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enter image description here

I am struggling to understand the CKMFITTER plot which is attached here. Please, someone, try to explain to me what are all these color bands. What are their meanings? Why one band is circular in shape, while one is boomerang-shaped? What is referring here to the excluded area, etc.?

I know some basics of the CKM matrix, like the angles of a unitary triangle $\alpha$, $\beta$, and $\gamma$. Also, I think these are various experimental results. But I am unable to understand what are all these color regions and others.

I know it will be a slightly bigger topic to explain. Also, a link to any nicely explained document on this will be greatly appreciated.

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  • $\begingroup$ I guess the figure came with a caption and some disucssion, copying that a long with the figure would help people write answers $\endgroup$
    – innisfree
    Commented Mar 1, 2021 at 7:53
  • $\begingroup$ Hi, I copied the CKMFitter plot from the ckmfitter.in2p3.fr/www/results/plots_summer19/… site. Which is managing such plots over the years. Any experts here on these CKM fitter plots can recognize/identify my doubts easily I hope. $\endgroup$
    – Twinklestar
    Commented Mar 1, 2021 at 8:02
  • $\begingroup$ Consider to spell out acronyms. $\endgroup$
    – Qmechanic ♦
    Commented Oct 16, 2023 at 9:08

1 Answer 1

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To have a clear understanding of what's going on requires a lot of knowledge. The basic idea is that using experimental, as well as theoretical data, one can constrain various SM parameters coming from different experiments and get out a best fit region in the $(\bar\rho,\bar\eta)$ plane for the unitarity triangle.

Clearly being every measurement accompanied by some error, and this is true even for theoretically evaluated results since most of the time they come from lattice QCD calculations of various weak and strong operators matrix elements, the path that a given fit traces in the $(\bar\rho,\bar\eta)$ plane is not a line, but a region. This region is the $95\%$ confidence region.

As to why certain parameters follow a circular path and others don't, you can have a look at this (somehow ancient) review by A.J. Buras.

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  • $\begingroup$ Hi, Thank You for your answer and for sharing the document. I shall go through this. $\endgroup$
    – Twinklestar
    Commented Mar 2, 2021 at 1:23

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