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New subatomic particles fulfill Canadian physicists’ prediction

The discovery of two subatomic particles means that researchers can now eliminate them from a list of particles that have turned up at the LHC but which have not yet been identified.

Peter Ginter/Courtesy of CERN

Two Canadian physicists are relishing the news that a pair of subatomic particles they predicted more than five years ago has turned up at the Large Hadron Collider (LHC), the world's premier particle physics experiment.

The result marks another in a series of milestones for the giant accelerator near Geneva, where the Higgs boson was famously discovered in 2012 and where researchers are methodically ticking off a list of other phenomena that were predicted to emerge from their data.

The finding is significant because only by definitively identifying such effects can scientists distinguish them from those that may be due to undiscovered forces of nature – the holy grail for particle physics.

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"To really be confident when we get to those bizarre new things, we want to be understanding all the details of the expected particles," said Randy Lewis, a professor of physics at York University in Toronto.

The two new particles are among those predicted in 2009 by Prof. Lewis and Richard Woloshyn of the TRIUMF accelerator in Vancouver, who deduced their properties using an elaborate computer simulation. The appearance of these properties, precisely confirmed by scientists at the LHC and posted online on Tuesday evening, speaks to the power of the method that the Canadian team used.

"We would have been really surprised had something not turned up in the range that we predicted," Dr. Woloshyn said.

The new particles are versions of what is known as the charged Xi baryon – a short-lived cousin of the proton, which is an essential component of every atom in the universe. Like the proton, they are made of three quarks each, which are even more fundamental constituents of matter. But unlike the proton, the three quarks that the new particles are made of – known as down, bottom and strange – are not easy to observe in combination. Both of the new particles reported this week survive for less than a billionth of a trillionth of a second after they are created in high-energy collisions at the LHC.

The discovery means that researchers have now pinned down the new particles with enough precision to eliminate them from a list of particles that have turned up at the LHC but which have not yet been identified. Further analysis of the particles may yield insights in the search for new laws of physics.

"It's one thing to predict that something should exist and another to see it and study it in detail," said Michael Williams a particle physicist at the Massachusetts Institute of Technology and a member of the LHCb collaboration, which spotted the new particles.

Physicists are hoping for a cornucopia of new results starting this spring, when the LHC restarts after a two-year hiatus. In its refurbished form, the accelerator is expected to produce collisions twice as energetic as those that led to the discovery of the Higgs boson as well as this week's find.

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