Some Comments on the Putative $\Theta^ +$ (1543) Exotic State

Abstract

We point out that existing $K^+d$ scattering data available in the PDG (Particle Data Group compilation) suggest some fluctuations in those momentum bins where the (Fermi motion broadened) $\Theta^+$[1543] resonance recently indicated in many gamma nuclear reactions and predicted six years ago by Diakonv Petrov and Polyakov might have shown up. The I=0, $J^P={1/2}^+$ P-wave channel should have a universal peak cross section of $\sim 37$ mb at resonance. The smallness of the effect seen in $K^+d$ with the $\delta \sigma $ fluctuations being less than 4 mb imply an indirect bound $\Gamma_{\Theta^+} < 6$ MeV, far stronger than the direct gamma-d measurements. This renders the theoretical interpretation of the new state very difficult.