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PHYSICAL REVIEW VOLUME 104, NUMBER 1 OCTOBER 4, 1956 Question of Parity Conservation in Weak Interactions* T. D. Ler, Colombia University, New York, ' Fork AND C.N. Yane.t Brookhaven National Laboratory, Upton, New Vork (Received fune 22, 1956) The question of parity conservation in § d sand in hyperon and meson decays is examined. Possible experiments are suggested which might test parity conservation in these interactions. ECENT experimental data indicate closely iden- tical masses' and lifetimes? of the ¢*(=:Kyz") and the 7+(=Kys*) mesons. On the other hand, analyses? of the decay products of +* strongly suggest on the grounds of angular momentum and parity conservation that the r* and é@ are not the same particle, This poses a rather puzzling situation that has been extensively discussed.* One way out of the dilficully is to assume that parity is not strictly conserved, so that 6+ and 7+ arc two different decay modes of the same particle, which necessarily has a single mass value and a single lifetime. We wish to analyze this possibility in the present paper against the background of the existing experimental evidence of parity conservation. It will become clear that existing experiments do indicate parity conserva- tion in strong and clectromagnetic interactions to a high degree of accuracy, but that for the weak inter- actions (i.e., decay interactions for the mesons and hyperons, and various [Fermi interactions) parity con servation is so far only an extrapolated hypothesi unsupported by experimental evidence. (One might even say that the present 0—7 puzzle may be taken as an indication that parily conservation is violated in weak interactions, This argument is, however, not to be taken seriously because of the paucity of our present knowledge concerning the nature of the strange par- ticles. It supplies rather an incentive for an examination of the question of parity conservation.) To decide unequivocally whether parity is conserved in weak interactions, one must perform an experiment to deter- mine whether weak interactions differentiate the right from the left. Some such possible experiments will be discussed, + Work supported in part by the U. S. Atomic Energy Com- mission. } Permanent address: Institute for Advanced Study, Prinecton, New Jersey. 1 Whitehead, Stork, Perkins, Peterson, and Birge, Bull. Am. Phys. Soc. Ser. IT, 1,184 (1956); Burkas, Heckman, and Smith, Bull, Am, Phys. Suc. Ser, IT, 1, 184 (1936). ? Harris, Orcar, and Taylor, Phys. Rev. 100, 932 (1938); Y. Hitch and K. Motley, Phys, Rev. 101, 496 (1956); Alvarez, Crawiord, Good, and Stevenson, Phys. Rev, 101, 303 (1956). ?R. Dalitz, Phil. Mag. 44, 1068 (1953); F. Fabri, Nuovo cimento 11, 479 (1954), See Orear, Harris, and Taylor [Phys. Rev. 102, 1676 (1956)]] for recent experimental results, * See, e.g., Report of the Sixth Annual Rochester Conference on High Energy Physics (Interscience Publishers, Tne., New York, to be published), PRESENT EXPERIMENTAL LIMIT ON PARITY NONCONSERVATION If parity is not strictly conserved, all atomic and nuclear states become mixtures consisting mainly of the state they are usually assigned, together with small percentages of slates possessing the opposite parity. The fractional weight of the latter will be called 5% It is a quantity that characterizes the degree of violation of parity conservation, The existence of parity selection rules which work well in atomic and nuclear physics is a clear indication that the degree of mixing, 3°, cannot be large. From such considerations one can impose the limit 5° (r/A)?, which for atomic spectroscopy is, in most cases, ~10-®. In general a less accurate limit obtains for nuclear spectroscopy. Parity nonconservation implies the existence of inter- actions which mix parities, The strength of such inter- actions compared to the usual interactions will in general be characterized by §, so that the mixing will be of the order 5?. The presence of such interactions would aifect angular disiributions in nuclear reactions, As we shall see, however, the accuracy of these experi- ments is not good. The limit on $* obtained is not better than 5? <10-4, To give an illustration, let us examine the polarization experiments, since they are closely analogous to some experiments to be discussed Jater. A proton beam polarized in a direction z perpendicular to its momentum was scattered by nuclei. The scattered intensities were compared® in two directions A and # related to each other by a reflection in the #-y plane, and were found to be identical to within ~1%. If the scattering ori; nates from an. ordinary parity-conserving interaction plus a pi nonconserving interaction (e.g., o-1), then the scattering amplitudes in the directions A and B are in the proportion (1+6)/(1—S), where 5 represents the ratio of the strengths of the two kinds of interactions in the scattering. The experimental result. thercfore requires <10-%, or 52<10-4, The violation of parity conservation, would lead to an electric dipole moment for all systems. The mag- nitude of the moment is moment~e5 (dimension of system). @) , Chamberlain, Sogré, Tripp, and ¥psilantis, Phys. Rew “98, 1830 (1954), 254 
