Physicists working at the world’s largest atom smasher, the Large Hadron Collider, have already found what they believe are hints pointing to the existence of the last undiscovered particle in the Standard Model of Physics, nicknamed the "God particle" because it is thought to answer fundamental questions about the universe.
But they have so far been unable to prove that the Higgs boson is anything more than a theoretical construct.
That may be about to change, however, as physicists in Australia and Switzerland are expected to announce they have gathered enough data to say with more certainty that the particle exists, though they may stop short of declaring the Higgs boson has been officially "discovered."
To mark the occasion in Canada, a few dozen physicists and other experts who have been working on the hunt for the Higgs boson at TRIUMF, a subatomic research lab located at the University of British Columbia, will be gathering to witness what could be a historic announcement in the scientific community.
“We’ll basically have a pajama party where we watch live the public unveiling of the results,” said Oliver Stelzer-Chilton, a researcher with TRIUMF who has been working on the ATLAS data.
Decades of work
The buildup of anticipation follows decades of work and billions of dollars spent as researchers at the European Organization for Nuclear Research, or CERN, worked to discover the particle.
Two experiments known as ATLAS and CMS at CERN's vast complex on the Swiss-French border have been gathering data in the hopes of glimpsing the Higgs boson for the first time.
The ATLAS collaboration includes researchers from around the world, including at a handful of Canadian universities, who have been working to analyze the vast amounts of data generated at CERN. One-tenth of the data generated by ATLAS is sent to a supercomputer site in Vancouver.
But the work has been gradual and there likely won't be a "Eureka moment," said Rob McPherson, a spokesperson for ATLAS' Canadian contingent, which includes about 150 researchers.
“It’s not an overnight ‘yes, the experiment worked,’” he said. “It’s really about progress, where we start to see a signal, then we’re sure we observed something but we’re not sure if it’s the Higgs yet, then we measure the properties of what we’re seeing to determine if it’s exactly what the theory predicts or not.”
Physicists leading the project won’t say the Higgs boson has been discovered until they can say with 99.99994 per cent confidence that they’re right, based on the data. That could take months or years to accomplish.
Smashing atoms to find Higgs
The Large Hadron Collider is expected to help scientists find the Higgs boson, if it exists, because it allows them to observe extremely high-energy collisions similar to those during the Big Bang. Those could in turn produce the previously undetected particle.
If a Higgs boson that behaves according to the Standard Model exists, Higgs's theory would be confirmed. However, if the Higgs boson doesn't behave according to predictions or if it is not detected at all, that would open the door to completely new physics outside the Standard Model and our current understanding of nature.
Inside the Large Hadron Collider, the ATLAS experiment collides protons, some of the building blocks of atoms. The collisions are expected to produce Higgs bosons, which have an unknown mass.
Each proton is made up of smaller particles called quarks and gluons that can have a wide range of energies following the collisions. At that point, the particles coming out of the collision hit a detector, which measures their energies. Theory predicts how many Higgs bosons should be produced by a collision of a certain energy if it has a certain mass.
Higgs bosons are extremely short-lived and decay before they can ever be detected. However, when they decay, a number of slightly longer-lived particles are expected to be produced. Those in turn decay into particles that can be detected.
Based on the particles detected, the researchers need to reconstruct the decay sequence and look for pairs of particles whose combined masses add up to the same number more often than might otherwise be expected.
Those are the types of signals that researchers have seen so far that hint at the existence of the Higgs boson at lower masses or energies.