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. 2014 Jun 20;112(24):242502.
doi: 10.1103/PhysRevLett.112.242502. Epub 2014 Jun 18.

Neutron skin of (208)pb from coherent pion photoproduction

C M Tarbert  1 , D P Watts  1 , D I Glazier  1 , P Aguar  2 , J Ahrens  2 , J R M Annand  3 , H J Arends  2 , R Beck  4 , V Bekrenev  5 , B Boillat  6 , A Braghieri  7 , D Branford  1 , W J Briscoe  8 , J Brudvik  9 , S Cherepnya  10 , R Codling  3 , E J Downie  3 , K Foehl  1 , P Grabmayr  11 , R Gregor  12 , E Heid  2 , D Hornidge  13 , O Jahn  2 , V L Kashevarov  10 , A Knezevic  14 , R Kondratiev  15 , M Korolija  14 , M Kotulla  6 , D Krambrich  4 , B Krusche  6 , M Lang  4 , V Lisin  15 , K Livingston  3 , S Lugert  12 , I J D MacGregor  3 , D M Manley  16 , M Martinez  2 , J C McGeorge  3 , D Mekterovic  14 , V Metag  12 , B M K Nefkens  9 , A Nikolaev  4 , R Novotny  12 , R O Owens  3 , P Pedroni  7 , A Polonski  15 , S N Prakhov  9 , J W Price  9 , G Rosner  3 , M Rost  2 , T Rostomyan  7 , S Schadmand  12 , S Schumann  4 , D Sober  17 , A Starostin  9 , I Supek  14 , A Thomas  2 , M Unverzagt  4 , Th Walcher  2 , L Zana  1 , F Zehr  6 ; (Crystal Ball at MAMI and A2 Collaboration)
Affiliations

Neutron skin of (208)pb from coherent pion photoproduction

C M Tarbert et al. Phys Rev Lett. .

Abstract

Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of (208)Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

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