Chronology of Milestone Events in Particle Physics

Chronology of Milestone Events in Particle Physics - PANOFSKY 1951

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PANOFSKY 1951

Panofsky, W.K.H.; Aamodt, R.L.; Hadley, J.;
The Gamma-Ray Spectrum Resulting from Capture of Negative π^– Mesons in Hydrogen and Deuterium
Phys. Rev. 81 (1951) 565;

Reprinted in
The Physical Review - the First Hundred Years, AIP Press (1995) 824.

Abstracts
π^– mesons produced in an internal wolfram target bombarded by 330 MeV protons in the l84-inch cyclotron are absorbed in a high pressure hydrogen target. The resulting gamma-ray spectrum is analyzed outside the shielding of the cyclotron by means of a 30-channel electron-positron pair spectrometer. The principal results are as follows.

(1): The gamma-rays result from two competing reactions: π^– p → n γ and π^– p → n π^o; π^o → 2γ.
(2): The ratio between the π^o yield to the single gamma-ray yield is =0.944 ± 0.20.
(3): The mass difference between the π^– meson and the π^o meson is given by 10.6 ± 2.0 electron masses.
(4): The π^– mass is 275.2 ± 2.5 electron masses.

The large mass difference between π^– and π^o precludes the conclusion that the unexpectedly small π^o to γ ratio is due to the small amount of momentum space available for π^o emission. It rather indicates that π^o emission is slowed down by the nature of the coupling of the π^o field to the nucleons. The experiment has been repeated by substituting D₂ for H₂ in the vessel. The result is that the reaction π^– deuteron → 2n and π^– deuteron → 2n γ compete in the ratio 2 : 1. The reaction π^– deuteron → 2n π^o is absent.

Accelerator LBL-CYC-184IN Detectors SPEC

Related references
More (earlier) information appears in
W. K. H. Panofsky, R. L. Aamodt, and H. F. York, Phys. Rev. 78 (1950) 825;
J. Steinberger, W. K. H. Panofsky, and J. Steller, Phys. Rev. 78 (1950) 802;
See also
F. Adelman and S. B. Jones, Science 111 (1950) 226;
W. Cheston and L. Goldfarb, Phys. Rev. 78 (1950) 320A;
W. K. H. Panofsky, Post Deadline Paper, New York Meeting A.P.S. (1950);
W. B. Fretter, Phys. Rev. 73 (1948) 41;
W. B. Fretter, Phys. Rev. 76 (1949) 216;
C. Y. Chao, Phys. Rev. 75 (1949) 581;
B. P. Gregory, B. Rossi, and J. Tinlot, Phys. Rev. 77 (1950) 299;
M. F. Kaplon, B. Peters, and H. L. Brandt, Phys. Rev. 76 (1949) 1735;
A. G. Carlson, J. E. Hooper, and D. T. King, Phil. Mag. 41 (1950) 701;
Manon, H. Muirhead, and Rachat, Phil. Mag. 41 (1950) 583;
M. Conversi, E. Pancini, and O. Piccioni, Phys. Rev. 68 (1945) 232;
R. Bjorklund et al., Phys. Rev. 77 (1950) 213;

Reactions

π^– p n γ p, mass, cs

π^– p n 2γ p, mass, cs

π^– deuteron 2n p

π^– deuteron 2n γ p

π^– deuteron 2n π^o p

π^o 2γ

Particles studied

π^– qn

π^o ex, mass

Record comments
Confirmation of the π^o and π^o → γ γ decay. Direct determination of the π^– parity.

New Comments List of Comments

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