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HADES versus DLS:  no puzzle anymore !

HADES versus DLS:  no puzzle anymore !. E lena Bratkovskaya 22.10.2007 , Workshop ‚Bremsstrahlung in dilepton production‘ GSI, Darmstadt. 10 years of DLS puzzle. DLS-puzzle (since 1997):

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HADES versus DLS:  no puzzle anymore !

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  1. HADES versus DLS:  no puzzle anymore ! Elena Bratkovskaya 22.10.2007 , Workshop ‚Bremsstrahlung in dilepton production‘ GSI, Darmstadt

  2. 10 years of DLS puzzle • DLS-puzzle (since 1997): • new (1997) DLS data for C+C and Ca+Ca at 1.04 A GeV are higher than the old (1995) DLS data by ~ a factor of 5-7 at 0.15<M<0.5 GeV • Transport models: • good description of p+p and p+d data from 1 to 5 GeV • missing yield at 0.15 < M < 0.5 GeV for C+C and Ca+Ca at 1.04 A GeV • (similar results obtained by HSD ‘97 , • UrQMD’98 and Tübingen QMD‘03) 10 years of waiting for HADES …

  3. Constraints on p, h by TAPS data: • HSD: good description of TAPS data • on p, h multiplicities and mT-spectra • => p (D), h dynamics under control ! Other channels: r, w: • accounting for in-medium effects (collisional broadening of vector meson spectral functions, dropping vector meson masses) does not provide enough enhancement at intermediate M • contribution from N(1520) (E.B.&C.M. Ko, PLB 445 (1999) 265) and higher baryonic resonances are small (cf. Gy. Wolf et al., PRC67 (2003) 044002) Also: • accounting for anisotropies in e+e- emission gives only a small effect A decade of search for the solution of the DLS puzzle HSD‘98

  4. DLS versus HADES Experiment: No contradictionbetween DLS and HADES ! What about theory ?

  5. Dileptons from transport models • HSD • UrQMD 1.3 (1998) • UrQMD 2.2 (2007) (Frankfurt) • RQMD (Tübingen) • IQMD (Nantes) • BRoBUU (Rossendorf)

  6. Basic concept of HSD • HSD – Hadron-String-Dynamics transport approach • for each particle species i (i = N, R, Y, p, r, K, …) the phase-space density fi followsthe transport equations • with collision termsIcoll describing: • elastic and inelastic hadronic reactions: baryon-baryon, meson-baryon, meson-meson • formation and decay of baryonic and mesonicresonances • string formation and decay (for inclusive particle production: BB -> X , mB ->X, X =many particles) • implementation of detailed balance on the level of 1<->2 • and 2<->2 reactions (+ 2<->n multi-particle reactions in HSD) • off-shell dynamics for short-lived states BB <-> B´B´, BB <-> B´B´m mB <-> m´B´, mB <-> B´ Baryons: B=(p, n, D(1232), N(1440), N(1535), ...) Mesons: m=(p, h, r, w, f, ...)

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

  8. Time integration method for dileptons ‚Reality‘: e+ only ONE e+e- pair with probability ~ Br(r->e+e-)=4.5 .10-5 r r w e- ‚Virtual‘ – time integ. method: t0 tabs e+ r time e- tF Calculate probability P(t) to emitan e+e- pair at each time t and integrate P(t) over time! r: t0 < t < tabs w: t0 <t < infinity tF – final time of computation in the code t0 – production time tabs – absorption (or hadronic decay) time

  9. The time integration method for dileptons in HSD Dilepton emission rate: e+ r e- t0=0 time tF Dilepton invariant mass spectra: tF < t < infinity 0 < t < tF

  10. g*->e+e- Phase-space corrected soft-photon cross section: Soft-Photon-Approximation (SPA): NN bremsstrahlung - SPA N N -> N N e+e- ‚quasi- elastic‘ N N -> N N elastic NN ‚off-shell‘ correction factor SPA implementation in HSD: e+e- production in elastic NN collision with probability:

  11. Kaptari&Kämpfer, NPA 764 (2006) 338 OBE-model: N N -> N N e+e- NN bremsstrahlung: OBE-model ‚pre‘ ‚post‘ ‚pre‘ ‚post‘ + gauge terms The strategy to restore gauge invariance is model dependent! charged meson exchange contact terms (from formfactors)

  12. 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)! • pp bremstrahlung is smaller than pn, however, not zero; consistent with the 1996 calculations from de Jong in a T-matrix approach 2007 (era of HADES): The DLS puzzle is solved by accounting for a larger pn bremsstrahlung !!!

