A new determination of the mass of the charged pion

First Direct Observation of Coulomb Explosion during the Formation of Exotic Atoms

“…In all cases, the linewidths found for the pN and mO transitions were significantly larger than in the case of pNe (Table II). In an earlier highstatistics measurement of the pN transition using also the crystal Z15 [15], a FWHM of almost 50 00 (seconds of arc) was found corroborating the present findings.…”

“…The results presented here were obtained from a study of linewidths of pionic and muonic x rays in the preparation of an experiment at the Paul-Scherrer-Institut (PSI) aiming at an improved determination of the charged pion mass [14][15][16]. The pion mass will be determined from the pN͑5g-4f͒ transition using the same transition in mO as calibration standard for a reflection-type crystal spectrometer (setup in Johann geometry [17,18]).…”

“…The experimental setup was similar to the one described in [15]. Using the 105 MeV͞c pion beam in the pE5 area at PSI, about 4 3 10 8 p 2 ͞s were injected into the new cyclotron trap [20] at a proton current of 1 mA from the accelerator.…”

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

“…al. [16] used this trap to decelerate and stop pions. The cyclotron trap II used in the present experiment was specifically designed with a larger gap between the magnet coils.…”

“…As shown in Fig. 1 following years the pion mass has been re-measured several times using X-ray spectroscopy of pionic atoms with continuously improved accuracy [10][11][12][13][14][15][16]. In parallel, additional results for the charged pion mass were obtained from the measurement of the muon momentum in the decay π + → μ + ν μ [17][18][19].…”