. Gl) W. A. Zajc

PHENIX PID 39 Rely on a variety of techniques to q Perform p/K/p… separation over a broad range u Time-of-flight in Beam-Beam/TOF-wall combination u Time-of-flight in Beam-Beam/Em. Cal combination u Use RICH above pion threshold ~ 4 Ge. V/c q Achieve e/p rejection in excess of 103 u RICH u TEC d. E/dx u Em. Cal shower shape, E/p match 15 -Nov-99 W. A. Zajc

PHENIX PID via TOF l 40 Superb Particle Identification for hadrons: q q Measure time difference between Beam (START) counters and “TOF” wall or Em. Cal elements. Beam-Beam: 2 x 64 Cerenkov radiators + PMT’s u s ~ 50 ps u q Time-of-Flight (TOF) wall: ~ 2000 PMT’s reading out ~1000 “slats” u s ~ 80 ps u q Em. Cal: Both Pb. Sc and Pb. Gl have timing capability (greatly extends coverage) u s(Pb. Sc) ~ 300 ps u s(Pb. Gl) ~ 400 ps u 15 -Nov-99 W. A. Zajc

41 PHENIX PID via Cerenkov Key Features: u u u 15 -Nov-99 Ring imaging Cherenkov with gaseous radiator Radiator gas: Most hadrons do not emit Cerenkov light ethane (n = 1. 00082) or methane (n = 1. 00044) Electron identification efficiency: ＲＩＣＨ Close to 100% for a single electron with momentum less than ~ 4 Ge. V/c Pion rejection factor: > 103 for a single charged pion. PMT array with momentum less than ~ 4 Ge. V/c Ring angular resolution: ~ 1 degree in both q and f Two ring separation: ~ few degrees in both q and f mirror Cerenkov photons from e+, e- are detected by an array of PMTs PMT array Central Magnet Electrons emit Cerenkov light in RICH gas volume W. A. Zajc

42 PHENIX PID via d. E/dx q q Additional quality PID information, especially for electron/hadron rejection, from energy loss measurements in Time Expansion Chamber: Key parameters: u Total of 29, 312 channels on day 1. 42, 944 channels after upgrade. u Determines particle species using d. E/dx information e / p < 2% at 500 Me. V/c with Xe gas e/ p ~ 5% at 500 Me. V/c with P 10 gas. i 15 -Nov-99 W. A. Zajc

PHENIX “Results” 43 High p. T hadrons: Vector mesons: q Superb e/p rejection q q q Very fine segmentation High rate capability Excellent momentum resolution 15 -Nov-99 W. A. Zajc

Di-Muon Physics 44 Much larger acceptance for vector mesons in either of the PHENIX muon arms è Physics rates compare well to existing fixed-target ``standards'': l Compilation by M. Leitch 15 -Nov-99 W. A. Zajc

RHIC ZDC’s l l ZDC Zero Degree Calorimeter Goals: q q l Uniform luminosity monitoring at all 4 intersections Uniform event characterization by all 4 experiments Process: q q 15 -Nov-99 45 Correlated Forward-Backward Dissociation stot = 11. 0 Barns (+/- few %) W. A. Zajc

RHIC Spin Physics l 46 A polarized hadron collider is uniquely suited to some spin measurements: q DG via u Direct photons u Hign p. T pions u J/Y production via q u W+/W- production u Polarized Drell-Yan l RHIC has been equipped q q To provide polarized beams of protons To make spin measurements of same in (at least) PHENIX and STAR 15 -Nov-99 W. A. Zajc

LHC l Heavy ion capabilities q l Pb+Pb at 5. 5 Te. V / nucleon (~ 25 times RHIC energy) Conditions q q q l 47 ~ 1027 cm-2 s-1 125 ns crossing time d. Nch/dy ~ 8000 Two experiments q q CMS ALICE (dedicated) 15 -Nov-99 W. A. Zajc

ALICE l l l 48 A large heavy ion experiment Both hadronic and muon capabilities Based on L 3 infrastructure 15 -Nov-99 W. A. Zajc

ALICE Design TOF RICH 49 Muon Tracker TPC Inner Tracking System PHOS 15 -Nov-99 W. A. Zajc

ALICE Technologies 50 Inner Tracking System 6 layers of Si drift, pixel, strip TPC |n| < 0. 9 (field cage prototype) TOF See Friday’s talk by M. Spegel 160 k PPC (150 m 2) RICH Cs. I photocathode (prototype in STAR) PHOS Pb-W 04 crystals Muon Tracking Cathode pad chambers 15 -Nov-99 W. A. Zajc

CMS l Use the superb muon resolution of CMS to study q q Upsilon sytematics Jet quenching opposite Z 0 m+m- 15 -Nov-99 51 See today’s talk by J. L. Faure W. A. Zajc

CMS and ALICE Muons 52 (Summary by G. Paic) 15 -Nov-99 W. A. Zajc

Summary l 53 The RHIC heavy ion community is ready to begin experiments with a set of detectors designed for the first dedicated heavy ion collider Great challenges in u Segmentation u Dynamic range u Data volumes have been or soon will be met l 15 -Nov-99 Even greater challenges await the heavy ion program at the LHC(!) W. A. Zajc