Search for Θ+ via π−p→K−X reaction near production threshold

We have searched for Θ+ via π−p→K−X reaction using 1.87 and 1.92GeV/cπ− beam at the K2 beam line of the KEK 12 GeV proton synchrotron. In the missing mass spectrum at beam momentum of 1.92GeV/c, a bump has been found at 1530MeV/c2 which is consistent with the mass reported by several experiments. The statistical significance of this bump, however, is only 2.5-2.7σ. Therefore we have derived the upper limit of Θ+ production cross section via π−p→K−Θ+ reaction which is 3.9 μb at 90% confidence level assuming that Θ+ is produced isotropically in the center of mass system.