Thursday, January 24, 2008

Higgs Hiding in Plain Sight?

I don't want to go into the details, since I don't have time and you probably aren't completely interested, but, one interesting result of supersymmetry is that it is possible for the Higgs field to be made of several particles. In this case, you could have a lower and higher mass Higgs.

If this is the case, it could be the low mass sector of the Higgs field is right under our noses in the current particle data. It was recently proposed how this could be the case and urges the physics community to look for it. If found to be correct it would be a good day for supersymmetry! :) From Science:

Thousands of particle physicists are spending billions to try to spot the elusive Higgs boson, which is key to explaining the origins of mass. But evidence of the Higgs boson--or at least a Higgs boson--may already be lying unnoticed in data from previous experiments, new calculations suggest.

All matter is made up of indivisible bits or particles, and at first blush, the prevailing theory--the Standard Model--seems to predict that all of them have no mass. Of course, that doesn't make sense--even electrons weigh something. But if theorists simply assign masses to the particles, the theory goes mathematically haywire.

Enter the Higgs boson. Physicists suspect that empty space is permeated by a Higgs field, which is a bit like an electric field. And just as an electric field consists of particles called photons, the Higgs field consists of particles called Higgs bosons. The Higgs field drags on particles to give them mass, akin to molasses tugging on a spoon. In particular, the field gives mass to subatomic particles called the W and Z bosons, which convey the weak nuclear force and weigh in at a staggering 86 and 97 times as much as a proton, respectively.

Finding the Higgs would complete the Standard Model, but physicists hope many more particles exist, too. A favorite scheme called supersymmetry predicts that every known particle has a much more massive partner that scientists haven't yet seen. Many versions of supersymmetry exist, and each requires at least five kinds of Higgs bosons. All those extra particles might seem like needless embellishments, but their presence would solve some technical and conceptual problems in the Standard Model. Physicists hope these particles might start to appear in experiments either at the Tevatron collider at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois (Science, 2 June 2006, p. 1302), or at the more-powerful Large Hadron Collider (LHC) at the European lab, CERN, near Geneva, Switzerland, which will power up this summer (Science, 23 March 2007, p. 1652).

But experimenters may have already overlooked a Higgs particle, argues theorist Chien-Peng Yuan of Michigan State University in East Lansing and his colleagues. They considered the simplest possible supersymmetric theory. Ordinarily, theorists assume that the lightest of theory's five Higgses is the one that drags on the W and Z. Those interactions then feed back on Higgs and push its mass above 121 times the mass of the proton, the highest mass searched for at CERN's Large Electron-Positron (LEP) collider, which ran from 1989 to 2000. But it's possible that the lightest Higgs weighs as little as 65 times the mass of a proton and has been missed, Yuan and colleagues argue in a paper to be published in Physical Review Letters.

How could that happen? The key is in how strongly the lightest Higgs interacts with the W and Z. The theorists show it's possible to make that interaction very weak. In that case, the lightest Higgs can be very light indeed, but it would not have been seen at LEP, because LEP experimenters were looking for an energetic collision that made a Z that then spit out a Higgs. That wouldn't happen very often if the lightest Higgs and the Z hardly interact. "Just within the simplest supersymmetric model, there's still room for Higgs that is missed," Yuan says.

However, this lightweight Higgs is not exactly the Higgs everyone is looking for, says Marcela Carena, a theorist at Fermilab. "The Higgs they are talking about is not the one responsible for giving mass to the W and Z," she says. It can't be because it hardly interacts with those particles, Carena says. Indeed, in Yuan's model, the role of mass-giver falls to one of the heavier Higgses, which is still heavier than the LEP limit, she notes.

Nevertheless, the new analysis has implications for current experiments, Yuan says. For one, evidence for the very light Higgs could be in data already in the can at Fermilab. And if the scheme isn't the one nature plays by, Yuan says, then the LHC will be able to prove that conclusively. "We're not saying the model is correct," he says. "We're saying it's possible and should be checked."

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