Final answer:
The question appears to confuse database operations with physics. In the physics context, which is the intended subject, pi mesons can decay into a positron or a muon, but not typically into a proton.
Step-by-step explanation:
The question you're asking about PSM likely refers to Persistent Stored Modules in the context of database systems, which where statements like UPDATE, INSERT, and DELETE can be used. However, it seems there's a mix-up with a physics question about pi (π) decay. Regarding the decay of a π (pi meson), let's clarify the possible products of this process. When a pi meson decays, the decay products may include various particles, depending on the type of pi meson and the decay channel. The options provided here are a positron (a), a muon (b), and a proton (c). While a positron and a muon could certainly be products of certain pi meson decay channels, protons are not a typical product of pi decay. Therefore, the correct answers reflecting the possible decay products of a pi meson would be a positron and a muon.