The parity of elementary particles
Tóm tắt
In determining the intrinsic parities of elementary particles, the invariance of the interactions under gauge transformations makes the relative parity of certain groups of particles a matter of convention. On the other hand, charge independence puts definite restrictions on the relative parities of the members of isotopic multiplets. The interplay of these conventions and restrictions is analysed and the general considerations applied to the known particles.
Tài liệu tham khảo
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To illustrate the freedom due to gauge groups and the restrictions imposed by charge independence, we can consider the pion-nucleon situation. The fact that the reaction π+ + d → n + n is observed to go for (spin zero) pions in s-states, establishes only that, of the three particles p, n, π+, just one has negative intrinsic parity. The gauge groups of charge and nucleon number allow two parities, (say p and n), to be chosen by convention. (The form of the interaction, ψpγ5ψnφ + h.c., implied by this result is independent of the convention). The assumption of charge independence now predicts that π0 also has negative parity — a prediction which could be checked directly by observing the polarization of the γ-rays in the π0-decay. (See e.g.L. Wolfenstein andD. G. Ravenahll:Phys. Rev.,88, 279 (1953)).