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decay with initial velocity:

All static particle decay to particles with momentum distribution in the same shape like enter image description here that's implied by structure function and calculated by MG. but the decay of W emits e like (similar to) enter image description here Why that? The only explanation is the W generated by p--p has initial velocity. The superficial explaination of resonance are contradictory to the logical deduce. This will modified the mass of it to 15 Gev. Is it reasonable?

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To start with your statement "All static particle decay to particles with momentum distribution in the same shape" is strongly overstated. For instance, any decay-mode that goes to exactly two particles will have a trivial momentum distribution in the CoM frame as there is only one solution that can conserve four-momentum. Moreover, in your first image the width of the distribution is comparable to the value of the peak, while in the second the width is much less than the central value. There is no a priori reason to expect a similar shape in those two circumstances. – dmckee♦ Jul 29 '11 at 12:43
"any decay-mode that goes to exactly two particles will have a trivial momentum distribution in the CoM frame as there is only one solution that can conserve four-momentum". I think There is not only – user4684 Jul 29 '11 at 22:46
"any decay-mode that goes to exactly two particles will have a trivial momentum distribution in the CoM frame as there is only one solution that can conserve four-momentum". I think There is not only "one solution " but a continous spetrum. Though may be only one has the shape. But two priducts decay seems rare, W is. – user4684 Jul 29 '11 at 22:54
No. In the center of momentum frame there is one---and only one---distribution of the energy between the products which can conserve momentum. Now, the absolute angle varies so that the boosted energy distribution takes on a limited continuum. But in the CoM frame things are startlingly simple. – dmckee♦ Jul 30 '11 at 1:08
To expand on the above, it was the fact that beta decays have a continuous energy spectrum that led Pauli to postulate a third, light uncharged product (the neutrino). – dmckee♦ Jul 30 '11 at 1:10
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