First observation of γ γ → p ¯ p K + K − and search for exotic baryons in p K systems

Abstract

The process γ γ → p ¯ 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 ¯ p K + K − and a Λ ( 1520 ) 0

( ¯¯¯ Λ ( 1520 ) 0 ) signal in the p K − ( ¯ p K + ) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540

MeV / c 2 , denoted as Θ ( 1540 ) 0 ( ¯¯¯ Θ ( 1540 ) 0 ) or Θ ( 1540 ) + + ( Θ ( 1540 ) − − ), is seen in the p K − ( ¯ p K + ) or p K + ( ¯ p K − ) invariant mass spectra. Cross sections for γ γ → p ¯ p K + K − , Λ ( 1520 ) 0 ¯ p K + + c . c . and the products σ ( γ γ → Θ ( 1540 ) 0 ¯ p K + + c . c . ) B ( Θ ( 1540 ) 0 → p K − ) and σ ( γ γ → Θ ( 1540 ) + + ¯ p K − + c . c . ) B ( Θ ( 1540 ) + + → p K + ) are measured. We also determine upper limits on the products of the χ c 0 and χ c 2 two-photon decay widths and their branching fractions to p ¯ p K + K − at the 90% credibility level.