After a quarter of a century of searching, physicists have discovered a rare particle decay that gives them an indirect way to test models of new physics.
Researchers with the CMS and LHCb collaborations at the Large Hadron Collider at CERN announced at the EPS-HEP Conference in Stockholm, Sweden, that their findings agreed closely with the Standard Model of particle physics, ruling out several models that predict new particles. CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics.
In this result, physicists showed for the first time enough evidence to declare the discovery of a decay of a particle made up of two kinds of quarks — anti-bottom quarks and strange quarks — into a pair of particles called muons.
The U.S. Department of Energy’s Fermi National Accelerator Laboratory serves as the U.S. hub for more than 1,000 scientists and engineers — including about a dozen Texas A&M University physicists — who participate in the CMS experiment. DOE and the National Science Foundation support involvement by about 2,000 scientists and students from U.S. institutions in the LHC experiments CMS, ATLAS, LHCb and ALICE — the vast majority participating at their home institutions via a powerful broadband network that ships data from CERN.
“This is a victory for the Standard Model,” said CMS physicist Joel Butler of Fermi National Accelerator Laboratory. “But we know the Standard Model is incomplete, so we keep trying to find things that disagree with it.”
The Standard Model predicts that the particle, called B-sub-s, will decay into two muons very rarely, only three times in every billion decays. However, the Standard Model assumes that the only particles involved in the decay are the ones physicists already know. If other, unknown particles exist, they might interfere, either making the decay happen more frequently than predicted or effectively canceling the decay out.
“This is the place to look for new physics,” said LHCb physicist Sheldon Stone of Syracuse University. “Small deviations from the predicted rate would firmly establish the presence of new forces or particles.”
What scientists found was a decay that followed the Standard Model’s predictions almost to the letter. This spells trouble for several models, including a number of models within the theory of supersymmetry, which predicts that each known particle has an undiscovered partner particle.
But the hunters of new particles have not lost hope; the result leaves room for other models of physics beyond the Standard Model to be correct.
Texas A&M University physicist Teruki Kamon describes today’s finding as a moment he’s been waiting for since 2002, when he co-authored a paper with fellow Texas A&M physicists Bhaskar Dutta and Richard Arnowitt proposing a powerful way to test a cosmologically consistent model of supersymmetry.
In addition to Kamon, fellow Mitchell Institute high-energy experimentalists Ricardo Eusebi, Alexei Safonov and David Toback are intensely involved with the CMS experiment at the LHC to discover the presence of new physics. At the same time, Mitchell Institute high-energy theorists Arnowitt and Dutta, along with Dimitri Nanopoulos, are utilizing LHC experiment results to understand the past, present and the future of the universe.
This story was originally published in the College of Science at Texas A&M University.
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