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Recent results from the HADES experiment at GSI: Dilepton production in 1-2 AGeV energy range:

Recent results from the HADES experiment at GSI: Dilepton production in 1-2 AGeV energy range:. Béatrice Ramstein Institut de Physique Nucléaire d’Orsay, groupe PHEN. Outline. Introduction: motivations of dilepton measurements status on medium effects signatures

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Recent results from the HADES experiment at GSI: Dilepton production in 1-2 AGeV energy range:

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  1. Recent results from the HADES experiment at GSI: Dilepton production in 1-2 AGeV energy range: Béatrice Ramstein Institut de Physique Nucléaire d’Orsay, groupe PHEN

  2. Outline • Introduction: • motivations of dilepton measurements • status on medium effects signatures • Results from heavy-ion and p+A reactions with HADES • pp and dp reactions with HADES inclusive/exclusive dilepton channels, hadronic channels • Perspectives with pion beam • Conclusions Béatrice Ramstein

  3. Hadronic physics: Quantum ChromoDynamics Strong interaction coupling constant Particle Physics Hadron Physics Nuclear Physics perturbative QCD Non perturbative QCD Meson and nucleon degrees of freedom asymptotic freedom • Confinement • Hadronic states • Origin of hadron mass Béatrice Ramstein

  4. phases of strongly interacting matter Quark Gluon Plasma ALICE/LHC Chiral Symmetry Restoration HADES/GSI  CBM/FAIR Quark Gluon Plasma LHC SPS RHIC FAIR AGS HADES SIS/GSI hadrons KEK,JLAB,TAPS QCD bound states (hadrons)  CLAS/JLab, PANDA/FAIR Twoways of studyingstrong interaction (Quantum Chromo Dynamics): Béatrice Ramstein

  5. - ppe+e- with PANDA e- e+ e+ e- One common ideal tool : the dilepton probeintensivelyexploited at IPN • An access to hadron electromagnetic structure pp/pn reactions with HADES N N N,  N N g* q2 > 0 q2 > 0 An undistorted probe of the hot and dense phase: Heavy-ion reactions with HADES, ALICE Béatrice Ramstein

  6. Dilepton mass spectrum on a large scale Physics issues: • Low mass: - continuum enhancement ? - modification of vector mesons ? • Intermediate mass: • thermal radiation ? • charm modification • High mass: • J/ suppression ? • enhancement ? • Drell-Yan focus in this talk is on low mass region! dilepton Béatrice Ramstein Lecture II: 6

  7. r, w,  e+ g* e- on-shell g* g* e+ r, w ,  e+ e- e- N Interest of vector meson study • V l+l- JP=1- direct coupling to * • Vector Dominance Model (Sakurai 1969): coupling of a real (or virtual) photon to any electromagnetic hadronic current is mediated by a vector meson • Sensitivity of vector meson mass to Chiral Symmetry Restoration electromagnetic elastic or transition form factor off-shell Béatrice Ramstein

  8. “melting of quark condensate “ Klimt, Lutz, Weise, Phys.Lett.B249(1990) 386 Vector meson in-medium modifications (I): 1st scenario: « dropping mass » Linked to Chiral Symetry Restoration In the limit of massless u,d,s quarks, exact symmetry of the QCD lagrangian But not of QCD vacuum and excited states (spontaneous breaking of chiral symmetry) • Scaling inspired by chiral effective models: • Brown-Rho PRL66(1991) 2720 • effect confirmed by QCD sum rules , Quark Meson Coupling • Hatsuda and Lee PRC46 (1992) 34 , Kwon et al. PRC78 (2008) 055203 • Saito et al. PRC55 (1997) 2637 Béatrice Ramstein

  9. cf. studies at Saturne, -holes excitations in nuclei M. Roy-Stephan et al. 1980-1997 N(1520)  r r r r D(1232) + ... + N-1 N-1 Vector meson modifications (II): schematic summary ! see e.g. Rapp and Wambach 0901.3289 for a recent review I 2nd scenario: « in-medium broadening » • Spectral functions of the mesons in the medium: coupling to resonances N.B. Connexion of vector meson spectral function to quark condensates via QCD sum rules Hadronic many-body approach Rapp and Wambach EPJA 6 (1999) 415 Rapp, Chanfray and Wambach NPA 617, (1997) 472 Béatrice Ramstein

