Dilepton Measurements In Heavy Ion Collisions: Fixed-target Versus Collider Experiments 2. Multiplicities

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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 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+e4. misidentified pions Background in muon measurements: π→μν, K→μν   μ+μ- (can be determined by   μ+μ- ) 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% Ring Imaging Cherenkov detector (RICH) Bestimmung der TeilchenGeschwindigkeit durch Messung von θ (Ringradius des Lichtkegels) cosθα = 1/(βn) 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 HADES at GSI HADES CERES/NA45 at SPS 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) 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 Muon identification: NA38/50/60 muon trigger 2.5 T dipole magnet targets vertex tracker hadron absorber muon other tracks Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muons before they suffer multiple scattering in the absorber and 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 iron wall magnetic field beam tracker and tracking 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 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 PHENIX Physics Capabilities designed to measure rare probes: Au-Au & p-p spin • • • 2 central arms: electrons, photons, hadrons – charmonium J/, ’ -> e+e– vector meson r, ,  -> e+e– high pT o, +, – 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 + high rate capability & granularity + good mass resolution and particle ID - limited acceptance   e- PC3 e+ DC PC1 magnetic field & tracking detectors • global detectors forward energy and multiplicity – event characterization PHENIX data •Data absolutely normalized •Cocktail filtered in PHENIX acceptance •Charm from submitted to Phys. Rev. Lett arXiv:0706.3034 – PYTHIA – Single electron non photonic spectrum w/o angular correlations sc= Ncoll x 567±57±193mb Low-Mass Continuum: enhancement 150