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The In-medium Widths of the w and f Mesons in Nuclei

The In-medium Widths of the w and f Mesons in Nuclei. M. H. Wood (Canisius College, Buffalo, NY, USA) M. Paolone , R. Nasseripour , D. P. Weygand, C. Djalali. and the CLAS Collaboration. Vector Meson-Nucleon Interaction. Elementary process –

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The In-medium Widths of the w and f Mesons in Nuclei

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  1. The In-medium Widths of the w and f Mesons in Nuclei M. H. Wood (Canisius College, Buffalo, NY, USA) M. Paolone, R. Nasseripour, D. P. Weygand, C. Djalali and the CLAS Collaboration M. H. Wood, EMIN2009

  2. Vector Meson-Nucleon Interaction • Elementary process – • experimentally studied by beam incident on hydrogen target. (T. H. Bauer, R. D. Spital, and D. R. Yennie, Rev. Mod. Phys. 50, 261 (1978)) • In-medium interactions – • Sum of elementary interactions? • Medium effects (modified meson properties)? • Review of V-N properties in the medium • (S. Leupold, V. Metag, and U. Mosel, arXiv:nucl-th/0907.2388 (2009)) • Mass decrease – more nucleon resonances to couple. • Width increase – modification of couplings and virtual loops. M. H. Wood, EMIN2009

  3. The Widths of w and fMesons in Nuclei With the g7a experiment at Jefferson Lab (JLab), access to the in-medium meson widths. Reaction : g+ A --> V X --> e+e- X ( no FSI) (Eg < 4 GeV) (Talk on r meson modifications – D. P. Weygand, 19 Sep) Mesonsr: M=768 MeVG= 149 MeV JP=1-w: M=782 MeVG = 8 MeVf: M=1020 MeVG = 4 MeV Measurement : nuclear transparency ratio provides access to in-medium wN and fN total cross sections. Get width from s*VN. Nuclear transparency ratio TA=sA/AsN M. H. Wood, EMIN2009

  4. south linac north linac injector C A B Jefferson Lab (JLab) • Superconducting e-Accelerator • Imax=200 mA • Emax=6 GeV , dE/E=10-4. • 1500 physicists, ~30 countries • operational since 1997 M. H. Wood, EMIN2009

  5. Particle Detection In CLAS Excellent /e discrimination: 5.4x10 -4 for one and 2.9x10-7for two leptons. M. H. Wood, EMIN2009

  6. CEBAF Large Acceptance Spectrometer (CLAS) Electromagnetic Calorimeter Lead-Scintillator for detecting electrons Superconducting Torus Magnet 6 Superconducting coils for deflecting charged particles EC e/p rejection factor : 10-2 e- : inbending tracks e+: outbending tracks Gas Cherenkov Counter e/p separation Drift Chambers Ar-CO2 6500 channels/sector to measure the path of a charged particle CC e/p rejection factor : 10-1 EC/CC rejection factor : 10-3 Rejection factor for e+e- : 10-6 Time-of-Flight Hodoscope 48 Scintillators/sector for measuring a particle’s travel time M. H. Wood, EMIN2009

  7. p e+ e- Event Selection Segmented target Foils of Carbon, Iron, Titanium, and Lead LD2 (LH2) as control Sample event Pb Fe Ti C C C C LD2 M. H. Wood, EMIN2009

  8. e+e- Mass Spectra Mass Spectra with r, w, and f mesons simulation Mass Spectra after subtraction of the r meson contribution. M. H. Wood, EMIN2009

  9. Giessen calculations Giessen calculations w/ Spring8 absorption strengths JLab SPring8 f Absorption Comparison to other work Comparison to Glauber calculations Normalized to carbon SPring8 g A gf A’ g K+K- A’ (Eg=1.5-2.4 GeV) T. Ishikawa et al. Phys. Lett. B 608, 215 (2005) In-medium: s*fN ~ 25 – 55 mb Elementary: sfN < 10 mb Needed for RHI calculations. M. H. Wood, EMIN2009

  10. Normalized to carbon w Absorption Thein-mediumwidthis G=G0+Gcollwherecoll =grv*VN Giessen calculations P. Mühlich and U. Mosel NPA 773, 156 (2006) Valencia calculations Kaskulov, Hernandez & Oset EPJ A 31, 245 (2007) JLab (upper/lower limits) CBELSA_TAPS M. Kotullaeta al., PRL 100, 192302 (2008) M. H. Wood, EMIN2009

  11. Momentum Dependence • Possible explanation for disagreement is momentum dependence of the in-medium interactions. • Average w meson momentum: • 1.1 GeV (CBELSA-TAPS) • 1.7 GeV (JLab) • Instead of scaling each result, compare a common momentum bin. • CBELSA-TAPS has data in five momentum bins. M. H. Wood, EMIN2009

  12. In-medium r-wInterference Decay channels JLab : w -> e+e- CBELSA-TAPS : w -> p0g Destructive Constructive M. H. Wood, EMIN2009

  13. r-wInterference Interference model after subtracting the r meson Data from the 2H target M. H. Wood, EMIN2009

  14. Summary and Conclusions CLAS was an excellent tool for these studies: • e+e- from rare leptonic decay of light vector mesons are identified. • Clear , wand fsignals in the invariant mass spectrum. The meson: • From transparency ratios, width >200 MeV! • Disagreement with CBELSA-TAPS result • momentum dependence? • in-medium destructive r-w interference? The meson: • From transparency ratios, in medium total cross section ~25-55mb • Agreement with SPring8 result. Next at Jlab: • High Statistics measurement of e+e- production on H2 (on tape) • Conditionallyapproved g7b high statistics data (LD2, C, Fe, Nb, Sn) M. H. Wood, EMIN2009

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