D. Chatellard

Determination of the πN scattering lengths from pionic hydrogen

Abstract The final results from the pionic hydrogen X-ray experiment at PSI are presented. With this experiment the strong interaction energy level shift e 1s and the total decay width Γ 1s of the 1s state of pionic hydrogen were obtained from a precise measurement of the 3p–1s X-ray line: e 1s =−7.108±0.013(stat.)±0.034(syst.) eV (attractive) and Γ 1s = 0.868±0.040(stat.)±0.038(syst.) eV. The corresponding hadronic π N s-wave scattering lengths for elastic scattering and single charge exchange are: a π − p→π − p =0.0883±0.0008 m −1 π and a π − p→π 0 n =−0.128±0.006 m −1 π . Combining the results of the pionic hydrogen and deuterium measurements, the isoscalar ( b 0 ) and isovector ( b 1 ) scattering lengths, corresponding to an isospin symmetric interaction, can be calculated: b 0 =0.0016±0.0013 m −1 π and b 1 =−0.0868±0.0014 m −1 π .

X-ray spectroscopy of the pionic deuterium atom

Abstract The low energy X-rays of the pionic deuterium 3P-1S transition were measured using a high resolution crystal spectrometer, together with a cyclotron 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 3075 eV. This energy was measured with a precision of 0.1 eV. Compared to conventional methods, the cyclotron trap allowed for a gain in stopping density of about an order of magnitude. The CCDs had excellent spatial and energy resolutions. Non-X-ray background could therefore be almost completely eliminated. The 1S strong interaction shift ϵ1S and total decay width Γ1S were determined from the position and line shape of the X-ray peak. They are ϵ 1S ( shift ) = 2.43 ± 0.10 eV ( repulsive ), Γ 1S ( width ) = 1.02 ± 0.21 eV , where the statistical and systematic errors were added linearly. The total (complex) pionic deuterium S-wave scattering length aπ−d was deduced: a π − d = −0.0259(±0.0011) + i 0.0054(±0.0011)m π −1 . From the real part of aπ−d a constraint in terms of the isoscalar and isovector πN′ scattering lengths b0 and b1 was deduced. From Im aπ−d we determined the isoscalar coupling constant for π− absorption: |g0| = (2.6 ± 0.3) 10−2mπ−2. The experiments of the pionic hydrogen and deuterium S-wave scattering lengths were analyzed within the framework of a search for i 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 present results.

Determination of the strong interaction shift in pionic hydrogen with a high resolution crystal spectrometer system

Abstract The 3P-1S X-ray transition energy was measured in pionic hydrogen with a double focussing silicon crystal spectrometer in combination with a cyclotron trap and CCD detectors: E = 2885.98 ± 0.17 (stat.) ± 0.15 (syst.) eV. The corresponding strong intera ction shift ϵ 1S = 7.12 ± 0.32 eV (attractive) yields the scattering length combination 1 3 (2a 1 + a 3 ) = 0.086 ± 0.004 m π −1 .

A high resolution reflecting crystal spectrometer to measure 3 keV pionic hydrogen and deuterium X-rays

Abstract A reflecting crystal spectrometer consisting of three cylindrically bent quartz (110) crystals is described, it was designed to measure the 3 keV Kβ X-rays from pionic hydrogen and deuterium. Charge coupled devices (CCDs) were used as X-ray detectors. Projecting the reflexes of all three crystals on one common focus, an instrumental energy resolution below 1 eV was obtained at an energy of 2.9 keV.

A double focusing crystal spectrometer for low energy X-rays

Abstract A high resolution double focusing crystal spectrometer is described. Thirteen single silicon crystals are used to reflect the X-ray beam onto three CCD detectors. An energy resolution of 4 eV FWHM was reached in a measurement of the 2.9 keV Kα1 and Kα2 lines in argon.

Measurement of the strong interaction shift and width of the 1S state in pionic hydrogen

Abstract The energy and line shape of the 3P-1S transition in pionic hydrogen have been measured with a reflecting crystal spectrometer combined with a cyclotron trap and Charge Coulped Devices (CCDs). The instrumental resolution was 0.7 eV (FWHM) at 2.9 keV. Results for the strong interaction energy shift and broadening of the ground state and the corresponding πN s-wave scattering lengths will be presented soon.