Saturday, April 09, 2022

W boson's surprise mass could upend the standard model

This is possibly the biggest news in physics so far this year! Very exciting!

"... Although the difference between the theoretical prediction and experimental value is only 0.09%, it is significantly larger than the result’s error margins, which are less than 0.01%. The finding also disagrees with some other measurements of the mass. ...
Since its discovery in 1983, experiments have calculated the W boson to weigh as much as 85 protons. But its exact mass has been challenging to quantify: the first experimental estimate had error margins of 5% or more. ...
With its cousin, the Z boson, the W is involved in most types of nuclear reactions, including the fusion that powers the Sun. The W and Z bosons carry the weak nuclear force — one of the four fundamental forces of nature — similar to how every electromagnetic interaction involves the exchange of photons. ..."

From the abstract:
"The mass of the W boson, a mediator of the weak force between elementary particles, is tightly constrained by the symmetries of the standard model of particle physics. The Higgs boson was the last missing component of the model. After observation of the Higgs boson, a measurement of the W boson mass provides a stringent test of the model. We measure the W boson mass, MW, using data corresponding to 8.8 inverse femtobarns of integrated luminosity collected in proton-antiproton collisions at a 1.96 tera–electron volt center-of-mass energy with the CDF II detector at the Fermilab Tevatron collider. A sample of approximately 4 million W boson candidates is used to obtain MW=80,433.5±6.4stat±6.9syst=80,433.5±9.4 MeV/c2, the precision of which exceeds that of all previous measurements combined (stat, statistical uncertainty; syst, systematic uncertainty; MeV, mega–electron volts; c, speed of light in a vacuum). This measurement is in significant tension with the standard model expectation."

Particle’s surprise mass threatens to upend the standard model Data from an old experiment finds that the mass of the W boson is higher than theory predicts, hinting at future breakthroughs.




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