A new determination of the $K^{0} \rightarrow \pi^{+} \pi^{-}$ decay parameters

In a short neutral beam the proper time-dependence of the decay K/sup 0/ to pi /sup +/ pi /sup -/ is measured. This time structure exhibits the interference between the short- and long-lived states and is in agreement with the general expectations of the CP violation phenomenology. This experiment gives new and more precise measurements of the following three parameters: (i) the decay width of the short- lived K/sub S/ component: Gamma /sub S/=(1.119+or-0.006)*10/sup 10/ sec/sup -1/; (ii) the modulus of the CP violating parameter eta /sub +-/: mod eta /sub +-/ mod =(2.3+or-0.035)*10/sup -3/; (iii) the phase of eta /sub +-/ as a function of the K/sub S/-K/sub L/ mass difference Delta m: phi /sub +-/=(49.4+or-1.0)/sup 0/+(( Delta m-0.540)/0.540) *305/sup 0/. (9 refs).