Large Hadron Collider could be about to find a new particle, upending our understanding of physics

The Large Hadron Collider could be about to find a new particle and upend our understanding of physics.

The atom smasher at CERN is getting turned back on for what could be even more important work than its biggest discovery yet, when it revealed the Higgs boson four years ago. The world’s biggest machine of its type is getting turned on at an even greater power, and as such might it might be able to find particles that have previously only been hinted at.

If they are found, they could lead to a re-writing of some of the most fundamental parts of physics. The Standard Model of physics, which explains how our universe is structured, has some important gaps – around dark matter, and potential other dimensions – which could be filled in by the new discovery.

When it gets switched back on, scientists will be looking to explore faint signs of a new particle that were picked up in December. Since then, researchers have been theorising wildly – but experts have cautioned that nothing will be known until more work can be done.

"It's a hint at a possible discovery," said theoretical physicist Csaba Csaki, who isn't involved in the experiments. "If this is really true, then it would possibly be the most exciting thing that I have seen in particle physics in my career — more exciting than the discovery of the Higgs itself."

After a wintertime break, the Large Hadron Collider, or LHC, reopened on 25 March to prepare for a restart in early May. CERN scientists are doing safety tests and scrubbing clean the pipes before slamming together large bundles of particles in hopes of producing enough data to clear up that mystery. Firm answers aren't expected for weeks, if not until an August conference of physicists in Chicago known as ICHEP.

On Friday, the LHC was temporarily immobilised by a weasel, which invaded a transformer that helps power the machine and set off an electrical outage. CERN says it was one of a few small glitches that will delay by a few days plans to start the data collection at the $4.4 billion collider.

The 2012 confirmation of the Higgs boson, dubbed the "God particle" by some laypeople, culminated a theory first floated decades earlier. The "Higgs" rounded out the Standard Model.

The LHC's Atlas and Compact Muon Solenoid particle detectors in December turned up preliminary readings that suggested a particle not accounted for by the Standard Model might exist at 750 Giga electron Volts. This mystery particle would be nearly four times more massive than the top quark, the most massive particle in the model, and six times more massive than the Higgs, CERN officials say.

More data is needed to iron those possibilities out, and even then, the December results could just be a blip. But with so much still unexplained, physicists say discoveries of new particles — whether this year or later — may be inevitable as colliders get more and more powerful.

Dave Charlton, who heads the Atlas team, said the December results could just be a "fluctuation" and "in that case, really for science, there's not really any consequence ... At this point, you won't find any experimentalist who will put any weight on this: We are all very largely expecting it to go away again."

"But if it stays around, it's almost a new ball game," said Charlton, an experimental physicist at the University of Birmingham in Britain. The unprecedented power of the LHC has turned physics on its head in recent years. Whereas theorists once predicted behaviors that experimentalists would test in the lab, the vast energy being pumped into CERN's collider means scientists are now seeing results for which there isn't yet a theoretical explanation.

"This particle — if it's real — it would be something totally unexpected that tells us we're missing something interesting," he said. Whatever happens, experimentalists and theorists agree that 2016 promises to be exciting because of the sheer amount of data pumped out from the high-intensity collisions at record-high energy of 13 Tera electron Volts, a level first reached on a smaller scale last year, and up from 8 TeVs previously. (CERN likens 1 TeV to the energy generated by a flying mosquito: That may not sound like much, but it's being generated at a scale a trillion times smaller.)

In energy, the LHC will be nearly at full throttle — its maximum is 14 TeV — and over 2,700 bunches of particles will be in beams that collide at the speed of light, which is "nearly the maximum," CERN spokesman Arnaud Marsollier said. He said the aim is to produce six times more collisions this year than in 2015.

"When you open up the energies, you open up possibilities to find new particles," he said. "The window that we're opening at 13 TeV is very significant. If something exists between 8 and 13 TeV, we're going to find it."

Still, both branches of physics are trying to stay skeptical despite the buzz that's been growing since December.

Csaki, a theorist at Cornell University in Ithaca, New York, stressed that the preliminary results don't qualify as a discovery yet and there's a good chance they may turn out not to be true. The Higgs boson had been predicted by physicists for a long time before it was finally confirmed, he noted.

"Right now it's a statistical game, but the good thing is that there will be a lot of new data coming in this year and hopefully by this summer we will know if this is real or not," Csaki said, alluding to the Chicago conference. "No vacation in August."

Additional reporting by agencies