On determining the cross section of the supposed pentaquark $\Theta^{+}_{}$ in the reaction pp $\rightarrow$ $\Theta^{+}_{}$ $\Sigma^{+}_{}$ $\rightarrow$ pK⁰ $\Sigma^{+}_{}$

Abstract.

This paper addresses the problem of how to extract an upper limit on the cross section for $\Theta^+$ production via the reaction $pp\rightarrow\Theta^+\Sigma^+$ , where the $\Theta^+$ is assumed to decay into the $pK^0$ subsystem. Recent data of the COSY-TOF Collaboration, namely the angular distribution of protons in the $\Sigma^+K^0$ helicity frame and the invariant mass spectrum of the $pK^0$ system, were scrutinised with regard to a resonance by applying the profile likelihood method. It is found that the former distribution is best suited for setting an upper limit on the $\Theta^+$ production, which varies between 90nb for an assumed $\Theta^+$ mass of 1500MeV/c^2 and 56nb for 1540MeV/c^2.