Quarks, leptons and hadronsEdexcel A-Level Physics: Mind map

Exam questions on Quarks, leptons and hadrons

1. Particle physicists classify the particles detected in high-energy collisions using the standard quark–lepton model. The up quark has charge +2/3 e, and the down and strange quarks have charge −1/3 e. Every quark has baryon number +1/3, and the proton is made of two up quarks and one down quark (uud).
   Show that the quark composition of the proton gives it a charge of +1 e and a baryon number of +1.2 marks
2. The omega-minus (Ω⁻) was first detected in a bubble chamber experiment in 1964. It is a baryon made of three strange quarks (sss). A strange quark has charge −1/3 e and baryon number +1/3. Every particle has an antiparticle.
   Deduce the charge and the baryon number of the antiparticle of the Ω⁻.2 marks
3. By 1977 physicists had identified five quarks (up, down, strange, charm and bottom) and six leptons (the electron, muon and tau, and their three neutrinos). The sixth quark, the top quark, was not discovered until 1995 at Fermilab. Its charge is +2/3 e.
   Explain how symmetry in the standard model led physicists to predict the existence of the top quark before it was discovered.3 marks