1. Dielectron Spectroscopy at SIS-18 Energies Joachim Stroth Nuclear Physics Institute, Goethe-University Frankfurt and GSI International School of Nuclear Physics Erice 16-24 September 2008

2. Motivation At 1-2 GeV/u (Au-Au) long lifetime of the dense system: –    fm/c >>  Rho Dilepton decays of vector mesons extremely rare probe: – P ee <10 -7 /collisions ?What is the microscopic structure of this matter – In-medium spectral functions ?What are the appropriate models to relate the microscopic properties to observables SIS-18 Chemical Freeze-out: A. Andronic, PBM, J. Stachel et al.; Cleymans, K. Redlich et al. B.J. Schäfer, J. Wambach priv. communication AGS SPS RHIC QGP hadrons 2Joachim Stroth SIS-100 SIS-300

3. Dielectron Spectroscopy at the Bevalac The puzzle ! Calculation: E.L.Bratkovskaya et al. Phys. Lett. B445 (1999) 265 Calculation: Ernst et al. Phys. Rev. C58 (1998) 447 1 AGeV Calculation: C. Fuchs et al. Phys. Rev. C68 (2003) 014904 Observed excess remained unexplained over years 3Joachim Stroth

4. Spectrometer concept Spectrometer with large acceptance and high rate capability. Demanding: 1.Strong magnetic field over large volume but with field free region around the target 2.Compact RICH with sufficient number of UV photons per ring 3.Fast tracking system with high granularity and minimal material budget 4.Real-time trigger on electron candidates by pattern recognition 1994: Funding approved 2001: Commissioning 6 years of R&D and construction 2002: First production run 1 m 4Joachim Stroth

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6. Electron Identification 1.Spatial correlation : – Ring center - Track – Track - META hit 2.Velocity condition 3.Shower condition – For p > 500 GeV/c e-e- e+e+ DATA C + C @ 2AGeV hadron admixture 1000 MeV/c)! 6Joachim Stroth

7. The DLS Puzzle 7Joachim Stroth

8. Reconstruction of the signal Not corrected for acceptance and efficiency Normalized to the number of produced p 0 (N πo = ½ (N π- + N π+ )) Comb. Background (CB) M ee < 150 MeV/c 2 Like-sign pairs M ee > 150 MeV/c 2 event mixing Signal: – S +- < 150 MeV/c 2 : ~17780 counts – S +- ≥ 150 MeV/c 2 : ~ 646 counts 8Joachim Stroth

9. C-C @ 1 GeV/u: Dielectron yield Joachim Stroth9 Large excess above cocktail! Data: HADES collaboration, Phys. Lett. B 663 (2008) 43-48 PLUTO (Monte Carlo Simulation Tool for Hadron Physics): I. Froehlich et al., arXiv:0708.2382 PLUTO Cocktail: Experimental data m t scaling where not available Cocktail A:  0 + η + ω “long lived components“ Cocktail B: Cocktail A + Δ + ρ

10. For a comparison of HADES and DLS results the HADES yield has to be extrapolated to full phase space. mid-rapidity HADES DLS HADES and DLS Phase Space Coverage 10Joachim Stroth

11. DLS Data: R.J. Porter et al.: Phys. Rev. Lett. 79(97)1229 Direct Comparison HADES and DLS data agree ! J. Carroll – presentation International Workshop on Soft Dilepton Production August 20-22,1997, LBNL Remaining uncertainties due to extrapolation into the  -Dalitz region (blue and cyan triangles). 11Joachim Stroth

12. C-C @ 2 GeV/u: Dielectron Yield and Cocktail Cocktail A:  0 + η + ω “long lived components“ Cocktail B: Cocktail A + Δ + ρ HADES collaboration, Phys. Rev. Lett. 98, 052302 (2007) 12Joachim Stroth

13. A closer look to the excess yield At SIS energies effectively all pions come from resonance decay (regeneration). Excess yield scales like  0 ! Hadron data R. Averbeck et al., TAPS coll., Z. Phys. A 359, 65 (1997) R. Holzmann et al., TAPS coll., Phys. Rev. C 56, R2920 (1997) 13Joachim Stroth

14. New transport results: HSD E. Bratkovskaya and W. Cassing,, Nucl.Phys.A807:214 250,2008 L.P. Kaptari and B. Kämpfer, Nucl. Phys. A 764 (2006) 338 New treatment of Bremsstrahlung in HSD! – Off-shell transport – Time integration method Based on results of a OBE calculation by Kaptari & Kämpfer – pn Bremsstrahlung larger by a factor 4 compared to what was used in transport before Incoherent treatment – Elastic: soft photon approximation – Inelastic: Explicit Resonance propagation and decay 14Joachim Stroth

