Dilepton measurements in heavy ion collisions:fixed-target versus collider experiments1. Experimental setups2. Multiplicities 3. Luminosities4. Rates

Dilepton sources in Heavy-ion Collisions

Single electron spectra central Au+Au collisions 25 AGeVBackground sources

1. external pair conversion: e+e-

2.Dalitz-decays:0 e+e- (BR = 1.210-2) e+e- (BR = 4.910-3)

3. Bremsstrahlung:pn pn e+e-

4. misidentified pionsBackground in muon measurements: , K +- (can be determined by +- )

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

Bestimmung der Teilchen-Geschwindigkeit durch Messungvon (Ringradius des Lichtkegels)Ring Imaging Cherenkov detector (RICH)cos = 1/(n)

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

HADES at GSI

HADES

CERES/NA45 at SPS

Electron-positron pairs from CERESCERES 2000: 159 AGeV Pb+Aubeam intensity: 106 ions / spill 1 spill = 4 s beam and 15 s pausetargets: 13 x 25 m Au ( ~ 1 % interaction)trigger: 8% most centralEvent rate = 470 / spill (~ 25 Hz = 15 Mio events/week)

Low mass vector mesons (CERES/CERN)D.Adamova et al., PRL 91 (2003) 042301 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 widthData: ~ 180 signal pairs

Muon identification: NA38/50/60Concept 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 determined2.5 T dipole magnetbeam trackervertex tracker

Dimuon pairs measured by NA60 (CERN)5-week-long run in Oct.Nov. 2003 ~ 4 1012 ions delivered in total440000 signal pairsIn+In 158 AGeV

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 Capabilities2 central arms: electrons, photons, hadronscharmonium J/, -> e+e-vector meson r, w, -> e+e- high pT po, p+, p-direct photonsopen charm hadron physics

2 muon arms: muonsonium J/, , -> m+m- vector meson -> m+m- open charm

combined central and muon arms: charm production DD -> em

global detectors forward energy and multiplicityevent characterizationdesigned to measure rare probes: + high rate capability & granularity+ good mass resolution and particle ID- limited acceptanceAu-Au & p-p spin

PHENIX dataData absolutely normalized Cocktail filtered in PHENIX acceptanceCharm from PYTHIA Single electron non photonic spectrum w/o angular correlations sc= Ncoll x 56757193mbLow-Mass Continuum: enhancement 150

CERN and the Large Hadron Collider (LHC)

The ALICE experiment at CERN

Transition radiationTotal energy = 1 /

Transition Radiation Detectors (TRD)p = 1 GeV/ce = 2000 = 7.1

storage and cooler rings beams of rare isotopes e A Collider 1011 stored and cooled antiprotons 0.8 - 14.5 GeV

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 accelerator technical challengesRapidly cycling superconducting magnetshigh energy electron coolingdynamical vacuum, beam losses Facility for Antiproton and Ion Research (FAIR)

DipolmagnetThe Compressed Baryonic Matter ExperimentRing ImagingCherenkovDetectorTransition Radiation DetectorsResistivePlate Chambers(TOF)ECALSiliconTrackingStation Tracking DetectorMuondetection System

Electron identification with RICH and TRDCherenkov ring radius (cm)RICHTRD

Critical endpoint:Z. Fodor, S. Katz, hep-lat/0402006S. Ejiri et al., hep-lat/0312006crossover at small B baryon density: B 4 ( mT/2)3/2 x [exp((B-m)/T) - exp((-B-m)/T)] baryons - antibaryonsFAIR/NICAGSISPSRHICLHCMapping the QCD phase diagram with heavy-ion collisions lattice QCD?Recent L QCD calculations:TC = 150 - 190 MeV

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

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

J/multiplicity210-523381.3BR ()0.064.610-5910-5310-5 multiplicity1.210-6110-33.410-33.710-4 min bias310-72.510-4810-4910-5

N1, N2 = beam particles per bunchB = number of bunch crossings per secF = beam size in cm2

Typical numbers:N1= N2 = 109B = 106 L = 1027 cm-2s-1 F = 10-3 cm2 Reaktion rate R = L = reaction cross section = (2 R)2 = 4 (r0A1/3)2 with r0=1.2 fmAu+Au collisions: A=197 = 6 barn, 1 barn = 10-24 cm2

Collider reaction rates for Au+Au: R = 1027 cm-2s-1 610-24 cm2 = 6000 s-1

Collider Luminosity: L = N1N2B / F [cm-2s-1]

NB = beam particles/secNT /F = target atoms/cm2 = NA d/A with Avogadros Number NA = 6.021023 mol-1, material density [g/cm3], target thickness d [cm] atomic number A

Typical numbers:NB = 109 s-1Au target: = 19.3 g/cm3, A = 197d = 0.3 mm (1% interaction rate)L = 1.81030 cm-2s-1

Fixed target reaction rates for Au+Au: R = L = 1.81030 cm-2s-1 610-24 cm2 = 107 s-1

Fixed target Luminosity: L = NBNT/ F [cm-2s-1]

Acceptances and Efficiencies

= p Det Trigg DAQ analysiswith = angular acceptance p = momentum acceptanceDet = detector efficienciesTrigg = trigger efficienciesDAQ = dead time correction of DAQanalysis = 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

Low-energy RHIC run at sNN= 9 GeV

peak luminosity ~ 2 1023 cm-2s-1Reaction rate Au+Au ~ 1 Hz

further reduction:average luminosity, large diamond

improvement by upgrades incl. e- cooling

NICA colliderluminosity design value ~ 1 1027 cm-2s-1

Expected dilepton yields for minimum bias Au+Au collisions at sNN= 7.1 GeV (25 AGeV)

Assumption: experimental efficiency = 10 %

Multiplicity of J/: M = 310-8 Multiplicity of : M = 810-5

Collider reaction rate 100 s-1Yield of J/: 310-8100 s-1 = 310-6 s-1 = 1.110-2 h-1 = 19 in 10 weeks Yield of : 810-5100 s-1 = 810-3 s-1 = 29 h-1 = 50000 in 10 weeks

Fixed target reaction rates:107 s-1 with J/ trigger: 1.9 106 J/ in 10 weeks 105 s-1 without trigger: Yield of : 5107 in 10 weeks

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