The Σ⁺ particle can decay into a π⁰ particle and another particle Y as shown in the Feynman diagram.

(i) Identify the exchange particle X.

(ii) Identify particle Y.

(iii) Outline the nature of the π⁰.

The π⁰ particle can decay with the emission of two gamma rays, each one of which can subsequently produce an electron and a positron.

(i) State the process by which the electron and the positron are produced.

(ii) Sketch the Feynman diagram for the process in (c)(i).

Discuss whether strangeness is conserved in the decay of the Σ⁺ particle in (a).

(i) W ^-; (allow W⁺,W boson)

(ii) proton;

(iii) π⁰ is a (neutral) meson;
π⁰ has integer spin/is a boson;
π⁰ is unstable;
π⁰ is its own antiparticle;

(i) pair production;

(ii)

single vertex showing photon and two correctly labelled particles;
arrow direction correct for e⁺ and e^-;
Allow time axis to run vertically.
If Feynman diagrams include the meson decay, only consider either gamma’s pair production.

strangeness is not conserved, changes from –1 to 0;
weak interaction does not have to conserve strangeness in decay of Σ⁺;
To award the mark reasoned answers are required.