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Steve Chaplin
IU Communications

Last modified: Tuesday, December 13, 2011

With mounting evidence from supercollider, IU physicists find themselves in thick of new results

Dec. 13, 2011

BLOOMINGTON, Ind. -- Indiana University physicists who've spent years working with scientists around the world looking for the Higgs boson, that theorized particle thought to give mass to other particles, today learned the experiment they are tied most closely to -- the ATLAS detector -- and a second independent experiment both have seen similar results providing the best proof yet that this particle does exist.

ATLAS experiment

Photo courtesy of the ATLAS Experiment at CERN,

At 45 meters long and 7,000 tons, with a $540 million price tag, the ATLAS detector at CERN is helping determine whether the Higgs boson exists.

IU physicists gathered at Swain Hall West on the Bloomington campus this morning, Dec. 13, to view the announcement from the European Organization for Nuclear Research -- or CERN -- that two of the $10 billion Large Hadron Collider's experiments, ATLAS and CMS, had collected and analyzed new data sufficient enough to make significant progress in the search for the Higgs boson. And while the new data was not enough to make any conclusive statement on the existence or non-existence of the elusive Higgs, predictions are that 2012 will be the year of confirmation.

The main conclusion, according to IU physicist Harold Evans, is that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 116-130 GeV by the ATLAS experiment, and 115-127 GeV by CMS. A GeV is a thousand million electronvolts and the collider at CERN is designed to speed subatomic protons up to energies of 7 trillion electron volts and smash them together in an attempt to re-create conditions from when the universe was less than a trillionth of a second old.

Scientists said that multiple independent measurements point to excesses in the region of 124 to 126 GeV as being most compatible with a Standard Model Higgs, but the statistical significance is not large enough to say anything conclusive yet. What was seen was either a background fluctuation or the presence of the Higgs boson, and that differentiation should be made in 2012 with refined analyses and additional data.

"The fact that the two experiments are seeing hints in the same region is extremely exciting," professor Evans said shortly after the CERN news conference. "If these hints are borne out then each experiment will definitively observe the Higgs with data taken in 2012. So, even though we can't claim discovery yet, we're still drinking champagne!"

Over the coming months, both experiments will be further refining their analyses. However, a definitive statement on the existence or non-existence of the Higgs will also require more data, retired professor Harold Ogren said. Ogren is another IU physicist who worked on the ATLAS detector's barrel Transition Radiation Tracker detector, one of three elements of ATLAS that reconstructs the trajectories of charged particles produced in proton-proton collisions.

"We only just saw the CMS results, and we're fantastically encouraged to see that they show hints at a similar mass to ATLAS'," Ogren said.

Staff and faculty in the IU College of Arts and Sciences' Department of Physics designed and built approximately one-half of the barrel Transition Radiation Tracker detector, a device that significantly enhances ATLAS' ability to identify electrons produced in the collisions. Because it can reconstruct trajectories of charged particles and identify produced electrons, the Transition Radiation Tracker is considered a critical detector element in ATLAS' search for the Higgs boson.

The team also partners with the University of Chicago in managing ATLAS' Midwest Tier2 computing center, which has hardware in Bloomington, at Indiana University-Purdue University Indianapolis and in Chicago. This center is one of only five such ATLAS computing centers in the U.S., and it makes heavy use of the Open Science Grid, to which IU has made major contributions.

IU scientists are also among the primary authors of eight peer-reviewed journal publications based on ATLAS data.

The current IU ATLAS group, in addition to professors Evans and Ogren, are assistant professor Sabine Lammers; professor and department chair Rick Van Kooten; research scientists Pauline Gagnon, Vivek Jain, Fred Luehring and Daria Zieminska; postdoctoral researchers Sylvie Brunet, Christopher Marino (now at University of British Columbia) and Darren Price; graduate students KyungEon Choi, John Penwell, Ben Weinert, Denver Whittington and Yi Yang; engineer Kirill Egorov and administrator Jenny Olmes-Stevens.

For more information contact Steve Chaplin, Indiana University Communications, at 812-856-1896 or Tweeting IU science: @IndianaScience