Photoabsorption and Photoproduction on Nuclei in the Resonance Region

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1 Photoabsorption and Photoproduction on Nuclei in the Resonance Region Susan Schadmand Institut für Kernphysik First Workshop on Quark-Hadron Duality Frascati, June 6-8, 2005

2 electromagnetic probes Hadron Physics hadronic probes COSY KEK GSI CERN PSI RHIC Why Why are are quarks quarks confined confined within within hadrons? hadrons? How How are are hadrons hadrons constructed constructed from from their their constituents? constituents? What What is is the the relation relation parton parton degrees degrees freedom freedom and and the the low low energy energy structure structure hadrons? hadrons? Do Do glueballs glueballs (ggg) (ggg) and and hybrids hybrids (qqg) (qqg) exist? exist? What What is is the the origin origin hadron hadron masses masses?? How How are are hadrons hadrons modified modified when when embedded embedded in in nuclei nuclei?? What What is is the the role role chiral chiral symmetry symmetry??

3 Photoabsorption on Nucleons Excited States the Nucleon N. Bianchi et al. PRC 54( 1996) 1688 γ + p γ + p D 13 P 11 S 11 from γ + d from γ + d broad and overlapping resonances characteristic meson decay tagging resonances

4 Meson Photoproduction from the Proton sum γ + p total partly preliminary! SAPHIR (Bonn) CBELSA (Bonn) DAPHNE, TAPS (Mainz) GRAAL (Grenoble) E γ (GeV) π o π + π + π - π + π o π o π o η ω K + Λ K + Σ o K o Σ φ S. Schadmand

5 Nuclear Photoabsorption: γ + A total cross section per nucleon V.Muccifora et al., PRC 60 (1999) γ + p total γ + A total (average nucleus) ELSA evidence for medium modification: no resonance structures above 0.6 GeV D 13 Nρ decay branch Mosel et al. modified ππ interaction/ interferences Hirata et al. Oset et al. resonance broadening in medium? study meson production (quasifree production)

6 ρ Meson in the Nuclear Medium effect on photoabsorption: J. Lehr et al., NPA 671 (2000) 503 W. Peters et al., NPA 632 (1998) 109 elementary momentum dependent potential modified D 13 N ρ width ρ N =ρ 0 prediction: in-medium broadening ρ meson coupling to D 13 (1520) effect on ρ e + e ρ ππ modified D 13 N ρ width depletion 2. resonance region possible

7 NUCLEAR PHOTOABSORPTION AT PHOTON ENERGIES BETWEEN 300 AND 850 MEV full calculation 1 pion (f) (g) 2 pion (h) cooperative effect the interference in two-pion photoproduction processes collision broadening and N * (1520) pion distortion in the nuclear medium the change the interference effect by the medium plays an important role

8 on baryon resonances: Medium Effects A(γ, π o ) B. Krusche et al., PRL 86 (2001) 4764 Fermi-motion meson decay N * N + meson collisional broadening Γ Γ (Pauli blocking) Γ N * N N * N quenching reduction meson yield N * N NN N * -propagation mass / width self energy investigating the second resonance region: comparison heavier nuclei with deuteron resonance contribution qualitatively not changed no indication for broadening or depletion on mesons: absorption/rescattering modified meson-meson interaction chiral symmetry restoration meson-resonance coupling

9 Meson Photoproduction from the Proton Meson Photoproduction from Nuclei sum π + ππ+η sum π o + π o π +η PRELIMINARY Photoabsorption (α = 1) Meson Production α = (2/3) p, C (γ, π o ) p, C (γ, π + ) p (γ, π + π - ) p, Pb (γ, π + π o ) p, Pb (γ, π o π o ) p, Pb (γ, η) S.Schadmand

10 The Role Chiral Symmetry Breaking m N = 938 MeV >> m q 5 10 MeV determined by interaction among partons chiral symmetry = fundamental symmetry QCD for massless quarks chiral symmetry broken on hadron level 1 +, ( 1535) 600 MeV χ-sym. nature ( 938) To understand the origin mass: can we (partially) restore chiral symmetry? changes hadron properties in the nuclear medium

11 Model predictions for ρ and ω mesons T. Renk et al., PRC 66, , 2002 ρ/ω W. Peters et al., NPA 632 (1998) 109 ρ hadronic many body effects S. Zschocke et al., Phys. Lett. B 562 (2003) 62 ω M. Lutz et al., Nucl. Phys. A 706 (2002) 431 ρ ω variation in ω-mass due to density dependence 4 quark condensate structure in spectral function due to coupling to baryon resonances

12 Experimental Method: 4π Photon Spectrometer ELSA E e =3.5 GeV Crystal Barrel CBELSA/TAPS γ MAMI-B E e =0.82 GeV MAMI-C E e =1.5 GeV γ Crystal Ball Crystal Ball@MAMI/TAPS

13 ω-mass in nuclei from photonuclear reactions J.G.Messchendorp et al., EPJ A11 (2001) 95 advantage: π o γ large branching ratio (8 %) no ρ-contribution (ρ π o γ : ) disadvantage: π o -rescattering background reactions: γa 2 π o + X mass resolution

14 ω-mass in nuclei from photonuclear reactions γ + Nb@ 1.2GeV; ω π ο γ J.G.Messchendorp et al., EPJ A11 (2001) 95 (including detector resolution) simulation: 2π o background reduce rescattering using cut on kinetic energy the pion supression background in the region interest visible shoulder in lineshape from mass shifted mesons

15 inclusive ω π 0 γ signal for LH 2 and Nb target D. Trnka et al. PRL (2005) difference in line shape ω signal for proton and nuclear target

16 contribution from ω in-medium decays D. Trnka et al. PRL (2005) ω decays in vacuum removed by subtracting ω mass distribution measured with LH 2 target (75%) strength in-medium ω decays concentrated around masses 722 MeV mass drop by about 8% at estimated baryon density about 0.6 ρ 0 consistent with m ω =m 0 ( ρ/ρ 0 )

17 Indications for Medium Modifications Mesons vector mesons ρ e + e - in ultra-relativistic heavy-ion collisions (CERES/CERN) ρ e + e - in pa collisions at 12 GeV (KEK) ω π o γ by comparison p(γ,ω) and A(γ,ω) Bonn) Φ K + K - systematics from A(γ,ω) (LEPS@SPRing8) π - p nω on bound protons planned at GSI pseudoscalar mesons K + and K - mesons from yields in near threshold heavy-ion reactions GSI) scalar mesons ``σ meson: π o π o interaction (TAPS@MAMI, Crystal Ball) charm sector J/ψ, D: experiments planned at PANDA@FAIR So far, experiments are in accordance with theoretical scenarios for changes hadron properties in the nuclear medium. Studying the in-medium behavior hadrons is a promising approach to learn more about the origin their mass.