The Dilepton Probe from SIS to RHIC

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1 The Dilepton Probe from SIS to RHIC Hendrik van Hees Justus-Liebig Universität Gießen April 14, 2010 Institut für Theoretische Physik JUSTUS-LIEBIG- UNIVERSITÄT GIESSEN Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

2 Outline 1 Electromagnetic probes in heavy-ion collisions 2 Dileptons at SIS energies 3 Dileptons at SPS and RHIC 4 Conclusions Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

3 Electromagnetic probes in heavy-ion collisions γ, l ± : no strong interactions reflect whole history of collision: from pre-equilibrium phase from thermalized medium QGP and hot hadron gas from VM decays after thermal freezeout dn/(dy dm) π 0, η Dalitz decays ρ/ω Φ DD J/ Ψ ψ Drell Yan π,... ρ/ω γ e e + Low Intermediate High Mass Region > 10 fm > 1 fm < 0.1 fm M [GeV/c] Fig. by A. Drees Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

4 Vector Mesons and electromagnetic Probes l + l thermal emission rates em. current-correlation function, Π µν [L. McLerran, T. Toimela 85, H. A. Weldon 90, C. Gale, J.I. Kapusta 91] dn e + e d 4 xd 4 q = α 2 gµν 3q 2 Im Π(ret) π3 µν (q) f B (q 0 ) q 2 =M 2 e + e vector-meson dominance model: Π µν = G ρ γ γ hadronic many-body theory for vector mesons ρ π B *, a 1, K 1,... ρ ρ ρ π N, K, π,... elementary processes cut self-energy diagrams Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

5 Relation to the QCD-phase diagram at high temperature/density: restoration of chiral symmetry Lattice QCD: Tc χ Tc deconf Mass Mechanism of chiral restoration? Two main theoretical ideas dropping masses : m had ψψ melting resonances : broadening of spectra through medium effects More theoretical question: Realization of chiral symmetry in nature? Spectral Function Spectral Function "ρ" "ρ" Dropping Masses? Melting Resonances? "a 1 " "a 1 " pert. QCD pert. QCD Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

6 Dileptons at SIS energies dileptons from heavy-ion collisions at DLS at E = 1A GeV [Porter et al, PRL 79, 1229 (1997)] large enhancement at low invariant masses unexplained DLS puzzle [Bratkovskaya et al (1999)] [Ernst et al (1998)] [Fuchs et al (2003)] Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

7 Experimental solution DLS measurement confirmed by HADES at GSI [Sudol et al, EPJC 62, 81 (2009)] Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

8 Theoretical HADES Puzzle one-boson-exchange models by Kaptari/Kämpfer, Shyam/Mosel,... importance of elementary pp- and pn-bremsstrahlung cross section also -Dalitz decays in CC collisions: little medium effects! Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

9 Theoretical HADES Puzzle one-boson-exchange model by Shyam/Mosel Bremsstrahlung in pp and pn collisions Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

10 Hendrik van Hees readjustment (JLU Gießen) of resonance The channels Dilepton Probenecessary? April 14, / 22 Theoretical HADES Puzzle elementary pp- and pn-cross sections discrepancy between models (KK vs. SM); resolution work in progress only difference: pseudo-scalar vs. pseudo-vector couplings (should be on-shell equivalent!) discrepancy of between theory and experiment in pn bremsstrahlung

11 Recent update dσ/dm [µb/(gev/c 2 )] p p 1.25 GeV π 0 decay DATA (1232) Bremsstrahlung N * (1520) Total QM M (GeV/c 2 ) [Shyam, private comm.] dσ/dm [ µ b/(gev/c 2 )] p n (with fermi folding) 1.25 GeV Full QM η Dalitz Decay (1630) Dalitz Decay 0 ρ decay M (GeV/c 2 ) pn: inclusion of Fermi motion (additional channels!) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

12 GiBUU (preliminary) Gießen Boltzmann-Uehling-Uhlenbeck transport model describes pp data pn: similar problems as with OBE models (work in progress) [J. Weil, private communication] Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

13 Dileptons at SPS and RHIC radiation from thermal sources: Hadronic many-body theory [R. Rapp, J. Wambach 99] baryon effects important n B +n B relevant quantity (not net-baryon density)! ρ π B *, a 1, K 1,... ρ ρ ρ π N, K, π,... Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

14 Dilepton rates: Hadron gas QGP in-medium hadron gas matches with QGP similar results also for γ rates quark-hadron duality!? consistent with chiral-symmetry restoration resonance melting rather than dropping masses Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

15 Sources of dilepton emission in heavy-ion collisions 1 initial hard processes: Drell Yan 2 core emission from thermal source [McLerran, Toimela 1985] 1 dn (thermal) = q T dmdq T d 4 x dy Mdϕ dn (thermal) d 4 xd 4 Acc(M, q T, y) q use cylindrical thermal fireball with QGP, mixed and hadronic phase 3 corona emission from primordial mesons (jet-quenching) 4 after thermal freeze-out emission from freeze-out mesons [Cooper, Frye 1975] d N (fo) 3 q = q 0 q µ dσ µ f B (u µ q µ /T ) Γ meson l + l Acc Γ meson Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

