Symmetry of the 2π Decay of the Neutral K Meson under Time Reversal (T) and CPT

概要

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It is shown that interference between the 2π States arising from coherent decay of the long-lived and short-lived K-mesons (K_L and K_S) provides a direct manifestation of the symmetry of the system under the transformation CP, T and CPT. The ratio η of the K_L to K_S 2π decay amplitudes is odd under CP, hence the sign of the interference term in the K-meson decay curve changes sign under CP while the other terms are unchanged. When the effect of T is appropriately defined so as to avoid the dissymmetry associated with transforming initial conditions, ηis found to contain, in general, both even and odd terms. To separate these terms, it is necessary to make use of measurements of decay amplitudes for all modes, including the 2π. It is shown how these amplitudes may be used to determine separately even and odd parts of the Ashkin-Kabir parameter Z, which is a measurable weighted average of the two values of η (for the π^+π^- and π^0π^0 modes). Available data lead to the conclusion that the odd term of Z is non-vanishing, hence the interference term in the decay rate will change under T, thereby giving a direct manifestation of violation of time-reversal invariance. The even term in Z would manifest CPT violation, but the data are consistent with its vanishing. However, more information is needed, especially on the K_S→3π amplitude, to place a reliable upper limit on its magnitude.
理論物理学刊行会の論文
1975-09-25