PHYSICS · Subjective · Fermi University Physics · Particle Physics & Quantum Fields · Interacting fields, Feynman diagrams and QED · Electroweak theory and the Standard Model
Particle Physics, Ch Exchange, range and coupling: diagrams as bookkeeping
Problem
Neutron beta decay is n→p+e−+νˉe. The neutron is udd and the proton is uud, so a single d quark turns into a u quark, with the extra charge carried away by a W− that itself decays to e−νˉe. (a) Describe the Feynman diagram for this process as bookkeeping: list the incoming and outgoing lines, the internal line, and every vertex, with time running to the right. (b) State which single vertex type from the four allowed vertices appears, and how many times it is used. (c) Check charge, baryon number and lepton number at each vertex separately.