# Conservation laws during particle decay?

• I
Gold Member

## Main Question or Discussion Point

I believe that conservation laws, like for energy and momentum, are obeyed during the particle decay process, e.g. the total energy of the new output particles is equal to the energy of the one input particle. But is that relationship subject to quantum fuzziness? Suppose we, somehow, prepare a coherent source of freely traveling massive particles. Then after some time, these particles each decay into two other particles. Is this decay process a quantum measurement event - does the wave function of the input particle collapse so that we are dealing with actual precise values of say energy when that energy is transferred to the two output particles?

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DrChinese
Gold Member
Is this decay process a quantum measurement event - does the wave function of the input particle collapse so that we are dealing with actual precise values of say energy when that energy is transferred to the two output particles?
The decay is only a measurement in the limited case as we learn something about the byproducts. When a neutron ejects an electron, you know you have a proton and a neutrino running around somewhere. That much is certain. Values for other properties do not collapse or otherwise take on well-defined values. So without knowing the initial momentum precisely, the child particles will not suddenly have certain values for momentum.

• Buzz Bloom
Gold Member
The decay is only a measurement in the limited case as we learn something about the byproducts. When a neutron ejects an electron, you know you have a proton and a neutrino running around somewhere. That much is certain. Values for other properties do not collapse or otherwise take on well-defined values. So without knowing the initial momentum precisely, the child particles will not suddenly have certain values for momentum.
Ok, thanks.

I guess I have a followup question: Suppose we know the initial momentum precisely. Is the conservation equation Momentum_in = Momentum_out obeyed precisely or is it subject to inherent quantum fuzziness do to the HUP, etc.?

DrChinese