Physicists say they’ve found evidence of three never-before-seen combinations of quarks in data from Europe’s Large Hadron Collider, just as the world’s largest particle smasher begins a new round of high-energy experiments.
The three exotic types of particles — including two four-quark combinations known as tetraquarks and a five-quark unit called a pentaquark — are fully consistent with the Standard Model, the decades-old theory that governed the structure of describes atoms.
In contrast, scientists hope the current run of the LHC will provide clues to physics beyond the Standard Model to explain the nature of mysterious phenomena like dark matter. Such evidence could point to new arrangements of subatomic particles or even additional dimensions in our universe.
The LHC had been shut down for three years to upgrade its systems for unprecedented power levels. That shutdown ended in April, and since then scientists and engineers at the CERN research center on the French-Swiss border have been preparing for today’s resumption of scientific operations.
CERN’s control center was in turmoil as the LHC began its third data collection and analysis.
“It’s a magical moment now,” CERN Director General Fabiola Gianotti said during today’s webcast. “We just had collisions with an unprecedented energy, 13.6 tera-electron volts, and this opens a new era of exploration at CERN.”
Gianotti said scientists at the LHC expect to collect as much data during this third run as they have collected over 13 years during the collider’s previous two runs. “Obviously this will increase our ability to discover or understand the fundamental laws of the universe,” she said.
The 27-kilometer ring of superconducting magnets and its particle detectors are expected to operate 24/7 during Run 3 for nearly four years.
Today’s start of the run comes 10 years and a day after LHC physicists announced their biggest discovery yet: evidence for the existence of the Higgs boson, a subatomic particle that helps explain the phenomenon of mass.
The three new types of subatomic particles described during a CERN seminar today are not Higgs-level revelations. But they suggest that the LHC is searching for even more previously unseen building blocks of the universe.
The Large Hadron Collider smashes protons at nearly the speed of light to study combinations of quarks known as hadrons.
“The more analyzes we do, the more types of exotic hadrons we find,” said Niels Tuning, physics coordinator for the collider’s LHCb detector, in a press release.
“We are experiencing a similar phase of discovery as in the 1950s, when a ‘particle zoo’ of hadrons was discovered and eventually led to the quark model of conventional hadrons in the 1960s. We create ‘Particle Zoo 2.0’.”
LHCb spokesman Chris Parkes said studying new combinations of quarks “will help theorists develop a unified model of exotic hadrons, the precise nature of which is largely unknown.”
Most hadrons are not that exotic. For example, protons and neutrons are made of three quarks bound together. (In fact, the origin of the word “quark” goes back to a line from Finnegans Wake by James Joyce: “Three quarks for Muster Mark!”) Pions are two-quark combinations.
Four-quark and five-quark combinations are much rarer and are thought to exist for only a moment before decaying into different types of particles.
Quarks come in six different “flavors”: up and down, up and down, charming and weird.
The LHCb team analyzed the decays of negatively charged B mesons and found evidence for the existence of a pentaquark consisting of a charm quark and a charm antiquark, as well as an up, down and strange quark. It is the first known pentaquark containing a strange quark.
The two newly identified tetraquarks involve a “doubly charged” combination of four quarks: a charm quark, a strange antiquark, an up quark, and a down antiquark.
This tetraquark was discovered in combination with its neutral counterpart, which has a charm quark, a strange antiquark, an up antiquark, and a down quark. CERN says this is the first time a pair of tetraquarks has been observed together.
Some theoretical models visualize exotic hadrons as single units of tightly bound quarks. Others see them as pairs of standard hadrons loosely bound together, much like atoms are bound together to form molecules.
“Only time and further study of exotic hadrons will tell whether these particles are one, the other, or both,” says CERN.
This article was originally published by Universe Today. Read the original article.