First Measurement of the K^{-} Escape Cross Section in the ^{12}C(K^{-},p) Reaction

We investigated the K[over ¯]-nucleus interaction through the simultaneous measurement of the inclusive ^{12}C(K^{-},p) and exclusive K^{-} escape ^{12}C(K^{-},pK_{esc}^{-}) reactions at 1.8  GeV/c at J-PARC. The present measurement explicitly focuses on the K^{-} escape process for the first time, successfully accomplishing a direct experimental determination of the imaginary part of the K^{-} optical potential. The differential cross section for the K^{-} escape reaction was determined to be 436±6(stat.)±44(syst.)  μb/sr. A simultaneous likelihood fit yielded real and imaginary potential strengths of V_{0}=-72_{-5}^{+3}(stat.)_{-8}^{+0}(syst.)  MeV and W_{0}=-100_{-1}^{+7}(stat.)_{-16}^{+0}(syst.)  MeV at the nuclear center, respectively. The derived W_{0} is significantly stronger than that predicted by theoretical models based on one-nucleon processes, ssuggesting possible contributions from processes involving multiple nucleons.