1. Motivation for studies of pion induced dilepton production Motivation for pion experiments (perspective from 2001): Subthreshold  /  production amplitudes in  N  VN a)Key measurement for in-medium  /  mass modification? b) unique tool to study Vector Meson coupling to baryon resonances Vector mesons production off nucleus

2. Spectral function of  meson    Vacuum:   one example W. Peters et.al. NPA 632(1998)109: Nuclear matter: additional terms +  N-1N-1 N(1520) +...  (1232)  N -1  dominant role of baryons (also for SPS) ! important for future CBM even at high T int. with baryons is dominant !

3. Direct  -N Interactions (‘Rhosobars’) In medium vector meson properties and  N scattering forward scattering amplitude low density theorem Optical and detailed balance theorem B.Friman N.PhysA610(1996) R. Rapp and J.Wambach In medium properties are related to elementary T VN !

4. Resonance contribution at vector mass region- off shell contributions? URQMD: arXiv:0811.4073v2: resonance modelHSD : arXiv:0712.0635v2

5. Resonance contribution at vector mass region- off shell contributions? data seems to favour smaller VM contribution at the pole

6. p-n puzzle? pp vs “quasi-free” pn @ 1.25 Model Calculations: a) NN-bremsstrahlung Kaptari & Kämpfer (K&K) b) ,  yield constraint by data.  Dalitz decay Krivoruchenko et al. Phys. Rev. D 65 (2001) 017502 + VMD form-factor (Q. Wan and F. Iachello, Int. J. Mod. Phys. A 20 (2005) 1846) pn data are not (yet) described by calculations ! off –shell  contribution with strong isospin depend.?

7. Vector meson production in πN I=1/2 (N * ) I=3/2(  ) 1.π - + p  n e+e- reactions in Isospin space  + n : exit channel  + n : exit channel I=1 isovectorI=1 isoscalar T VN π- + n = T I=0(  ) +T I=1(  ) different resonance probed via  /  2. π + + n : π - + p rotated in Isospin space around Y by 180 0 T VN π + +n = T I=0(  ) - T I=1(  ) opposite sign of iso-vector part (-1) I access to vector-meson Baryon interaction !

8. Meson and resonanse production with pion beams E thresh [GeV] M x [GeV/c 2 ]   //  pp->ppX  - p->Xn Meson production thresholds / / direct resonance excitation: second, third res. region strong off-shell contribution for  production D 13 (1520)  partial wave analysis of Nππ channel. What about  ? D. M. Manley et al.Phys. Rev. D 30(1984) 904 p>0.5 GeV/c weak contribution from  (1232)  (1232)->Ne+e- small !! N,  M. Effenberger et al. PHYS. REV. C 60(1999) 044614 p~1.3 GeV/c 1.211.521.68 ss

9. VDM model: f  /  decay couplings Relative phase of T  p->(  )N determines interference pattern  - n reactions  /  production in  - n reactions  - p ->e + e - n Exclusive:  - p ->e + e - n  + n ->e + e - p (via  + +d)?  + n ->e + e - p (via  + +d)?

10. T  /  amplitudes in  N  (  /  ) N reactions Coupled channels calculations(  N,  N,  N, ,…) - opposite sign of T  /  : destructive interferences in π - p and positive in  + n Large influence of I=1/2 below threshold: S 11 (1535) and D 13 (1520) T VN  - p  (  /  ) n  + n  (  /  ) p M.F.M. Lutz, B. Froman, M. Sayuer. / Nuclear Physics A 713 (2003) 97–118

11.  - n (published-2003)  /  interference yield in  - n (published-2003)  - n  e + e - n  + p  e + e - p M.F.M. Lutz, B. Friman, M. Sayuer Nuclear Physics A 713 (2003) 97–118

12.  /  interference: different models M.F.M. Lutz, B. Friman, M. Sayuer Nuclear Physics A 713 (2003) 97–118 B. Kaempfer, A Titov, R.Reznik Nucl. Phys. A721(2003)583 A.Titov, B.Kaempfer EPJA 12(2001)217 quantitatively same picture but differs in details: resonance contributions (i.e D 15 (1520) not important) coupling strengths (quark model vs coupled chann.) Virtual photon angular distributions in CM sensitive to res.contributions m e+e- =0.6 GeV

13. Becondary beams (C+Be, N+Be,..): 1.Primary beam intensity ? (~0.5*SCL) ~ 6.5*10 10 N 2 ions/cycle reached in tests (2005) 2.duty factor (fast ramping of SIS magnets)? 3.extraction efficiency (~0.85) ? Pion Beam profile at the target Pion momentum  p/p =4% : in beam detectors X1/X2 and Y3 (start) is necessary for pion mometum determination (  p/p =0.1% ) pion beams @GSI see Bjoern & Jurek talks

14. Proton & pion beams @GSI Intensity of pions/spill : expectations for SCL and 100% exctraction efficiency 0.6 < p <1.5 GeV/c operation region reached (2005 with N 2 beam-0.5 SCL): 1.8*10 6 /spill (4 sec long- 4 sec spill off ) @ p= 1.3 GeV/c fast ramping of SIS magnets : 1.5-2 increase in duty factor possible ?