16 CERES/NA45 dielectron spectra (dn ee /dm) / <N ch > [100 MeV/c 2 ] good agreement also for dielectron spectra in 158 GeV Pb-Au low-mass tail from baryon effects Pb(158 AGeV)+Au (7% central) <N ch >=335 CERES 00 in-med ρ+ω+φ 4π mix QGP DY total total (no bar ρ) p t >0.2GeV 2.1<η<2.65 Θ ee >35mrad M ee [GeV] (d 2 N ee /dηdm) / (dn ch /dη) [100MeV] % Central Pb(158AGeV)+Au <N ch >=250 Cocktail QGP CERES free ρ in-med ρ+ω+φ+qgp+4π p t >0.2GeV 2.1<η<2.65 Θ ee >35mrad 4π M ee [GeV] Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

17 Hadron spectra NA60: Extracted hadronic p T spectra from µ + µ cocktail analysis of cocktail : hadron-m T spectra comparison to fireball evolution fixes radial acceleration sequential freeze-out due to different coupling strength (1/m T ) dn/dm T (a.u.) prim+fo fo prim NA60 ρ 10 4 ρ (semicentral) (0.6 GeV<M<0.9 GeV) T c =T ch =175 MeV, a T =0.1 c 2 /fm m T -M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

18 Hadron spectra NA60: Extracted hadronic p T spectra from µ + µ cocktail analysis of cocktail : hadron-m T spectra comparison to fireball evolution fixes radial acceleration sequential freeze-out due to different coupling strength (1/m T ) dn/dm T (a.u.) prim+fo fo prim NA60 ω 10 4 ω (semicentral) T c =T ch =175 MeV a T =0.1 c 2 /fm, t fo =5 fm m T -M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

19 Hadron spectra NA60: Extracted hadronic p T spectra from µ + µ cocktail analysis of cocktail : hadron-m T spectra comparison to fireball evolution fixes radial acceleration sequential freeze-out due to different coupling strength (1/m T ) dn/dm T (a.u.) prim+fo fo prim NA60 φ 10 4 φ (semicentral) T c =T ch =175 MeV a T =0.1 c 2 /fm, t fo =4 fm m T -M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

20 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm all q T NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

21 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 0<q t <0.2 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

22 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 0.2 GeV<q t <0.4 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

23 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 0.4 GeV<q t <0.6 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

24 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 0.6 GeV<q t <0.8 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

25 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 0.8 GeV<q t <1.0 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

26 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 1.0 GeV<q t <1.2 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

27 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 2.0 GeV<q t <2.2 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

28 M spectra (in p T slices) norm corrected by 3% due to centrality correction (min-bias data: N ch = 120, calculation N ch = 140) (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) T c =T ch =175 MeV, a t =0.1 c 2 /fm 2.2 GeV<q t <2.4 GeV NA60 in-med ρ QGP prim ρ FO ρ 4π mix DY ω φ ω-t ex total +ω-t ex M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

29 Importance of baryon effects baryonic interactions important! in-medium broadening low-mass tail! (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) NA60 no baryons full model all q T T 10-9 c =T ch =175 MeV, a t =0.1 c 2 /fm M (GeV) Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

30 IMR: QGP vs. multi-pion radiation dn µµ /dm (counts) semicentral In-In all p T QGP (EoS-A) QGP (EoS-B) QGP (EoS-C) 4π (EoS-A) 4π (EoS-B) 4π (EoS-C) M (GeV) different critical and freeze-out temperatures T c = MeV, T chem = MeV M- and p T spectra comparably well described! reason: T vs. volume maximal l + l emission for T = T max = M/5.5 hadronic and partonic radiation dual for T T c compatible with chiral-symmetry restoration! inconclusive whether hadronic or partonic emission in IMR! Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

31 (Another) new Puzzle? huge enhancement in the LMR unexplained yet! /GeV) IN PHENIX ACCEPTANCE 2 (c dn/dm ee 10-1 min. bias Au+Au s = 200 GeV NN DATA cc ee (PYTHIA) R.Rapp & H.vanHees y < e p T > 0.2 GeV/c cc ee (random correlation) cocktail sum w/ ρ vacuum sum w/ ρ broadening sum/ ρ dropping) partonic yield (PY) /GeV) IN PHENIX ACCEPTANCE 2 (c dn/dm ee 10-1 min. bias Au+Au s = 200 GeV NN DATA cc ee (PYTHIA) y < 0.35 HSD e p > 0.2 GeV/c cc ee (random correlation) T cocktail sum w/ ρ broadening sum w/ ρ broad. + drop m ee (GeV/c ) model: Rapp, HvH [A. Adare et al (PHENIX), arxiv: [nucl-ex]] m ee (GeV/c ) model: HSD Bratkovskaya, Cassing [A. Adare et al (PHENIX), arxiv: [nucl-ex]] Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22

32 Conclusions and Outlook dilepton spectra in-medium em. current correlator SIS energies dominated by bremsstrahlung and Dalitz decays puzzle in OBE models: pp vs. pn bremsstrahlung SPS and RHIC energies excess yield dominated by radiation from thermal sources baryons essential for in-medium properties of vector mesons melting vector mesons with little mass shift IMR well described by scenarios with radiation dominated either by QGP or multi-pion processes (depending on EoS) quark-hadron duality of l + l rates around T c compatible with chiral symmetry restoration! new RHIC?!? recent review: R. Rapp, J. Wambach, HvH, Landolt-Börnstein, 1-23A arxiv: [hep-ph] Hendrik van Hees (JLU Gießen) The Dilepton Probe April 14, / 22