# Why are quarks fundamental particles?

1. Apr 30, 2015

### heartcomeback

Are quarks really considered fundamental particles that cannot be divided further? If an up quark can transmute to a down quark and release a W+ boson which decays to a positron and a neutrino (for example) - doesn't this mean that there is substructure to a quark?

What exactly is it that makes a particle fundamental and non divisible?

2. Apr 30, 2015

### haael

In Standard Model, yes.

No, it does not prove that.

A particle is either fundamental or it is a bound state. Bound states have more degrees of freedom. A fundamental particle is completely described by its internal quantum numbers, position, momentum and spin. The internal quantum numbers must be discrete.
In case of a bound state we have additional degrees of freedom related to the position and orientation of the constituents. These degrees of freedom are always continuous.