1. Motivations - HADES Dielectron analysis strategy Results & models comparison C+C 2 AGeV C+C 1AGeV HADES experiment: dilepton spectroscopy in C+C (1 and 2 AGeV) collisions Motivations - HADES Dielectron analysis strategy Results & models comparison C+C 2 AGeV C+C 1AGeV Witold Przygoda, Jagiellonian University, Cracow, for the HADES Collaboration 2nd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, Asilomar CA, 2006

2. 2 Motivation Probe the electromagnetic structure of hot and dense nuclear matter in the time-like region Additional self-energy terms due to meson- baryon coupling    p - beams SIS 18 SIS 200 T [MeV] 300 LHC RHIC SPS Partial restoration of chiral symmetry W. Weise et al. Brown-Rho scaling What are the relevant observables as nuclear density and/or temperature increase?

3. 3 The case of moderate beam energies 1020 30 t [fm/c] ≈ 10 fm/c comparatively long life-time...at moderate densities Particle production at or below threshold : – co-operative processes (i.e. multi step processes) – production confined to the high density phase ! NN → NΔ πNπN πN → ρ N multi step processes: i.e. c  10-15 fm/c Baryon density:  t(   > 2) ≈ 10 fm/c In-medium invariant mass reconstruction combinatorial background reduction Vector meson spectroscopy – in-medium effects investigation Meson Mass [MeV/c 2 ] Width  [MeV/c 2 ] Life time c  [fm/c]  (V  e+e-)  tot 00 7701501.34.4x10 -5  7828.423.47.1x10 -5  10204.444.43.1x10 -5 T. Renk et al., PRC 66 (2002) 014902

4. 4 Invariant mass spectrum decomposition Elementary processes: Meson Dalitz decays: Baryon Dalitza decays: Two-body decays:      e+ e-    e+ e-   e+ e- Example cocktail ( DLS data compared to HSD model )

5. 5 The DLS results The shape (0.05  M  0.35) can be explained by Dalitz decays of  0 and  if cross sections are scaled appropriately – but in contradiction with TAPS measurement... Data: R.J. Porter et al.: PRL 79 (1997) 1229 BUU model: E.L. Bratkovskaya et al.: NP A634 (1998) 168, in-medium spectral functions  DLS puzzle! Calculation: K. Shekhter, C. Fuchs et al. (Tübingen) Phys. Rev. C68 (2003) 014904 Done using strong or weak (s/w)  - N*(1535) coupling

6. 6 HADES … What and where?...

7. 7 High Acceptance Di-Electron Spectrometer  Installed at the SIS18, GSI Darmstadt  Spectrometer with high invariant mass resolution and high rate capability  Utilizes dedicated second level trigger processors to select rare events before mass storing Beams of: –Pions –Protons –Nuclei Geometry Full azimuth, polar angles 18  - 85  ( y = 0 – 2 ) Pair acceptance  0.35 ~ 80.000 channels, seg. solid or LH 2 targets

8. 8 HADES Spectrometer Side View START 1 m Fast particle identification Pre-Shower: 18 pad chambers & 12 lead converters between RICH: CsI solid photo cathode, C 4 F 10 radiator, N 0  80  90,  suppression: 10 4 TOF: 384 scintil. rods,   150 ps TOFino: 24 scintil. paddles,   450 ps  temporary solution, RPC in future Momentum measurement Magnet: super  conducting toroid: B  = 0.36 Tm MDC: 24 multi  wire drift chambers,  y  100  m single cell resolution

9. 9 Fast 2 nd level trigger up to 20 kHz LVL1 Fast multiplicity trigger full event information digitised on-line selection of electron candidates LVL2 triggered events are transported to mass storage Suppression 10 - 100

10. 10 Experimental (production) runs November 2002: C+C 2 AGeV, commissioning and physics runs 650 Mevents –target= 2 x 2.5% 650 Mevents –6 outer drift chambers (MDC) in 4 sectors February 2004: p+p 2 GeV 600 Mevents –target 5 cm LH 2, almost full spectrometer setup600 Mevents August 2004: C+C 1 AGeV 2500 Mevents –3x2 % target2500 Mevents September 2005: Ar+KCl 1.75 AGeV 1200 Mevents –4x1.5 % target1200 Mevents May 2006: p+p 1.25 GeV 3000 Mevents –Target 5 cm LH 2 3000 Mevents