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

  14. 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 !

  15. HSD: Dileptons from C+C at 1 and 2 A GeV - HADES Preliminary HADES data • 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

  16. HSD: Dilepton pT and y spectra from C+C at 1 A GeV - HADES Preliminary HADES data • HSD predictions for pT and y spectraare in good agreement • with the HADES data for all M-bins!

  17. M<0.15 GeV/c2 0.15<M<0.55 GeV/c2 M>0.55 GeV/c2 HSD: Dilepton pT and y spectra from C+C at 2 A GeV - HADES Preliminary HADES data • HSD predictions for pT and y spectraare in good agreement • with the HADES data for all M-bins!

  18. Ernst et al, PRC58 (1998) 447 Bremsstrahlung in UrQMD 1.3 (1998) SPA: Bremsstrahlung-UrQMD’98 smaller than bremsstrahlung-Kaptari’06 by a factor of 3-6 SPA implementation in UrQMD (1998): e+e- production in elastic NN collisions (similar to HSD)

  19. Ernst et al, PRC58 (1998) 447 Dileptons from pp and pd - UrQMD 1.3 • „old“bremsstrahlung: missing yield for p+d at 0.15 < M < 0.55 GeV at ~1-1.5 A GeV

  20. Ernst et al, PRC58 (1998) 447 Dileptons from A+A - UrQMD 1.3 • „old“bremsstrahlung: missing yield for A+A at 0.15 < M < 0.55 GeV at 1 A GeV • (consistent with HSD with „old SPA“)

  21. D. Schumacher, S. Vogel, M. Bleicher, Acta Phys.Hung.A27 (2006) 451 Dileptons from A+A - UrQMD 2.2 (2007) NO bremsstrahlung in UrQMD 2.2

  22. C. Fuchs et al., Phys. Rev. C67 025202(2003) Dileptons from pp and pd - RQMD (Tübingen) • NObremsstrahlung: missing yield for p+d at 0.15 < M < 0.55 GeV at ~1-1.5 A GeV

  23. C. Fuchs et al., Phys. Rev. C67 025202(2003) HADES - RQMD‘07 Dileptons from A+A - RQMD (Tübingen) DLS - RQMD‘03 1 A GeV • NO bremsstrahlung in RQMD • too strong D-Dalitz contribution (since no time integration?)

  24. M. Thomere, C. Hartnack, G. Wolf, J. Aichelin, PRC75 (2007) 064902 Bremsstrahlung in IQMD (Nantes) HADES: C+C, 2 A GeV SPA implementation in IQMD (?): e+e- production in each NN collision(i.e. elastic and inelastic) !? - differs from HSD and UrQMD’98 (only elastic NN collisions are counted!)

  25. H.W. Barz, B. Kämpfer, Gy. Wolf, M. Zetenyi, nucl-th/0605036 Bremsstrahlung in BRoBUU (Rossendorf) SPA implementation in BRoBUU (?): e+e- production in each NN collision(i.e. elastic and inelastic) ! - similar to IQMD (Nantes)

  26. Test in HSD:bremsstrahlung production in NN collisions (only elastic vs. all) In HSD assume: e+e- productionfrom „old“ SPA bremsstrahlung in each NN collision (i.e. elastic and inelastic reactions) => can reproduce the results by Gy. Wolf et al., i.e. IQMD (Nantes) and BRoBUU (Rossendorf) !

  27. Summary: Bremsstrahlung in transport models • Transport models give similar resultsONLY with the same • initial input ! • => REQUESTS: • „unification“ of the treatment of dilepton production in transport models: • Similar cross sections for elementary channels • Time-integration method for dilepton production • Off-shell treatment of broad resonances • + • Consistent microscopic calculations for e+e- • bremsstrahlung from NN and mN collisions! We need: clear separation of the individual contributions in a form applicable in transport codes, e.g. many-dimensional matrix (or parametrization) for ds/dMdydpT (s,M,y,pT )

  28. Summary HADES succeeded: the DLS puzzle is solved ! Outlook: need new pp and pd data from HADES for a final check!

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