Evidence for $\pi K$-atoms with DIRAC

TL;DR

The DIRAC experiment at CERN-PS provides the first evidence for electromagnetically bound $K$-atoms, measuring their production and setting a lower limit on their mean life, which relates to fundamental scattering lengths.

Contribution

This work reports the first observation of $K$-atoms and establishes a lower limit on their lifetime, advancing understanding of meson interactions and scattering lengths.

Findings

173 b1 54 K$-atoms observed

Lower limit for mean life is 0.8 fs at 90% CL

Evidence supports the production of $K$-atoms in proton-target collisions

Abstract

We present evidence for the first observation of electromagnetically bound $\pi^\pm K^\mp$-pairs ($\pi K$-atoms) with the DIRAC experiment at the CERN-PS. The $\pi K$-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the $\pi^\pm$ and $K^\mp$-mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173 $\pm$ 54 $\pi K$-atoms. The mean life of $\pi K$-atoms is related to the s-wave $\pi K$-scattering lengths, the measurement of which is the goal of the experiment. From these first data we derive a lower limit for the mean life of 0.8 fs at 90% confidence level.