  10. CBM QGP SPS HADES Na60 SIS-100 RHIC CBM AGS KEK,JLAB,TAPS hadrons SIS-18 G7 Experimental signatures ? meson studies inultra-relativistic heavy-ion reactions Arnaldi et al., PRL 100,022302 (2008) Mass shift excluded !  Experiments: HELIOS, CERES, Na50,Na60 at CERN RHIC,…. Excess over cocktail  • Most sensitive result • from Na60 / CERN in (158 AGeV) + In • Broadening of  spectral function is favoured, no mass shift • also results by STAR and PHENIX at RHIC Béatrice Ramstein

  11. Bevalac (1988-1993) HADES DLS Na60 • pp/pd, Ca+Ca, C+C 1.04 AGeV • mass resolution : 10-20% • 30-40% systematical error Data: R.J. Porter et al.: PRL 79(97)1229 Model: E.L. Bratkovskaya et al.: NP A634(98)168,BUU, vacuum spectral function Strong dilepton enhancement over hadronic cocktails not explained even by in-medium mass shifts and broadening DLS puzzle DLS Results for /o ~ 1-3, T < 100 MeV (Heavy-ion collisions E/A=1-2 AGeV) QGP SPS CBM RHIC AGS SIS-100 SIS-300 SIS-18 Bevalac hadrons KEK,JLAB,TAPS G7 Béatrice Ramstein

  12. G7/CLAS/Jlab QGP Na60 HADES SPS SIS-100 SIS-300 CBM RHIC AGS hadrons SIS-18 KEK,JLAB,TAPS G7 / in cold nuclear matter contradictory results for  • KEK p+A 12 GeV shift of  mass- 9% • G7/CLAS + A E = 0.6-3.8 GeV  slightly broadened P>0.8 GeV/c + A No modification of  spectral function observed but strong absorption Béatrice Ramstein

  13. Hades « strategy » • Study dilepton emission in dense and hot matter (cf.DLS/Berkeley) A+A reactions in the 1-2 AGeV energy range C+C, Ar+KCl, Ag+Ag, Au+Au • cold matter at normal nuclear density p+Nb (cf KEK and JLab) • Elementary collisions pp, dp and -p • reference to heavy-ion spectra • understand dilepton production mechanism (exclusive channels) • Simultaneous measurements of hadronic channels (pp NN, pp NN) Cross-checks on known channels, detailed information on baryonic resonance production • …. strangeness measurement program: K- , K0,, (1385), (1405) Béatrice Ramstein

  14. SIS The Collaboration • Catania (INFN - LNS), Italy • Cracow (Univ.), Poland • Darmstadt (GSI), Germany • Dresden (FZD), Germany • Dubna (JINR), Russia • Frankfurt (Univ.), Germany • Giessen (Univ.), Germany • Milano (INFN, Univ.), Italy • München (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 GSI Béatrice Ramstein

  15. HADES 2nd generation dilepton spectrometer Side View START • Acceptance:Full azimuth, polar angles 18o - 85o • Pair acceptance  0.35 • Particle identification: • RICH,Time Of Flight, Pre-Shower (pad chambers & lead converter) ( also MDC (K)) • Trigger: • 1st Level: charged particle multiplicity (~10 kHz) • 2nd Level: single electron trigger (~2.5 kHz) • Momentum measurement • Magnet: ∫Bdl = 0.1- 0.34 Tm • MDC: 24 Mini Drift Chambers • Leptons: x~ 140  per cell, p/p ~ 1-2 % • M/M ~ 2% at  peak Upgrade (2010) New DAQ ~20 kHz new MDCs for plane 1 RPC θ <45° FW  < 7° Béatrice Ramstein

