A joint Fermilab/SLAC publication

Fermilab's DZero experiment weighs in on W boson mass


The W boson mass measured by experiments across the world. The lines show the mass range while the dot shows the central value. Image: Fermilab

The DZero experiment at Fermilab's Tevatron collider made public today its most precise measurement of the mass of the W boson. Better understanding the mass of this force-carrying elementary particle tests the Standard Model of particle physics and puts constraints on the mass of the Higgs boson.

The CDF collaboration recently measured the W boson mass to be 80387 +/- 19 MeV/c2. The DZero collaboration measured the particle’s mass to be 80375 +-23 MeV/c2. The two new measurements, along with the addition of previous data from the earliest operation of the Tevatron, combine to produce a measurement of 80387 +- 17 MeV/c2, which has a precision of 0.02 percent.

The existence of the world we live in depends on the W boson mass being heavy rather than massless as the Standard Model predicts. The W boson is a carrier of the electroweak nuclear force that is responsible for such fundamental process as the production of energy in the sun.

“The W mass is a very distinctive feature of the universe we live in, and requires an explanation,” said Giovanni Punzi, CDF co-spokesperson and physicist from the University of Pisa. “Its precise value is perhaps the most striking evidence for something 'out there' still to be found, be it the Higgs or some variation of it.”

The new measurement comes at a pivotal time, just days before physicists from the Tevatron and the Large Hadron Collider at CERN will present their latest direct-search results in the hunt for the Higgs at the annual conference on Electroweak Interactions and Unified Theories known as Rencontres de Moriond in Italy. The CDF and DZero experiments plan to present their latest results on Wednesday, March 7.

“It is a very exciting time to analyze data at particle colliders,” said Gregorio Bernardi, DZero co-spokesperson and physicist at the Laboratoire de Physique Nucléaire et de Hautes Energies in Paris. “The next few months will confirm if the Standard Model is correct, or if there are other particles and forces yet to be discovered.”

These ultra-precise, rigorous measurements of the mass of the W boson took up to five years for the collaborations to complete independently. The collaborations measured the particle’s mass in six different ways, which all match and combine for a result that is twice as precise as the previous measurement. The results were presented at seminars at Fermilab over the past two weeks by physicists Ashutosh Kotwal from Duke University and Jan Stark from the Laboratoire de Physique Subatomique et de Cosmologie in Grenoble, France.

The combined measurement, the most precise ever, represents an important piece of the legacy of the Tevatron. Although the accelerator shut down in September 2011, scientists continue to mine the wealth of data it provided for new and improved insights into the smallest constituents of matter.

Read the entire press release on the W mass measurement by CDF and DZero.

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