# Isn't a Pi- = W-?

talanum52
Homework Statement:
pi- =W-?
Relevant Equations:
pi- = W- ?
They decay to identical particles but are they identical?

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vanhees71 and topsquark
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Homework Statement:: pi- =W-?
Relevant Equations:: pi- = W- ?

They decay to identical particles but are they identical?
Can you list the properties of each of these particles?

-Dan

vanhees71
talanum52
Can you list the properties of each of these particles?
They don't have the same mass and spin. Because they decay to the same particles, there must be additional particles in their decay formulas, that isn't the same, because spin is a conserved quantity.

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They don't have the same mass and spin. Because they decay to the same particles, there must be additional particles in their decay formulas, that isn't the same, because spin is a conserved quantity.
They do, indeed, have different masses. But why do you say they have different spins? They are both spin 1 bosons.

You are looking only at decay products. What you are not looking at is the more basic stuff. Here's a brief rundown.

A ##\pi^-## is made of a pair of bound quarks: a ##\overline{u}## and a d. It has a spin of 1 and an isospin of -1, and being made of quarks participates in the strong nuclear, weak nuclear, and electromagnetic forces.

A ##W^-## is a weak gauge boson and is a fundamental particle. It has a spin of 1 and an isospin of 0. It is not made of quarks and participates in the weak nuclear and electromagnetic forces.

(Also look up weak isospin.)

The mass difference doesn't imply that there are any particles missing from the decay lists, it just means that the decays from the ##W^-## are more energetic.

So the main difference is that the ##W^-## is a fundamental weak gauge boson and the ##\pi^-## is a composite meson.

-Dan

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The pions are pseudoscalar particles, the W-bosons vector ones. I've no clue, how one can get to the idea they were the same particles to begin with.

topsquark
talanum52
I've no clue, how one can get to the idea they were the same particles to begin with.
They decay to identical particles - that's why.

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They decay to identical particles - that's why.
Are decay products the same as their constituents?

Neutral pion decays into two photons, is the pion composed of photons?

Note that ##\pi^-## has several decay channels, same with the ##W^-## boson.

topsquark
talanum52
Are decay products the same as their constituents?

Neutral pion decays into two photons, is the pion composed of photons?
I'm arguing that structure is conserved. Then the neutral pion's substructures cancel (not the energy).

malawi_glenn
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I'm arguing that structure is conserved. Then the neutral pion's substructures cancel (not the energy).
It's an interesting idea, but it doesn't work well in practice. In fact, this example shows why you can't make this argument in general: the ##W^-## is a fundamental particle and does not have any structure to conserve. And as there are many ways in which it can decay it would be hard to say, just by looking at the daughters, what the original particle might have been before the decay. (Possible, of course, but hard.)

-Dan

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I'm arguing that structure is conserved. Then the neutral pion's substructures cancel (not the energy).

Define "structure"and how/why it would be conserved.

This is clearly not homework, looks more like own idea/speculation of yours.

##W^-## boson can decay into bottom quark (plus another lighter quark), ##\pi^-## can not. Case closed.

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vanhees71 and topsquark
talanum52
Define "structure"and how/why it would be conserved.
Structure is the quantum numbers, mass, velocity and the space points and left out points that carries it. In my model of particles. It just seems conserved because this is the most economical.

It is work at home.

malawi_glenn
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In my model of particles
This is personal theory, which is off limits here. Your legitimate question has been answered.