Physics buff BOMBS on simple question on The Chase
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W bosons are elementary particles named for the role they play in mediating the so-called weak force — one of the fundamental interactions alongside electromagnetism, gravitation and the strong force that holds protons and neutrons together to create atomic nuclei.
The weak force, which instead acts inside of individual protons and neutrons, is important because it underlies various forms of radioactive decay and underlies the nuclear fusion process that powers stars like the Sun.
Various efforts have been made previously to determine the exact mass of the W boson using data gathered from high-energy particle physics experiments — including the Tevatron collider at the Fermi National Accelerator Laboratory (Fermilab) near Chicago, Illinois.
Researchers within the Collider Detector at Fermilab (CDF) collaboration — a presently 400-strong group of experts — have been calculating increasingly precise measurements of the W boson for more than two decades.
Their latest estimate is based on data on some 4.2 million W boson candidates detected in the aftermath of high-energy particle collisions within the Tevatron from 1985 to when the machine ceased operations in 2011.
This dataset was around four times larger than the one used by the collaboration in its previous calculation of the W boson mass back in 2012,
Study leader and particle physicist Professor Ashutosh V. Kotwal of Duke University said: “The number of improvements and extra checking that went into our result is enormous.”
“We took into account our improved understanding of our particle detector as well as advances in the theoretical and experimental understanding of the W boson’s interactions with other particles.
“When we finally unveiled the result, we found that it differed from the Standard Model prediction.”
In the Standard Model, the mass of the W boson is linked to the measurements of the masses of two other particles — the top quark, which was first spotted by the Tevatron collider at Fermilab back in 1995, and the Higgs boson, the detection of which was reported by the Large Hadron Collider at CERN, on the France–Switzerland border in 2012.
Using these masses as a starting point, the Standard Model predicts that the W boson should have a mass of 80,357 ± 6 MeV/c2 — which is roughly 80 times the mass of a proton.
The latest analysis of the Tevatron data, in contrast, places the W boson mass at the slightly larger figure of 80,433 ± 6 MeV/c2.
According to the team, this measurement comes with a precision of 0.01 percent — a two-fold improvement on the last best estimate, and the equivalent of measuring the weight of an 800-pound gorilla to within 1.5 ounces.
University of Oxford physicist Professor Chris Hays, who is a member of the CDF collaboration, said, “The CDF measurement was performed over the course of many years.”
The measured value, he explained, was “hidden from the analysers until the procedures were fully scrutinised.
“When we uncovered the value, it was a surprise.”
The researchers explained that the new value is in agreement with a number of the previous efforts to pin down the mass of the W boson — but in disagreement with others.
Fermilab deputy director Joe Lykken added: “While this is an intriguing result, the measurement needs to be confirmed by another experiment before it can be interpreted fully.”
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CDF spokesperson and high energy physicist Professor Giorgio Chiarelli of the Italian National Institute for Nuclear Physics said: “Many collider experiments have produced measurements of the W boson mass over the last 40 years.
“These are challenging, complicated measurements, and they have achieved ever more precision.
“It took us many years to go through all the details and the needed checks.
“It is our most robust measurement to date, and the discrepancy between the measured and expected values persists.”
Fellow CDF spokesperson and high energy physicist Professor David Toback of the Texas A&M University added that the collaboration’s latest finding is an important contribution to tests of the accuracy of the Standard Model.
He said: “It’s now up to the theoretical physics community and other experiments to follow up on this and shed light on this mystery.
“If the difference between the experimental and expected value is due to some kind of new particle or subatomic interaction, which is one of the possibilities, there’s a good chance it’s something that could be discovered in future experiments.”
The full findings of the study were published in the journal Science.
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