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Dec. 14, 2011

Experiments at CERN Begin to Pinpoint the Higgs Boson

by Zach Lynn

Click to enlarge images

By Zach Lynn, Carleton College

CERN Director-General Rolf Heuer, ATLAS Spokesperson Fabiola Gianotti and CMS Spokesperson Guido Tonelli present the current results in the search for the Higgs Boson. Image: CERN

The Higgs boson, often referred to as the "God particle", has eluded physicists since its existence was first postulated by Peter Higgs in 1964. The Standard Model predicts that sub-atomic particles gain mass by interacting with the Higgs boson. However, the Higgs boson has never been directly or indirectly observed. That may change in the not too distant future. Yesterday, two research groups, both based at CERN in Geneva, Switzerland, presented the latest data from the search for the Higgs boson. They were unable to confirm or deny the existence of the Higgs boson, but they are close to a definitive answer.

The process of creating and detecting the Higgs boson and most other subatomic particles involves massive amounts of energy, space, brain power, and persistence. First, easily obtainable particles, usually protons, are accelerated to speeds very close to the speed of light in a particle accelerator. These massive machines, including the LHC, are several miles long and accelerate particles using voltage fields. When the accelerated particles collide with each other, new particles can be created from the excess energy. The mass of the created particles is related to the total kinetic energy and mass of the initial particles. The products of these collisions, including the Higgs boson, are often unstable and quickly decay into other types of particles. Physicists are able to predict what particles will be created and how they will behave based on the Standard Model.

The two experiments that yielded the data presented yesterday, ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid), are searching for contradictions to the predictions of the Standard Model. If, after a collision, researchers can find increased or decreased concentrations of certain particles, it could be a sign that the Higgs boson was created in the collision and they are observing its products. However, any deviations they might observe would be relatively miniscule compared to everything else occurring in the system. Particle physicists have to run tests thousands of times in order to be certain that what they are observing is not due to chance. By testing different initial energies (which correspond to the mass of the created particles) and confirming the predictions of the Standard Model, these experiments have narrowed down the range of possible masses for the Higgs boson.

The latest results are far from conclusive but they do significantly narrow the range of masses that the Higgs boson could inhabit. Both experiments gave a range of masses that the Higgs boson could possibly have. The ATLAS experiment gave a range of 116-130GeV and the CMS experiment gave a range of 115-127GeV. Their statistical certainties for this range, about 95%, were high, but not nearly high enough to confirm a discovery. In order for a discovery to be made officially, the results must have at least 99.9999% certainty -- or less than a one in a million chance of being a fluke. CERN's press release also revealed that "there are multiple independent measurements pointing to the region of 124 to 126 GeV", but these are little more than hints.

It's possible that after conducting more tests at the 124-126GeV range, the experiments will prove that the anomalies they observed were in fact due to coincidence. When these experiments determine definitively whether or not the Higgs boson exists, physicists will have reason to celebrate regardless of the result. If the Higgs boson does exist, it will confirm the Standard Model. However if the Higgs boson does not exist or interacts with matter in a different way than predicted, physicists will have to find a new way to explain why matter has mass.

While neither experiment can provide data definitively confirming or denying the existence of the Higgs boson yet, LHC physicist Joe Lykken assured Scientific American that "we will have a definitive answer about the Higgs. It’s just a question of when it will happen."

_________________
Zach first discovered his passion for science as a high school student at Trinity School in New York City. He now attends Carleton College, where he plans on majoring in Physics. His interests in science include high energy physics, medicine, and technology.

About Zach Lynn

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