Elsevier

Nuclear Physics A

Volume 457, Issues 3–4, 15–22 September 1986, Pages 709-730
Nuclear Physics A

New precision determination of the π mass from pionic X-rays

https://doi.org/10.1016/0375-9474(86)90476-8Get rights and content

Abstract

The wavelength of the pionic 4f-3d transition in 24Mg has been measured with a curved crystal spectrometer at SIN. The average population of the electronic K-shell during the pionic transition has been determined from the line shape of the pionic X-ray peak which allows a precise calculation of the electron screening correction to the transition energy. The wavelength calibration is based on the 25.7 keV γ-ray standard in the decay of 161Tb (λ = 48.334488 (64) pm). From the measured wavelength the new value of the pion-electron mass ratio is deduced to be mπ/me = 273.12677 (71). The obtained accuracy of 2.6 ppm is by a factor of 2.5 better compared with the best previous measurement. With this new π/e mass ratio the upper limit for the muon neutrino mass is reevaluated.

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    This work is based on the Ph.D. thesis of B. Jeckelmann (University of Fribourg, Switzerland, 1986); it was supported in parts by SIN and the Swiss National Science Foundation.

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