Proportional-Counter Selection of Cloud-Chamber Events

Author: Rouse, Carl Albert

Year: 1956

Degree: Dissertation (Ph.D.)

Advisors: Anderson, Carl D.; Cowan, Eugene W.

Committee Member: Unknown, Unknown

Option: Physics; Mathematics

DOI: 10.7907/8D6S-QT11

Abstract

The 48" magnet-cloud chamber has been controlled by a gated proportional counter and photographs taken of 5313 expansions have been analyzed.

The proportional counter was found to (1) select events of lower energy than penetrating shower detectors; and (2) select at a much lower hourly rate interactions in which V-particles were produced. However, the V-particles detected appeared on the average to be of lower energy, hence, could be measured with maximum cloud-chamber accuracy.

The µ-meson-induced electron showers detected by the proportional counter have been analyzed. Experimental and theoretical frequencies were obtained for the production of showers with a minimum of 40, 100, and 200 electrons. The frequencies for showers of 100 and 200 electrons were found to be the most reliable. These experimental frequencies are 1.6+0.8-0.4 x 10-6 per second and 0.44 ± 0.21 x 10-6 per second, respectively. The corresponding theoretical values computed from collision and bremsstrahlung probabilities for spin ½ µ-mesons of 10 x 10-6 per second and 3.5 x 10-6 per second reflect the uncertainties of cascade shower theory.

Two V-particles of particular interest were photographed. One, event 47202, appears to be strong evidence for the existence of the neutral τ-particle with the decay scheme, τ° → π⁺ + π⁻ + π° + Q ~ 78 Mev.

The second V-particle, event 46944, was a negatively charged K-particle that is consistent -- from ionization momentum measurements and decay dynamics -- with the decay scheme, θ⁻ → π⁻ + π°, P* = 206 Mev/c. The measured P* for the event is 207 ± 10 Mev/c. With other events that could be consistent with the θ⁻, this event helps to establish the existence of this K-particle.

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