11. 11 log. z axis ! e-e- e+e+ hadron : lepton suppression 10000 : 1 Analysis strategy Single electron analysis Classical: 2-dim cuts on RICH rings, Shower, p vs , hit matching... or: Bayes theorem: cut on pid prob. track fitting quality e+e- pair analysis close pair cuts opening angle  > 9° (tracks removed) Corrections for detector and reconstruction efficiencies  acceptance & reconstruction efficiency filters available e-e-e-e- e+e+e+e+  M inv = p1p1 p2p2 Target RICH

12. 12 C+C @ 2 AGeV - mass spectrum Combinatorial background (CB): –from like-sign pairs –CB = Signal: S +  = N e+e   CB +  signal < 140 MeV/c 2 : 20971 counts signal > 140 MeV/c 2 : 1937 counts ( picture above ) no acceptance / efficiency corrections limited resoultion ( ~DLS level ) only inner MDC chambers in 2002

13. 13 C+C @ 2 AGeV - mass spectrum corrected Efficiency corrected spectra - detector efficiency - reconstruction efficiency  normalized to the pion yield in HADES acceptance 12 C+ 12 C 2AGeV average number of participating nucleons A part = 8.6 extrapolated charged pion yield N  4  / A part = 0.135  0.015 PLUTO event gener. (HADES Collaboration)  0 and  well known (thermal freezout) based on TAPS measurements syst. error (~30%): uncertainty in normalization reconstruction efficiency corr. CB construction red bars – stat+syst err

14. 14 C+C @ 2 AGeV – HSD model vacuum in-medium ( data described quite well )

15. 15 C+C @ 2 AGeV – UrQMD model problems in the high mass region vacuum result ) Transport calculation ( vacuum result ) UrQMD Frankfurt M. Bleicher, D. Schumacher

16. 16 C+C @ 2 AGeV – RQMD model RQMD Tübingen D. Cozma, C. Fuchs subthreshold  /  production (via resonances) eVMD model in-medium:  collisional broadening  decoherence In-medium: problems in the intermediate mass region

17. 17 C+C @ 2 AGeV - comparison with models Included calculations: PLUTO evt generator HADES collaboration UrQMD Frankfurt M. Bleicher, D. Schumacher HSD Gießen (v2.5) E. Bratkovskaya, W. Cassing experimental data efficiency corrected pair cut  12 = 9  theor. models vacuum calculations Included calculations: RQMD Tübingen D. Cozma, C. Fuchs UrQMD Frankfurt M. Bleicher, D. Schumacher HSD Gießen (v2.5) E. Bratkovskaya, W. Cassing

18. 18 C+C @ 2 AGeV – rapidity – exp, PLUTO, HSD discrepancy in medium (PLUTO, HSD) and high mass (PLUTO) region dots - experiment dashed line - PLUTO solid line - HSD HSD solid line vacuum dashed line in-medium PLUTO – dashed HSD – solid

19. 19 C+C @ 2 AGeV – p T – exp, PLUTO, HSD PLUTO HSD solid line vacuum dashed line in-medium discrepancy in medium and high mass region

20. 20 C+C @ 1 AGeV - preliminary preliminary Comb. backgr. (CB): from like-sign pairs CB = S +  = N e+e   CB +  not efficiency corrected ! Direct comparison to DLS data possible –Exp. Data: no efficiency correction –PLUTO: filtered with HADES acceptance * efficiency Normalized to π 0 70% of the full data statistics only π 0, η is not sufficient to describe the data – model comparison in the future

21. 21 Summary HADES fully operational – 1 month experimental runs 12 C + 12 C 2 AGeV analyzed ( PRL paper submitted soon ) –di-electron spectrum efficiency corrected –systematic errors estimated (based on simulation) –   in agreement with TAPS / KAOS measurement –comparison with transport models –vacuum results failed to describe high mass region 12 C + 12 C 1 AGeV preliminary –5x higher data statistics – analysis on-going –direct comparison to DLS data possible A lot of physics ahead for the coming years – 40 Ar+ 39 K 37 Cl @ 1.75 AGeV analysis started soon –elementary reactions: p+p @ 2.2 GeV, 1.25 GeV, 3.5 GeV high momentum resolution achieved (σ = 3.5%)  form factor measurement feasible  in nucleus production –p,  heavy ion: high precision in-medium spectroscopy

