More precise measurements of the W boson

December 21, 2009 By Miranda Marquit, feature

( -- "The W boson is one of the very few major building blocks of matter," Dmitri Denisov tells "It is a member of a family of particles that is the most fundamental in nature. The W boson is responsible for weak interactions, which govern some of the most important processes in nature."

Denisov is a scientist at in Batavia, Illinois, and he is one of around 500 physicists from 19 countries that have been collaborating on the effort to increase the precision of measurement with regard to the width of the W . Their group is known as the D0 Collaboration. Some of the results of the D0 collaboration are available in : "Direct Measurement of the W Boson Width."

“Particle physicists are working hard to improve our knowledge of the fundamental particles of nature. We want precision measurements of all these particles, since their properties are important to understand world around us and for calculations used in developing and testing new theories,” Denisov explains. “The W boson is one of those that is worth looking at, because if its role in weak interactions. We wanted to measure the width, because that is directly related to its lifetime.”

Denisov points out that the W boson’s lifetime is connected to the way it decays. And the W boson also influences the way nuclei decay. “The W boson is especially known for its role in nuclear decay,” he says. “Modern theory predicts how different W boson decays, but there might be modes we don’t know, and the width of the W boson would be influenced by these modes. So with these more precise measurements of the W boson, we can start looking for things that we don’t know yet.”

In order to produce these new measurements of W boson width, which have the highest precision to date, the D0 Collaboration used the Tevatron at Fermilab. They gathered data from a specific form of decay, and measured the spectrum of energy from the that resulted. “The spectrum of energy in electrons is wider if it lifetime is shorter,” Denisov says. The scientists produced and then recorded a sample consisting of around half a million W bosons.

“The whole analysis process took about three years,” Denisov explains. “We had to collect data from the , and then analyze it. Scientists worked on developing Monte Carlo simulations to describe the detector performance. As a result, we have been able to come up with a very precise measure of W boson width and lifetime that can be used to develop physics theories and for precision description of world around us.”

Going forward, Denisov expects that the D0 Collaboration will continue to work to improve the precision of their measurements. “We have a good data set, and we are collecting more and more data quite literally as we speak. At this point, our measurement does not show any new particles affecting W boson lifetime. However, as we continue to improve the accuracy of our measurements, it’s possible that we could see a deviation. In about a year, we are hoping that we will be able to reduce current uncertainty substantially.”

“This work,” Denisov continues, “is very important for fundamental physics. Quite a few people put years of their lives into this measurement, to gain a better understanding of the forces which governs our world.”

Explore further: Precision measurement of W boson mass portends stricter limits for Higgs particle

More information: D0 Collaboration, “Direct Measurement of the W Boson Width,” Physical Review Letters (2009). Available online:


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5 / 5 (6) Dec 21, 2009
This article offers so little information - How about explaining WHY is measuring the W Boson important? How can this advance physics? How wide is it? I know it is a sub atomic particle and is extremely small, but if the width of the W Boson is the focus of the experiment, maybe give the reader an idea of the sizes observed.

Some of these articles are so vague...
5 / 5 (1) Dec 22, 2009
First the hot news, its width is 2.028 +- 0.072 GeV.

And having read the paper, I'm none the wiser.

Why can't the article explain what it means and why it matters for people who are interested in learning more?
not rated yet Dec 22, 2009
Because of Heisenberg uncertainty principle, any particle with a finite lifetime has a mass distribution of non-zero width. Each way of particle decay (so-called the decay channel) contributes to the total decay width due to a limited lifetime of decay product. For detection of Higgs and supersymmetry the dilepton channel decay of top quarks via the W-bosons is particularly important. It can bring a clue concerning CPT parity violation due to presence of right-handed W bosons (W-pairs production), which can serve for testing of Standard Model, in which top quark decays via the V-A charged weak current interaction.

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