Measurement of Pion-Pion Final State Interactions in η → π +π −γ with CLAS at Jefferson Lab

Abstract

Decays of pseudoscalar mesons proceed from the chiral anomaly, which arises from spontaneous chiral symmetry breaking. In the limit of massless quarks (chiral limit), the η → π +π −γ the decay width is determined solely by the box anomaly term in the Wess Zumino Witten Lagrangian. Since the physical quarks are not massless, the decay region of the η meson is far from the chiral limit and thus proper inclusion of the momentum dependence is essential to reproduce the measured decay width. Several theoretical frameworks have been proposed to describe these interactions. We report a new measurement of the α parameter which measures the contribution of pion-pion final state interactions to the differential decay width. The data was collected during the g11a run period using the CEBAF Large Acceptance Spectrometer located in Hall B at the Thomas Jefferson National Accelerator Facility in 2004. The data was collected using a tagged photon beam with energy range of 1.5-3.5 GeV incident on a liquid Hydrogen target. Our results are in agreement with the latest experimental measurement and theoretical calculations