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Dilepton cocktail in p +A experiments

Dilepton cocktail in p +A experiments. E lena Bratkovskaya 12-13 February 2009 , Meeting of HADES experiments with pion beams, Orsay, France.  - p bound  n at rest  ne + e -. “ at rest ”:. ‚History‘ of p - + A reactions. W. Schön , H. Bokemeyer, W. Koenig and V. Metag,

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Dilepton cocktail in p +A experiments

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  1. Dilepton cocktail in p+A experiments Elena Bratkovskaya 12-13 February 2009 , Meeting of HADES experiments with pion beams, Orsay, France

  2. -pbound  nat rest  ne+e- “at rest”: ‚History‘ of p-+ A reactions W. Schön, H. Bokemeyer, W. Koenig and V. Metag, Act. Phys. Pol. B 27 (1996) 2959 p-+ Pb, 1.3 GeV/c Study of in-medium effects such as dropping w mass within p-+ A reactions: => Possibility for an experimental observation of the mass shift of w: w decay ‚inside‘ Pb-nuclei

  3. Medium effects in the production and decay of vector mesons in p-+ A reactions First dynamical calculations of in-medium effects in p-+ A reactions: W. Cassing, Y.S. Golubeva, A.S. Iljinov, L.A. Kondratyuk, Phys. Lett. B 396 (1997) 26 Y.S. Golubeva, L.A. Kondratyuk, W. Cassing, Nucl.Phys.A625 (1997) 832 intranuclear cascade (INC) approach w w • Dropping mass of the vector mesons (w,f) • Collisional broadening of the vector meson width • Low momentum cuts for separation of the ‚inside‘ and ‚outside‘ components

  4. Study of in-medium effects with p-+ A reactions - BUU Similar studies with BUU:T. Weidmann, E.B., W. Cassing, U. Mosel, PRC 59 (1999) 919 • strong modification of dilepton spectra for in-medium scenarios (dropping mass and collisional broadening) • gate on low momenta (q<0.3 GeV/c) increases the signal

  5. p-+ N and p-+ A reactions - CBUU Similar studies with CBUU: M. Effenberger, E.B., W. Cassing, U. Mosel, PRC 60 (1999) 044614 -N at E = 1.3 GeV -A at E = 1.3 GeV due to R->Dr CBUU: dominant meson production via baryonic resonances (Manley model) => different model for the production of vector mesons in elementary pN and NN reactions

  6. Study of in-medium effects with p-+ A reactions - CBUU Similar studies with CBUU: M. Effenberger, E.B., W. Cassing, U. Mosel, PRC 60 (1999) 044614 -A at Ekin = 1.3 GeV • … • strong influence of baryonic resonances (e.g. N(1520)) on r-meson production

  7. p+n-> e+e-p p-p-> e+e-n constructive interference distructive interference Quantum interference of r0 and w-mesons in the p N -> e+e- N reaction M. Soyeur, M. F.M. Lutz; B. Friman, nucl-th/0003013;Nucl.Phys.A713 (2003) 97 RN+r(w) based on coupled-channel approach for m+N scattering  talk by M. Soyeur

  8. N(1520) distructive interference Baryon resonance dynamics in p+ N->N+V (V=r,w) reactions near threshold B. Kämpfer, A.I. Titov, B.L. Reznik, Nucl.Phys.A721 (2003) 583 M=0.6 GeV q=30o Invariant matrix elements squared as a function of the energy (M=0.6 GeV, q=30o) constructive interference

  9. Summary - I What systems ( p+N or p+A)? - physics key issues • p+A reactions: • in-medium effects - a collisional broadening and dropping mass of the vector mesons (r,w,f) • study of the mesonic and baryonic resonance dynamics impact on p+A, A+A • p+p(n) reactions: • control on different elementary channels • study of the baryon resonance dynamics near threshold • quantum interference of r0 and w-mesons at low energies possible ONLY for p+p(n) reactions!

