Masses of Identified Positive Heavy Mesons

The charged secondary particles from all presently known decay modes of positive $K$ mesons have been identified, and the masses of the primaries measured by the momentum-range method. More than 2000 $K$ mesons were found in a rather large stack of nuclear emulsion after its exposure, behind the strong-focusing magnetic spectrometer at the Bevatron, to a target plunged into the 6.2-Bev circulating proton beam. The mean $K$-meson momentum at the stack was 360 Mev/c, and the proper time of flight was 1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec. The masses of 263 systematically selected $K$ mesons were measured, and the averages for the various decay modes are ${M(\ensuremath{\tau}+{\ensuremath{\tau}}^{\ensuremath{'}})=966.6\ifmmode\pm\else\textpm\fi{}1.9{m}_{e}, M({K}_{\ensuremath{\pi}2})=966.9\ifmmode\pm\else\textpm\fi{}2.0{m}_{e}, M({K}_{\ensuremath{\mu}2})=967.2\ifmmode\pm\else\textpm\fi{}2.2{m}_{e},}{M({K}_{\ensuremath{\mu}3})=969\ifmmode\pm\else\textpm\fi{}5{m}_{e}, M({K}_{\ensuremath{\beta}3})=967\ifmmode\pm\else\textpm\fi{}8{m}_{e}.}$ The standard errors indicated apply to the relative masses; the uncertainties on the absolute masses are slightly larger. Various corrections are described. The results are discussed in the light of recent ideas concerning heavy-meson characteristics.