UC Davis seeks to validate Higgs boson finding

08/11/2014 12:00 AM

08/11/2014 12:30 AM

Two summers ago, the science world was agog over a physics discovery from far beneath the Alps of evidence of what seemed to be a long-sought elementary particle called a Higgs boson.

Since that major discovery, UC Davis researchers have gone back to work to check out the finding. That work might seem tedious to the non-science world, but it’s what scientists do when they find a new particle.

The collaboration that ran the revealing experiment – known as the Compact Muon Solenoid – published a study in June addressing the question of whether the detected particle is really the Higgs boson. So far, the answer is yes, but physicists continue looking for more proof.

New results test “whether we’ve really seen what we think we’ve seen,” said John Gunion, a theoretical physicist at UC Davis, which is a founding member of the collaboration, known as CMS for short.

At the Large Hadron Collider operated by CERN, the European Organization for Nuclear Research, CMS watches as protons collide, and then it uses powerful magnetic fields to help identify the particles that are thrown out by the collision.

The lifetime of the Higgs isn’t long enough to be seen directly, but it then decays into numerous different kinds of particles, many of which CMS captures, Gunion said.

The CMS study focuses on when the Higgs decays into particles known as fermions, which are different from the decays observed in the Higgs discovery.

In the more recent tests, the Higgs was seen decaying into some of the heavier fermions, a kind of particle that includes the protons and electrons of everyday matter. “Since they’re heaviest, they’re the group the Higgs couples more strongly to,” and therefore more likely to decay to, said Gunion.

Gunion said that the results so far match predictions from what is called the “standard model” of particle physics.

Had a different rate been measured, with either more or fewer decays, “that would have been an astounding thing,” said John Conway, a physicist at UC Davis and head of the CMS group there. It might have implied different properties for the Higgs boson, or that it was actually some other new particle.

The Higgs boson is of particular interest, furthering the understanding of “what mass is,” explained Conway.

The CMS is a particle detector situated at the Hadron collider where protons race around miles-long rings at nearly the speed of light.

Conway will be traveling to CERN in the fall, to help with the maintenance of the CMS before the collider resumes firing protons in early 2015. He said a planned increase in the energy of the protons and the number of collisions will open up the possibility of finding another, more massive Higgs boson, or other as-yet undiscovered particles.

“After a few years, we’ll have something like 300 integrated units of collisions,” said Gunion. “The analysis so far is based on just 25.”

Conway said that physicists are fairly certain that the standard model is not entirely correct because it predicts that the Higgs boson has infinite mass. “It used to be a theoretical problem about a hypothetical particle, but now it’s a theoretical problem about a real particle,” he said.

Conway compared the issue to the open questions in physics in the early 20th century, which led to the discovery of quantum mechanics and the modern technology that depends on it. “Whatever happens, I’m sure it’s going to lead to wonderful new things,” he said. Although, he added, “maybe not in my lifetime.”

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