Spin-polarizability experiment at Mainz

The group has been working on measurements of the proton spin-polarizabilities in Compton scattering experiments at the MAMI accelerator at the Johannes Gutenberg University in Mainz, Germany.  Whereas high energy experiments at Jefferson Lab, BNL and Compass measure the short-distance spin structure of the nucleon, in the 260-310 MeV experiments at Mainz we measure the long-distance spin structure of the nucleon. Somewhat akin to the electric and magnetic polarizabilities of the nucleon (alpha and beta), the spin-polarizabilities measures the stiffness of the nucleon spin in an external electromagnetic field.   For these experiments the incident photon has circular polarization, and the proton target has either longitudinal or transverse polarization.

The above figure shows some of the important apparatus used in the Mainz experiment.

This experiment was the subject of Phil Martel’s PhD thesis.  Phil, seen in the above photo, is a research staff member at Institute for Kernphysik at Mainz.


Phil Martel
Measuring Proton Spin-Polarizabilities with Polarized Compton Scattering


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