B How did we measure the mass of Quarks?

[mpolo]

I have searched the Internet and I have not found a simple layman's explanation other than this.
We observe their decay products of quarks and that is what the mass is reconstructed from. Is this correct? If so I would like to have that confirmed. I am just looking for a simple direct explanation of the process used. If there is a simple formula that goes with this process I would like to see that as well.

 

[PeterDonis]

Is this correct?

Sort of. "Decay products of quarks" is not really a correct description of what is observed in the high energy experiments that provide the data used to estimate quark masses. It would be more accurate to say that we shoot things at hadrons (strongly interacting particles that contain quarks, like protons or hyperons) and measure what comes out; sometimes what comes out is just what we shot in with its energy and momentum changed (as in the deep inelastic scattering experiments in the 1960s--electrons were shot at nucleons and behaved as though they were bouncing off point-like particles inside the nucleons, which ended up being identified as the up and down quarks), sometimes it's a more complicated mess of other particles which indicate the presence of quarks inside the hadrons (as in the experiments that discovered the bottom and top quarks).

I am just looking for a simple direct explanation of the process used.

Unfortunately, there isn't one, because the process used depends on the specific model we use, and there are multiple models that we use to estimate quark masses. This is fundamentally because we can't solve the equations that describe the strong interaction directly, so we have to use approximations, and we need to use different approximations for different situations.

 

[mpolo]

The plot thickens. The process is more complicated than I thought and it appears to be a very indirect method. I guess I can settle for the name of the process models used. No need to explain the process models any further unless someone would like to try in layman's terms. I can look up the models myself for more information.

 

[PeterDonis]

it appears to be a very indirect method

Yes, it has to be because quarks are confined and we can't observe them directly, so we can't measure their masses directly the way we can for particles like electrons.

I guess I can settle for the name of the process models used

It's not even that simple. There probably isn't a "B" level reference that will explain this, but you could try here for a start:

http://pdg.lbl.gov/2011/reviews/rpp2011-rev-quark-masses.pdf

 

[mpolo]

Whew, that is complicated. I wonder what the confidence level really is concerning the masses of the quarks? Has that been quantified by anyone? I am sure it must be an educated guess at best. Thanks for your help.

 

[PeterDonis]

I wonder what the confidence level really is concerning the masses of the quarks?

The chart on the Wikipedia page gives the current best values with error estimates:

https://en.wikipedia.org/wiki/Quark#Mass