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Dilepton measurements in heavy ion collisions: fixed-target versus collider experiments

Dilepton measurements in heavy ion collisions: fixed-target versus collider experiments. 1. Experimental setups 2. Multiplicities 3. Luminosities 4. Rates. Dilepton sources in Heavy-ion Collisions . Single electron spectra central Au+Au collisions 25 AGeV. Background sources

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Dilepton measurements in heavy ion collisions: fixed-target versus collider experiments

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  1. Dilepton measurements in heavy ion collisions:fixed-target versus collider experiments 1. Experimental setups 2. Multiplicities 3. Luminosities 4. Rates

  2. Dilepton sources in Heavy-ion Collisions

  3. Single electron spectra central Au+Au collisions 25 AGeV Background sources 1. external pair conversion:   e+e- 2.Dalitz-decays: 0  e+e- (BR = 1.2·10-2)   e+e- (BR = 4.9·10-3) 3. Bremsstrahlung: pn  pn e+e- 4. misidentified pions Background in muon measurements: π→μν, K→μν   μ+μ- (can be determined by  μ+μ- )

  4. The pioneering experiment: DLS at the Bevalac G. Roche et al., Phys. Lett. B 226 (1989) 228 Acceptance for e+e- pairs: 0.3% Massresolution: m/m = 10%

  5. Ring Imaging Cherenkov detector (RICH) Bestimmung der Teilchen- Geschwindigkeit durch Messung von θ (Ringradius des Lichtkegels) cosθα = 1/(βn)

  6. DLS data DLS-data: R.J. Porter et al.: Phys. Rev. Lett. 79 (1997) 1229 BUU calculation: E.L. Bratkovskaya et al.: Nucl. Phys. A634 (1998) 168

  7. HADES at GSI

  8. HADES

  9. CERES/NA45 at SPS

  10. Electron-positron pairs from CERES CERES 2000: 159 AGeV Pb+Au beam intensity: 106 ions / spill 1 spill = 4 s beam and 15 s pause targets: 13 x 25 μm Au ( ~ 1 % interaction) trigger: 8% most central Event rate = 470 / spill (~ 25 Hz = 15 Mio events/week)

  11. Low mass vector mesons (CERES/CERN) Data: ~ 180 signal pairs Calculations by R. Rapp: thick dashed line: unmodified rho thick dashed-dotted line: in-medium dropping rho mass thick solid line: in-medium spread rho width D.Adamova et al., PRL 91 (2003) 042301

  12. muon trigger and tracking iron wall magnetic field targets hadron absorber muon other tracks Muon identification: NA38/50/60 2.5 T dipole magnet vertex tracker beam tracker Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muonsbefore they suffer multiple scattering in the absorberand match them to the tracks measured in the muon spectrometer Improved kinematics; dimuon mass resolution at the :~20 MeV/c2 (instead of 80 MeV/c2 in NA50)Origin of muons can be accurately determined

  13. Dimuon pairs measured by NA60 (CERN) In+In 158 AGeV 5-week-long run in Oct.–Nov. 2003 ~ 4 × 1012 ions delivered in total 440000 signal pairs

  14. sNN = (E1 + E2)2 – (p1 + p2)2 collider: p1 + p2 = 0 → sNN = E1 + E2 fixed target: E2 = m, p2 = 0 sNN = (Ekin+ 2m)2 – p12 sNN = 2m·(Ekin+ 2m) for Ekin>> m : sNN = 1.4· Ekin

  15. g p DC e+ e- PC1 magnetic field & tracking detectors PC3 PHENIX Physics Capabilities designed to measure rare probes:+ high rate capability & granularity + good mass resolution and particle ID - limited acceptance Au-Au & p-p spin • 2 central arms: electrons, photons, hadrons • charmonium J/, ’ -> e+e- • vector mesonr, w,  -> e+e- • high pTpo, p+, p- • direct photons • open charm • hadron physics • 2 muon arms: muons • “onium” J/, ’,  -> m+m- • vector meson -> m+m- • open charm • combined central and muon arms: charm production DD -> em • global detectors forward energy and multiplicity • event characterization

  16. PHENIX data Data absolutely normalized Cocktail filtered in PHENIX acceptance Charm from PYTHIA Single electron non photonic spectrum w/o angular correlations sc= Ncoll x 567±57±193mb submitted to Phys. Rev. Lett arXiv:0706.3034 • Low-Mass Continuum:enhancement 150 <mee<750 MeV: 3.4±0.2(stat.) ±1.3(syst.)±0.7(model) • Intermediate-Mass Continuum: • Single-e  pt suppression & non-zero v2: charm thermalized? • PYTHIA single-e pT spectra softer than p+p but coincide with Au+Au • Angular correlations unknown • Room for thermal contribution?

