Bochum 2009 – scientific programme

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HK: Fachverband Hadronen und Kerne

HK 62: Accelerators and Instrumentation I

HK 62.6: Talk

Wednesday, March 18, 2009, 18:15–18:30, H-ZO 80

Polarimetry in Meson Photoproduction Reactions at MAMI — •Mark Sikora, Dan Watts, and Derek Glazier — University of Edinburgh, Edinburgh, UK

Accurately establishing the spectrum and properties of the excited states of the nucleon has proven to be elusive. Many states have poorly established properties and many resonances predicted by theoretical models of nucleon structure do not reveal themselves in the current experimental data. This could be because the data is not sensitive to these resonances or because the states do not exist.

Most attempts to address this situation utilise meson photoproduction from the nucleon. Such reactions can be described by 4 complex helicity amplitudes which include all the information on the process, including the excitation spectrum. Consequently, there are 16 experimental observables, of which 8 must be determined to fully constrain the amplitudes. This has led to major programmes of measurements exploiting polarised photon beams and polarised targets at the major electromagnetic beam facilities such as ELSA, JLAB and MAMI. However, the goal of a complete measurement cannot be achieved without measurements including recoil nucleon polarisation. With this aim the Edinburgh group has developed a novel design for a large aceptance recoil nucleon polarimeter for use in meson photoproduction reactions with the Glasgow/Mainz polarised photon beam and the Crystal Ball at MAMI. Preliminary measurements of double-polarisation observables in neutral pion photoproduction will be presented and compared with the various current partial wave analyses of the reaction.