Measurement of the charged pion mass using a low-density target of light atoms

¹ Institut des NanoSciences de Paris, CNRS, Sorbonne Universités, UPMC Univ Paris 06, F-75005, Paris, France
² Dept. of Materials Science and Engineering, University of Ioannina, GR-45110 Ioannina, Greece
³ Institut für Kernphysik, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
⁴ Laboratory for Particle Physics, Paul Scherrer Institut, CH 5232 - Villigen PSI, Switzerland
⁵ Institut de Physique de l’ Université de Neuchâtel, CH-2000 Neuchâtel, Switzerland
⁶ Laboratoire Kastler Brossel, UPMC-Sorbonne Universités, CNRS, École Normale Supérieure-PSL Research University, Collège de France, F-75005 Paris, France
⁷ Dept. of Physics and Astronomy, University of Leicester, Leicester LEI7RH, England

^* e-mail: martino.trassinelli@insp.jussieu.fr
^** present address: TU Munich, D-85747 Garching, Germany
^*** e-mail: d.gotta@fz-juelich.de
^**** present address: DAHER NUCLEAR TECHNOLOGIES GmbH, D-63457 Hanau, Germany
^† present address: Phys. Depart., National Tsing Hua Univ., Hsinchu 300, Taiwan
^‡ present address: Lab. de Physique des Lasers, Université Paris 13, Sorbonne Paris Cité, CNRS, France
^§ present address: ESA-ESTEC, PO Box 299, 2200 AG, Noordwijk, The Netherlands

Published online: 29 November 2016

Abstract

We present a new evaluation of the negatively charged pion mass based on the simultaneous spectroscopy of pionic nitrogen and muonic oxygen transitions using a gaseous target composed by a N₂/O₂ mixture at 1.4 bar. We present the experimental set-up and the methods for deriving the pion mass value from the spatial separation from the 5g − 4f πN transition line and the 5g − 4f μO transition line used as reference. Moreover, we discuss the importance to use dilute targets in order to minimize the influence of additional spectral lines from the presence of remaining electrons during the radiative emission. The occurrence of possible satellite lines is investigated via hypothesis testing methods using the Bayes factor.