First observation of long-lived π+ π- atoms

Original · EN

After observing and investigating the double-exotic π+π- atom with the ground state lifetime τ of about 3 × 10⁻¹⁵ s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about 10⁻¹¹ s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived π+π- atoms amounts to 436±61, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between p and s atomic states and so to determine ππ scattering lengths.