Angular distribution in s-channel formation of the pentaquark $\hat{I}{˜}^{+}$ baryon

Abstract

Using the DIANA data on the charge-exchange reaction $K^{+}n\to p{K}^0$ on a bound neutron, in which the s-channel formation of the pentaquark baryon $\hat{I}{˜}^{+}(1538)$ has been observed, we analyze the dependence of the background-subtracted $\hat{I}{˜}^{+}\to p{K}^0$ signal on the $K^0$ emission angle in the $p{K}^0$ rest frame. In order to describe the observed $\cos \hat{I}{˜}_K^{\mathrm{cms}}$ distribution, invoking the interference between the nonresonant s-wave and the $\hat{I}{˜}^{+}$-mediated higher-wave contributions to the amplitude of the charge-exchange reaction is required at a 2.8$\ddot{I}ƒ$ level. The spin--parity assignment of 1/2${}^{-}$ for the $\hat{I}{˜}^{+}$ baryon is ruled out at a statistical level of 2.9 standard deviations. A physically-meaningful selection in $\cos \hat{I}{˜}_K^{\mathrm{cms}}$ based on the observed angular dependence of the $\hat{I}{˜}^{+}\to p{K}^0$ signal allows to boost the statistical significance of the signal up to 7.1 standard deviations. This is far in excess of previously reported signals and renders the $\hat{I}{˜}^{+}$ existence more credible.

13 pages, 7 figures