1. GDR 20141 B. Ramstein, IPN Orsay Perspectives of recent HADES experiments with a pion beam 16/12/2014, GDR annual meeting, Ecole Polytechnique B. Ramstein

2. Outline GDR 2014 B. Ramstein 2  Introduction: General motivations of HADES experiments  Results from NN reactions with HADES Role of baryonic resonances in dilepton emission  Perspectives of HADES measurements with the GSI pion beam ( data taking in summer 2014)  Conclusions

3. Present explanation of dilepton spectra at ultra-relativistic energies (NA60, STAR, PHENICS) Dileptons: a probe of in-medium vector meson modifications : Rapp and Wambach EPJA 6 (1999) 415 Rapp, Chanfray and Wambach NPA 617, (1997) 472 « in-medium broadening » In-medium spectral function depends on  NN* coupling main players: N(1520), N(1720),  (1910) Source of  mesons at 1-2 AGeV NN  NR  NN   N  R  N  Dominant source of  mesons at ultra relativistic energies  +  -  Coupling of ρ to baryonic resonances can be studied in NN and  N collisions at 1-2 GeV GDR 2014 B. Ramstein 3

4. 4 The Collaboration SIS  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 4 GDR 2014 B. Ramstein HADES strategy: e + e -, strangeness, charged hadron production Nuclear matter studies: A+A,p+A, π - +A Elementary reactions p+p, quasi-free np, π - +p

5. 5 Acceptance: Full azimuth, polar angles 18 o - 85 o Pair acceptance  0.35 Particle identification: RICH, Time Of Flight, Pre-Shower (pad chambers & lead converter) ( also MDC (K  )) Trigger: ~ 50 kHz Momentum measurement Magnet: ∫ Bdl = 0.1- 0.34 Tm MDC: 24 Mini Drift Chambers Leptons:  x~ 140  per cell,  p/p ~ 1-2 % HADES 2 nd generation dilepton spectrometer GDR 2014 B. Ramstein 5  M/M ~ 2% at  peak Electromagnetic Calorimeter for experiments with SIS 100/FAIR SIS Larger plane of drfit chambers built at IPNO

6. Exclusive analysis : pp  ppe + e - at 1.25 GeV 6 p pp e+e+ ++ p p1p1 q 2 =M 2 inv (e + e - )=M 2  * e-e- First measurement ! Dalitz decay branching ratio in agreement with QED value (4.2 10 -5 ) BR= 4.42 10 -5  20% ( syst.)  9% (stat) Supported by the analysis of 1  production channels PhD T. Liu Orsay 2010 HADES collab: E.P.J. A48 (2012) 74 on-going Partial Wave Analysis (collab. With Bonn-Gatchina)

7. pp  e + e - X E=2.2 GeV, 3.5 GeV GDR 2014 B. Ramstein 7 E=2.2 GeV E=3.5 GeV Comparison to cocktail of point-like dilepton sources Direct production of  /  Dalitz decay of  resonance (point-like) Effect of electromagnetic form factors / Coupling of  to baryonic resonances ? Hades data, PRC85 054005 (2012) Hades data, EPJA48 (2012) 64 Exclusive analysis G. Agakishiev et al. Eur.Phys.J. A50 (2014) 8

8. From NN to πN reactions From NN to πN reactions GDR 2014 B. Ramstein 8 J. Weil, H. van Hees and U. Mosel, EPJA 48, 111 (2012) GiBUU transport model  ρ is modified in elementary collisions, due to coupling to baryonic resonances  Strong constraints for medium effects interpretation Advantages of  - p  ne + e - :  interaction better known  fixed mass of the resonance in s channel  much larger acceptance for exclusive channels electromagnetic  - p  ne + e - hadronic  - p  p  --, n  +  --, p  0  --  N -1 N*/  pp 3.5 GeV  e+e+ e-e-  R N

9. GDR 2014 B. Ramstein 9 Pion beam experiments GSI pion beam momentum 0.6 < p <1.5 GeV/c Unique facility in world at present able to bring new pion beam data All what we know about N* couplings to ρ N,  π,  N is based on the analysis of 240000 events (bubble chamber < 1980)  s (GeV) ω η 114 kevents 72 kevents SAID, data base, CNS, GWU http://gwdac.phys.gwu.edu 1.42.1.61.8  s (GeV)

10. GDR 2014 B. Ramstein 10 Pion beam experiments 2 Double-Sided Silicon sensors 100 x100mm 2, 300 μ m thick 2 x128 channels Pion beam tracker: Diamond detectors  Two beam periods at GSI in summer 2014 in beam sharing mode  Restricted program due to limitations on Beam time: last operation period before SIS100 integration (FAIR) Pion flux: up to 120000/s (radiation safety limit) Beam optics calculation: responsibility IPNO

11. Pion beam: in-medium strangeness production GDR 2014 B. Ramstein 11 targetK 0 _S K+K+ K-K- Λ ϕ W102k100k4.2k92k213 C129.5k99.7k6.9k78.6k398 φ production Very premiminary 1st data set: π - +A p=1.7 GeV/c Interest of IRFU to include strangeness in INCL cascade calculations main goal= strangeness production

12. GDR 2014 B. Ramstein 12 Pion beam: ρNN(1520) couplings 2 nd data set: energy scan in π - + p around N(1520) Main goal: determine precisely the ρNN(1520) couplings by measuring  - p  - p,  - p  -  + n,  - p  -  0 p  crucial to constrain the predictions of in-medium modifications of the ρ meson spectral function  fundamental interest: structure of N(1520) GDR 2014 V. Shklyar Hades symposium, Seillac 2011 Controversial results with Manley PWA analysis: Bonn-Gatchina PWA analysis ρ contribution factor 10 lower dominated by Δπ contribution π-pπ+π pπ-pπ+π p π-pπ+π pπ-pπ+π p

