Physicists from the Large Hadron Collider beauty (LHCb) collaboration at CERN’s Large Hadron Collider (LHC) today announced the sighting of a strange pentaquark, a doubly charged tetraquark and its neutral partner.
Quarks are elementary particles and come in six flavors: high, low, charm, strange, high, and low.
They usually combine in groups of two or three to form hadrons such as the protons and neutrons that make up atomic nuclei.
More rarely, however, they can also combine into four- and five-quark particles, or into tetraquarks and pentaquarks.
These exotic hadrons were predicted by theorists at the same time as conventional hadrons about six decades ago, but only relatively recently, within the last 20 years, have they been observed by LHCb and d ‘other experiences.
Most of the exotic hadrons discovered in the last two decades are tetraquarks or pentaquarks containing a charmed quark and a charmed antiquark, with the remaining two or three quarks being an up, down or strange quark or their antiquarks.
In 2020, LHCb physicists discovered a tetraquark consisting of two charmed quarks and two charmed antiquarks, and two “open charm” tetraquarks consisting of a charmed antiquark, an up quark, a down quark and a strange antiquark.
And in 2021, they found the first-ever instance of a “double open charm” tetraquark with two charmed quarks and an up and down antiquark.
Discoveries announced today by the LHCb collaboration include new exotic hadrons: the strange pentaquark PΛψs(4338)0the doubly charged tetraquark Tacs0(2900)++ and its neutral partner Tacs0(2900)0.
Observed in an analysis of the decays of negatively charged B mesons, PΛψs(4338)0 is a pentaquark composed of a charmed quark and a charmed antiquark and an up quark, a down quark and a strange quark. It is the first pentaquark containing a strange quark.
Jacs0(2900)++ is an open charm tetraquark composed of a charm quark, a strange antiquark, an up quark and a down antiquark.
He was spotted with his neutral counterpart, Tacs0(2900)0in a conjoint analysis of the decays of positively charged and neutral B mesons.
“The more analyzes we do, the more exotic hadron types we find,” said LHCb physics coordinator Dr Niels Tuning.
“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 a ‘particle zoo 2.0’,” he added.
“Discovering new types of tetraquarks and pentaquarks and measuring their properties will help theorists develop a unified model of exotic hadrons, the exact nature of which is largely unknown,” said Dr. Chris Parkes, spokesperson for the LHCb collaboration.
“It will also help to better understand conventional hadrons.”