15. Beam focus at the target position LH 2 Target: entrance part diamter 15 mm LH 2 cell diameter 25 mm  d=2*10 23 atoms/cm 2 25mm

16. Bunch mark:  production in  - p reactions large cross sections AND kinematically complete measurement ! Reaction rates total rates : LH 2 at top I π =0.5*10 6 /sec and  reac =80 mb  e+e- @ 1.3 GeV (   = 2.5mb * 7.2 * 10 -5 =180 nb) rec. in HADES : Yield per day (24 day)= R*0.5(DAQ)*0.7(DF machine)=54/day (~ 10/day measured for pp run) measured in 2006 !

17.  - n (in times  /  interference yield in  - n (in times when HADES proposal was prepared-2001) Optimal energy @  s=1.55GeV 80 nb

18.  /  production in  - N reactions  - p   n M e+,e- >0.5 GeV dominated by  and  e + e - decays Note: very small  ->Ne+e- !  - n    -,  - n  n  -  is subthreshold ! M e+,e- >0.5 GeV dominated by  ->e + e - F 37 (1930), D 35 (1950) with I 3/2 = -1/2 important for π - A reactions ! (see Elena’s talk) E.Bratkovskaya Phys.Rev.C60(1999) E kin= 1.3 GeV (  s=1.89)

19. Simulations HADES proposal-2001 e+e- missing mass e+e- missing mass:  - + n  e+e- n + X selection of  /  suppression:  ->e+e- ,  0  0, …. cocktail 4  cocktail HADES acc e+e- miss. Mass

20. Landolt-Boernstein, New Series I / 12b PLUTO simulation’s (HADES proposal 2003) 8o nb: ~20 day 180 nb: ~50 day missing mass cut on nutron !  e+e-  suppressed!

21. Omega production in  A p e+e- < 300 MeV/c  - p bound  n  e + e - n  „at rest”: mass modifications in  0  e+ e- 208 Pb -- HADES W.Schoen et al. Acta Phys.PolB27(1996)2959 M.Effenberger et al. Nucl-th/9901039 in‘99 spectacular effects predicted…

22. Measured:  +A (CBTAPS/CLAS) incident photon energy range E  = 900 – 2200 MeV Preliminary V.Metag priv. comm. no mass shift in-medium broadenning: transparency measurement   ~ absorption =  v  abs  90 MeV !  (  ) =217  14 p e+e- >0.8 GeV/c arXiv:0707.2324v3 00 CLAS

23. Theory’2008: Sensitivity to an in-medium mass shift E  = 1500 – 2200 MeV for E  = 1500 – 2200 MeV effect only observable for extremely hard cut on ω momentum: E  = 900 – 1200 MeV possible mass shift observable near threshold even without cut on ω momentum Gi-BUU simulations: K. Gallmeister et al. Prog. Part. Nucl. Phys. 61 (2008) 283 3 scenarios: 1.) no in-medium modification 2.) broadening 3.) broadening and mass shift

24. Any chance for HADES? HADES proposal 2006 HSD: calculations (E. Bratkovskaya, D. Mishra)  experiment exp. rates: 25 day at 1.3 GeV/c and maximal luminosity p+Nb @ 3.5 GeV/c rates: expected 40/day measured 10/day 1.17 GeV 3.5 GeV

25. Vector mesons  /  at SIS p+p at 3.5 GeV PRELIMINARY    2005 40 Ar+ 38 KCl 1.75 AGeVp+ 92 Nb 3.5 GeV  2007 2008 “on-line spectrum!” Data are available! No quick answer to the question on in-medium  /  spectral function ! Only comprehensive analysis (in progress) of the pp/p+A/and A+A can give answer resonance contribution?

26. Conclusions ( to be work-out during this meeting ) π - p (π + n ) reactions below  threshold – sensitive tool to study baryon-vector meson dynamics : 1.relevant for in-medium properties (SIS/18/300->SPS) 2.separation of vector/isovector em.current (intereference pattern) πA reactions –probe for in-medium vector meson properties and low momentum + see other contributions (Madaleine, Laura, Elena, Gyuri,…) Experiments: very challenging !!! beam intensity, in-beam pion tracking, broad focus->large background

27. Di-electrons from  - A reactions  - Pb @ E kin= 1.3 GeV R->  R->  E.Bratkovskaya et.al. Phys.Rev.C60(1999) No mass modifications R->  and mass modifications Final result depend on unknown elementary cross sections !!