13. Quality of pion beam data : di-pion production GDR 2014 B. Ramstein 13 π + π - production (CH) n C Very premiminary

14. Pion beam:dielectron channels GDR 2014 14 Controversial yield predictions: Highly dependent on ρNN* couplings and ρ/ω interference B. Kaempfer, A Titov, R.Reznik NPA 721(2003)583 M.F.M. Lutz, B. Friman, M. Soyeur Nuclear Physics A 713 (2003) 97–118 VDM electromagnetic form factors: M. Zetenyi and G. Wolf, Phys.Rev. C86 (2012) 065209 Resonance model: J.Weil Sensitivity of M ee distribution to to Δπ and ρN contributions (Bonn-Gatchina predictions) B. Ramstein 3 rd data set: π - + p  n e + e - at  s=1.49 GeV close to N(1520) pole mass and below η threshold Main goal : Time-Like electromagnetic structure of N-N(1520) transition/ coupling to ρ meson  e+e+ e-e-  R N

15. Pion beam : quality of di-electron channels GDR 2014 B. Ramstein 15 Dielectrons from (CH) n target M ee >0.12 GeV/c 2 Very preliminary Contribution of C under the neutron peak ~25%, can be easily subtracted  selection of about 300 evts π - + p  ne + e - M ee >140 MeV/c 2 π - + p  Xe + e - n On-going analysis : Electron ID, Combinatorial Background subtraction,…. F. Scozzi, PhD (IPNOrsay, TU Darmstadt)

16. Conclusion GDR 2014 B. Ramstein 16 HADES results (focus on pp/pn reactions)  selective study of e + e - production from Dalitz decay of baryonic resonances  sensitivity to Baryonic resonances Time-Like electromagnetic structure/coupling to ρN  Indispensable complement for in medium studies Recent pion beam experiment  Very promising data: strangeness, π + π -, e + e -  expected precise determination of N(1520) coupling to ρN  Continuation at SIS18 in 2017-2018 ? HADES at FAIR : pp, pA with an ECAL

17. Thank you GDR 2014 B. Ramstein 17 Hubert Kuc (codirection IPNO/UJ Kracow) PhD defense Thursday 18 December, Salle des conseils IPN Orsay,14h30 « Di-pion and di-electron production in quasi-free np reactions with HADES »

18. Baryon Resonance electromagnetic Dalitz decays GDR 2014 B. Ramstein 18 QED: point-like R-  * vertex M. Zetenyi et al. PRC 67, 044002 (2003). extended Vector Dominance Model M. I. Krivoruchenko et al. Ann. Phys. 296, 299 (2002). Covariant model (bare quark core + meson cloud) G. Ramalho and T. Pena, Phys.Rev. D85 (2012) 113014 π+π -  π+π -   Fixed « Δ » mass p+p 3.5 GeV

19. 19 Motivations of  - p  ne + e - experiments with HADES Motivations of  - p  ne + e - experiments with HADES  e+e+ e-e-  R N   N -1 N(1520) +... Time-Like electromagnetic form factors e+e+ n e -- **  - - R q 2 > 0 variable p e+e+ e-e- e-e- ** -- R p Space-Like electromagnetic form factors q 2 <0 fixed studied at JLab/CLAS Inverse pion electroproduction p unique chance to study the Time-Like electromagnetic structure of N*(1520) to constrain the in-medium modifications of the ρ meson spectral function  - p  ne + e - below ρ/ω production threshold at  s=1.52 GeV/c 2 “off-shell ρ production” GDR 2014 B. Ramstein 19

20. Subtraction of long-lived sources The  meson in hot and dense hadronic matter from SIS18 to SPS Source of  mesons Source of  mesons at 1-2 AGeV NN  NR  NN   N  R  N   Source of  mesons Dominant source of  mesons at ultra relativistic energies  +  -  Depends on RN  coupling 20 Coupling of ρ to baryonic resonances can be studied in NN collisions at 1-2 GeV mass shift excluded ! Arnaldi et al., PRL 100,022302 (2008) agreement with in-medium ρ meson broadening G. Agakishiev et al. Phys.Rev. C84 (2011) 014902 Dilepton excess over long-lived sources In +In 158 GeV/u GDR 2014 B. Ramstein

21. GDR 2014 B. Ramstein 21

22. π N  N π π : Existing data SAID, data base, CNS, GWU http://gwdac.phys.gwu.edu 7.3 kevents 114 kevents 72 kevents 69 kevents 15 30 15 pπ- π0 pπ- π0 nπ+ π-nπ+ π- nπ+π+nπ+π+ pπ+π0pπ+π0 1.42. W (GeV) 1.61.8 More recent data (TRIUMF,LAMPF,BNL) do not cover the region between 1.32 and 1.9 GeV  high statistics differential distributions are needed 22

23. Resonance excitation in 2  channel ss N(1440,1710) +  (1910) N(1535) +  (1620) N(1720) +  (1600) N(1520) +  (1700) N(1680) +  (1905) N(1675) +  (1925)  s =1.5 dominance of resonance channels D 13 (1520) & P 11 (1440) Predictions: 2014: B-G (A.Sarantsev) K-matrix approach constraints from  N,  N  - p  R   N,  (I=0)N,  (I=1)N + non resonant contributions