Jul 28, 2019 · $\pi^+$ and $\pi^-$ decay into muon(or electron) and neutrino and $\pi^0$ decays into photons. So there is a weak interaction in the decay process of $\pi^+$ and $\pi^-$.

If an EM decay is possible, it is so much faster that it will dominate. You can see this in the overall $\pi^0$ decay rate compared to the charged pion decay rate. The neutral pion decays $10^9$ times faster because it is an EM decay. The charged pions have to decay weakly as there is nothing they can decay into electromagnetically.

May 2, 2016 · In this imaginary world the decay of the pion in lepton plus neutrino would be prohibited: you could not conserve both the total spin (zero) and the total momentum, in that this would imply emitting two particles both with the spin in the direction of motion (i.e. right handed).

If that is the case, quantum effects still allow the pseudoscalar bound state (particles) to decay into two photons due to the quantum anomaly. However, quarks are not massless, and neutral pion can decay even at classical level into two gammas, in the same way, as para-positronium (e+e-) quantum state annihilates = decays into two gammas.

May 24, 2021 · The pion has a rest frame where it has 0 momentum. Photons do not have rest frames, so if the pion decays into one photon, that photon will have momentum in every frame. So momentum cannot be conserved. With two photons, the net momentum between them can be zero, and so momentum conservation in the pion's rest frame is possible.

Feb 14, 2023 · Photon energies after neutral pion decay. 0. Maximum Momentum of Neutral Pion. 0.

Dec 26, 2018 · The photons have intrinsic spin (or, better, helicity) one, so the pair can have odd orbital angular momentum, still conserving total angular momentum (which has to be zero, as the pion is spinless).

Feb 16, 2018 · Leading, ultimately, to the charged pion rate $\Gamma \propto G_F^2 f_\pi^2 m_\pi$..., Whereas one need do the Steinberger triangle fermion loop to get the neutral pion decay, which Schwartz covers, yielding the dreaded $\Gamma\propto \alpha^2 m_\pi^3/f_\pi^2 $.

Mar 25, 2019 · It is called conservation of lepton number . The pion has lepton number zero. The names: neutrino and antineutrino have been assigned to the neutral leptons carrying the opposite lepton number of the electron (+1) electron antineutrino (-1), positron (-1) positron antineutrino (+1), so that the original particle and the final state have both lepton number zero.

As summarized by Wikipedia, different sources use different choices for the (pion) decay constant.This means that the numerical value can vary between $$ \sqrt 2\ f_\pi \quad\leftrightarrow\quad f_\pi \quad\leftrightarrow\quad \frac{1}{\sqrt 2}\ f_\pi $$