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Recent Results from HADES

Recent Results from HADES. Physics Motivation Low mass lepton pair enhancements SPS and DLS data The HADES detector at GSI Darmstadt Experimental Results 12 C+ 12 C and the DLS Puzzle p+p, p+d Ar+KCl Summary and Outlook. Electromagnetic Probes – Penetrating Probes. PHENIX, STAR. T.

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Recent Results from HADES

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  1. Recent Results from HADES • Physics Motivation • Low mass lepton pair enhancements • SPS and DLS data • The HADES detector at GSI Darmstadt • Experimental Results • 12C+12C and the DLS Puzzle • p+p, p+d • Ar+KCl • Summary and Outlook Wolfgang Kühn, Universität Giessen

  2. Electromagnetic Probes – Penetrating Probes PHENIX, STAR T • Experiments at different s probe different regions of phase diagram • RHIC ee pairs and g sQGP • SPS ee, mm pairs transition region • SIS ee pairs dense hadronic matter • HADES Quark Matter CERES, NA60 TC~170 MeV DLS, HADES thermal freeze out Color Superconductor chemical freeze out SIS Hadron Resonance Gas temperature Nuclear Matter baryon chemical potential 1200-1700 MeV 940 MeV mB Wolfgang Kühn, Universität Giessen

  3. CERES: Low-mass dilepton enhancement Nucl-ex/0203004 • Central N-N collisions exhibit a strong enhancement of low-mass dilepton production as compared to p-N reactions (CERES, HELIOS, NA60) • A large fraction of the excess is probably due to pion annihilation, which does not contribute in p-N reactions • There is no quantitative description of the data using vacuum properties of vector mesons • Possible explanation: • in-medium modifications of vector meson properties • Broadening and/or mass shift of the rho meson Nucl-ex/0203004 Wolfgang Kühn, Universität Giessen

  4. The DLS@BEVALAC - Puzzle • DLS Experiment observed large excess of di-electrons when compared to dominant known sources • Pion, eta Dalitz decays • Effect much stronger than at SPS energies • Visible also in light ion induced reactions • For many years, no conclusive theoretical explanation available • Experimental problem? • New physics? • Not well understood old physics? Wolfgang Kühn, Universität Giessen

  5. Side view • Acceptance: Full azimuth, polar angles 18o - 85o • Pair acceptance  0.35 • Particle identification: • RICH: CsI solid photo cathode, C4F10 radiator, • Time Of Flight: Scintillator paddles  MUL limitation <450, RPC from 2009 • Pre-Shower: pad chambers & lead converter • 2' Level single leg electron trigger (Me>=1) • Momentum measurement • Magnet: B = 0.36 Tm + • MDC: 24 Midi Drift Chambers, single-cell resolution  140 m Wolfgang Kühn, Universität Giessen

  6. Hadron Identification • Momentum vs velocity (β) + dE/dx in MDC & TOF: • example: Ar + KCl @ 1.75 A GeV • TOF:  >450 • particle mass spectra with dE/dx (TOF & MDC) selection •  kaon identifcation Wolfgang Kühn, Universität Giessen

  7. DATA velocity vs. momentum with RICH condition e+ e- Electron Identification • Spatial correlations • RICH rings ↔tracks • PID : e+, e- • β vs momentum correlation • PreShower condition C + C @ 2AGeV • Hadron contamination < 5% (p>1000 MeV) Wolfgang Kühn, Universität Giessen

  8. Exclusive reactions Clean and consistent reconstruction of hadronic and Dalitz decays for p0, h Cross check for detector simulations pp0ppe+e- Nexp= 2726 ± 53,SIM=2677 Nexp= 195 ± 19, SIM=196 ppppe+e- p+p @ 2.2 GeV : Exclusive 0/  reconstruction pppp pp+-° total signal background M 548 MeV/c2 /M 3.5 % HADES 70±8 b Wolfgang Kühn, Universität Giessen

  9. LOW mass excess : "DLS" puzzle" Wolfgang Kühn, Universität Giessen

  10. Cocktail B: Cocktail A + Δ(Ne+e-) + ρ short lived component Inclusive e+e- pairs from C+C collisions A. Agakichiev accepted by Phys. Lett.B A. Agakichiev Phys.Rev. Lett 98(2007) 052302 • Normalization N(0)= ½(N+ + N-) • Cocktail A: 0 + η + ω long-lived component (0/ constraint by TAPS data) Wolfgang Kühn, Universität Giessen

