New evidence strengthens case that scientists have discovered a Higgs boson

On July 4, physicists on the CMS and ATLAS experiments announced the discovery of a particle with a close resemblance to a Higgs, a particle thought to give mass to other elementary particles. The discovery of such a particle could finish a job almost five decades in the making: It could confirm the last remaining piece of the Standard Model of particle physics, a menu of the smallest particles and forces that make up the universe and how they interact.

Although scientists will need to analyze substantially more data before they can conclusively declare the new particle is the Standard Model Higgs boson, results announced today at the Rencontres de Moriond conference in La Thuile, Italy, bolster scientists' confidence that the particle they discovered is the Standard Model Higgs.

"Clear evidence that the new particle is the Standard Model Higgs boson still would not complete our understanding of the universe," said Patty McBride, head of the CMS Center at Fermilab. "We still wouldn't understand why gravity is so weak and we would have the mysteries of dark matter to confront. But it is satisfying to come a step closer to validating a 48-year-old theory."

Researchers look for the Higgs boson at the LHC by accelerating protons to high energies and crashing them into one another. The energy of those colliding protons can briefly convert into mass, bringing into being heavier particles such as the Higgs bosons. The heavy particles are unstable and decay almost immediately into pairs of less massive particles.

Scientists have specific predictions for how often a Standard Model Higgs boson of a certain mass will decay into different patterns of particles. The latest results indicate that the new particle is sticking to the Standard Model's script.

The ATLAS and CMS collaborations have analyzed two and a half times more data than was available for the discovery announcement in July, and, in their preliminary results, they find that the new particle is looking more and more like a Higgs boson.

"When we discovered the particle, we knew we found something significant," ATLAS scientist and New York University professor Kyle Cranmer said. "Now, we're just trying to establish the properties."

The analysis included the data from about 500 trillion proton-proton collisions collected in 2011 and from about 1,500 trillion collisions in 2012. The LHC stopped operation on Feb. 16, for two years of maintenance and upgrades, but researchers will continue to study the data collected before the shutdown.

Hundreds of scientists and students from American institutions have played important roles in the search for the Higgs at the LHC. Fermi National Accelerator Laboratory and Brookhaven National Laboratory host the U.S. contingents of the CMS and ATLAS experiments, respectively. 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, detector operations, and upgrades at the LHC, as well as supplies computing for the ATLAS and CMS experiments.

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. Working collaboratively, these international organizations are able to analyze an incredible amount of data.

After further analysis, scientists will be able to say whether this new particle is the Standard Model Higgs boson or something more surprising.