There is a new exotic subatomic particle in the atom buster. Physicists working with the beauty collaboration of CERN’s Large Hadron Collider (LHCb) have found a new form of the elusive four quark particle called tetraquark that they have never seen before.
The newly identified particle is made up of four quarks of the same flavor and is likely, scientists say, the first of a previously undiscovered class of particles.
The document that describes it has been uploaded to arXiv and has not yet been peer-reviewed, but it joins a growing body of evidence supporting the existence of alien particles.
Quarks are elementary particles that are one of the fundamental building blocks of matter. The protons and neutrons, the subatomic particles in the atomic nuclei that make up all visible matter (including us), each contain three quarks, bound together by the strong nuclear force.
Particles containing other configurations, such as four, five, and six quark particles, are much rarer (and six quark particles remain hypothetical). Such particles are so rare that we didn’t even have confirmation of the existence of tetraquarks until just a few years ago.
Quarks can be classified in different ways. There are six different types or flavors: up, down, up, down, weird and charming. Each of these flavors has its own antiquark particle. And they have different masses: the top, lovely and bottom quarks are the ‘heavy’ quarks.
The new tetraquark setup does two things we’ve never seen before. It is made up of four quarks of the same flavor; and all four are heavy quarks.
“The particles formed by four quarks are already exotic, and the one we have just discovered is the first formed by four heavy quarks of the same type, specifically two charming quarks and two charming antiquarks,” said the LHCb physicist and outgoing spokesman. Giovanni Passaleva of the National Institute of Nuclear Physics in Italy.
“Until now, the LHCb and other experiments have only observed tetraquarks with a maximum of two heavy quarks, and none with more than two quarks of the same type.”
The unusual particle was discovered by reviewing the data collected and retained from the two operational runs of the Large Hadron Collider, first from 2009 to 2013, and then from 2015 to 2018 after significant updates.
The team analyzed these data using a new technique to search for new particles that involves searching for excess collision events. The researchers found this excess for a type of particle called the J / ón meson, which consists of two quarks: a charm quark and a charm antiquark.
The J / ones mesons are, like all mesons, unstable; they break down in less than a zeptosecond, which means they are difficult to detect directly. What we can detect is the muon particles in which the J / mesons decompose, and infer their presence in this way.
But the stumps of muon particles that the team detected were too strong for the simple decomposition of the J / ones mesons. Interestingly, however, they were right in the middle of the predicted energy range for fully enchanted tetraquarks (since the particle type is quite charming), within the standard deviation threshold to claim the discovery of a new particle.
It is still unclear, at this stage, how the tetraquarks are structured. They may be true tetraquarks, consisting of four closely linked quarks. But it is also possible that they consist of pairs of loosely bonded two quark particles.
The same possibility is true for pentaquarks and hexaquarks: they consist of joined pairs of smaller particles, rather than a tightly bound particle.
Discovering more of these exotic particles, and more types of these exotic particles, like this new discovery, could help unravel this mystery. In turn, that could shed more light on the strong nuclear force that binds quarks into protons and neutrons, allowing matter to exist.
“These exotic heavy particles provide extreme, but theoretically quite simple, cases with which models can be tested that can then be used to explain the nature of ordinary matter particles, such as protons or neutrons,” said the particle physicist. and new LHCb spokesperson Chris Parkes of the University. from Manchester in the UK.
“So it is very exciting to see them appear in collisions at the LHC for the first time.”
The team document is available on the arXiv preprinted website.
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