  16. IPN contribution IPN team Jean-Louis Boyard (retired 2008) Jean-Claude Jourdain (retired 2001) Thierry Hennino Malgorzata Gumberidze (post-doc) Hubert Kuc (PhD 2010-2013) Tingting Liu (PhD 2010) Emilie Morinière (PhD 2008) Béatrice Ramstein Michèle Roy-Stephan (retired 2006) …+Jacques Van de Wiele (phenomenology) R&D détecteurs, B. Genolini, M. Imre, J.P. Le Normand, A. Maroni, T. Nguyen Trung, J. Pouthas, V. Poux, P. Rosier C. Théneau, 4th plane of 6 drift chambers drift cell (14x10 mm2) active area 3.5 m2 Béatrice Ramstein

  17. HADES subdetectors Magnet Coils MDC I RICH PreShower LH2 target (IPN) TOF Béatrice Ramstein

  18. Lepton Identification with HADES Drift Chamber: Track reconstruction Pre-Shower condition RICH pattern e- + + + momentum % velocity momentum ∙ charge C+C 2 AGeV

  19. Dielectron DATA analysis: g e+ Q~ 2.20 e- • Conversion pairs reduction • Close partner (e+e- <90 ) removal • Momentum cut 80 < P [MeV/c] < 2000 • Track fitting quality cut • Comb. Background subtraction Mee < 150 MeV/c2 Like-sign pairs Mee > 150 MeV/c2 event mixing • Efficiency correction using GEANT simulation • Normalization: Heavy-ion: 0 yield (Nπo = ½ (Nπ- + Nπ+)) pp/dp: elastic scattering Measured rates span over 5 orders of magnitude Systematic errors: 20% efficiency correction 10% combinatorial background 15% 0 normalization 22% - 27% Total Béatrice Ramstein

  20. First HADES data: e+e- production in C+C excess e+e- yield over long-lived sources Well known dilepton sources ° Dalitz decay: °  e+e- (BR ~ 1.2 %) N N  Dalitz decay   e+e- (BR ~ 0.6 %) « long-lived source » N,  Direct ω  e+e- (B.R. 7.2 10-5) Dalitz ω  °e+e- (B.R. 7.7 10 -4) n p Not measured ! p n Efficiency-corrected di-electron spectra, normalized to the number of neutral pions: Cocktail generated with PLUTO Phys. Lett. B 663(2008)43 Phys.Rev. Lett 98(2007) 052302 Excess yield related to radiation from nucleon (NN Bremstrahlung) NN NNe+e-and baryonic resonances (Dalitz decays) Cocktail A:0+η+ ω = “long-lived” components only Excess in the intermediate mass region Béatrice Ramstein

  21. Calculation: E.L.Bratkovskaya et al. Nucl. Phys. A634 (1998) 168 Hadron String Dynamics E. Bratkovskaya and W.Cassing, nucl-th/0712.0635 DLS DLS M [GeV/c²] HADES first HADES data put an end to the DLS puzzle 1997:transport models failed to explain DiLeptonSpectrometer (Berkeley) data 2007:DLS and HADES agree and are compatible with new transport model calculations G.Agakichiev et al. Phys. Lett. B 663,43 (2008) M [GeV/c²] Solved by improved treatment of elementary dilepton sources Béatrice Ramstein

  22. BUU Barz et al. UrQMD Bleicher et al. IQMDThomere et al. RQMD: E.Santini et al C+C 2 AGeV  Dalitz NN HADES data: Phys Rev. Lett 98 , 052302 (2007) However, theoretical situation is still unclear ! DLS puzzle solved by better treatment of elementary processes ? NN reactions needed to constrain  Dalitz decay and NN Bremsstrahlung Béatrice Ramstein

  23. Using NN collisions as a reference Apart = 38 „reference”     N-1 N-1  regeneration  N NN   0 e+e- PLB690(2010)118  subtracted N e+e- + N-N bremsstr. 0.25 0.5 0.75 1.0 Mee[GeV/c2] • Only small excess in C+C with respect to NN collisions • Large enhancement in intermediate mass region in Ar+KCl Béatrice Ramstein

