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New Revelations From Particle Colliders Past, Present & Future

July 27th, 2010 07:03 admin Leave a comment Go to comments

lhc-tunnelParticle physicists hunting for the Higgs boson reported their latest findings yesterday at the International Conference on High Energy Physics in Paris. The big two–Europe’s Large Hadron Collider and Fermilab’s Tevatron Collider (in Illinois)–gave updates, and other conference buzz included talk of a new facility, the International Linear Collider, which may one day give physicists a cleaner look at the other colliders’ results.

Large Hadron Collider — More Detailed Models Help the Search

Currently operating at 7  Tera electron Volts (TeV), the Large Hadron Collider is the world’s most powerful particle accelerator. Though electrical malfunctions hindered the collider in 2008, now LHC scientists report that they have made up for lost time: finding in months, what took the Tevatron, with its 2 TeV collisions, decades.

“The scientific community thought it would take one, maybe two years to get to this level, but it happened in three months,” said Guy Wormser, a top French physicist and chairman of the conference.[AFP]

As Symmetry (a Fermilab/SLAC publication) notes, these findings are more than a test of strength–or a simple retracing of the Tevatron’s footsteps. LHC physicists have to show that their facility can reproduce the results other machines have already seen, if one day they are to be sure that their data indicate something new.

As also reported by Symmetry, because the LHC is running at energies 3.5 times the Tevatron’s, these higher energies allow LHC physicists to refine their previous understandings, teasing out details impossible to see at lower energies. Such details may help physicists refine their search for the Higgs, the particle that presumably gives mass to all other particles.

CERN, the European umbrella organization that runs the LHC, says that these tests show the collider is ready for that search.

“Rediscovering our ‘old friends’ in the particle world shows that the LHC experiments are well prepared to enter new territory” said CERN’s Director-General Rolf Heuer. “It seems that the Standard Model is working as expected. Now it is down to nature to show us what is new.”[CERN]


Tevatron — Telling  Physicists Where Not to Look

Meanwhile, Tevatron researchers have narrowed the expected mass of the missing particle. The diagram above shows the expected mass ranges, and those excluded by the new Tevatron data and previous Fermilab experiments. For reference, the proton has a mass of a little less than one GeV/c^2.

[P]hysicists’ standard model of the fundamental particle does not predict how much the Higgs itself will weigh. So scientists must go searching for it. Previous experiments show that it probably has a mass between 114 and 185 giga-electron volts (GeV), or 121 and 197 times the mass of the proton. Last year, experimenters working with D0 (aka DZero) and the Tevatron’s other particle detector, CDF [Collider Detector at Fermilab], took a chunk out of that possible range, reporting that the Higgs most likely does not weigh between 162 GeV and 166 GeV. Now, they’ve widened that “exclusion window” to between 158 GeV and 175 GeV.[Science Now]

Given such results, physicists have submitted a proposal to Fermilab asking that the Tevatron’s life be extended beyond 2011 to 2014, but the lab can’t guarantee that given its limited resources and other ongoing experiments and new projects.

Currently CERN officials have scheduled an LHC shutdown for 15 months also in 2011, which might give an operating Tevatron a chance to find the Higgs, Robert Roser of the Tevatron’s CDF detector told The Guardian.

“The LHC won’t be able to say anything about the Higgs particle until well into 2013. If we can run until 2014, we should be able to see the Higgs boson whatever mass it has,” said Roser. [The Guardian]

International Linear Collider — A Future, Cleaner Look?

Given results from the LHC and Fermilab, scientists continue to discuss new colliders, such as the International Linear Collider. Unlike the Tevatron and the LHC, which spin particles in a circle and then collide them, the International Linear Collider will force electrons and their antimatter-pair, positrons, to face off in a straight, approximately 20-mile long tube. Researchers say the collider would complement ongoing research at the LHC, by giving scientists a less powerful but cleaner look at the data, in part because the linear setup will ensure that particles that didn’t smash in the initial collision won’t continue circulating through the detector, Popular Science reports. They hope to start building the detector in 2012, but it will require international funding, the AP reports, amounting to $12.85 billion. Barry Barish, director of the proposed collider, told the AP:

“If we are going to build an ambitious machine, then it’s got to be a global machine.”[AP]

A video describing the ILC is available, here.

Images: CERN, Fermilab

Source: New Revelations From Particle Colliders Past, Present & Future

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