QCAA Physics Alternative Sequence The Standard Model

The initial and final states both consist of an electron and a positron, so the total mass remains exactly the same.

Electrons and positrons are leptons, not baryons. The baryon number is zero before and after the interaction, so it does not change.

Lepton number is a conserved quantity. The initial state ($e^-$ and $e^+$) has a total lepton number of $1 + (-1) = 0$, which perfectly matches the final state's lepton number.

The interaction starts with two particles (an electron and a positron) and ends with two particles, meaning the total number of particles remains constant.

This is correct. Mesons are a type of hadron consisting of a bound state of one quark and one antiquark.

This is incorrect. Leptons, such as electrons and neutrinos, are fundamental particles, whereas mesons are composite particles made of quarks.

This is incorrect. The elementary gauge bosons exchanged between quarks to mediate the strong force are called gluons, not mesons.

This is incorrect. Subatomic particles composed of exactly three quarks are classified as baryons, which include protons and neutrons.