Quick questions on The Standard Model: WACE Year 12 Physics Unit 4

Four fundamental interactions govern all of physics. The strong force binds quarks into nucleons and nucleons into nuclei, acting only over nuclear distances. The electromagnetic force acts between charges over unlimited range. The weak force is responsible for beta decay and changing one type of quark into another.

In the Standard Model forces act by exchanging carrier particles (gauge bosons). The photon carries the electromagnetic force, gluons carry the strong force between quarks, and the W and Z bosons carry the weak force. The Higgs boson, confirmed in 2012, is associated with how particles acquire mass. Gravity's hypothetical carrier, the graviton, has not been observed.

A common task is to deduce or check the quark content of a particle from its charge. Remember the first-generation quark charges: up is $+\tfrac{2}{3}e$ and down is $-\tfrac{1}{3}e$, with antiquarks carrying the opposite sign. A baryon is three quarks and a meson is a quark-antiquark pair, so for a baryon you choose three quarks whose charges sum to the particle's charge. For example, a charge of $+1$ requires uud (the proton), while a charge of $0$ requires udd (the neutron).