Physicists say they’ve found evidence in data from Europe’s Large Hadron Collider for three never-before-seen combinations of quarks, just as the world’s largest particle destroyer begins another round of high-energy experiments.
The three exotic types of particles—including two combinations of four quarks known as tetraquarks, plus a unit of five quarks called pentaquarks—are fully consistent with the Standard modelthe decades-old theory describing the structure of atoms.
In contrast, scientists hope the LHC’s current run will provide evidence of physics beyond the Standard model to explain the nature of mysterious phenomena, such as: dark matter† Such evidence could point to: new series of subatomic particlesor even extra dimensions in our universe†
The LHC was shut down for three years to upgrade its systems to handle unprecedented levels of energy. That shutdown ended in Apriland since then, scientists and engineers at the CERN research center on the Franco-Swiss border have been gearing up for the resumption of today’s scientific operations.
CERN’s control center was in turmoil as the LHC embarked on its third set of data collection and analysis.
“It’s a magical moment now,” said CERN Director General Fabiola Gianotti during… today’s webcast† “We’ve just had collisions with an unprecedented energy, 13.6 tera-electron volts, and this opens up a new era of exploration at CERN.”
Gianotti said the LHC scientists expect to collect as much data as they have collected during this third run over the course of 13 years during the collider’s previous two runs. “This will, of course, increase our ability to discover or understand the fundamental laws of the universe,” she said.
The 27-kilometer-round (17-mile-round) ring of superconducting magnets and its particle detectors are expected to operate 24 hours a day for nearly four years during Run 3.
The start of today’s run comes 10 years and a day after LHC physicists announced their biggest discovery yet: evidence for the existence of the Higgs bosona subatomic particle that helps explain the phenomenon of mass.
The three new types of subatomic particles, described today during a CERN seminar, aren’t exactly Higgs-level revelations. But they do suggest that the LHC is on its way to discovering even more previously invisible building blocks of the Universe.
The Large Hadron Collider crushes protons at speeds close to the speed of light to study combinations of quarks known as hadrons†
“The more analyzes we do, the more species of exotic hadrons we find,” said Niels Tuning, physics coordinator for the collider’s LHCb detector, said in a press release†
“We are witnessing a period of discovery similar to the 1950s when a ‘Particle Zoo’ of hadrons was discovered and eventually led to the quark model of conventional hadrons in the 1960s. We are creating ‘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 exact nature of which is largely unknown.”
Most hadrons are not that exotic. For example, protons and neutrons are made up of three quarks bonded together. (In reality, the origin of the word “quark” goes back to a line of Finnegan’s Wake by James Joyce: “Three quarks for Muster Mark!”) Pawns are combinations of two quarks.
Combinations of four quarks and five quarks are much rarer, and are thought to be exist for just a moment before it decays into different kinds of particles.
Quarks come in six different “flavors”: up and down, up and down, charming and strange.
The LHCb team analyzed the decay of negatively charged B mesons and saw evidence for the existence of a pentaquark consisting of a charm quark and a charm antiquark, plus an up, down and strange quark. It is the first pentaquark known to contain a strange quark.
The two newly identified tetraquarks comprise a “doubly electrically charged” combination of four quarks: a charm quark, a strange antiquark, an up quark and a down antiquark.
That tetraquark was spotted paired 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 have been observed together.
Some theoretical models visualize exotic hadrons as discrete units of tightly bound quarks. Others see them as pairs of standard hadrons loosely bonded together, similar to the way atoms are bonded together to form molecules.
“Only time and more studies of exotic hadrons will tell if these particles are one, the other, or both,” CERN says.