Researchers make progress in search for elusive Higgs Boson

Large HC

Claudia Marcelloni

Moving the calorimeter on side A of the ATLAS cavern, January 2011.

A machine designed to recreate the conditions just after the Big Bang now stands on the doorstep of a long-awaited discovery.

On Tuesday, Dec. 13, researchers at the Large Hadron Collider (LHC), the $9 billion, 17-mile-long particle accelerator located underground near the French-Swiss border, announced that they had made significant progress in their search for the Higgs Boson, a particle theorized to be responsible for imbuing other particles with mass.

Penn physicists have played an integral part in this research since before the giant machine was constructed. Four faculty members and more than 20 students, as well as postdoctoral fellows and technicians have all contributed to the ATLAS (A Toroidal LHC ApparatuS) project, one of the LHC’s two main particle detectors.   

“The LHC is looking for tons of things, but right now the search for the Higgs Boson is the most interesting, and most in the spotlight,” says Brig Williams, a professor of physics and astronomy in the School of Arts and Sciences, whose search for the Higgs began more than a decade ago.


Maximilien Brice

Views of the LHC tunnel sector 3-4.

Penn’s main contributions to ATLAS are developing the electronics that help capture the proton collision outcomes in its Inner Detector, and a process that helps the researchers record only the most noteworthy collisions. The LHC produces millions of collisions a second, so even with the most advanced computer system in the world, researchers can only store a fraction of the data.  

Higgs Bosons are only rarely created in these collisions and almost instantly decay into other kinds of particles; researchers must then look for the resulting pieces and trace their trajectories back to the point where the Higgs Bosons split apart. With enough data, researchers can reconstruct the mass of the original particle, but because the Higgs could hypothetically contain a range of masses, researchers must repeatedly find a particle at a consistent weight to confirm that it actually exists.      

“We think that the Higgs has one particular mass, so what we’re looking for is an accumulation of events where we can see how heavy the original object was,” says Williams. “We’ll eventually see a peak of events at that mass.”    

The new findings from ATLAS, announced on Dec. 13, suggest the Higgs may be hiding at around 125 gigaelectron volts (GeV), and has explicitly excluded everything outside 116-130 GeV. The increasing rate at which the LHC is producing data and further constraining the range of masses for the Higgs makes Williams hopeful that a final discovery will be announced sometime next year.

Originally published on December 15, 2011