In recent years there has been an upsurge in interest in Compton scattering experiments as a means to understand the internal structure and dynamics of the nucleon. Compton Scattering was the subject of a Nobel Prize in 1972, when Arthur Holly Compton was cited for “the effect named after him”. Since then, it has become an undergraduate laboratory standard experiment. However recent technological advances have allowed Compton scattering to once again become a tool used for research at the forefront of hadronic physics, probing the polarizabilities of the proton. These fundamental properties are used in many areas of physics, but recent theoretical studies have shown the scalar polarizabilities to be less well defined than previously understood, while the spin polarizabilities have never before been independently extracted.
In the A2 Collaboration of the Institut für Kernphysik in Mainz, we use the MAMI accelerator in combination with the Glasgow Mainz Photon Tagger to produce a quasi-monoenergetic photon beam. This beam is then applied to a variety of targets from liquid hydrogen to polarized 3He and butanol. The reaction products are detected in the Crystal Ball and TAPS large acceptance spectrometer array to minimize background and allow clean separation of the low-cross-section hadronic Compton scattering process. Cross sections and single- and double-spin asymmetries are measured and used to extract scalar and spin polarizabilities of the nucleon. We will present the motivation, the experimental methodology, first results and future prospects of the polarisability program at Mainz.
Argonne Physics Division Seminar Schedule