Room for an $S=+1$ pentaquark in $K^{+}$-nucleus phenomenology

Evidence for excitation of exotic $S=+1$ pentaquark degrees of freedom is presented by studying optical-potential fits to $K^{+}$-nucleus total, reaction and elastic-differential cross section data at $p_{\mathrm{lab}}~500\text{−}700$ MeV/c. Estimates of the underlying two-nucleon absorption $K^{+}\mathit{nN}\to {\Theta }^{+}N$ reaction cross section are made and are used for discussing the anticipated cross section of the strangeness exchange reaction $K^{+}N\to \pi {\Theta }^{+}$.

Figure 1

Data and calculations [2] for $K^{+}$ reaction cross sections per nucleon (${\sigma }_R/A$) at $p_{\mathrm{lab}}=488$ MeV/c are shown in the upper part. Calculated $K^{+}$ absorption cross sections per nucleon (${\sigma }_{\mathrm{abs}}/A$) are shown in the lower part, see text.

Figure 2

Comparison between measured differential cross sections for $K^{+}$ elastic scattering at $p_{\mathrm{lab}}=715$ MeV/c on ${}^6\mathrm{Li}$ and ${}^{12}\mathrm{C}$ [13] and best-fit calculations using Eq. (8) (dashed lines) and Eq. (9) (solid lines).