Monday, December 5, 2016

Progress Made In Measuring Bottom Quark Yukawa Coupling

In the Standard Model, the rest mass of the bottom quark at various energy scales arises from its Yukawa coupling to the Higgs boson, but this is hard to measure with precision directly. Direct measurements have a precision of only about +/- 20%.

There are other ways to more precisely measure quantities related in principle to the bottom quark Yukawa coupling. But, it has been challenging to convert the measured quantities to the theoretically fundamental Yukawa coupling in a precise and rigorous way.

A new paper has refined the formula for converting the more easily measured mass quantities to the more fundamental Yukawa coupling value associated with it. It does so by making a calculation out to more loops than is customary, by including QED corrections which are important, while omitting corrections that are difficult to calculate but are demonstrated in the paper to be immaterial in magnitude relative to other sources of error, in this particular calculation.

The increased precision in the indirectly measured experimentally determined value of the bottom quark Yukawa coupling to the Higgs boson is particularly helpful in refining Standard Model predictions for the rate at which a Standard Model Higgs boson should decay to bottom-antibottom quark pairs (the most common mode of Higgs boson decay, although not the easiest to measure due to background processes that inject noise into the Higgs boson decay signal).

Reducing the Standard Model theoretical prediction error to a minimum increases the power of any given experimental test of the accuracy of that prediction somewhat.

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