Measurement of pion-proton bremsstrahlung for pions at 299 MeV.

Abstract

We have measured the fivefold differential cross section ${d}^{5}$\ensuremath{\sigma}/d${\ensuremath{\Omega}}_{\ensuremath{\pi}}$d${\ensuremath{\Omega}}_{\ensuremath{\gamma}}$${\mathrm{dE}}_{\ensuremath{\gamma}}$ for the process ${\ensuremath{\pi}}^{+}$p\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$p\ensuremath{\gamma} with incident pions of energy 299 MeV. The angular regions for the outgoing pions (55\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\pi}}\mathrm{\ensuremath{\le}}95}$\ifmmode^\circ\else\textdegree\fi{}), and photons (${\ensuremath{\theta}}_{\mathrm{lab}{}^{\ensuremath{\gamma}}=241\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\ifmmode\pm\else\textpm\fi{}10}$\ifmmode^\circ\else\textdegree\fi{}) in coplanar geometry are selected to maximize the sensitivity to the radiation from the magnetic dipole moment of the ${\ensuremath{\Delta}}^{++}$(1232) resonance. At low photon energies, the data agree with the soft-photon approximation to pion-proton bremsstrahlung. At forward pion angles the data agree with older data and with the latest theoretical calculations for 2.3${\ensuremath{\mu}}_{p}$\ensuremath{\le}${\ensuremath{\mu}}_{\ensuremath{\Delta}}$\ensuremath{\le}3.3${\ensuremath{\mu}}_{p}$. However at more backward pion angles where no data existed, the predictions fail.