Precise measurement of the pion axial form factor in the pi+-->e+nugamma decay.
/ Authors
E. Frlež, D. Počanić, V. Baranov, W. Bertl, M. Bychkov, N. Khomutov, A. Korenchenko, S. Korenchenko, T. Kozłowski, N. Kravchuk
and 16 more authors
N. Kuchinsky, W. Li, R. Minehart, D. Mzhavia, B. Ritchie, S. Ritt, A. Rozhdestvensky, V. V. Sidorkin, L. Smith, I. Supek, Z. Tsamalaidze, B. Vandevender, E. Velicheva, Yanchu Wang, H. Wirtz, K. Ziock
/ Abstract
We have studied radiative pion decays pi(+)-->e(+)nugamma in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 41 601 events we have evaluated absolute pi-->enugamma branching ratios in the three regions. Minimum chi(2) fits to the integral and differential (E(e(+)),E(gamma)) distributions result in the axial-to-vector weak form factor ratio of gamma identical with F(A)/F(V)=0.443(15), or F(A)=0.0115(4) with F(V)=0.0259. However, deviations from standard model predictions in the high-E(gamma)-low-E(e(+)) kinematic region indicate the need for further theoretical and experimental work.
Journal: Physical review letters