Physicists on experiments at the Large Hadron Collider announced today (July 4, 2012) that they have observed a new particle. Whether the particle has the properties of the predicted Higgs boson remains to be seen.
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 (DOE) national laboratories--helped design, build and operate the LHC accelerator and its four particle detectors. The United States, through DOE'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.
The results announced today are labeled preliminary. They 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 the experiments with more data.
The new particle is in the mass region around 125-126 GeV. Publication of the analyses shown today is expected around the end of July.
"I congratulate the thousands of scientists around the globe for their outstanding work in searching for the Higgs boson," said U.S. Secretary of Energy Steven Chu. "Today's announcement on the latest results of this search shows the benefits of sustained investments in basic science by governments around the world. Scientists have been looking for the Higgs particle for more than two decades; these results help validate the Standard Model used by scientists to explain the nature of matter."
The CMS and ATLAS experiments in December announced seeing tantalizing hints of a new particle in their hunt for the Higgs, the missing piece in the Standard Model of particle physics. Since resuming data-taking in March 2012, the CMS and ATLAS experiments have more than doubled their collected data. The statistical significance of the earlier hints has grown.
"What has been announced today could not have been accomplished without the cooperation of scientists and nations throughout the world in seeking an understanding of the fundamental laws of nature," said Ed Seidel, NSF's assistant director for the Mathematical and Physical Sciences. "If the particle announced today at CERN is confirmed to be the Higgs boson, this represents a keystone in our knowledge of the elementary forces and particles that exist in our universe."
Scientists on experiments at the LHC announced their latest results at a seminar at the home of the LHC, the CERN particle physics laboratory on the border of Switzerland and France. Physicists from across the United States gathered at laboratories and universities in the middle of the night to watch a live-stream of the seminar online. The vast majority of U.S. scientists participate in the LHC experiments from their home institutions, remotely accessing and analyzing the data through high-capacity networks and grid computing.
Scientists will give more detailed presentations about the results this week at the biannual International Conference on High Energy Physics, held this year in Melbourne, Australia.
The Standard Model of particle physics has proven to explain correctly 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 our 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. Experiments at the LEP collider at CERN and the Tevatron collider at the Department of Energy's Fermilab have searched for the Higgs boson, but it has eluded discovery. Only now, after decades of developments in accelerator and detector technology and computing--not to mention advancements in the understanding of the rest of the Standard Model--are scientists approaching the moment of knowing whether the Higgs was the right solution to this problem.
"What we are observing is very likely a new particle with very large mass that would have to be a boson," said University of California Santa Barbara physicist Joe Incandela, spokesperson of the CMS experiment. "This is potentially an historic and very profound step forward in our understanding of the underlying structure of our universe. "
When protons collide in the Large Hadron Collider, 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.
Theoretical physicists have predicted the rate at which the Higgs boson will be produced in high-energy proton-proton collisions at the LHC and also how it decays into certain combinations of observable particles. Experimental physicists at the ATLAS and CMS experiments have been studying the collisions and have observed a new particle. They will need to collect more data and run further analysis to determine its properties.
"If the new particle is determined to be the Higgs, attention will turn to a new set of important questions," said University of California Irvine physicist Andy Lankford, deputy spokesperson of ATLAS. "Is this a Standard Model Higgs, or is it a variant that indicates new physics and other new particles?"
Discovery of the Higgs -- or another new particle -- would represent only the first step into a new realm of understanding of the world around us.
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