# How much energy is carried away by neutrinos in matter-antimatter annihilation?

Some people say that neutrinos carry away most of the energy, some others say just a fraction. So what is the truth ? what is the percentage of energy lost due to neutrinos ?

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That question sounded so poetic to me that I converted it into a poem: "How much energy is carried away", "by a neutrino in an annihilation", "Of matter and antimatter", "Some say the most", "Some say the the fraction", "So what's the truth", "So what's the percentage", "of energy lost due to", "Neutrinos...." –  ssg Jan 20 '13 at 13:42

Annihilation of baryon antibaryon proceeds mainly by a multiplicity of pions . In this study , table 1, experimental.

Charged pions have a lifetime of of about $10^{-8}$ seconds and will decay into muons and neutrinos (anti too conserving quantum numbers), muons will decay with similar lifetime to electrons (positrons) and corresponding neurinos. The end stable particles will be neutrinos and electrons to share the charged pions energy.

Neutral pions decay within $10^{-16}$ seconds to two gammas.

Statistically, 2/3 of the energy goes to charged pions, and this is shared between neutrinos 3/4 and electrons 1/4 (2 $\nu_{\mu}$ and 1 $\nu_e$ and an electron).

Roughly neutrinos will get 1/2 of the available energy.

Gammas take 1/3 of the total energy.

So

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So would it be correct if we said about 50% of the energy is carried away by neutrinos ? –  Hurricane Jan 20 '13 at 18:25
yes, but as @JimGraber says if one waits for the end of the universe it will all be cold photons. –  anna v Jan 20 '13 at 18:38
It is interesting of course to ask "over what distance scales are you measuring". At ranges of centimeters to decimeters the uncharged pions have decayed, but the many of the charged ones remain; out to meters some muons (first generation products of the pion decays) remain. –  dmckee Jan 20 '13 at 19:05
@dmckee true, average energy,lifetime, and at what time after the annihilation. I asumed something on cosmic scales. –  anna v Jan 20 '13 at 19:15