The Catalysis of Nuclear Reactions by mu Mesons

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In the course of a recent experiment involving the stopping of negative K mesons in a 10-inch liquid hydrogen bubble chamber, an interesting new reaction was observed to take place. The chamber is traversed by many more negative {mu} mesons than K mesons, so that in the last 75,000 photographs, approximately 2500 {mu}{sup -} decays at rest have been observed. In the same pictures, several hundred {pi}{sup -} mesons have been observed to disappear at rest, presumably by one of the ''Panofsky reactions''. For tracks longer than 10 cm, it is possible to distinguish a stopping {mu} meson from a ... continued below

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Alvarez, L.W.; Bradner, H.; Crawford Jr, F.S.; Crawford, J.A.; Falk-Vairant, P.; Good, M.L. et al. December 10, 1956.

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In the course of a recent experiment involving the stopping of negative K mesons in a 10-inch liquid hydrogen bubble chamber, an interesting new reaction was observed to take place. The chamber is traversed by many more negative {mu} mesons than K mesons, so that in the last 75,000 photographs, approximately 2500 {mu}{sup -} decays at rest have been observed. In the same pictures, several hundred {pi}{sup -} mesons have been observed to disappear at rest, presumably by one of the ''Panofsky reactions''. For tracks longer than 10 cm, it is possible to distinguish a stopping {mu} meson from a stopping {pi} meson by comparing its curved path (in a field of 11,000 gauss) with that of a calculated template. In addition to the normal {pi}{sup -} and {mu}{sup -} stoppings, we have observed 15 cases in which what appears (from curvature measurement) to be a {mu}{sup -} meson comes to rest in the hydrogen, and then gives rise to a secondary negative particle of 1.7 cm range, which in turn decays by emitting an electron. (A 4.1-Mev {mu} meson from {pi} - {mu} decay has a range of 1.0 cm.) The energy spectrum of the electrons from these 15 secondary particles looks remarkably like that of the {mu} meson. There are four electrons in the energy range 50 to 55 Mev, and none higher; the other electrons have energies varying from 50 Mev to 13 Mev. The most convincing proof that the primary particle actually comes to rest, and does not--for example--have a large resonant cross section for scattering at a residual range of 1.7 cm, is the following: In five of the 15 special events, there is a large gap between the last bubble of the primary track and the first bubble of the secondary track. This gap is a real effect, and not merely a statistical fluctuation in the spacing of the bubbles, since in some cases the tracks form a letter X, and in another case the secondary track is parallel to the primary, but displaced transversely by about 1 mm at the end of the primary. These real gaps appear also (although perhaps less frequently) between some otherwise normal-looking {mu}{sup -} endings and the subsequent decay electron; they are thought to be the distance traveled by the small neutral mesic atom.

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  • Report No.: UCRL--3620
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.2172/878129 | External Link
  • Office of Scientific & Technical Information Report Number: 878129
  • Archival Resource Key: ark:/67531/metadc875220

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  • December 10, 1956

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  • Sept. 21, 2016, 2:29 a.m.

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  • Nov. 3, 2016, 7:49 p.m.

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Alvarez, L.W.; Bradner, H.; Crawford Jr, F.S.; Crawford, J.A.; Falk-Vairant, P.; Good, M.L. et al. The Catalysis of Nuclear Reactions by mu Mesons, report, December 10, 1956; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc875220/: accessed August 19, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.