Pentaquark as a kaon-nucleon resonance

Several recent experiments have reported evidence for a narrow feature in the $K^{+}$-neutron system, an apparent resonant state $\sim 100\mathrm{MeV}$ above threshold and with a width $<~25\mathrm{MeV}.$ This state has been labeled as ${\Theta }^{+}$ (previously as $Z^{*}),$ and because of the implied inclusion of a strange antiquark is referred to as a pentaquark, that is, five quarks within a single bag. We present an alternative explanation for such a structure, as a higher angular momentum resonance in the isospin zero $K^{+}N$ system. One might call this an exit channel or molecular resonance. In a nonrelativistic potential model we find a possible candidate for the kaon-nucleon system with a relative angular momentum $L=3,$ while $L=1\mathrm{}$ states possess centripetal barriers much too low to confine the kaon and nucleon at an energy so high above threshold. Under some circumstances, however, an $L=2\mathrm{}$ state can exist.