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The Higgs boson and beyond: Particle Physics at the College

Prof. Marc Sher (The College of William & Mary - Physics Dept.)The hunt for the Higgs boson has been one of the most publicized scientific endeavors of recent years. It is essential to the Standard Model, the theory of particle physics which focuses on twelve fundamental particles and includes three of the four fundamental forces, as it not only provides mass to the fundamental particles but explains the symmetry breaking seen within it. The announcement of a conference and press release at CERN has many speculating that this hunt is about to be declared over. Despite the International Conference on High Energy Particles (ICHEP) being only two days away, CERN’s decision to hold its own conference and press release indicates important news that it would not want to announce in a non-member nation. The discovery of the Higgs boson would be one of the biggest discoveries of particle physics and would certainly be cause for a special event. While the conference is currently only billed as providing an ‘update’ on the Higgs boson search, physicists around the world, including those at William and Mary, expect big news.

Marc Sher in particular is invested in what could be announced on July 4 th. While many in the W&M Physics Department are involved in particle physics, Sher is the Higgs boson expert, with research in the field spanning thirty years. He is best known for his contributions on narrowing down the Higgs boson mass in the Standard Model, its variations and its extensions. His work has helped rule out different models by finding bounds on the Higgs boson mass; finding upper limits enables researchers to know that if the Higgs boson is not found within certain GeV mass ranges, their models are inaccurate and therefore must be modified or dismissed. Sher also postulated a theory along with Ta-Pei Cheng in which there were two Higgs fields rather than one, known as Model III, which alleviated the tight experimental constraints on flavor-changing neutral currents seen in the previous two-Higgs models by utilizing what is now known as the Chang-Sher ansatz. This ansatz provided a reasonable assumption regarding the size of couplings between the Higgs fields and quarks. With all the research he has invested into the particle, it is no wonder he’s been anticipating news of a discovery for thirty years.

Confirming the discovery of the Higgs boson is no easy task, however. “How you see the Higgs is in its death,” David Armstrong explains. “You’re looking for an excess of certain combinations of particles with certain energies and angles such that they come from a particle with a well-defined mass.” To do this, a spectrum is made in which the distribution of a combination of particles can be seen. If there is a ‘bump’ above the smooth distribution, this could indicate the Higgs boson’s existence. To confirm it is not a fluctuation of data, however, the mass the peak is seen at must be confirmed to five standard deviations. There can be no room for statistical error in such a major discovery.

Such extreme precision is a focus of Armstrong’s. Along with Wouter Deconinck’s, their research examines particle physics at the precision frontier. As with Sher’s work in finding constraints on the Higgs mass helping to focus research, Armstrong and Deconinck’s work helps to focus the direction of particle physics by providing highly accurate measurements which models of physics must accommodate. In particular, they test the Standard Model itself. While the Standard Model has incredible predicative abilities and is one of the most exhaustively researched and successful models available, its shortcomings cannot be ignored. For this reason, research going beyond the Standard Model is vital, with many professors at the College looking into it.

“We’re still really not sure about of a lot of things we’d like to understand. Just knowing that there is a Higgs boson is not enough,” Josh Erlich stated in regards to going beyond the Standard Model. His work seeks to do precisely that by exploring other models, either with or without the Higgs boson. Erlich has toyed with the idea that the particle does not exist and has sought alternate models, such as in his work with the technicolor model which provided an alternate explanation for the symmetry breaking and fundamental particle mass thought to be caused by the Higgs boson in the Standard Model, as well as models of supersymmetry. More recently, he has also been investigating reconciling these models with the existence of the Higgs boson and using them to understand things that the Standard Model does not provide for. The Standard Model’s undeniable shortcomings, such as its inability to account for gravity or dark matter, will persist even with the discovery of the Higgs.

There is a nightmare scenario, however, as outlined by Sher and hinted at by Armstrong: the Higgs boson is discovered, yet nothing else is, indicating an inability to find particles or other evidence needed to investigate models such as supersymmetry at attainable energy levels. In this event, it would be impossible to experimentally confirm the underlying theory with viable methods. However, the opposite it also possible; the Large Hadron Collider could begin to discover particles that would confirm supersymmetry or other models, or would at least provide enough indication for them to ensure future funding. Regardless, the search for viable, more inclusive models beyond the Standard Model will continue, aided and focused by enhanced knowledge about the Higgs boson. As assured by Erlich, particle physics does not end here.