the pentaquark and the very first pair of tetraquarks

LHCb discovers three new exotic particles: the pentaquark and the first-ever pair of tetraquarks

The new pentaquark, shown here as a pair of standard hadrons loosely connected in a molecular-like structure, consists of a charm quark and a charm antiquark, as well as an up, a down, and a strange quark. Photo credit: CERN

The international LHCb collaboration at the Large Hadron Collider (LHC) has observed three never-before-seen particles: a new type of pentaquark and the first-ever pair of tetraquarks containing a new type of tetraquark. The results, presented today at a CERN seminar, add three new exotic members to the growing list of new hadrons found at the LHC. They will help physicists better understand how quarks combine to form these composite particles.

Quarks are elementary particles and come in six flavors: top, bottom, charm, weird, top and bottom. They usually combine in groups of two and three to form hadrons like the protons and neutrons that make up atomic nuclei. More rarely, however, they can also combine to form four-quark and five-quark particles, the so-called “tetraquarks” and “pentaquarks”. These exotic hadrons were predicted by theorists at the same time as conventional hadrons some six decades ago, but only relatively recently, in the last 20 years, have they been observed by LHCb and other experiments.

Most of the exotic hadrons discovered in the last two decades are tetraquarks or pentaquarks, containing one charm quark and one charm antiquark, the remaining two or three cottage cheese be an up, down or strange quark or their antiquark. But in the last two years, LHCb has discovered different types of exotic hadrons. Two years ago, the collaboration discovered a tetraquark composed of two charm quarks and two charm antiquarks, and two “open charm” tetraquarks composed of a charm antiquark, an up quark, a down quark, and a strange antiquark. And last year it found the first-ever instance of a “double open charm” tetraquark with two charm quarks and an up and a down antiquark. Open charm means that the particle contains a charm quark without an equivalent antiquark.

LHCb discovers three new exotic particles: the pentaquark and the first-ever pair of tetraquarks

The two new tetraquarks, shown here as single units of tightly bound quarks. One of the particles consists of a charm quark, a strange antiquark and an up quark and a down antiquark (left), the other consists of a charm quark, a strange antiquark and an up antiquark and a down Quark (right) . Photo credit: CERN

The discoveries announced today by the LHCb collaboration include new types of exotic hadrons. The first type observed in an analysis of “decays” of negatively charged B mesons is a pentaquark, which consists of a charm quark and a charm antiquark, as well as an up, a down, and a strange quark. It is the first pentaquark containing a strange quark. The finding has a whopping 15 standard deviations of statistical significance, well in excess of the 5 standard deviations required to claim the observation of a particle particle physics.

The second type is a doubly electrically charged tetraquark. It is an open-charm tetraquark composed of a charm Quark, a strange antiquark and an up quark and a down antiquarian, and it was discovered along with its neutral counterpart in a joint analysis of positively charged and neutral B meson decays. The new tetraquarks, observed with a statistical significance of 6.5 (doubly charged particle) and 8 (neutral particle) standard deviations, represent the first time a pair of tetraquarks has been observed.

“The more analyzes we do, the more types of exotic hadrons we find,” says LHCb physics coordinator Niels Tuning. “We are witnessing a phase of discovery similar to that of the 1950s when a ‘particle zoo’ of hadrons was discovered and eventually led to discovery Quark Model of conventional hadrons in the 1960s. We create ‘Particle Zoo 2.0’.”

“Finding new types of tetraquarks and pentaquarks and measuring their properties will help theorists develop a unified model of exotic hadrons whose exact nature is largely unknown,” says LHCb spokesman Chris Parkes. “It will also help to better understand conventional hadrons.”

while a few theoretical models describe exotic hadrons as single units of tightly bound quarks, other models see them as pairs of standard hadrons loosely connected in a molecular-like structure. Only time and further study of exotic hadrons will tell if this is the case particles are one, the other, or both.


New exotic matter particle, a tetraquark, discovered


More information:
Read more on the LHCb website: lhcb-outreach.web.cern.ch/2022 … its-neutral-partner/

Citation: LHCb discovers three new exotic particles: the pentaquark and the first-ever pair of tetraquarks (July 5, 2022) retrieved July 5, 2022 from https://phys.org/news/2022-07-lhcb-exotic-particles-pentaquark – first.html

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