PRECISE DETERMINATION OF THE K/sub L/--K/sub s/ MASS DIFFERENCE BY THE GAP METHOD (UNIVERSITY OF CHICAGO--UNIVERSITY OF ILLINOIS CHICAGO CIRCLE COLLABORATION).

The ${K}_{L}\ensuremath{-}{K}_{S}$ mass difference, $\ensuremath{\Delta}m\ensuremath{\equiv}\frac{({M}_{L}\ensuremath{-}{M}_{S}){c}^{2}}{\ensuremath{\hbar}}$, has been redetermined in a high-statistics experiment performed at the zero-gradient synchrotron of Argonne National Laboratory, using the "gap method" originally developed at Princeton. Two independent measurements, using ${\mathrm{B}}_{4}$C and Cu, respectively, as regenerators, were performed and gave consistent results. Their mean is $\ensuremath{\Delta}m=(0.542\ifmmode\pm\else\textpm\fi{}0.006)\ifmmode\times\else\texttimes\fi{}{10}^{10}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. With this value, the result of our recent determination of arg ${\ensuremath{\eta}}_{+\ensuremath{-}}$ by "vacuum regeneration" is recalculated to be (44.7 \ifmmode\pm\else\textpm\fi{} 5.0)\ifmmode^\circ\else\textdegree\fi{}, where the error allows for the uncertainty in $\ensuremath{\Delta}m$ given above.