  11. mid-rapidity mid-rapidity Comparison of DLS and HADES Acceptance Wolfgang Kühn, Universität Giessen

  12. Comparison to DLS C+C @1.04 GeV J. Carroll – presentation International Workshop on Soft Dilepton ProductionAugust 20-22,1997, LBNL DLS Data: R.J. Porter et al.: Phys.Rev.Lett. 79 (1997) 1229 • Very good agreement between both experiments •  Full confirmation of DLS effect Wolfgang Kühn, Universität Giessen

  13. TAPS Photon data R. Averbeck et al., TAPS Col., Z.Phys. A 359 (1997) 65 R. Holzmann et al., TAPS Col., Phys.Rev. C 56 (1997) R2920 Beam energy dependence of the excess • Enhancement scales like pions ! • Baryon resonance decays ? • N-N bremsstrahlung ? Wolfgang Kühn, Universität Giessen

  14. Comparison with Up-to-Date Transport Calculations IQMD:M. Thomèreet al. Phys.Rev.C75 064902 (2007) HSD: E.L. Bratkovskaya and W. Cassing arXiv:0712.0635v1 and private communication New treatment of Bremsstrahlung: L.P. Kaptari and B. Kämpfer, Nucl.Phys. A 764 (2006) 338 • Important contributions from Δ Dalitz decay and Bremsstrahlung • Cruical input: • Elementary reactions • pp, pn Wolfgang Kühn, Universität Giessen

  15. pp and pn 1.25 GeV • Not efficiency corrected • Not corrected for trigger bias • Analysis in progress Online spectrum (data from May 2007 ) very preliminary preliminary PhD thesis T.Galatyuk • New precise input of elementary cross sections for model calculations Wolfgang Kühn, Universität Giessen

  16. Vector meson production Wolfgang Kühn, Universität Giessen

  17. preliminary online calibration ~70% statistics HADES pairs from pp @ 3.5 GeV Preliminary (not efficiency corrected, no normalization) • e+e- signal (tot~20 nb! ) ~35 MeV/c2 • Reference for p+A (2008) Wolfgang Kühn, Universität Giessen

  18. Signal Pairs from Ar+KCl • No efficiency correction • Ne+e- = 114.000 pairs (~7k for M>M0 ) • e+e- decay seen for the first time at SIS/Bevelac energies ! Preliminary Me+e- > 0.4 GeV/c2 Wolfgang Kühn, Universität Giessen

  19. Summary and Outlook Low mass enhancement : • DLS pair excess has been confirmed by the HADES CC data : • No puzzle any more (at least not from the experimental point of view) • Combined CC, pp and pn data @1.25 GeV indicate that most of the excess originates from p-n reactions • Strong isospin dependence of pair production • New HADES data on elementary reactions provide important input for the understanding of HI data • Implications for low mass lepton continuum in a baryon rich environment • Importance of resonance decays • Correct description of Bremsstrahlung • Interference between these processes ??? Vector meson production • e+e- decay observed for a first time at SIS/Bevalac energies • pp @ 3.5 GeV and Ar+KCl @ 1.75 AGeV Wolfgang Kühn, Universität Giessen

  20. HADES runs: Outlook & plans for next years p+A @ 3.5 GeV upgrade: RPC, DAQ Ni+Ni p+N,A Au+Au 8 AGeV Subject to Approval SIS FAIR SIS Wolfgang Kühn, Universität Giessen

  21. SIS The collaboration • Catania (INFN - LNS), Italy • Cracow (Univ.), Poland • Darmstadt (GSI), Germany • Dresden (FZR), Germany • Dubna (JINR), Russia • Frankfurt (Univ.), Germany • Giessen (Univ.), Germany • Milano (INFN, Univ.), Italy • Munich (TUM), Germany • Moscow (ITEP,MEPhI,RAS), Russia • Nicosia (Univ.), Cyprus • Orsay (IPN), France • Rez (CAS, NPI), Czech Rep. • Sant. de Compostela (Univ.), Spain • Valencia (Univ.), Spain • Coimbra (Univ.), LIP, Portugal Wolfgang Kühn, Universität Giessen

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