  17. CERN and the Large Hadron Collider (LHC)

  18. The ALICE experiment at CERN

  19. Transition radiation Total energy  γ Θ = 1 /γ

  20. Transition Radiation Detectors (TRD) p = 1 GeV/c γe = 2000 γ = 7.1

  21. Facility for Antiproton and Ion Research (FAIR) primary beams • 5x1011/s; 1.5-2 GeV/u; 238U28+ • factor 100-1000 increased intensity • 4x1013/s 90 GeV protons • 1010/s 238U 35 GeV/u ( Ni 45 GeV/u) secondary beams • rare isotopes 1.5 - 2 GeV/u; • factor 10 000 increased intensity • antiprotons 3(0) - 30 GeV storage and cooler rings • beams of rare isotopes • e – A Collider • 1011 stored and cooled antiprotons • 0.8 - 14.5 GeV accelerator technical challenges • Rapidly cycling superconducting magnets • high energy electron cooling • dynamical vacuum, beam losses

  22. The Compressed Baryonic Matter Experiment Transition Radiation Detectors Tracking Detector ECAL Muon detection System Resistive Plate Chambers (TOF) Ring Imaging Cherenkov Detector Silicon Tracking Station Dipol magnet

  23. Electron identification with RICH and TRD RICH TRD Cherenkov ring radius (cm)

  24. Mapping the QCD phase diagram with heavy-ion collisions ε=0.5 GeV/fm3 first order phase transition LHC RHIC Critical endpoint: Z. Fodor, S. Katz, hep-lat/0402006 S. Ejiri et al., hep-lat/0312006 crossover at small μB lattice QCD SPS FAIR/NICA ? Recent L QCD calculations: TC= 150 - 190 MeV GSI baryon density: B  4 ( mT/2)3/2 x [exp((B-m)/T) - exp((-B-m)/T)] baryons - antibaryons

  25. Meson production in central Au+Au collisions GSI W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745

  26. Vector meson yields for central Au+Au collisions at sNN= 7.1 GeV (25 AGeV)

  27. Collider Luminosity:L = N1·N2·B / F [cm-2s-1] N1, N2 = beam particles per bunch B = number of bunch crossings per sec F = beam size in cm2 Typical numbers: N1= N2 = 109 B = 106 → L = 1027 cm-2s-1 F = 10-3 cm2 Reaktion rate R = L · σ σ= reaction cross section σ = · (2 ·R)2 = 4 ·(r0·A1/3)2 with r0=1.2 fm Au+Au collisions: A=197  σ = 6 barn, 1 barn = 10-24 cm2 Collider reaction rates for Au+Au: R = 1027 cm-2s-1 · 6·10-24 cm2 = 6000 s-1

  28. Fixed target Luminosity:L = NB·NT/ F [cm-2s-1] NB = beam particles/sec NT /F= target atoms/cm2 = NA ··d/A with Avogadros Number NA = 6.02·1023· mol-1, material density  [g/cm3], target thickness d [cm] atomic number A Typical numbers: NB = 109 s-1 Au target:  = 19.3g/cm3, A = 197 d = 0.3 mm (1% interaction rate) L = 1.8·1030 cm-2s-1 Fixed target reaction rates for Au+Au: R = L · σ = 1.8·1030 cm-2s-1 · 6·10-24 cm2 = 107 s-1

  29. Acceptances and Efficiencies • = · p ·Det · Trigg · DAQ · analysis with •  = angular acceptance • p = momentum acceptance • Det = detector efficiencies • Trigg = trigger efficiencies • DAQ= dead time correction of DAQ • analysis = efficiency of analysis • (track finding, cuts for background suppression , ...) Typical values:  0.5, p 0.8, Det 0.9, Trigg  0.9,DAQ  0.5,analysis  0.3,  0.05

  30. Low-energy RHIC run at sNN= 9 GeV peak luminosity ~ 2·1023 cm-2s-1 Reaction rate Au+Au ~ 1 Hz further reduction: average luminosity, large diamond improvement by upgrades incl. e- cooling NICA collider luminosity design value ~ 1·1027 cm-2s-1

  31. Expected dilepton yields for minimum bias Au+Au collisions at sNN= 7.1 GeV (25 AGeV) Assumption: experimental efficiency ε = 10 % Multiplicity of J/ψ: M·ε = 3·10-8 Multiplicity of ω: M·ε = 8·10-5 Collider reaction rate 100 s-1 Yield of J/ψ: 3·10-8·100 s-1 = 3·10-6 s-1 = 1.1·10-2 h-1 = 19 in 10 weeks Yield of ω: 8·10-5·100 s-1 = 8·10-3 s-1 = 29 h-1 = 50000 in 10 weeks Fixed target reaction rates: 107 s-1 with J/ψ trigger: 1.9 ·106J/ψin 10 weeks 105 s-1 without trigger: Yield of ω: 5·107 in 10 weeks

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