symmetry magazine

dimensions of particle physics

dimensions of particle physics

A joint Fermilab/SLAC publication

 

W boson squeezes Higgs particle

March 11, 2009

W boson squeezes Higgs particle

The W boson will help to corner the elusive Higgs particle. And photographer Robert Tilden has a photo to prove it.

The W boson is squeezing the Higgs boson: plush toys by artist Julie Peasley, photo by Robert Tilden.

The W boson is squeezing the Higgs boson: plush toys by artist Julie Peasley, photo by Robert Tilden.

The DZero collaboration at the Department of Energy's Fermilab has achieved the world's most precise measurement of the mass of the W boson by a single experiment. Combined with other measurements, the reduced uncertainty of the W boson mass will lead to stricter bounds on the mass of the elusive Higgs boson.

This inspired Tilden, a software engineer at Northwestern University and photographer, to create a photo of the W boson squeezing the Higgs boson in a vise. Artist Julie Peasley created the plush toys representing the particles, and they are available for sale on http://www.particlezoo.net/

The W boson is a carrier of the weak nuclear force and a key element of the Standard Model of elementary particles and forces. The particle, which is about 85 times heavier than a proton, enables radioactive beta decay and makes the sun shine. The Standard Model also predicts the existence of the Higgs boson, the origin of mass for all elementary particles.

Precision measurements of the W mass provide a window on the Higgs boson and perhaps other not-yet-observed particles. The exact value of the W mass is crucial for calculations that allow scientists to estimate the likely mass of the Higgs boson by studying its subtle quantum effects on the W boson and the top quark, an elementary particle that was discovered at Fermilab in 1995.

Scientists working on the DZero experiment now have measured the mass of the W boson with a precision of 0.05 percent. They announced their result in a Fermilab press release today. The exact mass of the particle measured by DZero is 80.401 +/- 0.044 GeV/c2. The collaboration presented its result at the annual conference on Electroweak Interactions and Unified Theories known as Rencontres de Moriond last Sunday.

"This beautiful measurement illustrates the power of the Tevatron as a precision instrument and means that the stress test we have ordered for the Standard Model becomes more stressful and more revealing," said Fermilab theorist Chris Quigg.

The DZero team determined the W mass by measuring the decay of W bosons to electrons and electron neutrinos. Performing the measurement required calibrating the DZero particle detector with an accuracy around three hundredths of one percent, an arduous task that required several years of effort from a team of scientists including students.

Since its discovery at the European laboratory CERN in 1983, many experiments at Fermilab and CERN have measured the mass of the W boson with steadily increasing precision. Now DZero achieved the best precision by the painstaking analysis of a large data sample delivered by the Tevatron particle collider at Fermilab. The consistency of the DZero result with previous results speaks to the validity of the different calibration and analysis techniques used.

"This is one of the most challenging precision measurements at the Tevatron," said DZero co-spokesperson Dmitri Denisov, Fermilab. "It took many years of efforts from our collaboration to build the 5500-ton detector, collect and reconstruct the data and then perform the complex analysis to improve our knowledge of this fundamental parameter of the Standard Model."

The W mass measurement is another major result obtained by the DZero experiments this month. Less than a week ago, the DZero collaboration submitted a paper on the discovery of single top quark production at the Tevatron collider. In the last year, the collaboration has published 46 scientific papers based on measurements made with the DZero particle detector. About 550 physicists from 90 institutions in 18 countries work on the DZero experiment.