X-RAY SPECTROSCOPY OF THE PIONIC DEUTERIUM ATOM

The low energy X-rays of the pionic deuterium 3P-1S transition were me asured using a high resolution crystal spectrometer, together with a c yclotron trap (a magnetic device to increase the pion stopping density ) and a CCD (charge-coupled device) detector system. The spectrometer resolution was 0.65 eV FWHM for a measured energy of approximately 307 5 eV. This energy was measured with a precision of 0.1 eV. Compared to conventional methods, the cyclotron trap allowed for a gain in stoppi ng density of about an order of magnitude. The CCDs had excellent spat ial and energy resolutions. Non-X-ray background could therefore be al most completely eliminated. The 1S strong interaction shift epsilon(1S ) and total decay width Gamma(1S) were determined from the position an d line shape of the X-ray peak. They are epsilon(1S)(shift) = 2.43 +/- 0.10 eV (repulsive), Gamma(1S)(width) = 1.02 +/- 0.21 eV, where the s tatistical and systematic errors were added linearly. The total (compl ex) pionic deuterium S-wave scattering length a(pi-d) was deduced: a(p i-d) = -0.0259(+/-0.0011) + i0.0054(+/-0.0011)m(pi)(-1). From the real part of a(pi-d) a constraint in terms of the isoscalar and isovector pi N scattering lengths b(0) and b(1) was deduced. From Im a(pi-d) we determined the isoscalar coupling constant for pi(-) absorption: \g(0) \ = (2.6 +/- 0.3)10(-2)m(pi)(-2). The experiments of the pionic hydrog en and deuterium S-wave scattering lengths were analyzed within the fr amework of a search for isospin symmetry violation. The data are still compatible with isospin conservation. The scattering lengths deduced from the Karlsruhe-Helsinki phase shift analysis disagree with the pre sent results. (C) 1997 Published by Elsevier Science B.V.