Physicists on the ATLAS and CMS experiments at the Large Hadron Collider announced today that they have observed a new particle. Whether the particle has the properties of the predicted Higgs boson remains an open question.
The announcement came during a seminar at the home of the LHC, the CERN particle physics laboratory on the border of Switzerland and France. Both experiments observe a new particle in the region of 125 to 126 GeV, approximately 130 times the mass of the proton.
“I can tell you that things are very intense here at CERN,” said James Pilcher, professor in physics at the University of Chicago and a member of the LHC’s ATLAS collaboration. “We are struggling to fully understand the physics message of the data and new insight unfolds every day.”
When protons collide in the LHC, their energy can convert into mass, often creating short-lived particles. These particles quickly decay into pairs of lighter, more stable particles that scientists can record with their detectors.
The preliminary results announced today are based on data collected in 2011 and 2012, with the 2012 data still under analysis. A more complete picture of today’s observations will emerge later this year after the LHC provides more data. Publication of the analyses shown today is expected near the end of July.
“What we are observing is very likely a new particle with very large mass that would have to be a boson,” said alumnus Joe Incandela, BA’81, MS’85, PhD’86, spokesperson of the CMS experiment and a physicist at the University of California, Santa Barbara. “This is potentially an historic and very profound step forward in our understanding of the underlying structure of our universe.”
The Standard Model of particle physics has correctly explained the elementary particles and forces of nature through more than four decades of experimental tests. But it cannot, without the Higgs boson, explain how most of these particles acquire their mass, a key ingredient in the formation of the universe.
Scientists proposed in 1964 the existence of a new particle, now known as the Higgs boson, whose coupling with other particles would determine their mass.
The CMS and ATLAS experiments in December announced seeing tantalizing hints of a new particle in their hunt for the Higgs. Since resuming data-taking in March 2012, the CMS and ATLAS experiments have more than doubled their collected data, growing the statistical significance of their findings.
Hundreds of scientists and graduate students from American institutions have played important roles in the search for the Higgs at the LHC. More than 1,700 people from U.S. institutions — including 89 American universities and seven U.S. Department of Energy national laboratories — helped design, build and operate the LHC accelerator and its four particle detectors. Fermi National Accelerator Laboratory is a member of the CMS collaboration, while Argonne National Laboratory belongs to the ATLAS collaboration.
The UChicago ATLAS Group consists of 28 faculty members, postdoctoral scientists, graduate students, software professionals, engineers and staff members. Pilcher’s faculty collaborators are Florencia Canelli, assistant professor in physics; Young-Kee Kim, professor in physics and deputy director of Fermilab; Frank Merritt, professor in physics; Mark Oreglia, professor in physics; and Melvyn Shochet, the Elaine M. and Samuel D. Kersten Jr. Distinguished Service Professor in Physics.
The United States, through the U.S. Department of Energy’s Office of Science and the National Science Foundation, provides support for research and detector operations at the LHC and also supplies computing for the ATLAS and CMS experiments.
Previous experiments at CERN and Fermilab have searched for the Higgs boson, but it has eluded discovery.
“Henry Frisch and I probably are going to lose a bet,” said Jonathan Rosner, professor emeritus in physics at UChicago, before the CERN announcement. Frisch, professor in physics, and Rosner are members of the Collider Detector at Fermilab collaboration, which also has been searching for the Higgs.
In January 2011 they wagered dinner at a Hyde Park restaurant with Mark Oreglia and Frank Merritt of the UChicago ATLAS collaboration that the Higgs would remain undiscovered as of January 2013.
“We thought it was going to take longer,” Rosner said, emphasizing the difficulty of the discovery. “But it looks like CERN has really made a lot of progress.”
—Prof. Jacqueline Stewart
