Quarks come in different 'flavors', such as up, down, strange, charm, bottom, and top.
A change in a quark's flavor, meaning the transformation of one type of quark into another, is a hallmark of the weak nuclear force. This force is unique in its ability to cause such transformations, which is not possible under the influence of the strong nuclear force.
In the example of Lambda decay, \(\Lambda^0\), composed of up (u), down (d), and strange (s) quarks, transforms into a proton, which consists of up (u) and down (d) quarks, and a pion, which includes up (u) and anti-down (\(\bar{d}\)) quarks. The strange quark (s) from the initial Lambda particle undergoes a change to a down quark (d), and in the process, a pion is formed. This is a quark flavor change, specifically, \(s \rightarrow d\), indicating the involvement of the weak nuclear force, as the strong force does not cause such changes.
Recap of Quark Transformation:
- Lambda particle quarks: uds
- Proton quarks: uud
- Pion quarks: u\(\bar{d}\)
This evidence of quark flavor change conclusively shows that the decay of the Lambda particle is mediated by the weak nuclear force, despite the conservation of baryon number that might initially suggest otherwise.