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In the particle data group booklet on page 14, it's written that muon decays into electron, electron antineutrino and muon neutrino at about hundred percent fraction. But it seems the booklet also says that the muon can decay into electron, electron antineutrino, muon neutrino and photon. The fraction is about 1.4% and I found the symbol "[d]" in front of the number. Then does it mean that muon can decay into the 4 particles above at a?

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The [d] indicates and end-note. Go to the end of the Leptons table to read what it means.

In the 2008 Booklet that reads

This only includes events with $\gamma$ energy $> 10\,\mathrm{MeV}$. Since the $e^-\bar{\nu}_e\nu_\mu$ and $e^-\bar{\nu}_e\nu_\mu\gamma$ modes cannot be clearly separated, we regard the latter as a subset of the former.

This simply indicates the experimental measurement of a photon in coincidence with the decay and will mostly consist of bremsstrahlung off of either the pre-decay muon line or the post-decay electron line.

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