World’s Best Measurement of W Boson Mass
2 March 2012
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The CDF experiment at the Fermilab Tevatron collider has released a new measurement of the mass of the W boson that is, by some margin, the most precise in the world. The new measurement by CDF, M(W) = 80387 +/- 19 MeV/c2, has a smaller uncertainty than all the previous measurements combined, and is the result of several years' painstaking work by physicists including a team from UCL. When combined with a new measurement from the D0 experiment, also announced this week, the combined data give a result 80387 +- 17 MeV/c2 , which has a precision of 0.02 percent.
How the W boson, the carrier of the weak force responsible for nuclear beta-decay, acquires its large mass is currently a mystery. The interaction of the W boson with the as-yet undiscovered Higgs particle is a leading possibility. Indeed a precise measurement of the W boson mass, when combined with other data, gives us an indirect determination of the mass of the Higgs boson. The new W mass measurement further restricts the allowed range for the Higgs, implying that it must have a mass less than 150 GeV/c2. This means that if the Higgs does exists, it lies on the threshold of discovery at the Large Hadron Collider.
UCL high energy physicists worked on this analysis for many years. Professor Mark Lancaster, Dr. Emily Nurse and Dr. David Waters led the UCL team including Ilija Bizjak and PhD students Dan Beecher, Sarah Malik, Tom Riddick.