Can Up Quark Absorb Negative W Particle to Become Strange?

[KBriggs]

Can an up quark absorb a negative W particle and become a strange quark? I know s can turn into u via the opposite process (emission of positive W), but can the interaction go the other way?

This arises when trying to draw the Feynman diagram for the rather unlikely decay

$$B^+\to D_s^++\bar{K^0}$$

 

[Spinnor]

From this it looks possible,

http://en.wikipedia.org/wiki/Quark#Weak_interaction

 

[kloptok]

The process can always go both ways, as long as energy is conserved.

 

[KBriggs]

Thanks. I guess then the only quark that could not be reached this way would be top quark, since its mass is so much larger than the mass of the W bosons.

 

[arivero]

An interesting question, related to this, was why experimentally the calculated rates of the process didn't match with the expected for a three quarks model, so a fourth quark, the charm, was postulated. See GIM mechanism.

 

[kloptok]

Thanks. I guess then the only quark that could not be reached this way would be top quark, since its mass is so much larger than the mass of the W bosons.

Hey, with enough accelerator energy everything is possible The top mass is 175 GeV, and the available energy at for example LHC ($\sqrt{\hat{s}}$ ) is probably a couple of TeV, i.e. many times the top mass

Though you are correct in your reasoning, the transition amplitude between d and t quarks is a very small number, so transitions from down/strange to top are very unlikely. See Wiki: Cabibbo-Kobayashi-Maskawa matrix, the numbers to look for are non-diagonal ones in the third row, these describe transitions between top and lighter down-type quarks.