An announcement today by CERN scientists speaking from the Moriond Conference in La Thuile, Italy, generated media attention around the globe; the scientists affirmed the greatly celebrated particle discovery announced last summer on July 4 by both the ATLAS and CMS experiments looks strikingly like a Higgs boson, though it is too early to confirm that it is the single Higgs boson of the standard model of physics. It might still be one of a family of Higgs bosons predicted in "beyond the standard model" theories.
Physicists believe the energy field of the elusive boson is what gives mass to matter—making its existence fundamental to the formation of the universe and just about everything in it. The Higgs had been the only missing piece of the standard model (SM) of physics, first proposed nearly 50 years ago.
The discovery announced last summer was based on the analysis of the outcomes of millions of high-energy proton-proton collisions at the $10 billion Large Hadron Collider (LHC) particle accelerator, which forms a 17-mile ring-shaped tunnel beneath the Swiss-French border. ATLAS and CMS scientists had sufficient data last July to declare a discovery of a new boson consistent with the Higgs, but were reluctant to call it the Higgs boson before the full 2012 data set had been analyzed.
Now the two multi-national teams of physicists have sifted through two-and-a-half times the amount of data that had been compiled by July 4, giving a much clearer picture of the particle’s characteristics. Whether or not it is a Higgs boson is demonstrated by how it interacts with other particles, and its quantum properties. For example, a Higgs boson is postulated to have no spin, and in the standard model its parity—a measure of how its mirror image behaves—should be positive. CMS and ATLAS have compared a number of options for the spin-parity of this particle, and these all prefer no spin and positive parity. This, coupled with the measured interactions of the new particle with other particles, strongly indicates that it is a Higgs boson.
University of Illinois high energy physicists
Steven Errede,
Deborah Errede,
Tony Liss, and
Mark Neubauer, along with their many team members—postdocs, graduate students, and undergraduate students—have worked with the ATLAS collaboration since 1994, contributing substantially to the design, building, commissioning, data taking, and data analysis at the ATLAS experiment at CERN.
Liss said, "This is an important milestone because it represents the full dataset from the last year of running. But the case is not closed yet on whether this is the standard model Higgs. We have more work to do."
"If this is the only such particle the CMS and ATLAS experiments ever discover—ever—this particle would then be identified as the Higgs boson of the standard model. Only one such particle is predicted to exist in the SM,” said Steven Errede. “But the decay modes, decay branching ratios, and signal strengths of the observed 126-GeV-mass spin-0 boson are also in good agreement with those predicted for the SM Higgs boson within 'beyond standard model' theories. In one such theory, more than one such particle is predicted to exist."
Errede explained that, while years of searching have not turned up evidence of additional Higgs-like bosons, that doesn’t mean they don’t exist. In his opinion, "until further data is collected after the upgrades due to be completed in 2015 at the LHC, the possibility that other such bosons exist can't be ruled out."
The University High Energy Physics group is supported by the US Department of Energy, Grant No. DOE DEFG02-91ER40677O/C. MSN also is supported by the National Science Foundation CAREER 1056987. The conclusions presented are those of the scientists and not necessarily those of the funding agencies.