GATE 2026 PH – Question 38

Correct answer: (B) The decay $\Lambda\to p^++\pi^-$ is allowed and strangeness is violated.

Explanation

Check each statement.

• **A. In $\mu^+\to e^++\nu_e+\bar\nu_\mu$, CPT is violated.** False: CPT is a symmetry of all known interactions, and this decay conserves it.- **B. The decay $\Lambda\to p^++\pi^-$ is allowed and strangeness is violated.** True. $\Lambda$ has $S=-1$, and the proton and pion have $S=0$, so strangeness changes by one unit, which is allowed in a **weak** decay. ✓
• **C. $p^+\to e^++\gamma$ is allowed.** False: it violates baryon number and lepton number conservation.
• **D. $\Omega^-\to\Xi^0+K^-$ is allowed.** The mass of $\Omega^-$ (1672 MeV) is smaller than the sum of the masses of $\Xi^0$ (1315 MeV) and $K^-$ (494 MeV), which is 1809 MeV, so it is kinematically forbidden. ✗

Answer **B**.