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Dilepton Cocktail in P+A Reactions: Medium Effects & Resonance Dynamics Study

Explore the history, effects, and dynamics of dilepton production in P+A reactions, discussing in-medium effects, resonance dynamics, and quantum interference in elementary reactions. Investigate the impact of baryonic resonances and dropping mass of vector mesons on dilepton spectra. The study includes research on constructive and destructive interference in vector meson production, as well as the influence of baryonic resonances on meson production.

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Dilepton Cocktail in P+A Reactions: Medium Effects & Resonance Dynamics Study

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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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