Chronology of Milestone Events in Particle Physics

Chronology of Milestone Events in Particle Physics - HODSON 1954

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HODSON 1954

Hodson, A.L.; Ballam, J.; Arnold, W.H.; Harris, D.R.; Rau, R.R.; Reynolds, G.T.; Treiman, S.B.;
Cloud-Chamber Evidence for a Charged Counterpart of the Θ^o Particle
Phys. Rev. 96 (1954) 1089;

Abstracts
A photograph obtained in a Wilson cloud chamber, operated in a magnetic field, shows the following unusual event: A positive particle, produced in an interaction above the cloud chamber, decays in flight into a positive particle less massive than a K meson. Four other lightly ionizing particles also originate from the decay point; these appear in the form of two small-angle pairs, each pair consisting of one positive and one negative particle. The observed momenta and ionizations are consistent with three of these four particles being either electrons or mesons; the fourth must be an electron.
The event may be interpreted as the decay: K⁺ → π⁺ choose μ⁺ π^o + Q MeV, followed by the decay of the π^o meson into four electrons (a possible but hitherto unobserved mode of decay): π^o → e⁺ e^– e⁺ e^–. This interpretation leads to a remarkable internal consistency of the data and is supported by the following experimental facts:

(i): There is good overall transverse-momentum balance in two mutually perpendicular planes.
(ii): If we assume that all the particles in the above group of four are electrons resulting from the decay of a neutral particle the mass of the latter, determined from energy-momentum balance, is (255_-10⁺¹⁵)m_e, in good agreement with the known mass of the π^o meson.
(iii): A transformation to the rest system of the π^o meson shows that in this frame the four electrons come off as two small-angle pairs traveling in opposite directions. This is the most probable configuration in the four-electron decay of a π^o meson.

The Q values calculated for the K⁺ decay are: Q(π⁺, π^o) = (213⁺¹⁵_-10) MeV and Q(μ⁺, π^o) = (207⁺¹⁵_-10) MeV. Comparison of the first Q values with that for the θ^o particle Q(π⁺, π^–) = 214 ± 5 MeV, suggests that the unstable meson observed in this event and designated phenomenologically above as a K⁺ meson may be a charged counterpart of the θ^o particle.
This interpretation may explain at least some of the cases, observed by other workers, in which γ rays appear to be associated with S particles.
Other possible interpretations of the event are considered.

Accelerator COSM Detectors CLOUD

Related references
See also
D. R. Harris and A. L. Hodson, Phys. Rev. 95 (1954) 661A;

Reactions

K⁺ π⁺ π^o

Particles studied

K⁺ ex

Record comments
Evidence for K⁺ → π⁺ π^o decay.

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