  10. ‚History‘of dilepton cocktails Gy. Wolf et al.,Nucl.Phys.A517 (1990) 615 [Similar to : C.M. Ko et al., NPA 512 (1990) 772] BUU: • first calculation of dilepton production in heavy-ion collisions within a transport model • implementation of the basic dilepton channels • time integration (‚shining‘) method • discussion of in-medium effects E.B.,W. Cassing, Nucl.Phys.A807 (2008) 214 HSD : • … + • off-shell transport dynamics • dynamical treatment of resonances with broad spectral functions • in-medium effects (dropping mass, collisional broadening)

  11. e+ e+ g* N N R g* R N R N N N N e- N e- = Dilepton cocktail in HSD • All particles decaying to dileptons are first produced in BB, mB or mm collisions electromagnetic decays • ‚Factorization‘ of diagrams in the transport approach: • The dilepton spectra are calculated perturbatively with the time integration method.

  12. p N R R p p, h, r, ... Zoom: Dilepton cocktail • All particles decaying to dileptons are first produced in BB, mB or mm collisions p+p, p+A collisions p+p, p+A collisions heavy-ion collisions Lowenergy p+p reactions are dominated by resonance production and decay(important as secondary channels in heavy-ion collisions!) p-+ p

  13. Zoom: Dilepton channels electromagnetic decays  under control! p,h,D,w,r,f,...production – can be controlled by exp. data! not for HADES NN, pN bremsstrahlung = ‚background‘ radiation - hard to control by exp. data!  reliable theoretical model for NN and pN bremsstrahlung is needed!

  14. g*->e+e- Phase-space corrected soft-photon cross section: Soft-Photon-Approximation (SPA): NN and pN bremsstrahlung - SPA N N -> N N e+e- (orp N ->p N e+e-) (p) (p) ‚quasi- elastic‘ N N -> N N p N -> p N elastic NN (pN) ‚off-shell‘ correction factor SPA implementation in HSD: e+e- production in elastic NN (pN) collisions with probability: (as in Gy. Wolf et al.,NPA517 (1990) 615)

  15. Bremsstrahlung – a new view on an ‚old‘ story New OBE-model (Kaptari&Kämpfer, NPA 764 (2006) 338): • pn bremstrahlung is larger by a factor of 4 than it has been calculated before (and used in transport calculations before)! • pp bremstrahlung is smaller than pn, however, not zero; consistent with the 1996 calculations from F.de Jong in a T-matrix approach 2007 ‚DLS puzzle‘ : Experimentally: HADES = DLS ! Theory: the DLS puzzle is solved by accounting for a larger pn bremsstrahlung !

  16. HSD: Dileptons from A+A at 1 A GeV - DLS • bremsstrahlung and D-Dalitz are the dominant contributions in A+A for 0.15 < M < 0.55 GeV at 1 A GeV ! E.B., Cassing, NPA807 (2008) 214

  17. HSD: Dileptons from C+C at 1 and 2 A GeV - HADES • HADES data show exponentially decreasing mass spectra • Data are better described by in-medium scenarios with collisional broadening • In-medium effects are more pronounced for heavy systems such as Au+Au E.B., Cassing, NPA807 (2008) 214

  18. From A+A to N+N reactions Does Δ Dalitz and NN Bremsstrahlung explain the excess?  verification in NN collisions is needed

  19. HSD: Dileptons from p+p and p+d - DLS • bremsstrahlung is one of the dominant contributions in p+d for 0.15 < M < 0.55 GeV at ~1-1.5 A GeV

  20. pp, pn (pd) reactions • DLS data (low statistics and mass resolution) do not allow for definite conclusions • new (good quality) HADES data on pp, pn (pd) reactions provide an independant check for the elementary channels involved in A+A

  21. pp @ 1.25GeV : new HADES data PLUTO • D-Dalitz decay is the dominant channel (HSD consistent with PLUTO) • HSD predictions:good description of new HADES data for p+p! E.L.B. &W. Cassing, NPA 807 (2008) 214