22. 22 HADES collaboration G.Agakishiev 7, C.Agodi2, H.Alvarez-Pol19, A.Balanda5, R.Bassini10, G.Bellia2,3, D.Belver19, J.Bielcik6, A.Blanco4, M.Böhmer14, C.Boiano10, A.Bortolotti10, J.Boyard16, S.Brambilla10, P.Braun-Munzinger6, P.Cabanelas19, S.Chernenko7, T.Christ14, R.Coniglione2, M.Dahlinger6, J.Díaz20, R.Djeridi9, F.Dohrmann18, I.Durán19, T.Eberl14, W.Enghardt18, L.Fabbietti14, O.Fateev7, P.Finocchiaro2, P.Fonte4, J.Friese14, I.Fröhlich9, J.Garzón19, R.Gernhäuser14, M.Golubeva12, D.González-Díaz19, E.Grosse18, F.Guber12, T.Heinz6, T.Hennino16, S.Hlavac1, J.Hoffmann6, R.Holzmann6, A.Ierusalimov7, I.Iori10,11, Ivashkin12, M.Jaskula5, M.Jurkovic14, M.Kajetanowicz5, B.Kämpfer18, K.Kanaki18, T.Karavicheva12, D.Kirschner9, I.Koenig6, W.Koenig6, B.Kolb6, U.Kopf6, R.Kotte18, J.Kotulic-Bunta1, R.Krücken14, A.Kugler17, W.Kühn9, R.Kulessa5, S.Lang6, J.Lehnert9, L.Maier14, P.Maier-Komor14, C.Maiolino2, J.Marín19, J.Markert8, V.Metag9, N.Montes19, E.Moriniere16, J.Mousa15, M.Münch6, C.Müntz8, L.Naumann18, R.Novotny9, J.Novotny17, W.Ott6, J.Otwinowski5, Y.Pachmayer8, V.Pechenov7, T.Pérez9, J.Pietraszko6, J.Pinhao4, R.Pleskac17, V.Pospísil17, W.Przygoda5, A.Pullia10,11, N.Rabin13, B.Ramstein16, S.Riboldi10, J.Ritman9, P.Rosier16, M.Roy-Stephan16, A.Rustamov6, A.Sadovsky18, B.Sailer14, P.Salabura5, P.Sapienza2, A.Schmah6, W.Schön6, C.Schroeder6, E.Schwab6, P.Senger6, R.Simon6, V.Smolyankin13, L.Smykov7, S.Spataro2, B.Spruck9, H.Stroebele8, J.Stroth8,6, C.Sturm6, M.Sudol8,6, V.Tiflov12, P.Tlusty17, A.Toia9, M.Traxler6, H.Tsertos15, I.Turzo1, V.Wagner17, W.Walus5, C.Willmott19, S.Winkler14, M.Wisniowski5, T.Wojcik5, J.Wüstenfeld8, Y.Zanevsky7, P.Zumbruch6 1)Institute of Physics, Slovak Academy of Sciences, 84228 Bratislava, Slovakia 2)Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, 95125 Catania, Italy 3)Dipartimento di Fisica e Astronomia, Università di Catania, 95125, Catania, Italy 4)LIP-Laboratório de Instrumentação e Física Experimental de Partículas, Departamento de Física da Universidade de Coimbra, 3004-516 Coimbra, Portugal 5)Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30059 Cracow, Poland 6)Gesellschaft für Schwerionenforschung mbH, 64291 Darmstadt, Germany 7)Joint Institute of Nuclear Research, 141980 Dubna, Russia 8)Institut für Kernphysik, Johann Wolfgang Goethe-Universität, 60486 Frankfurt, Germany 9)II.Physikalisches Institut, Justus Liebig Universität Giessen, 35392 Giessen, Germany 10)Istituto Nazionale di Fisica Nucleare, Sezione di Milano, 20133 Milano, Italy 11)Dipartimento di Fisica, Università di Milano, 20133 Milano, Italy 12)Institute for Nuclear Research, Russian Academy of Science, 117312 Moscow, Russia 13)Institute of Theoretical and Experimental Physics, 117218 Moscow, Russia 14)Physik Department E12, Technische Universität München, 85748 Garching, Germany 15)Department of Physics, University of Cyprus, 1678 Nicosia, Cyprus 16)Institut de Physique Nucléaire d'Orsay, CNRS/IN2P3, 91406 Orsay Cedex, France 17)Nuclear Physics Institute, Academy of Sciences of Czech Republic, 25068 Rez, Czech Republic 18)Institut für Kern- und Hadronenphysik, Forschungszentrum Rossendorf, PF 510119, 01314 Dresden, Germany 19)Departamento de Física de Partículas. University of Santiago de Compostela. 15782 Santiago de Compostela, Spain 20)Instituto de Física Corpuscular, Universidad de Valencia-CSIC,46971-Valencia, Spain