Paris (AFP) – Six years after tracking down the Higgs boson, the subatomic particle that confers mass on matter, physicists said Tuesday they have “at long last” witnessed it decaying into tiny bits called “bottom quarks”.
The predicted decay was observed at the Large Hadron Collider (LHC) famous for the Nobel-capped discovery of the Higgs particle in 2012, Europe’s CERN physics lab announced.
“During the early preparations of the LHC, there were doubts on whether this observation could be achieved,” the ATLAS scientific collaboration said of the “elusive interaction” now documented at the massive particle accelerator.
Because Higgs bosons themselves are hard to find, and other particles also break up into bottom quarks, it has been difficult to track down those attributed specifically to Higgs decay.
Researchers say the long-awaited observation serves as further verification of the Standard Model of physics — the mainstream theory of the fundamental particles that make up the Universe and the forces that govern them.
Under the model, developed in the early 1970s, quarks and leptons are the most basic building blocks of matter.
There are six types of quarks, of which bottom quarks — also called beauty quarks — are among the heaviest.
The Standard Model predicted that Higgs decay would yield pairs of bottom quarks about 60 percent of the time.
But finding these quarks has been “among the most demanding analyses carried out by ATLAS so far,” the team said in a statement.
– New physics? –
Scientists probing the nature and workings of the Higgs and other particles are on the lookout for anything that does not fit with Standard Model predictions.
This is because the model doesn’t explain dark matter or dark energy, and appears to be incompatible with the theory of gravity.
Some other model of “new physics” is needed to explain these.
Proposed alternatives have included the existence of extra dimensions, or “supersymmetry” which postulates the existence of a sibling of equal mass for every known Standard Model particle.
Evidence for neither has yet been found.
The latest observation was also “consistent with” the Standard Model, said the CMS team that worked with ATLAS on the project. But it “still leaves room for contributions from new physics.”
“It’s another point for the Standard Model,” physicist Pauline Gagnon told AFP.
While it was an important scientific breakthrough, the observation was also “a disappointment (for physicists) because the Standard Model has not yet been disproven.”
Physicists have sifted through mountains of experimental data these last years to piece together a profile of the elusive Higgs boson first predicted in 1964.
They have so far observed its mass, spin, and lifetime.
“In the coming years, much more data will be collected and the precision will be improved in our quest to see if the Higgs boson reveals the presence of physics beyond the Standard Model,” said the CMS collaboration.