15. Elementary Reactions 2 m 7 m FW spectator proton deuteron beam 15Joachim Stroth

16. PLUTO: resonance model! Teis et al, ZPA356 (97) 421  angular distrib. from Dmitriev et al, NPA459 (86) 503 N 1440 ang. distr. from Aichelin, priv. comm.  decay angle varied from 1+0.6cos² (Wicklund et al. PRD 35 (87) 2670) to 1- 3cos² Exclusive reconstruction of the    e + e -  1223 N1440 N1535  1600 16Joachim Stroth

17. Inclusive Dielectron Production Strong isospin dependence! 17Joachim Stroth

18. Inclusive Dielectron Production & HSD Joachim Stroth18/24 preliminary

19. Bremsstrahlung in p-p and n-p collisions N N N N ** N N N N VM R ** N N N N R ** 19Joachim Stroth  contribution is taken out.

20. Comparison of C-C and elementary collisions C-C yield can be explained by properly scaling p-p and d-p results. No sensitivity on transverse momentum of spectator proton No evidence for “medium effects” in C-C collisions 20Joachim Stroth preliminary

21. Vector Mesons 21Joachim Stroth

22. Vector meson production in p-p at 3.5 GeV Preliminary (not efficiency corrected, no normalization)  e+e (  tot ~20 nb! )  ~ 35 MeV/c 2 reference for p+A (2008)  /  :Yield excess below  /  : extended VDM? Ch. Fuchs et al., Phys. Rev. C68 (2003) 014904 Mass resolution in the  region < 2,7 % Cocktail: meson multiplicity from HSD  0 /  / ( ,  ) = 0.46/0.031/0.011 (  meson /  inelastic ) 22Joachim Stroth

23. Ar-KCl 1.75 GeV/u Preliminary efficiency correction. Still uncertainty in absolute normalization with respect to the cocktail (< factor 2). Strong excess in mass region M > 0.5 MeV/c 2. Cocktail: PLUTO First  signal in HI collisions at SIS-18 energies 23Joachim Stroth

24. The HADES upgrade project Cope with multiplicities of Au+Au 1.5 AGeV Accept up to 20 KHz trigger rate Measures: – Replace TOFINO with high-granularity RPC – Add forward hodoscope – Upgrade DAQ (new Trigger and Read-out Board) – Extend RICH radiator – Replace plane I tracking chambers RPC full size prototype successfully commissioned in November 2007. Expected resolution below 80 ps. 85.1 ps 74.9 ps 24Joachim Stroth

25. Summary First round of data taking (almost) finished  upgrade in 2009!  C-C @1 and 2 GeV/u Excess yield above long-lived components established Can be fully attributed to contributions from NN scattering – no “medium effects”  p-p 1.25, 2.2, 3.5 GeV, d-p 1.25 GeV/u Strong isospin effect in e + e - from NN scattering Elastic or inelastic Bremsstrahlung ( ,N * Dalitz)?  Ar+KCl 1.76 GeV/u  signal in e + e - decay channel observed K +, K -,K 0,  and  reconstructed -> go to SQM 2008  p-Nb 3.5 GeV (running just now) Is there a  mass shift or broadening  Bright future Au+Au,  -induced a SIS-18 and later A+A at SIS-100 25Joachim Stroth

