Scientists at the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN) have confirmed the existence of a new class of the exotic particles known as “tetraquarks.” The discovery was made by researchers from Syracuse University who analyzed the data gathered by the LHCb experiment at CERN.
“When I first saw the structures jumping out of the data, little did I know this analysis would be such an aporetic saga,” LHCb researcher Thomas Britton, who analyzed the data as part of his PhD thesis at Syracuse University, told Symmetry magazine. “We looked at every known particle and process to make sure these four structures couldn’t be explained by any pre-existing physics. It was like baking a six-dimensional cake with 98 ingredients and no recipe — just a picture of a cake.”
Quarks, the fundamental particles that make up protons and neutrons, come in six different “flavors” — up, down, strange, top, bottom and charm. Each quark has an antimatter equivalent known as antiquark. Quarks usually come in packages of two or three. Both protons and neutrons — contained within the nucleus of an atom — are made up of three quarks bound together.
The 1964 model that first proposed the existence of quarks also postulates the existence of tetraquarks, composed of four quarks, and pentaquarks, composed of five quarks.
Last August, scientists at CERN’s Large Hadron Collider announced the discovery of a pentaquark, in which quarks were arranged in a pattern never before seen in over 50 years of experimental searches. Prior to that, in 2014, experiments at LHC had also provided strong evidence of the existence of a tetraquark.
And, earlier this year, physicists at the DZero collaboration — one of the two experiments conducted at Fermilab’s Tevatron Collider before it was shut down in 2011 — announced the discovery of X(5568), believed to contain four distinct flavors of quarks and antiquarks — bottom, strange, up and down. However, the discovery was met with skepticism after scientists at CERN failed to confirm it.
The new particles, described in two studies published online on the arXiv server, have been named X(4140), X(4274), X(4500) and X(4700), based on their respective masses in mega-electronvolts. Each particle contains two charm quarks and two strange quarks. This marks the first time four-quark particles composed entirely of heavy quarks have been discovered.
“What we have discovered is a unique system,” Tomasz Skwarnicki, a physics professor at Syracuse University, who was part of the team that confirmed the existence of the tetraquark particles, told Symmetry magazine. “We have four exotic particles of the same type; it’s the first time we have seen this and this discovery is already helping us distinguish between the theoretical models.”