2. Bremsstrahlung* B. Kämpfer Research Center Dresden-Rossendorf Technical University Dresden * braking radiation, free-free radiation, * discovered by Nikola Tesla during high frequency research between 1888 and 1897Nikola Tesla * with L. P. Kaptari + Gy. Wolf & H.W. Barz 1. Hadron masses 2. If we would have a theory 3. Modelling, parametrizing, guessing

3. Hadrons = Excitations of QCD Ground State QCD ground state (vacuum) n,T  StarkZeeman

4. Dilute Gas Approx. Hadron Masses (Facts) hadron masses = strong interaction energy non-perturbative regime: QCD condensates / chiral symmetry

5. Hadron Masses (Visions) SU(3): numerically small pot. important Weise: enhancement via chiral gap hypothesis Hadron Masses (Facts, contd) QCD SR: QCD lattice: Poles of propagators with V quantum numbers

6. HADES data: Agakishev et al. PRL `07 BUU: Barz et al. `06/optim. C(2AGeV) + C T = 108 MeV NA50 Gallmeister et al. `01 T = 170 MeV

7. DLS Puzzle Solved by Bremsstrahlung? Barz et al.Bratkovskaya, Cassing M [GeV] Aichelin 2008: differing #(NN) vs. sqrt(s) in different models C(1 AGeV) + C 1997: bremsstrahlung... contribution was found to be small 2007: DLS puzzle... may be solved when incorporating a stronger bremsstr. contribution C(1 AGeV) + C (known since 111 years)

8. If we had a Theory, e.g. QED naive (standard perturbative) QED 2. In medium (LPM effect): strong modifications by multiple scatterings + destruct. interference 1. Scattering problem in vacuum: Gauge Invariance 3. No theory: modelling, parameterizing, guessing No Brain – No Pain

9. Virtual Bremsstrahlung S N N N N e+ e- OBE approx.: NN: np: Kroll-Ruderman

10. NNM

11. Effective Models at Work confirmed by ANKE

12. ISI + FSI Jost function formalism (important at kinematical limit of e+ e- mass) Form Factors and Gauge Invariance NN M check numerically gauge inv.

13. bremsstr. (N only) Delta total constants „adjusted“ to Shyam-Mosel results: KK  SM(4 pi)  DLS

14. no new parameters very different w/o contact term

15. Bremsstrahlung only

16. Contact term may be decisive: e.g. Compton scatt. 1. QED 2. scalar QED + = 0 (Coulomb gauge)

17. contact Contact Terms may be Large

18. VMD danger: double counting N only w/ Delta

19. question: output = input? Bethe-Salpeter amplitude with same OBE kernel:

20. x = 0.45 x = 0.50 x = 0.55

21. factorization works: sub-threshold production: w/ VDM

22. HADES: data for pp and pn at the same energy are at our disposal Spectator Distribution 1.25 1.90 3.50 pn/pp is not described

23. Conclusions - Unambigious interpretation of HADES (e+e-) data is challenging - Careful tests of elementary channels in NN - Careful test of elementary channels in pA - Careful tests of elementary channels in AA - May be bremsstrahlung solves DLS puzzle - Identification of medium modifications of vector mesons is still an interesting perspective: M, pT, y spectra required - Isolating rho spectral function (as NA60)?

24. Vor etwa vierzig Jahren schrieb der Brite Peter Higgs (* 29. Mai 1929) an einen Studenten: "Ich habe etwas völlig Nutzloses entdeckt". P. Higgs: „My Life as Boson“

25. BUU Transport Code propagation of broad resonances (Kadanoff-Baym  Cassing-Juchem, Leupold) C(2 AGeV) + C

26. Elementary Cross Sections BUU: resonsonance model  no indep. cross sects. fit of many elemt. channels at once

27. Spectral Functions

28. Gauge Invariance

29. QCD Sum Rules 4-quark condensates (factorization fails: Borel QCD condensates pert. term Landau damp. )  CB-TAPS constraints?

30. 4-q cond. = order parameter of chiral symmetry?

31. BK, Pavlenko, Zschocke, PavlenkoZschocke EPJA ´03 The Case of phi Meson fireball evolution for SIS18