Measurement of the Panofsky Ratio inHe3

Abstract

The photon spectrum from radiative and charge-exchange capture of pions in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ was measured in a high-resolution pair spectrometer yielding the new value of the Panofsky ratio $P_3=\frac{({\pi }^{-}+{}_{}{}^3{}_{}{}^{}\mathrm{He}\to {}_{}{}^3{}_{}{}^{}\mathrm{H}+{\pi }^0)}{({\pi }^{-}+{}_{}{}^3{}_{}{}^{}\mathrm{He}\to {}_{}{}^3{}_{}{}^{}\mathrm{H}+\gamma )}=2.68\mathrm{}\pm 0.13$. An impulse-approximation analysis is presented which gives a value $P_3=2.5\mathrm{}$. In addition, the branching ratios for the ${}_{}{}^3{}_{}{}^{}\mathrm{He}+{\pi }^0$, ${}_{}{}^3{}_{}{}^{}\mathrm{H}+\gamma$, and the combined ${}_{}{}^2{}_{}{}^{}\mathrm{H}+n+\gamma$ and $p+n+n+\gamma$ channels are measured to be 17.8± 2.3, 6.6± 0.8, and 7.4± 1.0%, respectively.