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Electromagnetic probes MAMI, Jefferson Lab & MAX-Lab

Electromagnetic probes MAMI, Jefferson Lab & MAX-Lab. Daniel Watts University of Edinburgh. Scope of talk. Outline the present engagement of the Glasgow and Edinburgh groups at these facilities. No attempt to be comprehensive Choose two topics reflecting current research:

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Electromagnetic probes MAMI, Jefferson Lab & MAX-Lab

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  1. Electromagnetic probes MAMI, Jefferson Lab & MAX-Lab Daniel Watts University of Edinburgh

  2. Scope of talk • Outline the present engagement of the Glasgow and Edinburgh groups at these facilities. • No attempt to be comprehensive • Choose two topics reflecting current research: • Neutron skins • The nucleon excitation spectrum

  3. Timelines, upgrades & UK investment 2005 2010 2015 2020 2025 MAX@ 0.25 GeV 106gs-1MeV-1 MAMI@ 1.5 GeV 105gs-1MeV-1 JLab@ 12 GeV 108gs-1 Facility upgrade

  4. Timelines, upgrades and investment 2005 2010 2015 2020 2025 UK Hardware at Max-lab Edinburgh Ge-6 Array Glasgow active target MAX@ 0.25 GeV 106gs-1MeV-1

  5. Timelines, upgrades and investment • UK investment at MAMI • Glasgow photon tagger • Edinburgh Particle-ID detector • Edinburgh nucleon polarimeter • Glasgow photon beam profiler 2005 2010 2015 2020 2025 MAMI@ 1.5 GeV 105gs-1MeV-1 Facility upgrade

  6. Timelines & Upgrades 2005 2010 2015 2020 2025 UK Investment at Jefferson Lab Polarised beam setup (Glasgow) Big bite focal plane array(Glasgow) Part of neutron polarimeter for Gen (Glasgow) Nucleon polarimetry R&D (Edinburgh) JLab@ 12 GeV 108gs-1

  7. Neutron Skins Our knowledge of the shape of stable nuclei is presently incomplete e.g. 208Pb: RMS charge radius known to < 0.0001 fm RMS neutron radius only known to ~0.2 fm !! Horowitz PRC63 025501 (2001) New techniques to attack this fundamental problem are important and timely Relativistic mean field Skyrme HF URCA Cooling n → p + e- + n e- + p → n + n

  8. Neutron skins • Angular distribution of p0 → accurate information about matter distribution ds/dW ~ A2(q/kg)P32|Fm(q)|2sin2qp Photon probe  Interaction well understood p0 meson – produced with ~equal probability on protons AND neutrons. Select reactions which leave nucleus in ground state Reconstruct p0 from p0→2g decay

  9. Neutron Skins : Preliminary analyses 208Pb(g,p0) Eg=185±5 MeV No neutron skin 0.2fm neutron skin 2nd Max. No skin 1st minima No skin One of over 30 spectra!!

  10. Excitation spectrum of nucleon • A primary motivation of the new EM beam facilities • → better establish the nucleon excitation spectrum • Use meson photoproduction reactions • g + N → N* → N + p • t small → resonances are broad (DEDt ~ ħ) D(1232)P33 N(1440)P11 N(1520)D13 N(1535)S11 D(1600)P33 Cross section 0.5 1.0 1.5 Eg (GeV)

  11. The way forward – double polarisation Polarisation of g target recoil Observable

  12. Edinburgh Recoil Polarimeter: Cx, OX, T, P Graphite scatterer Hydrogen target cell n(q,f) =no(q){1+A(q)[Pycos(f)–Pxsin(f)]

  13. Edinburgh Recoil Polarimeter: Cx, OX, T, P p(g,p)p0 SAID PWA MAID PWA First proof of principle for a 4p nucleon polarimeter !! 1000 hours of approved → pion photoproduction Future h, w, multipion etc.

  14. Double polarisation at Jefferson Laboratory Worldwide activity Frozen spin polarised target development – beam-target experiments start 2008 (Glasgow, Edinburgh) Strange meson photoproduction e.g. g + p → K+ + L0 Self-analysing (weak) decay → recoil polarimetry !! Beam-recoil experiments under analysis (Glasgow) Polarised target will enable complete measurement C.Gordon, K. Livingston et. al.

  15. Summary Worldwide activity New generation of EM beam facilities offer unique opportunities to address fundamental questions in nuclear and hadron physics Other EM beam research programmes with UK leadership Magnetic moments of nucleon resonances Nuclear three-body forces Nuclear short-range correlations Tests of chiral perturbation theory in strange quark sector Search for multiquark states Exotic hybrid mesons and glueballs Nucleon form factors

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