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PLANO 1959

Plano, R.; Prodell, A.G.; Samios, N.P.; Schwartz, M.; Steinberger, J.;
Parity of the Neutral Pion
Phys. Rev. Lett. 3 (1959) 525;

Summary
Here we present a preliminary report of a study of certain angular correlations in the decay π^o → e⁺ e^– e⁺ e^–. This decay is expected theoretically, and is calculable on the basis of quantum electrodynamics. It is the internal conversion of the two photons of the normal decay. The planes of the pairs "remember'' the polarization of the virtual intermediate photons; the correlation of these planes reflects then the polarization correlation of Yang. The correlation of the planes in double internal conversion has been calculated by Kroll and Wada.
The experimental difficulty is due to the rarity of the decay (1/30000) in combination with the necessity of establishing at least the relative orientation of the planes of the two pairs. In this experiment, the π^o's are produced in the capture reaction π^– p → π^o n. About 60% of the negative pions coming to rest in hydrogen undergo this reaction, emitting 4 MeV π^o mesons. A liquid hydrogen bubble chamber, 30 cm diam., 15 cm deep, in a field of 5500 gauss, is exposed to a stopping π^–-beam. 700000 pictures have been taken, and there are ~ 15 stopping mesons per picture. We expect therefore that ~ 200 events will be found eventually. We report here an analysis of the first 103 events, since we believe that this already permits a convincing conclusion! (Extracted from the introductory part of the paper.).

Accelerator NEVI-CYC Detectors HBC-30CM

Related references
See also
C. N. Yang, Phys. Rev. 77 (1950) 242;
K. A. Brueckner, R. Serber, and K. M. Watson, Phys. Rev. 81 (1951) 575;
H. M. Kroll and W. Wada, Phys. Rev. 98 (1955) 1355;
Analyse data from
W. Chinowsky and J. Steinberger, Phys. Rev. 95 (1954) 1561;
W. K. H. Panofsky, R. L. Aamodt, and J. Hadley, Phys. Rev. 81 (1951) 565;
W. Chinowsky and J. Steinberger, Phys. Rev. 100 (1955) 1476;

Reactions

	π– p n πo	0 GeV (Plab)
	πo 2e– 2e+	4 MeV (Plab)	cor, ang

Particles studied

πo

qn

Record comments
First direct determination of the parity of the π^o.

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