26. GSI collaboration G. Agakishiev 8, C. Agodi 1, A. Balanda 3,e, G. Bellia 1,a, D. Belver 15, A. Belyaev 6, A. Blanco 2, M. Böhmer 11, J. L. Boyard 13, P. Braun-Munzinger 4, P. Cabanelas 15, E. Castro 15, S. Chernenko 6, T. Christ 11, M. Destefanis 8, J. Díaz 16, F. Dohrmann 5, A. Dybczak 3, T. Eberl 11, L. Fabbietti 11, O. Fateev 6, P. Finocchiaro 1, P. Fonte 2,b, J. Friese 11, I. Fröhlich 7, T. Galatyuk 4, J. A. Garzón 15, R. Gernhäuser 11, A. Gil 16, C. Gilardi 8, M. Golubeva 10, D. González-Díaz 4, E. Grosse 5,c, F. Guber 10, M. Heilmann 7, T. Hennino 13, R. Holzmann 4, A. Ierusalimov 6, I. Iori 9,d, A. Ivashkin 10, M. Jurkovic 11, B. Kämpfer 5, K. Kanaki 5, T. Karavicheva 10, D. Kirschner 8, I. Koenig 4, W. Koenig 4, B. W. Kolb 4, R. Kotte 5, A. Kozuch 3,e, A. Krása 14, F. Krizek 14, R. Krücken 11, W. Kühn 8, A. Kugler 14, A. Kurepin 10, J. Lamas-Valverde 15, S. Lang 4, J. S. Lange 8, K. Lapidus 10, L. Lopes 2, M. Lorenz 7, L. Maier 11, A. Mangiarotti 2, J. Marín 15, J. Markert 7, V. Metag 8, J. Micel 7, B. Michalska 3, D. Mishra 8, E. Morinière 13, J. Mousa 12, C. Müntz 7, L. Naumann 5, R. Novotny 8, J. Otwinowski 3, Y. C. Pachmayer 7, M. Palka 4, Y. Parpottas 12, V. Pechenov 8, O. Pechenova 8, T. Pérez Cavalcanti 8, J. Pietraszko 4, W. Przygoda 3,e, B. Ramstein 13, A. Reshetin 10, M. Roy-Stephan 13, A. Rustamov 4, A. Sadovsky 10, B. Sailer 11, P. Salabura 3, A. Schmah 4, R. Simon 4, Yu.G. Sobolev 14, S. Spataro 8, B. Spruck 8, H. Ströbele 7, J. Stroth 7,4, C. Sturm 7, M. Sudol 4, A. Tarantola 7, K. Teilab 7, P. Tlusty 14, M. Traxler 4, R. Trebacz 3, H. Tsertos 12, I. Veretenkin 10, V. Wagner 14, H. Wen 8, M. Wisniowski 3, T. Wojcik 3, J. Wüstenfeld 5, S. Yurevich 4, Y. Zanevsky 6, P. Zhou 5, P. Zumbruch 4 1 Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, 95125 Catania, Italy 2 LIP-Laboratório de Instrumentação e Física Experimental de Partículas, 3004-516 Coimbra, Portugal 3 Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-059 Kraków, Poland 4 Gesellschaft für Schwerionenforschung mbH, 64291 Darmstadt, Germany 5 Institut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, 01314 Dresden, Germany 6 Joint Institute of Nuclear Research, 141980 Dubna, Russia 7 Institut für Kernphysik, Johann Wolfgang Goethe-Universität, 60438 Frankfurt, Germany 8 II.Physikalisches Institut, Justus Liebig Universität Giessen, 35392 Giessen, Germany 9 Istituto Nazionale di Fisica Nucleare, Sezione di Milano, 20133 Milano, Italy 10 Institute for Nuclear Research, Russian Academy of Science, 117312 Moscow, Russia 11 Physik Department E12, Technische Universität München, 85748 München, Germany 12 Department of Physics, University of Cyprus, 1678 Nicosia, Cyprus 13 Institut de Physique Nucléaire (UMR 8608), CNRS/IN2P3 - Université Paris Sud, F-91406 Orsay Cedex, France 14 Nuclear Physics Institute, Academy of Sciences of Czech Republic, 25068 Rez, Czech Republic 15 Departamento de Física de Partículas, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain 16 Instituto de Física Corpuscular, Universidad de Valencia-CSIC, 46971 Valencia, Spain

27. Bonus Slides 27Joachim Stroth

28. W.K. Wilson (DLS coll.), Acta Phys. Pol. 29 (98) 3291 28Joachim Stroth

29. 29Joachim Stroth

30. 30Joachim Stroth

31. E. Bratkovskaya et al. Nucl. Phys. A 31Joachim Stroth

32. Needless to show preliminary 32Joachim Stroth

33. 33 Comparison to L. Kaptari, B. Kämpfer calculations [Phys. Rev. C 58, 2667 - 2670 (1998), H. Calén et al., “Measurement of the quasifree pn→pn  reaction”] Black points – data Red poins – (data –  Joachim Stroth

34. Efficiency and acceptance corrected pp data, comparison to transport model calculation 34 IQMD Δ→e + e - N seems to explain e + e - yield in p+p at 1.25 GeV Joachim Stroth

35. Efficiency and acceptance corrected np data, comparison to transport model calculation (np cocktail) 35 IQMD preliminary Data are not explained satisfactorily! preliminary Joachim Stroth

36. Efficiency and acceptance corrected np data, comparison to transport model calculation (dp cocktail) 36 IQMD preliminary dp cocktail do not explain data are not explained satisfactorily! preliminary Joachim Stroth

37. Closer look to HSD 37 An effect of the internal Fermi motion of the nucleons in the deuteron is hardly visible Joachim Stroth

38. 38Joachim Stroth