Induced Pseudoscalar Coupling Constant

Abstract

The recent TRIUMF experiment for ${\mu }^{-}p\to n{\nu }_{\mu }\gamma$ gave a surprising result that the induced pseudoscalar coupling constant $g_P$ was larger than the value obtained from ${\mu }^{-}p\to n{\nu }_{\mu }$ experiment as much as 44 %. Reexamining contribution of the axial vector current, we found an additional term to the matrix element of Beder and Fearing which was used to extract the $g_P$ value from the measured photon energy spectrum. This additional term plays a key role to restore the reliability of $g_P(-0.88m_{\mu }^2)=6.77g_A(0)$.

11 pages, 2 figures