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? v_μ + → + X A) e⁻ B) τ⁻ C) μ⁻ D) π⁻

Question

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In the given reaction, there is a muon (μ) with lepton number +1 on the left-hand side. Since lepton number is conserved, the particle X must also have a lepton number of +1. Among the given options, only option C μ⁻ has a particle with lepton number +1. All other options have either a particle with a different lepton number or a meson (π), which does not have lepton number. Option E is not a valid choice as it is not a particle or a known symbol. Therefore, the correct answer is C.

In Addition to Charge and Baryon Number, Another Conserved Quantity