Pion and Kaon Polarizabilities and Radiative Transitions

TL;DR

This paper discusses CERN COMPASS experiments measuring pion and kaon polarizabilities and radiative transitions via Primakoff reactions, testing chiral symmetry predictions and exploring the chiral anomaly through various gamma-meson interactions.

Contribution

It presents the experimental setup, motivations, and initial data analysis plans for measuring meson polarizabilities and radiative transitions, including related studies at FNAL SELEX.

Findings

Preparation of experimental setup and trigger requirements.

Initial data analysis targeting reactions related to chiral anomaly.

Expected to test chiral symmetry predictions and measure polarizabilities.

Abstract

CERN COMPASS plans measurements of gamma-pi and gamma-K interactions using 50-280 GeV pion (kaon) beams and a virtual photon target. Pion (kaon) polarizabilities and radiative transitions will be measured via Primakoff effect reactions such as pi+gamma->pi'+gamma and pi+gamma->meson. The former can test a precise prediction of chiral symmetry; the latter for pi+gamma->a1(1260) is important for understanding the polarizability. The radiative transition of a pion to a low mass two-pion system, pi+gamma->pi+pi0, can also be studied to measure the chiral anomaly amplitude F(3pi) (characterizing gamma->3pi), arising from the effective Chiral Lagrangian. We review here the motivation for the above physics program. We describe the beam, target, detector, and trigger requirements for these experiments. We also describe FNAL SELEX attempts to study related physics via the interaction of 600 GeV pions with target electrons. Data analysis in progress aims to identify the reactions pi+e->pi'+e'+pi0 related to the chiral anomaly, and pi+e->pi'+e'+gamma related to pion polarizabilities.