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As particle physicists gather this week for a conference in Paris, they’re reporting progress toward finding the elusive Higgs boson, with two groups suggesting a Higgs discovery may not be far off.

Physicists from Fermilab in Illinois announced they combined the results of two experiments to refine their search for the Higgs, sometimes called the “God particle” because it is thought to endow particles with mass.

Calculations of quantum effects that involve the Higgs say it has to be a certain size, between 114 and 185 GeV/c2. That means giga-electron volts divided by the speed of light squared. It’s easier to think in terms of relative sizes, so for comparison: 100 GeV/c2 is equivalent to 107 times the mass of a proton. That means the Higgs is a lot more massive than a proton.

The latest Fermilab tests rule out about a quarter of the Higgs’ expected size range. This means physicists can look for the Higgs in a much smaller range, which might make their search simpler.

Some theories say the Higgs boson is toward the thin side; others propose a fat one. But scientists working with the DZero experiment at the Tevatron say they are close to ruling out a fat Higgs. Three years ago, they would not have expected the particle accelerator’s detectors to be sensitive enough to find a low-mass Higgs.

Last year, Tevatron scientists threw down the gauntlet and said they’d find the Higgs before CERN did, although the Large Hadron Collider is much more powerful.

Experiments at the LHC show the huge European accelerator is one step closer to finding it, however.

Before the LHC finds the Higgs, it must first re-discover particles previously found at the Tevatron and other accelerators. The LHC just found some particles that might be top quarks, which is a key milestone for the accelerator. Top quarks are the heaviest known elementary particles.

Physicists believe the top quark has a special relationship with the Higgs boson, so finding top quarks is an important step toward uncovering the Higgs.

It has to do with the way particles “decay” in high-energy physics. Scientists are seeking particles much heavier than protons, so they spin protons at superfast speeds around a ring. Their excessive speed makes them essentially larger. When they collide, they break into a family of parts that make up the Standard Model. Some of the parts are not stable, and they decay into other parts.

If the Higgs boson is fat, it might reveal itself by decaying into a top quark. If it is thin, a top quark might decay into a Higgs.

Either way, the knowledge that the LHC can find top quarks is a key step. The results still need to be verified, however.

[PhysOrg,
R&D Mag]

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