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Vector Mesons in the Nuclear Medium

Vector Mesons in the Nuclear Medium. Volker Metag II. Physikalisches Institut, Universität Gießen. introduction. medium modifications of vector-mesons: 1) -meson: CERES, KEK-PS325 2) -meson: CB/TAPS@ELSA. outlook: medium modification in the charm sector: D-mesons: PANDA@FAIR. summary.

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Vector Mesons in the Nuclear Medium

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  1. Vector Mesons in the Nuclear Medium Volker Metag II. Physikalisches Institut, Universität Gießen introduction medium modifications of vector-mesons: 1) -meson: CERES, KEK-PS325 2) -meson: CB/TAPS@ELSA outlook: medium modification in the charm sector: D-mesons: PANDA@FAIR summary invited talk given at CHIRAL-05, RIKEN, Tokyo, Japan, 15. –17. February 2005

  2. Mass [GeV] Motivation Hadrons = excitations of the QCD vacuum QCD-vacuum: complicated structure characterized by condensates • In the nuclear medium: • condensates are changed • change of the hadronic excitation energy spectrum • widespread experimental activities to search for in-medium modifications of hadrons

  3. 1.) lowering of in-medium mass 2.) broadening of resonance for rB, T  theoretical predictions for mass changes of vector mesons in the nuclear medium T. Renk et al., PRC 66 (2002) 014902 experimental approach: dilepton spectroscopy: r, w, f e+e- reconstruction of invariant mass from 4-momenta of decay products: essential advantage: no final state interaction

  4. -mass in nuclei M. Effenberger et al. W. Schön et al.Act. Phys. Pol. B 27 (96) 2959 PRC 60 (1999) 044614 expected signal: -A at p = 1.3 GeV/c -pbound  nat rest  ne+e- “at rest”: | pw |  | pF | exp: detect e+e- HADES

  5. gA   + X p g p0g g  w p0 g g -mass in nuclei from photonuclear reactions J.G.Messchendorp et al., Eur. Phys. J. A 11 (2001) 95 advantage: • p0g large branching ratio (8 %) • no -contribution (  0 : 7  10-4) disadvantage: • p0-rescattering

  6. expected mass distribution for p, Nb (including detector resolution and 2p0 background) after cut on p0kinetic energy within 0.6 < Mp0g< 0.8 :

  7. The accelerator facility ELSA at Bonn ELSA = Elektron Strecher Anlage

  8. The Crystal Barrel/ TAPS detector @ELSA tagging spectrometer: tagging range: 31% -94% of Ebeam CB: 1280 CsI modules TAPS: 540 BaF2 modules E = Ebeam - Ee

  9. 4 p detector system CB/TAPS @ ELSA Crystal BarrelTAPS 1290 CsI 528 BaF2 front view of TAPS side view g • = 00 to 3600  = 300 to 1680 • = 00 to 3600  = 50 to 300

  10. comparison of meson masses and lineshapes for LH2 and nuclear targets 0   No change of mass and lineshape for longlived mesons (0, , ) decaying outside nuclei

  11. inclusive 0 signal for LH2 and Nb target D. Trnka (Giessen) after background subtraction difference in line shape of  signal for proton and nuclear target

  12. contribution from  in-medium decays • decays in vacuum removed bysubtracting  mass distribution measured with LH2 target (64%) • strength of in-medium • decays concentrated around masses of 725 MeV • mass drop by about 7% at estimated baryon density of about 0.55 0 consistent with m =m0 (1 -  /0); for  = 0.15

  13. momentum dependence of  signal • mass modification only for p 0.5 GeV/c first indication for an in-medium modification of the  meson mass !!

  14. photoproduction of  mesons off nuclei • A   A at E  1.2 GeV (CB/TAPS@ELSA) in-medium  mass distribution (0) exp: D. Trnka (Giessen) theo: P. Mühlich et al., nucl-th/0310067 m =m0 (1 -  /0); for  = 0.16 comparison to BUU calculation assuming first experimental indication for a dropping  mass in the nuclear medium

  15. CB/TAPS @ MAMI C g-Beam TAPS forward wall 528 BaF2 - modules Crystal Ball 672 NaI - modules

  16. Charmed mesons in the medium @ PANDA in-medium spectral function of charmonia: consequence of dropping D-mass (cu) in the medium Ye.S.Golubeva et al., nucl-th/0212074  (3770) A. Hayashigaki, PLB487 (2000) 96

  17. FAIR Facility for Antiproton and Ion Research SIS 100 SIS 300 GSI as of today CBM HESR Super-FRS PP Elec.Cooler PANDA Atom. Phys. CR+RESR FLAIR NESR

  18. summary vector mesons: :  first evidence for medium modifications from e+e- in ultra-relativistic nucleus-nucleus-collisions (CERES/CERN);  indications for medium modifications at normal nuclear matter density from e+e- in pA collisions at 12 GeV (KEK);  :•first evidence for medium-modifications at normal nuclear matter density from 0 by comparison of p(,) and A(,) (CB/TAPS @ ELSA); • -pn on bound protons, planned at HADES/GSI; • mesons with charm: • D:planned experiments at FAIR

  19. conclusion Experiments so far are in accordance with theoretical scenarios for changes of hadron properties in the nuclear medium. Studying the in-medium behaviour of hadrons is a promising approach to learn more about the origin of their mass. We have come a little closer to understanding the mass of matter Thanks:CBELSA/TAPS collaboration (Bonn) A2-collaboration (Mainz) Giessen-team: in particular Johan Messchendorp, Susan Schadmand, David Trnka Giessen-Theory: W. Cassing, St. Leupold, U. Mosel, P. Mühlich

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