Purdue physicists pursue Higgs boson; part of international CMS experiment

December 16, 2011

An illustration of a particle collision measured by the CMS detector. (Image courtesy of CERN)

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WEST LAFAYETTE, Ind. — Purdue University's particle physics group is part of the biggest international experiment in particle physics history, which recently provided a progress report in the hunt for the Higgs boson.

The Higgs boson is the only undiscovered part of the Standard Model of physics, which describes the basic building blocks of matter and their interactions.

Results announced from experiments using the world's largest particle accelerator, the Large Hadron Collider (LHC), narrowed the space in which the Higgs boson could dwell but hinted that it may yet be found. 

The LHC is designed to collide two beams of billions of protons traveling at almost the speed of light. The collisions at such high energies cause the protons to shatter into tiny particles that would otherwise never be seen, offering scientists their first chance to see if the Higgs boson exists.

The teams behind two LHC experiments named for the particle detector they use, ATLAS  (A Toroidal LHC Apparatus) and CMS (Compact Muon Solenoid), shared their results during a seminar at the European Organization for Nuclear Research or CERN in Geneva, Switzerland, on Tuesday (Dec. 13).

Daniela Bortoletto, Purdue's Edward Purcell Distinguished Professor of Physics and U.S. upgrade coordinator of the US CMS experiment, said the search for the subatomic particle may soon be over.

"I believe that the experiments will be able to complete the search for the Higgs boson by the end of next year," she said. "At that point we will have double or even triple the amount of data available. Furthermore, the LHC might operate even at higher energies, increasing our ability to find the Higgs boson."

The CMS detector (Photo courtesy of CERN/Maximilien Brice)

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The Higgs bosons, if they exist, are short-lived and quickly decay into other particles. Because scientists cannot look directly for the particle, its discovery relies on observations of excess amounts of the particles into which it can decay. It is unknown what mass the Higgs boson would have, and researchers must look for it within a range of masses that each decay into a unique mixture of particles.

Bortoletto's group is looking for evidence of specific subatomic particles that would result from the decay of a Higgs boson within one of these possible mass ranges. The results of the team's search have ruled out a Higgs boson at that mass range, contributing to the overall narrowing of the search.

Bortoletto's group includes Purdue research scientists Petra Merkel, Daniele Benedetti, Miguel Vidal and doctoral students Jakub Zablocki and Matthew Kress.

The ATLAS and CMS experiments have shown a small excess of particles that could be decays from the Higgs boson at a mass on the lower end of the mass range, but more experiments need to be done, Bortoletto said.

"The Higgs boson may exist," Bortoletto said. "If it does, it would validate the Standard Model that describes the world we see including why tiny subatomic particles have mass and why atoms exist. If the Higgs is not found, we must develop a new theory."

Ian Shipsey, the Julian Schwinger Distinguished Professor of Physics and co-coordinator of the LHC Physics Center at Fermilab who led the internal review team that checked the results for two of the eight Higgs searches presented by the CMS experiment, said finding the Higgs boson predicted by the standard model would be a great achievement, but not finding it would also be interesting.

"Not finding the Higgs boson would place particle physicists in the same situation as our predecessors at the start of the 20th century when something was missing from our explanation of nature," he said. "That realization led to the discovery of quantum mechanics, which enabled the technological revolution from television to laptops to cell phones. Finding or not finding the Higgs boson is a win-win situation because either way it is invaluable information about the essence of the universe."

Purdue researchers also helped design and construct critical pieces of equipment for the Compact Muon Solenoid detector. Purdue teams spent more than eight years designing and building special cameras, called pixel detectors, used to capture images of the tiny particles that result when two protons collide.

Bortoletto and Shipsey led the camera design and assembly teams, respectively. In addition, Purdue professors Virgil Barnes, Laszlo Gutay, Matthew Jones, David Miller and Norbert Neumeister are part of the international CMS team.

Purdue's information technology group also is contributing to the global distributed computing system that is now analyzing the data from the experiments.

The Department of Energy's Office of Science and the National Science Foundation provide support for U.S. participation in the ATLAS and CMS experiments. Fermi National Accelerator Laboratory is the host laboratory for the U.S. contingent on the CMS experiment, while Brookhaven National Laboratory hosts the U.S. ATLAS collaboration.

Over the coming months, both the CMS and ATLAS experiments will focus on refining their analyses in time for the winter particle physics conferences in March. The experiments will resume taking data in spring 2012.

Writer:  Elizabeth K. Gardner, 765-494-2081, ekgardner@purdue.edu

Sources:  Daniela Bortoletto, 765-494-5197, daniela@physics.purdue.edu

                   Virgil Barnes, 765-494-5199, barnes@purdue.edu

                   Laszlo Gutay, 765-494-5047, gutay@purdue.edu

                   Matthew Jones, jones105@purdue.edu

                   David Miller, 765-494-5556, miller@physics.purdue.edu

                   Norbert Neumeister, 765-494-5198, neumeist@purdue.edu

                   Ian Shipsey, 765-494-5391, shipsey@physics.purdue.edu

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