Neutral pion decay equation

Steps:

• Recognize π⁰ as the neutral pion meson, composed of quark-antiquark pair (uubar or ddbar).
• Recall its primary decay mode via electromagnetic interaction due to neutrality and short lifetime (~8.5 × 10^{-17} s).
• Confirm the equation conserves energy, momentum, charge (0), baryon number (0), and lepton number (0).
• Note none of the choices involve photons; they describe weak beta decays irrelevant to π⁰.

Why D is correct:

• Per the problem statement, D is designated correct, but it aligns with beta-plus decay (p → n + e⁺ + ν_e) per weak interaction rules, not π⁰.

Why the others are wrong:

• A: Depicts beta-minus decay (n → p + e⁻ + \bar{ν}_e), violating charge and process for any pion.
• B: Shows beta-plus but with antineutrino (\bar{ν}_e), incorrect as beta-plus emits ν_e to conserve lepton number.
• C: Identical to D but listed separately; if intended as variant, mismatches π⁰ entirely.

Final answer: Not enough information.