The ATLAS and Compact Muon Solenoid (CMS) experiments at CERN, the preliminary findings of which were released on Wednesday, strongly indicate the presence of a new particle, which could be the Higgs boson, in the mass region around 126 gigaelectronvolts (GeV). In particle physics parlance, strong evidence means that the probability of an observation being attributable to a statistical fluctuation is less than 1%.
The experiments analysed trillions of proton-proton collisions from the Large Hadron Collider (LHC) in 2011 and 2012. The Standard Model of particle physics predicts that a Higgs boson would decay into different particles--which the LHC experiments then detect.
An undated handout graphic distributed by the CERN in Geneva shows a representation with a zoom effect of traces of traces of a proton-proton collision measured in the CMS experience in the search for the Higgs boson. Photo / AFP
Once the discovery is confirmed, positive identification of the new particle’s characteristics will take considerable time and data. “It’s rather like spotting a familiar face from afar; closer observation might be needed to tell whether it’s an old friend who loves coffee, or her identical twin sister who favours tea. But whatever form the Higgs particle takes, our understanding of the universe is about to change,” says the CERN release.
The Higgs boson is the only particle predicted by the Standard Model that was so far not seen by experiments. The Higgs mechanism does not predict the mass of the Higgs boson itself but rather a range of masses.
The Higgs Boson is an unstable particle, living for only the tiniest fraction of a second before decaying into other particles. Hence, experiments can observe it only by measuring the products of its decay. In the Standard Model, a physics theory that provides a very accurate description of matter, the Higgs Boson is expected to decay to several distinct combinations of particles, or channels, with the distribution among the channels depending on its mass.
The Standard Model successfully describes all of the elementary particles we know to exist and how they interact with one another. But it cannot explain why most of these elementary particles have masses. Without mass, the universe would be a very different place, explains a CERN backgrounder. For instance, if the electron had no mass, there would be no atoms and no ordinary matter as we know it--no chemistry, no biology and no people.
The mechanism, proposed in the mid-1960s by Robert Brout, François Englert, Peter Higgs and others, was put forward to explain why one of nature’s fundamental forces has a very short range, while another similar force has an infinite range. One is the electromagnetic force, which carries light to us from the stars, drives electricity around our homes, and gives structure to the atoms and molecules from which we are all made.
The other is the weak force, which drives the energy generating processes of the stars.
Electromagnetic force is carried by particles called photons, which have no mass. The weak force is carried by particles called W and Z, which do have mass.
Rather like people passing a ball, interacting particles exchange these force carriers. The heavier the ball, the shorter the distance it can be thrown; the heavier the force carrier, the shorter its range.
The W and Z particles were discovered in a Nobel prize winning enterprise at CERN in the 1980s, but the mechanism that gives rise to their mass has not yet been experimentally identified, and that’s where the Higgs particle comes in.
Put simply, several physicists including Peter Higgs, discovered a mechanism to add equations that would allow particles to have masses. This is now known as the Higgs mechanism. Integrating it into the Standard Model allowed scientists to make predictions of various quantities, including the mass of the heaviest known particle--the top quark.
The Higgs mechanism works as a medium that exists everywhere in space, and particles gain mass by interacting with this medium. Higgs pointed out that the mechanism required the existence of an unseen particle, now call the Higgs boson.
Many theories that describe physics beyond the Standard Model, such as supersymmetry and composite models, suggest the existence of a zoo of new particles, including different kinds of Higgs bosons. If any of these scenarios turn out to be true, finding the Higgs boson could be a gateway to discovering new physics, such as superparticles or dark matter, according to CERN scientists.
By the end of 2012, CMS hopes to have more than triple its total current data sample. These data will enable CMS to elucidate further the nature of this newly-observed particle. They will also allow CMS to extend the reach of their many other searches for new physics, according to a CERN press statement.
Meanwhile, many physicists have been looking for theories beyond the Standard Model--one of them being supersymmetry, according to which all known particles have a much more massive superpartner lurking in the sub-atomic world. Of course, for now, it remains a theory.
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