  22. "quasi-free" p+n 1.25 GeV e+e->90 PLUTO   Quasi-free pn (pd) reaction: HADES data @ 1.25 GeV  HSD predictions underestimate the HADES p+n (quasi-free) data at 1.25 GeV: 0.2<M<0.55 GeV: h-Dalitz decay by a factor of ~10 is larger in PLUTO than in HSD since the channels d + p pspec + d + (‘quasi-free’ h-production -dominant at 1.25GeV!) and p + n d +  were NOT taken into account before! Note: these channels have NO impact for heavy-ion reactions and even for p+d results at higher energies! *In HSD:p+d = p + (p&n)-with Fermi motion according to the Paris deuteron wave function

  23. Quasi-free pn (pd) @ 1.25 GeV: h-channel Add the following channels: 1) p + n d +   2) d + p pspec + d +  Now HSD agreeswith PLUTO on the h- Dalitz decay!

  24. Quasi-free pn (pd) @ 1.25 GeV: N(1520) ?! HSD: preliminary ! N(1520) 2)M > 0.45 GeV: HSD very(!) preliminary result for p+d @1.25 GeV shows that the missing yield might be attributed to subthreshold r-production via N(1520) excitation and decay ?! N(1520) Similar to our NPA686 (2001) 568 Model for N(1520): according to Peters et al., NPA632 (1998) 109

  25. Summary II Transport models give reliable results for A+A ONLY with reliable initial input, i.e. if the elementary reactions are under control => REQUESTS: cross sections for elementary channels: experim. information baryon-baryon p+p, p+A reactions meson-baryon p+p, p+A reactions meson-meson (for higher energies) Warning: additional complication due to coherence effects in p+d reactions ! Similar ‚problems‘ with p+d reactions ?

  26. p-+ p reactions - HSD HSD: preliminary subthreshold r-meson production via N(1520) excitation and decay!

  27. p-+ A reactions: study of the baryon resonance dynamics - HSD HSD: preliminary Exp. signal: strong excess of dilepton spectra at M>0.4 GeV due to the subthreshold r-meson production via N(1520) excitation and decay! Optimal energy: Tkin < 0.7 GeV

  28. p-+ A reactions: study of the in-medium effects - HSD HSD: preliminary • in-medium scenario - a collisional broadening and dropping mass of the vector mesons (r,w,f)

  29. p-+ A reactions vs. medium effects - HSD • accounting of the in-medium effects - a collisional broadening and dropping mass of the vector mesons (r,w,f) – leads to changes of the final spectra: • reduction of the r,w,f peaks • enhancement of the dilepton yield for 0.4<M<0.7 GeV • effect is stronger for heavy nuclei HSD: preliminary HSD’09 => similar to W. Cassing, Y.S. Golubeva, A.S. Iljinov, L.A. Kondratyuk, Phys. Lett. B 396 (1997) 26

  30. p+A vs. p+A reactions Dilepton emission point of w: projection of the dN/db/dz distribution, b=(x2+y2)1/2 • p+A and p+A reactions probe the nuclear matter at (max.) normal nuclear density • vector mesons are produced dominantly at the surface and travel through the nuclei medium effects • about ½ of w‘s decay ‚outside‘, i.e. in the vacuum  experimental separation of in- and out- components by implementing low momentum cuts (as suggested in W. Cassing, Y.S. Golubeva, A.S. Iljinov, L.A. Kondratyuk, Phys. Lett. B 396 (1997) 26)

  31. p+A vs. p+A reactions : in-medium effects • p+A and p+A reactions: in-medium effects – comparable • p+A reactions: probe dominantly baryon+baryon dynamics • p+A reactions: probe dominantly meson+baryon dynamics A+A reactions

  32. Summary What systems ( p+N or p+A)? - physics key issues • p+A reactions: • in-medium effects - collisional broadening and dropping mass of the vector mesons (r,w,f) • study of the mesonic and baryonic resonance dynamics impact on p+A, A+A • p+p(n) reactions: • control on different elementary channels • study of the baryon resonance dynamics near threshold • quantum interference of r0 and w-mesons at low energies possible ONLY for p+p(n) reactions!

  33. Thanks to HADES collegues: Beatrice, Yvonne, Gosia, Romain, Piotr, Joachim, Tatyana, Volker … + Wolfgang

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