  24. Transport model predictions for Ar+KCl pp  ppω HSD OBE HSD: E.L. Bratkovskaya, W. Cassing, Nucl.Phys.A 807 (2008) 214 -250. HADES data : Phys.Rev.C84:014902,2011. Inclusive /ω cross-sections not known important ingredient of transport model calculations  can be measured in pp reactions Béatrice Ramstein

  25. NN reactions needed as reference for heavy-ion dilepton spectra to provide inputs or constraints for models Intrinsic interest : dilepton emission is probing time-like electromagnetic structure of hadronic transitions! pp E=1.25 GeV, 2.2 GeV ,3.5 GeV and dp at 1.25 GeV Béatrice Ramstein

  26. Results for pp reaction at 1.25 GeV p p p p D+ * e+ e-- GM(q2) GM(0)~3 0.6m2 q2 = M2inv(e+e-) = M*2 > 0 • below  threshold • only 2 dilepton sources HADES: Phys.Lett.B690 (2010)118 • ° Dalitz decay ° =4.5 mb branching ratio ° → e+e-1.2 % •  Dalitz decay : =3/2 ° branching ratio  → Ne+e-(QED :4.2 10-5) • pp bremstrahlung expected to be small Time-like N-  transition electromagneticform factors Iachello and Wan • Resonance model results: • ° Dalitz • Dalitz)+ effect of Iachello FF Béatrice Ramstein

  27. Form factors GM(q2), GE(q2), GC(q2) Take into account intrinsic hadronic structure q20 : « Time like « electromagnetic structure of N -  transition complex functions known only at q2=0 from N →  → N GM(0)=3, GE(0)=0.04, GC(0)=0.2 models available, VDM p p D+ * + → p e+ D+ q2=M2inv(e+e-)=M2* >0 e-  q2 = 0 e+ Complementary to Space-Like region: e- Radiative decay BR=0.56%0.04% Data: Mainz, JLab D+ * q2=M2* <0 p  Dalitz decay differential width exact QED calculation : 3 amplitudes: e.g. Magnetic, Electric and Coulomb Krivoruchenko et al. Phys.Rev.D 65 (2001) 017502 Froehlich et al EPJA45:401-411,2010 Inconsistencies in the litterature, see Béatrice Ramstein

  28. Results for pp reaction at 1.25 GeV p p p p D+ * e+ e-- GM(q2) GM(0)~3 0.6m2 q2 = M2inv(e+e-) = M*2 > 0 • below  threshold • only 2 dilepton sources HADES: Phys.Lett.B690 (2010)118 • ° Dalitz decay ° =4.5 mb branching ratio ° → e+e-1.2 % •  Dalitz decay : =3/2 ° branching ratio  → Ne+e-(QED :4.2 10-5) • pp bremstrahlung expected to be small Time-like N-  transition electromagneticform factors Iachello and Wan • Resonance model results: • ° Dalitz • Dalitz)+ effect of Iachello FF Béatrice Ramstein

  29. exclusive analysis ppppe+e-at 1.25 GeV preliminary p p1 p2 p D+ e+ q2=M2inv(e+e-)=M2* e- (p,e+,e-) invariant mass(GeV/c2) • reconstructed by (p,e+,e-) Mee>140 MeV/c2 No acceptance corrections ! first simulations: E.Morinière (PHD Orsay) data analysis: W. Przygoda (Cracovie) Helicity studies: T. Liu (PHD Orsay) B. Ramstein et al., Hadron 2009 proceedings simulation of  production followed by Dalitz decay consistent with  production studied via hadronic channels acceptance corrected preliminary • First measurement of  Dalitz decay! • Branching ratio in agreement with QED value (4.2 10 -5) within ~20% • Helicity consistent with 1+cos2 • constraint on pp Bremsstrahlung contribution Béatrice Ramstein cos(CMpe+e-)

  30. Increasing the energy in ppreactions Inclusive e+e- production in HADES acceptance ° e+e- e+e- e+e- (, ) M. Gumberidze, IPN Orsay R. Holzmann, GSI Ne+e- Béatrice Ramstein 30

