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# Relatavistic Decay watch

1. hey another university first year question any help is appreciated, have tried everything!!

http://i45.tinypic.com/2it0cpy.jpg

the answer is (masspion)^2 + (mass(u)^2)/ 2(masspion)

thanks!!
2. (Original post by equinox3o0o)
hey another university first year question any help is appreciated, have tried everything!!

http://i45.tinypic.com/2it0cpy.jpg

the answer is (masspion)^2 + (mass(u)^2)/ 2(masspion)

thanks!!
Which part are you stuck on? If it is a), start with time dilation.
For b), consider the reference frame of the particle that would result in the total energy being 140MeV, and the momentum of the resulting particles having a net momentum of 0.

A further hint is in the spoiler:

Spoiler:
Show
A pion decays at rest
3. so wait, a pion decays at rest?:O why does it say thats its travelling at a speed 0.93c so shouldnt its energy be gamma*m*c*c i.e its rest energy + kinetic energy
4. (Original post by Mathematician!)
Which part are you stuck on? If it is a), start with time dilation.
For b), consider the reference frame of the particle that would result in the total energy being 140MeV, and the momentum of the resulting particles having a net momentum of 0.

A further hint is in the spoiler:

Spoiler:
Show
A pion decays at rest
just wanted to quote
5. hmm to my luck i typed in to google the question and they have a step by step solution but the one thing i cant quite understand is why there is no quantity dictating the momentum of the neutrino in the full E^2 version of the equation, all it says is E(u)^2= (P(u)c)^2 + (rest mass of pion)^2. Shouldnt there also be a CP term for the momentum of the neutrino?
6. this it the website btw http://teachers.web.cern.ch/teachers...servation1.htm

i dont get the part where it asks to subtract E(u) from 2.3 to give the total energy of muon
7. (Original post by equinox3o0o)
so wait, a pion decays at rest?:O why does it say thats its travelling at a speed 0.93c so shouldnt its energy be gamma*m*c*c i.e its rest energy + kinetic energy
You have to consider the inertial reference frame for the pion, so it travelling at 0.93c is insignificant for the pion (but not for it's decay products!)
8. (Original post by equinox3o0o)
hmm to my luck i typed in to google the question and they have a step by step solution but the one thing i cant quite understand is why there is no quantity dictating the momentum of the neutrino in the full E^2 version of the equation, all it says is E(u)^2= (P(u)c)^2 + (rest mass of pion)^2. Shouldnt there also be a CP term for the momentum of the neutrino?
Which step in their working is this from (i.e. (2.x))?

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