Understanding the Higgs Boson

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The Standard Model of particle physics is a theoretical framework explaining the forces exerted on and the interactions between elementary, subatomic particles. Because of its success in explaining a wide variety of experimental results, the Standard Model is sometimes regarded as a “theory of everything.” It is, essentially, a mathematical ingredients list for all the particles that exist in nature, and their properties— and when we run this list through a fancy calculator, it give us equations that describe how these particles behave. However, when scientists tried to include mass as a property of particles, the equations displayed error. Physicists needed to come up with a better recipe of particles— something that would explain mass in the final equations without it being put in the initial data.

To understand the theory and history of the Higgs Boson, we begin with quantum physicist and Nobel Laureate Eugene Wigner. Wigner dealt heavily with the concepts of group theory, which is a mathematical branch of abstract algebra that studies concepts of symmetry. Familiar algebraic structures, such as rings, fields, and vector spaces, all can be understood through group theory. Wigner prompted particle physicists to see that symmetry is vital to their understanding of the physical world.

CMS_Higgs-eventIn the 1960s, theories appealing to symmetry were taking over. The problem was: perfect symmetry in our equations seemed to imply that the fundamental particles would be massless, which would correspond to a universe in which atoms couldn’t even exist. Physicists had to figure out a way that the universe could both be symmetric and contain massive particles.

In 1964, Peter Higgs and his colleagues were able to appeal to mathematical symmetry in order to make their prediction. They claimed the existence of a particle-wave-field that gave mass to other particles and to itself. Thus, the Higgs boson and the Higgs field were theorized entirely by appealing to the mathematical idea of symmetry. Other theoretical physicists had also published papers about the possibility from 1954 to 1961.

The employment of symmetries enabled Steven Weinberg to predict the existence of the Z boson and the actual masses of the Z and the two W bosons— which act inside nuclei of matter to produce radioactive decay. In doing this work, Weinberg utilized the concept of what he called “the Higgs mechanism.” He hypothesized that this mechanism broke symmetry of the early universe, thus imparting masses to these three boson particles—and presumably also to all other matter in the cosmos.

This theoretical advance in 1964, combined with Weinberg’s Nobel paper of 1967, enabled the Higgs mechanism to emerge triumphant as an explanation of mass. Further, mass was shown to be conferred to particles because of mathematical symmetry and this theory serves to highlight the powerful relationship between pure mathematics and theoretical physics.

But how do you test for the Higgs Boson? First, you head to CERN’s Large Hadron Collider, situated a few hundred feet beneath the Franco-Swiss border. The LHC is designed to accelerate protons to near the speed of light and force them to smash together in four giant detectors, spread around its 17 mile circumference. Built at a cost of about $4.3 billion, it is the most expensive scientific instrument ever created by man. Interestingly, the main argument for the creation of the LHC was to discover the Higgs boson.

To find evidence of the Higgs, the LHC forced together protons at incredibly high speeds, counting out the many elementary particles created from these massive collisions. The Higgs boson is a heavy particle, which means it almost immediately decays into simpler fragments. Physicists were trying to search for characteristic decays that would indicate the existence of the Higgs. Since the process is very complicated and involves so many variables, particle physicists use statistics to interpret their results — in order to show that a small excess of certain decays is not just a coincidence. What they were looking for was the safety of a 5-sigma result, which has only a one in 3 million chance of happening randomly.

And, on July 4, 2012, CERN announced: “[We] observe an excess of events at a mass of approximately 125 GeV with a statistical significance of five standard deviations (5 sigma) above background expectations. The probability of the background alone fluctuating up by this amount or more is about one in three million.” This degree of certainty has caused physicists and laymen alike to call a Higgs, well, a Higgs.

Now, over a year after its ‘discovery’, there is much surrounding the Higgs boson that remains enigmatic: like that the quantum excitation seemed to have about a 100 trillion times less energy than what the Standard Model predicts. And the Standard Model itself isn’t a complete description of the physical universe. It misses out on: gravity as described by general relativity, it doesn’t predict the accelerating expansion of the universe, and it also does not correctly account for tau neutrinos and their non-zero masses. It would serve to advance understanding for physicists if, with further testing, the Higgs boson turns out to behave in ways we completely don’t expect, in ways we couldn’t predict under the Standard Model. Then we might get some new clues about the universe by being presented with further questions, issues, and complexities. It could indicate the presence of new physics, such as supersymmetry, that could build on the Standard Model and possibly fix certain problems with it. Unfortunately, we will have to wait awhile until we see such issues resolved. The LHC is having maintenance conducted and not scheduled to be in use until late 2014 at the earliest.

“I would be delighted if this new state is a Higgs boson, but perhaps not the Standard Model Higgs boson,” physicist Fabiola Gianotti of the LHC’s ATLAS experiment said after the announcement, with an apology aside to Peter Higgs, “because this will open the road to something else.”

Photo: Wikimedia Commons

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