State the quark structures of a meson and a baryon.

Explain which interaction is responsible for this decay.

Draw arrow heads on the lines representing \({\bar u}\) and d in the \({\pi ^ - }\).

Identify the exchange particle in this decay.

Outline one benefit of international cooperation in the construction or use of high-energy particle accelerators.

Meson: quark-antiquark pair
Baryon: 3 quarks

Alternative 1

strange quark changes «flavour» to an up quark

changes in quarks/strangeness happen only by the weak interaction

Alternative 2

Strangeness is not conserved in this decay «because the strange quark changes to an up quark»

Strangeness is not conserved during the weak interaction

Do not allow a bald answer of weak interaction.

arrows drawn in the direction shown

Both needed for [1] mark.

W ⁻

Do not allow W or W⁺.

it lowers the cost to individual nations, as the costs are shared

international co-operation leads to international understanding OR historical example of co-operation OR co-operation always allows science to proceed

large quantities of data are produced that are more than one institution/research group can handle co-operation allows effective analysis

Any one.