The Higgs particle just got 8% lighter

The Higgs particle just got a bit lighter, and the race to find it a little tighter, thanks to the most precise measurement yet of the mass of the W boson.

Physicists at the Collider Detector at Fermilab (CDF) near Chicago announced on Monday that the W boson - one of the particles that mediate the weak nuclear force - has a mass of 80.413 gigaelectronvolts (GeV).

reposted from: New Scientist 13 January 2007
my highlights / emphasis / edits

The standard model of particle physics links the masses of W boson, the "top" quark and the Higgs boson. Using the newly measured mass of the W and the already well-known mass of the top quark, the team recalculated the predicted mass of the elusive Higgs, which is thought to give all other particles their mass. The upper limit for the mass of the Higgs is now 153 GeV, down from the previous limit of 166 GeV.

Physicists already know that the Higgs is heavier than 114 GeV, because searches up to that energy have found nothing.

Until now, the Large Hadron Collider at CERN near Geneva, due to start working later this year, was the firm favourite to find the Higgs. But the lighter Higgs is well within the range of the Tevatron collider running at Fermilab. "For us at the Tevatron and CDF, it is very good news," says Mark Lancaster, CDF team member at University College London.

If the colliders do not find the Higgs at these energies, physicists will be forced to look beyond the standard model.

From issue 2586 of New Scientist magazine, 13 January 2007, page 5

Will the Standard Model of physics be verified sooner?

reposted from: http://blog.wired.com/wiredscience/2007/01/the_god_particl.html

Tuesday, 9 January 2007

The God Particle Maybe Loses Some Weight
Topic: physics

Fascinating story today over at Nature's web site (here) on a new calculation for the mass of the W particle, the particle that carries the weak nuclear force—the one that does radioactive decay.

See, you're yawning. But author Jenny Hogan does a fantastic job of putting the W's lighter weight into context.

If the W is lighter, then so must be the much-sought-after Higgs boson, the theoretical particle that is responsible for mass—everything weighs something, and the Higgs is thought to explain why. It's so important that physicists have nicknamed it "the God particle."

And if the Higgs is lighter than physicists thought, then we might not have to wait for the Large Hadron Collider, a brand new, massive particle smasher, to come online at CERN, the European particle physics lab. The LHC is scheduled to start smacking stuff into each other this year. Instead, the folks who run the Tevatron, the big collider at Fermilab in Illinois, might be able to nab the Higgs first.

On 8 January, the estimate was tightened when the CDF [Collider Detector at Fermilab] announced it had pinned down the mass of the W boson, which mediates the weak nuclear force involved in processes such as radioactive decay. The new measurement is in agreement with previous estimates, but towards the upper end of the range. This, along with the added precision in the measurement, brings the upper limit for the Higgs' mass down to 153 giga electronvolts from 166 GeV. Previous experiments have shown that the Higgs must be heavier than 114 GeV.

A lighter Higgs suits the Tevatron, which is only capable of finding the particle if its mass is less than around 170 GeV. The closer a particle's mass is to this upper limit, the harder it would be to find.

Anything heavier than 170 GeV would certainly have to wait for the LHC, which will smash protons together harder to probe higher energies.

So I suppose you might ask, why would anyone believe the Fermilab guys on the new weight for the W when it clearly favors them in the race for the Higgs. And the answer is...um...physics? And the folks at Fermilab readily admit their desire to get there first. But author Hogan rightly points out that finding the Higgs is going to take years of data collection and analysis at both labs (see this Wired story if you want to know more about the LHC's number-crunching plans). She further points out that if the Standard Model of physics, the one that lists all the known and theoretical particles, is wrong, then there might not be a Higgs boson.

That, my friends, is context.

Higgs boson explains why other particles have mass

reposted from: http://news.bbc.co.uk/1/hi/sci/tech/6244899.stm
Experts home in on 'God particle'

Cern's Atlas detector will search for the elusive "God particle" (Image: Cern/Maximilien Brice) Enlarge Image

Scientists may be closing in on the most sought-after particle in physics.

The hypothetical Higgs boson, often dubbed the "God particle", is fundamental to our understanding of the Universe but has yet to be detected.

Now, data from the Tevatron particle collider at Fermilab, in the US, has enabled the most precise calculation yet to be made for its predicted mass.

And this, the international team says, narrows the window in which to locate the elusive particle.

Adding weight

The Higgs boson has been proffered to explain the mystery of why other particles have mass, and forms the missing piece in the puzzle that is the Standard Model - the current theory used to describe the fundamental nature of matter.

For years, researchers have been searching the sub-atomic "soup" created when particles are smashed together in colliders - but no sign of the Higgs has been seen.

In obtaining a more precise predicted mass for the Higgs, the particle's existence can be confirmed or ruled out within two to three years, scientists believe.

The calculation has been done by making the finest measurement to date of the mass of another elementary particle, one that is well known, the W boson.

After more than 10 years, we are now homing in on the Higgs Dr Mark Lancaster

The W boson is the carrier of weak nuclear force, one of the fundamental forces in nature, and its mass is believed to be linked to that of the Higgs'.

Using this new measurement, together with the calculated mass of another fundamental particle, the top quark, the Fermilab team has worked out a new predicted mass for the Higgs boson, discovering it might be lighter than previously thought.

Dr Mark Lancaster, UK spokesman for the Collider Detector at Fermilab (CDF), from University College London, said: "These findings narrow down the mass region that we expect the Higgs to appear in.

"After more than 10 years, we are now homing in on it."

And searching data within this region at Fermilab's Tevatron and Europe's Large Hadron Collider at Cern, which switches on next year, could reveal whether the Higgs boson is present or not by the middle of 2009, he added.

"And if we don't find it, it is going to be back to the drawing board for particle physics."

The Standard Model is a theory devised to explain how sub-atomic particles interact with each other There are 16 particles that make up this model (12 matter particles and 4 force carrier particles). But they would have no mass if considered alone The Higgs boson explains why these particles have mass. Particles acquire their mass through interactions with an all-pervading field, called the Higgs field, which is carried by the Higgs boson.