A pure beam passes through a thin slab of matter of thickness

PHYSICS · Multi-part · Fermi University Physics · Particle Physics & Quantum Fields · Flavour, neutrinos and CP violation · Flavour, neutrinos and CP violation

Symmetry and Flavour, Ch Neutral kaons: mixing, strangeness oscillation and CP violation

Problem

A pure KLK_L beam passes through a thin slab of matter of thickness dd. At rest, the strong-interaction reaction Kˉ0p→Λπ+\bar K^0 p \to \Lambda\pi^+ is energetically open, while K0p→Λπ+K^0 p \to \Lambda\pi^+ would require the strangeness of the initial state to change by two units in a strong process and is forbidden. ((a)) Explain why this fact makes the forward scattering amplitude fˉ\bar f of Kˉ0\bar K^0 on a nucleon different from the forward scattering amplitude ff of K0K^0 on the same nucleon. ((b)) Writing KLK_L in the (K0,Kˉ0)(K^0, \bar K^0) basis, explain why the beam that emerges from the slab is no longer purely KLK_L, and identify, up to a proportionality constant, what the amplitude of the emerging KSK_S (i.e. K1K_1) component is proportional to. ((c)) State what the interference of this regenerated KSK_S with the surviving KLK_L decays downstream is used to measure.

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