Study of the ReactionK+n→K+N*0at 12 GeV/c

We have studied the reaction $K^{+}n\to K^{+}{N}^{*0\mathrm{}}\to K^{+}{\pi }^{-}p$ at 12 GeV/c using data obtained in an exposure of the deuterium-filled SLAC 82-in. bubble chamber to an rf-separated $K^{+}$ beam. The $M\left(p{\pi }^{-}\right)$ spectrum exhibits a very large enhancement below 1.8 GeV which we identify as primarily a diffractive effect. A partial-wave analysis of this enhancement shows that the data can be interpreted in terms of $P_{\frac{1}{2}}$, $D_{\frac{3}{2}}$, and $F_{\frac{5}{2}}$ contributions. The $P_{\frac{1}{2}}$ contribution which dominates at very low momentum transfers appears to peak around 1.25 GeV. If this state is associated with the Roper resonance, a mechanism which produces a downward mass shift of about 200 MeV for the diffractively produced $p{\pi }^{-}$ decay mode is implied.