Dileptons in NN and AA collisions Hendrik van Hees Goethe-Universität Frankfurt November 28, 2011 Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 1 / 24
Outline 1 Electromagnetic probes in heavy-ion collisions 2 Dileptons at SIS energies (with GiBUU) 3 Dileptons at SPS and RHIC (QGP+hadronic many-body+fireball) 4 Conclusions Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 2 / 24
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 0 1 2 3 4 5 M [GeV/c] Fig. by A. Drees [R. Rapp, J. Wambach, HvH, Landoldt-Börnstein, I/23, 4-1 (2010), arxiv: 0901.3289 [hep-ph] ] Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 3 / 24
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 = g µν α 2 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 (GU Frankfurt) The Dilepton Probe November 28, 2011 4 / 24
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 (GU Frankfurt) The Dilepton Probe November 28, 2011 5 / 24
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)] DLS measurement confirmed by HADES! [Fuchs et al (2003)] Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 6 / 24
Motivation for Transport Models description of various nuclear reactions within one framework pa, γa, ea, νa, AA time evolution of system need dynamical approach transport models well suited for Monte-Carlo simulations (test-particle approach) strongly interacting many-body system: medium modifications of hadrons challenging task: description of broad resonance-like excitations off-shell transport with consistent dynamical evolution of spectral properties conservation laws thermodynamic consistency in this talk: GiBUU model [O. Buss et al arxiv: 1106.1344 [hep-ph]; accepted@phys. Rept.] dileptons in pp and pnb collisions (HADES) work with J. Weil, K. Gallmeister,... Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 7 / 24
The Boltzmann-Uehling-Uhlenbeck Equation time evolution of phase-space distribution functions [ t + ( p H i ) x ( x H i ) p ]f i (t, x, p) = I coll [f 1,..., f i,..., f j ] Hamiltonian H i selfcons. hadronic mean fields, Coulomb pot., off-shell pot. collision term I coll two- and three-body decays/collisions multiple coupled-channel problem at low reaction energies: resonance model at high reaction energies: (modified) PYTHIA new: extend resonance model to cover whole HADES range Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 8 / 24
Resonance Model reactions dominated by resonance scattering: ab R cd Breit-Wigner cross-section formula σ ab R cd = 2s R + 1 4π (2s a + 1)(2s b + 1) p 2 lab sγ ab R Γ R cd (s mr 2 )2 + sγ 2 tot applicable for low-energy nuclear reactions [Teis (PhD thesis 1996)] Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 9 / 24
Dileptons in GiBUU uses strict vector-meson dominance (J µ had. em. V µ ) Resonance model in Teis: NN NR, ; extension NN RR (m R 2 GeV) Teis: describes exclusive π, 2π, ρ, η production extension: πη, πρ, 3π, 2η, 2ρ,... lack of experimental data fit to PYTHIA πρ, πη dominant for HADES energies s max = 3.2 GeV NN R (Nπ)(ηN), (Nπ)(ρN) new production channels NN S 11 (1535) NNπη, NN N NNπρ with N {D 13 (1520), S 11 (1650), F 15 (1680), P 13 (1720)}; NN NNπρ with {S 31 (1620), D 33 (1700), F 35 (1905) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 10 / 24
ρ-production spectrum mass spectrum for ρ e + e production in 3.5 GeV pp collisions ( s = 3.18 GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 11 / 24
ρ-production spectrum mass spectrum for ρ production in 3.5 GeV pp collisions ( s = 3.18 GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 12 / 24
Dileptons in 3.5 GeV pp collisions Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 13 / 24
Dileptons in 3.5 GeV pp collisions Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 14 / 24
Dileptons in 1.25 GeV pp collisions pp well described pn from dp trouble for pn (work in progress) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 15 / 24
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 (GU Frankfurt) The Dilepton Probe November 28, 2011 16 / 24
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 (GU Frankfurt) The Dilepton Probe November 28, 2011 17 / 24
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 q Acc(M, q T, y) 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 (GU Frankfurt) The Dilepton Probe November 28, 2011 18 / 24
CERES/NA45 dielectron spectra (dn ee /dm) / <N ch > [100 MeV/c 2 ] -1 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 good agreement also for dielectron spectra in 158 GeV Pb-Au low-mass tail from baryon effects 10 6 1.8 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 0 0.2 0.4 0.6 0.8 1 1.2 M ee [GeV] (d 2 N ee /dηdm) / (dn ch /dη) [100MeV] -1 10-5 10-6 10-7 35% Central Pb(158AGeV)+Au <N ch >=250 Cocktail QGP CERES 95+ 96 free ρ in-med ρ+ω+φ+qgp+4π p t >0.2GeV 2.1<η<2.65 Θ ee >35mrad 4π 10-8 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 M ee [GeV] Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 19 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 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) -1 10-5 10-6 10-7 10-8 10-9 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 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 20 / 24
Importance of baryon effects baryonic interactions important! in-medium broadening low-mass tail! (1/N ch ) d 2 N µµ /(dm dη) (20 MeV) -1 10-6 10-7 10-8 NA60 no baryons full model all q T T 10-9 c =T ch =175 MeV, a t =0.1 c 2 /fm 0.2 0.4 0.6 0.8 1 1.2 1.4 M (GeV) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 21 / 24
IMR: QGP vs. multi-pion radiation dn µµ /dm (counts) 200 150 100 semicentral In-In all p T QGP (EoS-A) QGP (EoS-B) QGP (EoS-C) 4π (EoS-A) 4π (EoS-B) 4π (EoS-C) 50 0 0.9 1 1.1 1.2 1.3 1.4 M (GeV) different critical and freeze-out temperatures T c = 160... 190 MeV, T chem = 160... 175 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 (GU Frankfurt) The Dilepton Probe November 28, 2011 22 / 24
Dileptons@RHIC: (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 y < 0.35 e p > 0.2 GeV/c cc ee (PYTHIA) cc ee (random correlation) R.Rapp & H.vanHees cocktail T -2 10 sum w/ ρ vacuum sum w/ ρ broadening -3 10 10-4 sum/ ρ dropping) partonic yield (PY) -5 10 model: Rapp, HvH [A. Adare et al (PHENIX), PRC 81, 034911 (2010)] 0 0.2 0.4 0.6 0.8 1 1.2 2 (GeV/c ) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 23 / 24 m ee
Conclusions and Outlook dilepton spectra in-medium em. current correlator SIS energies GiBUU for pp, pn with resonance modell for all HADES energies pn still a problem (work in progress) p Nb, AA work in progress similar study within UrQMD in progress (with S. Endres) 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 puzzle @ RHIC?!? studies in UrQMD+hydro hybrid model planned (with S. Endres) Hendrik van Hees (GU Frankfurt) The Dilepton Probe November 28, 2011 24 / 24