Experimental evidence for piK-atoms

Abstract

Electromagnetically bound π ± K ∓ -pairs (πK-atoms) have been observed by the DIRAC-II experiment at the CERN-PS. The πK-atoms were produced by the 24 GeV/c proton beam impinging on a thin Pt-target. The π ± -and K ∓ -mesons from the atom dissociation were analyzed in a two-arm magnetic spectrometer. An enhancement was observed at low relative momentum, corresponding to the production of 173 ± 54 πK-atoms. From these first data a lower limit for the mean life of 0.8 fs was derived at the 90% confidence level. The mean life being related to the S-wave πK-scattering lengths a 1 and a 3 in the isospin 1/2 and 3/2 states, one then obtains an upper limit for the difference |a 1 − a 3 | of 0.58 m −1 π at the 90% confidence level.