Precision measurement of the pion mass differencemπ−−mπ0
Citations Over Time
Abstract
We have studied the time-of-flight spectra of neutrons produced by the charge-exchange reaction ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}n$ of ${\ensuremath{\pi}}^{\ensuremath{-}}p$ atoms in liquid hydrogen, at flight distances up to 18.1 m. We have found the neutron velocity for ${\ensuremath{\pi}}^{\ensuremath{-}}p$ atoms at rest to be 0.894 266\ifmmode\pm\else\textpm\fi{}0.000 063 cm/ns, corresponding to a pion mass difference ${m}_{{\ensuremath{\pi}}^{\ensuremath{-}}}\ensuremath{-}{m}_{{\ensuremath{\pi}}^{0}}=4.59364\ifmmode\pm\else\textpm\fi{}0.00048$ MeV. As an additional result, we have observed a broadening of the neutron time-of-flight peak with increasing flight distance, which implies that the kinetic-energy distribution of the ${\ensuremath{\pi}}^{\ensuremath{-}}p$ atoms just before the charge-exchange reaction has one component extending up to \ensuremath{\sim}1 eV and another component extending up to \ensuremath{\sim}70 eV; each component contains about half of the ${\ensuremath{\pi}}^{\ensuremath{-}}p$ atoms.