Experimental Method

The experimental method consisted of setting the initial pion beam part of the channel to a momentum of 150 MeV/c while the muon spectrometer part was scanned in momentum steps of 0.5 MeV/c around the expected momentum for muons from the hypothetical decay (1) p_m ~ p_p · m_m / m_p, i.e. p_m ~ 113.5 MeV/c. For each spectrometer momentum setting the pulse-height and timing information for all counters were recorded for a given number of proton signals on an event-by-event basis. In total 6 such scans were performed, each of 38 momenta.

In order to deduce the position and shape of the muons from decay(1) in such a momentum spectrum, both `pion'- and `muon'-scans were performed. The former consisted of setting the whole beam-line for 150 MeV/c pions and then scanning the spectrometer part, in momentum, to measure the pion momentum shape, width and position. For a `muon'-scan the whole beam-line was set to a momentum of 113.5 MeV/c and the spectrometer part scanned to measure the same parameters for beam muons.