CERN May be Close to the Planet’s “Page One” Story –Discovering the Source of the Universe’s Mass


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 “It is truly amazing to be looking, albeit on a microscopic scale, at the conditions and state of matter that existed at the dawn of time.

Guido Tonelli -CERN's CMS Experiment

This past week, CERN announced that both of the main LHC detectors, ATLAS and CMS (Compact Muon Solenoid) experiment, have uncovered hints of a lightweight Higgs. he most coveted prize in particle physics – the Higgs boson – may have been glimpsed, say researchers reporting at the Large Hadron Collider (LHC) in Geneva. The particle is purported to be the means by which everything in the Universe obtains its mass. But the LHC does not yet have enough data to claim a discovery.

As the leading theory for how particles and forces interact, the standard model works only on the assumption that the Higgs boson actually exists. The huge challenge has been that the standard model cannot predict what the Higgs itself weighs. Years of experiments have steadily ruled it out except for a narrow range between 115 and 141 GeV.

Finding the Higgs is crucial for allowing us to make sense of the Universe, but has never been observed by experiments. The Higgs is a sub-atomic particle that was proposed as a mechanism to explain mass by six physicists, including Peter Higgs, in 1964 It imparts mass to other fundamental particles via the associated Higgs field It is the last missing member of the Standard Model – the "instruction booklet" that describes how particles and forces interact.

If it proves true, the only remaining gap in the standard model would be filled. A Higgs of this mass, about 125 gigaelectronvolts, would also provide a bridge to uncharted supersymmetry terrain. This lightweight Higgs would need at least one new type of particle to stabilise it. 

According to the Standard Model, the remarkably successful theory of how all the fundamental particles interact, the Higgs boson is responsible for endowing every other particle with mass. And as the last remaining particle pr edicted by the Standard Model yet to be detected, its discovery is one of the chief goals of the LHC, the most powerful particle accelerator on Earth and perhaps the most complex scientific endeavor ever attempted.

The LHC accelerates protons around an underground  ring almost five miles wide to nearly the speed of light, producing two proton beams that careen toward each other. Most of the protons just keep on going past each other, but a small fraction of them collide, creating other particles in the process. But these particles are fleeting, decaying into lighter particles before they can be detected. The challenge for physicists is to pick out hints of new, exotic physics from the flurry of newly minted particles. By sifting through the data, they hope to tease out signs that some of these particles are Higgs bosons.

The LHC is equipped with several detectors, but the ones that are the largest and are going after the Higgs are called ATLAS (A Toroidal LHC Apparatus) and the Compact Muon Solenoid (CMS); Caltech plays a prominent role in the latter. Both experiments recently reported what physicists are calling "excess events." 

That is, the LHC appears to have created slightly more events than would be expected if the Higgs does not exist. The bump occurred in the region between 130 and 150 gigaelectron volts (GeV—a unit of energy that is also a unit of mass, via E = mc2, where the speed of light, c, is set to a value of one), which is the expected mass range of the Higgs. 

But the data are not yet statistically significant enough to be called a definite signal, let alone a discovery of the Higgs particle, says Harvey Newman, professor of physics.

There are two possible explanations for these results, he says. The bump in the data could just be background events due to some unknown source or it could be the first signs of the Higgs. "One could speculate that it's an unusual statistical fluctuation," he says. "But I don't think so."

The LHC is now operating with 7 teraelectron volts (TeV, a thousand times higher than a GeV) of energy at the center of mass between the two proton beams, and may increase to 8 TeV next year (the maximum energy is 14 TeV, which will be reached by 2014).

Physicists will continue to ramp up the LHC, boosting it to higher energies and increasing the number of collisions to improve the chances of producing Higgs bosons. With several times more particle interactions, the physicists are continuing to close in on the Higgs, as well as other new particles and interactions. There's a chance that by the end of next year, they may determine, once and for all, whether the Higgs exists.

If it turns out that the Higgs does not exist, then physicists will have to do some serious rethinking about the Standard Model. "But even if the Higgs exists, the Standard Model still has fundamental problems," Newman says. For example, the theory is not self-consistent. "The most natural way to solve these problems," he says, "is with supersymmetry."

Evidence for supersymmetry, abbreviated SUSY ("soosie"), is also something that physicists had anticipated at the LHC. The theory proposes that each fundamental particle has a supersymmetric partner—for example, a quark's partner is called a "squark."

There are many versions of the theory, from simple toy models to subtler ones. So far, however, the LHC hasn't detected any signs of supersymmetry. "Many of the models we're excluding are toy models," says Maria Spiropulu, an associate professor of physics. 

So even though people might be disappointed, it's way too early to rule out the theory. "Some people get depressed that SUSY is being excluded. But it's quite the opposite—we're confirming that nature is much more subtle than what the obvious thing would be."What Exactly Is a Higgs Boson? 

In 1964, a physicist named Peter Higgs proposed the existence of a field that permeates the whole universe. Just as a magnetic field interacts with iron filings, the so-called Higgs field, which permeates the vacuum between every particle in the universe, interacts with every fundamental particle. These interactions slow a particle as it moves through the field. Because an electron, for example, doesn't interact with the Higgs field that much, it can zip through the field with ease like a sleek anchovy swimming through the ocean, and, as a result, has little mass. 

Particles like the top quark interact with the Higgs field a lot more strongly, however, so to them, the field is more like an ocean of molasses than of water. The top quark is thus heavy and sluggish, weighing in at more than 300,000 times the mass of an electron.

In physics, every field has an associated particle; the electromagnetic field is associated with the photon, for instance. For the Higgs field, the associated particle is the Higgs boson. By interacting with itself, it's responsible for its own mass.Beyond finding the Higgs, one of the most fascinating discoveries of our new century may be imminent if the Large Hadron Collider produces nano-blackholes. According to the best current physics, such nano blackholes could not be produced with the energy levels the LHC can generate, but could only come into being if a parallel universe were providing extra gravitational input.

Versions of multiverse theory suggest that there is at least one other universe very close to our own, perhaps only a millimeter away. This makes it possible that some of the effects, especially gravity, "leak through," which could be responsible for the production of dark energy and dark matter that make up 96% of the universe.

The Daily Galaxy via California Institute of Technology


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