Slide 1

HADES versus DLS: no puzzle anymore ! Elena Bratkovskaya 22.10.2007, Workshop Bremsstrahlung in dilepton production GSI, Darmstadt Slide 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 0.15e+e-)=4.5. 10 -5 Calculate probability P(t) to emit an e+e- pair at each time t and integrate P(t) over time! : t 0 < t < t abs : t 0 NN bremsstrahlung - SPA Soft-Photon-Approximation (SPA): N N -> N N e + e - - >e + e - Phase-space corrected soft-photon cross section: SPA implementation in HSD: e + e - production in elastic NN collision with probability: elasticNN quasi- elastic N N -> N N off-shell correction factor Slide 11 NN bremsstrahlung: OBE-model OBE-model: N N -> N N e + e - prepost postpre + gauge terms charged meson exchange contact terms (from formfactors) The strategy to restore gauge invariance is model dependent! Kaptari&Kmpfer, NPA 764 (2006) 338 Slide 12 Bremsstrahlung a new view on an old story 2007 (era of HADES): The DLS puzzle is solved by accounting for a larger pn bremsstrahlung !!! New OBE-model (Kaptari&Kmpfer, NPA 764 (2006) 338): pn bremstrahlung is larger by a factor of 4 than it has been pn bremstrahlung is larger by a factor of 4 than it has been calculated before (and used in transport calculations)! 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 pp bremstrahlung is smaller than pn, however, not zero; consistent with the 1996 calculations from de Jong in a T-matrix approach Slide 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 bremsstrahlung is the dominant contribution in p+d for 0.15 < M < 0.55 GeV at ~1-1.5 A GeV Slide 14 HSD: Dileptons from A+A at 1 A GeV - DLS bremsstrahlung and -Dalitz are the dominant contributions in A+A for 0.15 < M < 0.55 GeV at 1 A GeV ! bremsstrahlung and -Dalitz are the dominant contributions in A+A for 0.15 < M < 0.55 GeV at 1 A GeV ! Slide 15 Preliminary HADES data HSD: Dileptons from C+C at 1 and 2 A GeV - HADES HADES data show exponentially decreasing mass spectra HADES data show exponentially decreasing mass spectra Data are better described by in-medium scenarios with collisional broadening Data are better described by in-medium scenarios with collisional broadening In-medium effects are more pronounced for heavy systems such as Au+Au In-medium effects are more pronounced for heavy systems such as Au+Au Slide 16 HSD: Dilepton p T and y spectra from C+C at 1 A GeV - HADES HSD predictions for p T and y spectra are in good agreement HSD predictions for p T and y spectra are in good agreement with the HADES data for all M-bins! with the HADES data for all M-bins! Preliminary HADES data Slide 17 HSD: Dilepton p T and y spectra from C+C at 2 A GeV - HADES HSD predictions for p T and y spectra are in good agreement HSD predictions for p T and y spectra are in good agreement with the HADES data for all M-bins! with the HADES data for all M-bins! M0.55 GeV/c 2 0.15 can reproduce the results by Gy. Wolf et al., i.e. IQMD (Nantes) and BRoBUU (Rossendorf) ! Slide 27 Summary: Bremsstrahlung in transport models Transport models give similar results ONLY with the same initial input ! => REQUESTS: unification of the treatment of dilepton production in transport models: Similar cross sections for elementary channels Similar cross sections for elementary channels Time-integration method for dilepton production Time-integration method for dilepton production Off-shell treatment of broad resonances 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 d /dMdydp T (s,M,y,p T ) Slide 28 Summary HADES succeeded: the DLS puzzle is solved ! Outlook: need new pp and pd data from HADES for a final check!