Physicists say they have found evidence in data from Europe’s Large Hadron Collider for three never-before-seen quark combinations, just as the world’s largest particle breaker begins a new series of high-energy experiments.
The three exotic types of particles — which include two combinations of four quarks, called tetraquarks, plus a unit of five quarks called a pentaquark — are fully consistent with the Standard Model, the decades-old theory that describes the structure of atoms.
On the other hand, scientists hope that the current operation of the LHC will provide evidence of physics that goes beyond the Standard Model to explain the nature of mysterious phenomena such as dark matter. Such evidence could point to new arrays of subatomic particles, or even extra dimensions in our Universe.
The LHC had been shut down for three years to upgrade its systems to handle unprecedented energy levels. That shutdown ended in April, and since then scientists and engineers at CERN’s research center on the Franco-Swiss border have been preparing for the resumption of today’s science operations.
The CERN control center was buzzing as the LHC began its third campaign of data collection and analysis.
“It’s a magical moment now,” CERN Director-General Fabiola Gianotti said in today’s webcast. “We have just had collisions at an unprecedented energy, 13.6 tera-electronvolts, and this opens a new era of exploration at CERN.”
Gianotti said LHC scientists expect to collect as much data in this third run as they collected in the 13 years during the collider’s previous two runs. “This, of course, will increase our opportunities for discovery or understanding of the fundamental laws of the Universe,” she said.
The 27-kilometre (17-mile) ring of superconducting magnets and its particle detectors are expected to operate around the clock for nearly four years during Phase 3.
Today’s start of operation comes 10 years and a day after LHC physicists announced their biggest discovery to date: proof of the existence of the Higgs boson, a subatomic particle that helps explain the mass phenomenon.
The three new types of subatomic particles, described today at a CERN seminar, are not quite Higgs-level revelations. But they suggest the LHC is well on its way to discovering even more never-before-seen building blocks of the Universe.
The Large Hadron Collider crushes protons at speeds near the speed of light to study combinations of quarks called hadrons.
“The more analyzes we do, the more exotic hadron types we find,” said Niels Tuning, physical coordinator of the collider’s LHCb detector, in a press release.
“We are seeing a period of discovery similar to the 1950s, when a ‘particle zoo’ of hadrons began to be discovered and eventually led to the quark model of conventional hadrons in the 1960s. We are creating the ‘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 so exotic. Protons and neutrons, for example, are made up of three quarks bound together. (In fact, the origin of the word “quark” goes back to a line of Finnegan’s Wake by James Joyce: “Three quarks for Muster Mark!”) Pions are combinations of two quarks.
Combinations of four and five quarks are much rarer and are thought to only exist for a moment before decaying into different types of particles.
Quarks come in six different “flavors”: high and low, high and low, charm and strange.
The LHCb team analyzed the decays of negatively charged B mesons and revealed the existence of a pentaquark composed of a charmed quark and a charmed antiquark, plus an up, down and strange quark. It is the first known pentaquark to include 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.
This tetraquark was spotted 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 that are loosely bound together, the same way atoms are bound together to form molecules.
“Only time and further studies of exotic hadrons will tell if these particles are one, the other or both,” says CERN.
This article was originally published by Universe Today. Read the original article.
