The Energy Spectrum of the Decay Particles and the Mass and Spin of the Mesotron

Abstract

To evaluate the integral we introduce the representation /i 2 (s) = (l/ir) f M2zsind)dfl and obtain, with the change of variable v~sirup, I~(l/2ir) \ sm~l(pd(p\ Ji(2a smd &\n<p)dd.where # = sin# sin<£>, doo = sm$d$d<p, and the integration extends over the surface of the hemisphere on which x is positive. The replacement of x by s( = cos#) corresponds to a rotation of the coordinate system and does not affect the value of the integral. HenceRegarding #, ^ as the polar angles of a point on ,a which allows the verification of Eq. (4.6) in the text.Energy values determined from curvature measurements of 75 cloud-chamber tracks of decay particles of cosmic-ray mesotrons at sea level, in a magnetic field of 7250 gauss, are here reported. The observed spectrum extends from 9 Mev to 55 Mev with an apparently continuous distribution of intermediate energy values and a mean energy of 34 Mev. The shape of the spectrum and the value of its upper limit are strong evidence that the mesotron disintegrates into an electron and two neutrinos. It is concluded that the mesotron has half-integral spin. The value of the observed upper limit of the energy spectrum corresponds to a mass value of the mesotron equal to 217±4 electron * Assisted by the joint program of the ONR and AEC.

Precision muon physics

“…The µ → eν ν decay scheme was established through cosmic-ray measurements of the decay electron energy spectrum. It was demonstrated-via the continuum distribution and the energy endpoint-that muons decay into three or more particles with small or zero masses [14]. Fermi's theory of nuclear β-decay was consequently expanded to accommodate µ → eν ν decay thus affording the first glimpse of weak universality.…”

“…While the history of µ → e experiments is well covered in Ref. [72], here we concentrate on the two major efforts 14 that ambitiously aim at single-event sensi-tivities approaching ≈ 3×10 −17 , a 4 order of magnitude improvement compared to present limits. The two projects-Mu2e [82] at Fermilab and COMET [83] at J-PARC-share many similar conceptual design features, while individual technical solutions differ.…”

Lepton spectroscopy

“…In parallel with work on nuclear p decay and the accompanying neutrino, information was accumulating on the muon ('mesotron' as it was then called) and its decay characteristics. Discovered in cloud chamber pictures of cosmic rays (Anderson andNeddermeyer 1937, Street andStevenson 1937) it was shown by Conversi et a1 (1947) not to be a strongly interacting particle and therefore distinct from the particle proposed by Yukawa (1935) to mediate the nuclear force. The kinematics of its decay into an electron was studied, for example, by Leighton et a1 (1949) who measured the curvature of 75 electron tracks from muon decay at rest in a cloud chamber.…”

Mise au point sur les propriétés principales des mésons

“…-Pour interpréter l'existence d'un spectre continu d'énergie pour l'électron, il est nécessaire de supposer que le néson &#x3E; se décompose en trois particules au moins. La mesure de l'énergie moyenne de l'électron montre qu'en fait deux autres particules neutres seulement sont émises et la valeur maxima du spectre, que ces deux particules sont de masse faible [5].…”