  31. Transport models for pp E=3.5 GeV Transverse momentum Ne+e- 0.47<Mee[GeV/c2]]<0.7 UrQMD: K. Schmidt, et al. Phys. Rev. C 79, 064908 (2009) Invariant mass Too strong  Dalitz decay contribution and vector meson contribution from resonances N(1520),… HADES data in pp reactions provide efficient checks for models Béatrice Ramstein

  32. The most sensitive check :exclusive final state ppe+e- ppppe+e- E=3.5 GeV • Non –mesonic sources ! • Resonance Dalitz decay: • N(1520), (1680) ? • Electromagnetic form factors ? • on-going comparison to model predictions Mmisspe+e- ~ Mp • limitations in pp reactions: • resonance production mechanism • resonance mass distribution •  induced reactions will provide better sensitivity Béatrice Ramstein A. Dybczak, Cracow

  33. Baryonic resonances Dalitz decay and Vector Dominance Model electromagnetic Form Factors: Towards a consistent description including interferences • point-like R-* vertex • coupling fixed from known RN decays ppppe+e- E=3.5 GeV + /  e+e- M. Zetenyi and Gy. Wolf. arXiv:nucl-th/0202047v1, Phys. Rev. C 67, 044002 (2003). • extented Vector Meson Dominance (eVDM) • uses coupling of resonances to vector mesons M. I. Krivoruchenko et al., Ann. Phys. 296, 299 (2002). Béatrice Ramstein

  34. n qn p p D++ Hadronicchannels: exclusive pion production at 1.25 and 2.2 GeV • absolute normalisation • from elastic scattering • Very good agreement with resonance model • Teis et al. ZPA 356(1997) 421 + refinements in both isospin channels • Consistent picture at E=1.25 GeV and 2.2 GeV • important check for dilepton analysis (° and resonances are dilepton sources !)  production: 1 exchange T. Liu PhD Orsay,13/12/2010 arXiv:0909.3399[nucl-ex] preliminary 2 production analysis: M. Gumberidze, Orsay Béatrice Ramstein

  35. Hadronic channels: pp (E=2.2 and 3.5 GeV), pp (3.5 GeV)     MX (MeV/c2) ppppXpp+- °E=3.5 GeV E=3.5 GeV pppppp+- ° pppp pppp role of N*(1535) in  production p invariant mass K.Teilab PhD (U.Frankfurt) Cross-check of dilepton analysis Béatrice Ramstein

  36. Cross-section measurements Using both leptonic and hadronic channels / inclusive cross sections pp→ppρX and pp→ppωX E=3.5 GeV o HADES O inclusive • exclusive  inclusive/exclusive cross sections ᵒ Béatrice Ramstein

  37. Perspectives of pion beam experiments Béatrice Ramstein

  38. GSI pion beam Expected Intensities for Space Charge Limit and 100% extraction efficiency I ~ 106/s Pion momentum 0.6 < p <1.5 GeV/c Seuils pour mesons, resonances s 1.21 1.52 1.68 acceptance p/p = 4% η ω Béatrice Ramstein

  39. N(1520)  r r r r D(1232) + ... + N R g* N-1 N-1 e+ r, w, e- • well-known production mechanism • fixed resonance mass MR=sqrt(s) • exclusive - p  n e+e- channels ( contribution can be rejected ) Motivations of N experiments with HADES Time-Like electromagnetic form factors Space-Like electromagnetic form factors n  - q2 <0 fixed e+ R * e+ p * R q2 > 0 variable p e- e- - e-- p studied at JLab/CLAS • Vector Dominance Model  link between resonance Dalitz decay and / coupling • Essential input for understanding dilepton production in nuclear medium Béatrice Ramstein

  40. Simulations for dilepton production below  threshold P=0.8 GeV/c (omega threshold pth=1.03 GeV/c)  -+ pe+e-X Efects of electromagnetic form factors ? Important interference effects expected between I=0 (ω) and I=1 (ρ) channels Linked to coupling to baryonic resonances M. Lutz, B. Friman, M. Soyeur, NPA 713 (2003) 9 Titov and Kämpfer EPJA 12 (2001) 217 after missing mass cut -pe+e- n H. Kuc PhD Orsay/Cracovie Mee(GeV/c2) Béatrice Ramstein

