presentation by t. gogami 2015/6/15 (mon). equation state of neutron matter
TRANSCRIPT
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NH Colloquium
C.M. Tarbert et al., PRL 112, 242502 (2014):
Neutron Skin of 208Pb from Coherent Pion
Photoproduction
Presentation by T. Gogami2015/6/15 (Mon)
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Equation state of neutron matter
where,
Symmetry energy factor
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Density dependence of the symmetry energy
HIC exp.
Heavy ion collision Nuclear binding energy Isobaric analog state Neutron skin thickness
M.B.Tsang, …, T.Murakami et al., PRC 86, 015803 (2012)
𝑆 (𝜌 )=𝑆0−𝐿𝜀+12𝐾 𝑠𝑦𝑚 𝜀
2+𝑂 [𝜀3]
𝜀=(𝜌0−𝜌)/(3𝜌 0)
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Neutron skin thickness:
Δ 𝑟𝑛𝑝 (¿𝑆 )=√¿𝑟𝑛2>¿−√¿𝑟𝑝
2 >¿¿¿Difference of RMS radii between neutrons and protons
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L vs
Neutron skin thickness of 208Pb Constraint for L
L.W. Chen et al., PRC 72, 064309 (2005)
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Measurements up to nowProton scattering:
fm [20]Pion scattering:
fm [21]Annihilation of antiprotons:
fm [22,23]Iso-spin diffusion in heavy ion collisions:
fm [24]Pygmy dipole resonances and electric dipole
polarizabilities of nuclei: fm [15,17,25]
[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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208Pb Radius Experiment (PREX)Elastic scattering of polarized electrons from 208Pb 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)𝜟𝒓𝒏𝒑=𝟎 .𝟑𝟑 ±𝟎 .𝟏𝟕
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Coherent Photoproduction of π0 meson from 208Pb
dependenceTwo-parameter Fermi distribution (2PF):
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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 photonTagged photon resolution ~ 2 MeV full width2×105γ s-1MeV-1
Enriched 208Pb(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 photonTagged photon resolution ~ 2 MeV full width2×105γ s-1MeV-1
Enriched 208Pb(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 2γπ0 momentumq = (Pγ - Pπ)Cross section as a function of q
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Analysis (Yield of Coherent Reaction)
Δ 𝐸𝜋diff .=𝐸𝜋
c .m .−𝐸𝜋det .
π0 energy assuming coherent reaction
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Efficiency etc.
• π0 detection efficiency: ~40%• Photon tagging efficiency: ~40%• π0 not originating from target: ~1%
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Fitting to the experimental results
𝜌 (𝑟 )=(𝑍 / 𝐴)𝜌𝑝 (𝑟 )+(𝑁 / 𝐴)𝜌𝑛(𝑟 )
Known: ap=0.447 fm, cp=6.680 fm
cn = 6.28 to 7.07 fm an = 0.35 to 0.65 fm σq = 0.02 – 0.03 fm-1 depending on Eγ
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Results
fm
fm
fm
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Neutron skin of 208Pb Halo character
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Summary
Coherent photoproduction of π0 from 208Pb fmConsistent with previous experiments