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Presentation by T. Gogami 2015/6/15 (Mon)
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Equation state of neutron matter
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Density dependence of the symmetry energy Heavy ion collision Nuclear binding energy Isobaric analog state Neutron skin thickness M.B.Tsang, …, T.Murakami et al., PRC 86, 015803 (2012)
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Difference of RMS radii between neutrons and protons
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Neutron skin thickness of 208 Pb Constraint for L L.W. Chen et al., PRC 72, 064309 (2005)
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Measurements up to now [22] B. Klos et al., PRC 76 (2007) 014311 [23] B.A. Brown et al., PRC 76 (2007) 034305 [24] L.W. Chen et al., PRC 72 (2005) 064309 [25] A. Krasznahorkay et al., PRL 66 (1991) 1287 [15] A. Carbone et al., PRC 81 (2010) 041301 [17] A. Tamii et al., PRL 107 (2011) 062502 [20] J. Zenihiro et al., PRC 82 (2010) 044611 [21] E. Friedman, NPA 396 (2012) 46
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Experiments with electromagnetic probes Different systematic errors from strongly interacting probes No successful measurements of the neutron distribution
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Elastic scattering of polarized electrons from 208 Pb Parity-violating asymmetry: Weak Form factor Neutron density S. Abrahamyan et al., PRL 108, 112502 (2012) X. Roca-Maza et al., PRL 106, 252501 (2011)
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Coherent Photoproduction of π 0 meson from 208 Pb
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MAMI at Johannes Gutenberg-Universität Mainz Okazaki Gutenberg Exp. hall
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Schematic drawing of Experimental setup Beam: 180 – 240 MeV tagged photon Tagged photon resolution ~ 2 MeV full width 2×10 5 γ s -1 MeV -1 Enriched 208 Pb (0.52 mm, 99.5%) Crystal Ball: 672 NaI (94% of 4π) C.M. Tarbert et al., PRL 100, 132301 (2008)
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Schematic drawing of Experimental setup Beam: 180 – 240 MeV tagged photon Tagged photon resolution ~ 2 MeV full width 2×10 5 γ s -1 MeV -1 Enriched 208 Pb (0.52 mm, 99.5%) Crystal Ball: 672 NaI (94% of 4π) C.M. Tarbert et al., PRL 100, 132301 (2008)
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Analysis Energies and angles of 2γ π 0 momentum q = (P γ - P π ) Cross section as a function of q
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Analysis (Yield of Coherent Reaction) π 0 energy assuming coherent reaction
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Efficiency etc. π 0 detection efficiency: ~40% Photon tagging efficiency: ~40% π 0 not originating from target: ~1%
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Fitting to the experimental results Known: a p =0.447 fm, c p =6.680 fm c n = 6.28 to 7.07 fm a n = 0.35 to 0.65 fm σ q = 0.02 – 0.03 fm -1 depending on E γ
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Results
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Neutron skin of 208 Pb Halo character
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Summary
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