Fermilab scientists find W Boson, giving clues to the mass of the Higgs

[LongTomH]

Last edited Sat Feb 25, 2012, 12:30 PM - Edit history (1)

Fermilab's Tevatron, formerly the world's most powerful particle accelerator, was closed down in 2009; however, data from the Tevatron's final days has helped Fermilab physicists determine the mass of the W boson, which may help LHC scientists narrow down the search for the Higgs boson:

The W boson’s new mass is 80.387 giga electron volts, or GeV, plus or minus 0.019 GeV. (Scientists often give a particle’s mass in units of energy because, according Einstein’s famous E=MC² equation, the two are interchangeable.) The most precise previous measurement had an uncertainty of about 0.060 GeV.

At the subatomic scale, such little differences are immense.

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Researchers with the CDF collaboration at Fermilab produced the estimate using data from the now-closed Tevatron, formerly the world’s premier particle accelerator, where measurements of collisions between protons and antiprotons fired around a 4-mile-long track provide insight into the subatomic world. Though CERN’s Large Hadron Collider has eclipsed the Tevatron, the result shows that the U.S. lab still has a few tricks up its sleeve.

The W boson, along with its counterpart the Z boson, are responsible for carrying the weak force, much the same way that photons convey electromagnetic force. Together with gravity and strong nuclear force, these comprise the four fundamental forces of nature. The W boson’s discovery in 1983 was a major success for the Standard Model, developed by physicists to explain the interactions of all subatomic particles and forces, and its mass is an important input for many nuclear and astrophysical calculations.

Scientists at the Large Hadron Collider are leading the world in the search for the Higgs boson; but:

Though the Large Hadron Collider has progressed further in the Higgs search, Fermilab scientists still hope to be part of the discovery. Next month they will present their latest Tevatron data, which may include a Higgs signal. And even if Fermilab doesn’t find the Higgs themselves, the LHC may never be able to measure the W boson with comparable precision. Its mass may be one of the Tevatron’s great legacy calculations, said Roser.

Read more here: Physicist Pinpoint W Boson, Narrow Search for Higgs



Edited to add: Since Congress, in its infinite lack of wisdom, chose not to finish building the Superconducting Supercollider (They did appropriate a billion dollars to fill in the tunnel dug for the SSC!); the Tevatron was the last great hurrah of American physics. If evidence of the Higgs is found in Tevatron data, it's an opportunity for the American scientists to claim a victory over the Europeans.

[laconicsax]

1. Is it that the decay of a Higgs results in pair a Ws or a W and a Z?

It's been a while since I read what signature they're looking for to identify a Higgs and I don't remember what some of the tell-tale signatures they're looking for are.

[LongTomH]

2. I'm gonna have to look that up!

nft

[LongTomH]

3. OK, here's are some 'PopSci' explanations...

From the Particle Zoo:

The Z boson, like the W boson, is a carrier of the weak interaction. It is formed at modifications of elementary particles, where only the spin, but not the charge and the particle type change. W and Z bosons are the only particles (probably together with the very weak graviton), that interact with neutrinos. Neutrinos can fission deuterium and thereby create a Z boson, which almost immediately decays again in a fermion and its antiparticle. The Z boson is about as heavy as an atom of the element technetium.

From Symmetry Magazine:

The Z boson is a heavy particle that is one of the carriers of the ‘weak force’. It is a partner of the W+ and W- bosons that mediate radioactive decay processes.

The Z boson was first discovered as an intermediary of a new type of neutrino reaction. This so-called ‘neutral current interaction’ was the missing piece of a puzzle in which the forces created by the W bosons fit together neatly with the force of electromagnetism, due to the photon. Together, these four particles create the forces that form a beautifully unified theory of ‘electroweak’ interactions.

In the 1990s, accelerators at the Stanford Linear Accelerator Center and CERN produced 12 million of these Z bosons in a controlled setting and studied the decays of the Z in great detail. The Z decays to pairs of all types of quarks and leptons, except for the heavy top quark. These experiments made high precision tests of the electroweak theory and the properties of quarks and leptons. Quarks produced from the Z radiate gluons, and so these experiments also give some of the highest-precision information about the carrier of the ‘strong’ interactions.

I found these explanations with a quick Google search, so don't regard me as an expert.