Someone argues: "The long-lived neutral kaon has

PHYSICS · Multi-part · Fermi University Physics · Particle Physics & Quantum Fields · Symmetry, groups and the quark model · Flavour, neutrinos and CP violation

Particle Physics, Ch Parity, charge conjugation, time reversal and CPT

Problem

Someone argues: "The long-lived neutral kaon KLK_L has CP=−1CP = -1, but it is seen to decay to π+π−\pi^+\pi^-, a state with CP=+1CP = +1, in about 2×10−32\times10^{-3} of its decays. A decay that changes CPCP is a decay that changes the product of charge conjugation and parity, so this measurement is really a violation of the CPT theorem, since CPT is built from the same three operations." ((a)) Find the error in this reasoning. ((b)) State precisely what the KL→π+π−K_L \to \pi^+\pi^- measurement does establish, and what it leaves unexplained.

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