In addition to charge and baryon number, another conserved quantity in particle interactions is lepton number. The six leptons have lepton number +1, and their antiparticles have lepton number −1. The lepton numbers for each generation (electron, muon, tau) are separately conserved. For example, an electron has electron-lepton number +1, while the electron antineutrino has electron-lepton number −1. What is the missing particle X in the following reaction? μ⁻+ p → n + X A) e⁻ B) π⁰ C) v_e D) v_μ E) γ

Question

Quizplus · Accepted Answer

In this reaction, a muon (μ) is being transformed into a neutrino (v), which means that lepton number is not conserved. Therefore, we need a particle X that has a lepton number of +1 in order to conserve lepton number overall. The only option that includes a particle with a lepton number of +1 is the neutrino (v) in choice D, so that must be the correct answer.

In Addition to Charge and Baryon Number, Another Conserved Quantity