[填空题]
If a proton is movinn(u et+p: 9-a t:czb*;yxptn qg at very high sxli/e9mtdil+ex nc 5hn/q) 75peed, so that its kinetic energy is much greater than+ti5xl 7xedqc 9hl)m//ei5nn its rest energy ($mc^2$), can it then decay via $p \to n + \pi^+$?
参考答案: no
本题详细解析: No, even if the proton has an extremely large kinetv63;.e o frto+4eqs8t c5y jqwic energy (and, thus, an extremely lay+q o t83s4j freecqw6ot;v.5 rge momentum), there is no way to conserve both energy and momentum during such a decay $( \text{p} \to \text{n} + \pi^+ )$. Observed from the rest frame of the proton, the decay is energetically impossible, and so it is energetically impossible in every other reference frame as well. In the frame in which the proton is moving fast, the decay products must move very fast as well in order to conserve momentum, and with this constraint, there will still not be enough energy to make the decay energetically possible.
