New precision measurement of the pionic deuteriums-wave strong interaction parameters

The x rays of the pionic deuterium 2p-1s transition were measured with a high resolution crystal spectrometer including a cyclotron trap (a magnetic device to increase the pion stopping density) and a CCD (charge-coupled device) detector system. The 1s strong interaction shift ${\ensuremath{\epsilon}}_{1s}$ and total width ${\ensuremath{\Gamma}}_{1s}$ were determined from the position and line shape of the x-ray peak. The (complex) pionic deuterium s-wave scattering length ${a}_{{\ensuremath{\pi}}^{\ensuremath{-}}d}$ was deduced. Its real part was related to the pion-nucleon scattering lengths, and the isoscalar coupling constant for ${\ensuremath{\pi}}^{\ensuremath{-}}$ absorption was deduced from the imaginary part.