First observation of $\gamma \gamma \to p\bar{p}{K}^{+}{K}^{-}$ and search for exotic baryons in $pK$ systems

Abstract

The process $\gamma \gamma \to p\bar{p}{K}^{+}{K}^{-}$ and its intermediate processes are measured for the first time using a 980~fb${}^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The production of $p\bar{p}{K}^{+}{K}^{-}$ and a $\Lambda (1520{)}^0(\bar{\Lambda }(1520{)}^0)$ signal in the $p{K}^{-}$~($\bar{p}{K}^{+}$) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540~MeV/$c^2$, denoted as $\Theta (1540{)}^0$~($\bar{\Theta }(1540{)}^0$) or $\Theta (1540{)}^{++}$~($\Theta (1540{)}^{--}$), is seen in the $p{K}^{-}$~($\bar{p}{K}^{+}$) or $p{K}^{+}$~($\bar{p}{K}^{-}$) invariant mass spectra. Cross sections for $\gamma \gamma \to p\bar{p}{K}^{+}{K}^{-}$, $\Lambda (1520{)}^0\bar{p}{K}^{+}+c.c.$ and the products $\sigma (\gamma \gamma \to \Theta (1540{)}^0\bar{p}{K}^{+}+c.c.)\text{BR}(\Theta (1540{)}^0\to p{K}^{-})$ and $\sigma (\gamma \gamma \to \Theta (1540{)}^{++}\bar{p}{K}^{-}+c.c.)\text{BR}(\Theta (1540{)}^{++}\to p{K}^{+})$ are measured. We also determine upper limits on the products of the ${\chi }_{c0}$ and ${\chi }_{c2}$ two-photon decay widths and their branching fractions to $p\bar{p}{K}^{+}{K}^{-}$ at the 90\% credibility level.

Comments: 9 pages, 9 figures