# How to determine the decay mode probability of a pion

by rwooduk
Tags: decay, determine, mode, pion, probability
 P: 136 Hi, Given the initial energy of a pion is it possible to calculate the probability and mode of its decay? Ive looked everywhere for a relevent formula but everywhere simply states the probability and mode.... Wiki "The primary decay mode of a pion, with probability 0.999877, is a purely leptonic decay into an anti-muon and a muon neutrino"... "The second most common decay mode of a pion, with probability 0.000123, is also a leptonic decay into an electron and the corresponding electron antineutrino." I considered doing some sort of conservation of energy / momentum, but how am i supposed to do that if i dont know what it decays into? ive spent at least two hours trying to find an equation, i found something called the "branching ratio" is that at all related? any direction on this would be appreciated.
 P: 328 There is no rule to determine the decay modes. In principle, a particle can decay in every final state allowed by conservation laws. First of all the total mass of the final state must be lighter than the decay particle. Then the right quantum numbers must be conserved (total angular momentum, lepton number and so forth). Once you chose what particular final state you want to study you can compute the decay width for that particular final state using the Quantum Field Theory methods. A good reference on how to actually do this kind of calculation can be: De Wit - Field Theory in Particule Physics (Chapter 3) Is a very practical book that shows you how to compute cross sections and decay widths. I hope this is useful
 P: 136 That's very very useful! Thank you!!
 Thanks P: 1,948 How to determine the decay mode probability of a pion The decay is truly random. There is no way to tell ahead of time which of the possible outcomes will actually happen. All you can tell are the probabilities of each possible outcome.
 Mentor P: 12,029 The energy of the pion does not matter - in particular, you can always consider it in its rest frame. Branching ratios are exactly the probabilities of the decay modes you are looking for.
P: 136
 Quote by mfb The energy of the pion does not matter - in particular, you can always consider it in its rest frame. Branching ratios are exactly the probabilities of the decay modes you are looking for.
if the energy of the pion is completely independent of its decay mode then that again that answers my question because the only information given in the question is the pions total energy. So finding the main decay mode calculatively would not be possible.

Thanks all!
Mentor
P: 12,029
 Quote by rwooduk if the energy of the pion is completely independent of its decay mode then that again that answers my question because the only information given in the question is the pions total energy. So finding the main decay mode calculatively would not be possible.