  41. Motivations of N experimentswith HADESup-dateafterSeillac symposium (I) V.Shklyar and U. Mosel (Giessen) B. Saghai (Saclay) E. Oset (Valencia) Data (differential cross-sections) badly needed for updated Phase Shift Analysis Many open problems N2N (N* contributions to N,,N,…) P=0.8 GeV/c s1/2=1.56 GeV M cos N* →ρ n → +- n N* N* →+-n M H. Kuc PhD Orsay/Cracovie Béatrice Ramstein

  42. Motivations of N experimentswith HADESup-dateafterSeillac symposium (II) •  - p n • Low quality and contradictory data • coupling of η to S11(1650),P11(1710) , • origin of resonance like structure seen in n … and also •  - p  n,  - p  K, -p  N • (1405) structure issues: (1405) →K- p and (1405) → πΣ(1194) B. Saghai (Saclay), E. Oset (Valencia) Béatrice Ramstein

  43. Conclusions: HADES experiments • Heavy-ion program: • a lot of data: dilepton invariant mass, pt, rapidity, helicities in C+C, Ar+KCl, p+Nb • No evidence yet for unexplained medium effects • Not mentioned: very fruitful strangeness production program • HADES upgrade completed Au+Au in 2012, Ag+Ag in 2014 • HADES@FAIR in 2018 (only part of the collaboration) but a consistent description of dilepton production in all systems is needed !! • Elementary reaction program • Selectivity on dilepton sources (  Dalitz decay (first measurement ) ,  Dalitz decay,  production,…) • Cross section measurements • Sensitivity to time-like electromagnetic form factors of nucleon and resonances • perspectives of pion beam experiments ( 2013) • Dilepton channels  Unique chance to study Time-Like electromagnetic structure of higher lying resonances • Eta production, two pion production, new data (differential spectra) needed • Electromagnetic calorimeter  neutral meson detection Perspectives for IPN team up to 2014-2015 in parallel to PANDA Béatrice Ramstein

  44. Merci de votre attention Béatrice Ramstein

  45. Béatrice Ramstein

  46. B’ B’ V= , ,  B B 0.6m2 GMN-/3GD Constituent quark core meson cloud GM(q2) Iachello two-component quark model Collaboration with F. Iachello Wan & Iachello, int. J. Mod. Phys. A20(2005) 1846 Direct coupling Coupling mediated by vector mesons • unified description of baryonic form factors • analytical derivation of form factor starting from wave functions • N- transition: 4 parameters fitted on • elastic nucleon FF (SL+TL) • SL N- transition GM • analytical continuation to Time-Like region Béatrice Ramstein Emilie Morinière’s PhD

  47. Motivations of dilepton spectroscopy in A experiments • New HSD calculations HSD: preliminary • strong medium effects are predicted HSD’09 => similar to W. Cassing, Y.S. Golubeva, A.S. Iljinov, L.A. Kondratyuk, Phys. Lett. B 396 (1997) 26 Béatrice Ramstein

  48. d/dp M < 140 MeV/c2 M > 140 MeV/c2 p momentum in d reference frame - QF simulation Note: absolute normalization! Scaling factor for massive pairs Experimental tests of Quasi-Free (p,n): Spectator tagging is under control - QF simulation Béatrice Ramstein

  49. A Photon Calorimeter for HADES • Adding a calorimeter to HADES offers: • Better lepton ID • Neutral mesons in p+A & A+A • Direct photons in p+A & A+A • Hadron zoo in p+p & π+p Photon decays: π0 →γγ η →γγ η’ →γγ ω→π0γ→γγγ + Dalitz decays Béatrice Ramstein

  50. Strangeness production with HADES the  (1405) case missing °    (1405) mass 4 particles detected pp 3.5 GeV p,K+ missing mass Béatrice Ramstein

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