A brand new exotic particle has just been identified at CERN: the tetraquark

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The European Organization for Nuclear Research (CERN) recently announced the discovery of a new physical particle called a ‘tetraquark’, which could help scientists better understand how protons and neutrons are formed.

Many mysterious elementary particles

Described in a document viewable on the pre-publication server ArXiv, the discovery of this tetraquark created from four charmed quarks (one of six types or ” flavors »Quarks) is a major breakthrough in a research process that started several decades ago. Fruits of the collaboration LHCb at CERN, the largest particle physics center in the world located near Geneva, this work, which involved more than 800 researchers, was presented at a recent seminar and should soon be the subject of peer review.

Due to the recent nature of this discovery, physicists generally know little about the tetraquark itself. However, this should help them better understand how quarks bind together to form particles such as protons or neutrons.

Quarks are elementary particles, that is to say, as far as we can verify, at the base of everything. So far, researchers have observed them coming together in groups of two or three to form hadrons (composite particles), and also hypothesized that there were hadrons of four and five quarks.

Particles composed of four quarks are already exotic, and the one we have just discovered is the first to be composed of four heavy quarks of the same type, namely two charmed quarks and two charmed antiquarks. “, Explain Giovanni Passaleva, spokesperson for the LHCb collaboration. ” Until now, the LHCb and other experiments have only observed tetraquarks with two heavy quarks at most and none with more than two quarks of the same type.. “

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An ideal “laboratory” for studying strong interaction

For the researchers, these unusual particles constitute a ” laboratory »Ideal for studyingstrong interaction, which represents one of the four known fundamental forces of nature and constitutes what elementary particles bind together to form atoms and matter. Therefore, understanding it better could allow physicists to better understand which particles should and should not be able to form under normal conditions.

From this point of view, the new tetraquark is ideal, because it is a relatively simple particle allowing scientists to test their current models. Although researchers still do not know whether or not this is a ” real tetraquark », Ie if it is a particle of four quarks or two particles of two quarks interacting in the state of a molecule.

Scientists discovered this tetraquark by looking for an excess of collisions over a known background value (taking the form of peaks or bumps) in the recordings of the first and second series of the Large Hadron Collider (most powerful particle accelerator in the world), obtained between 2009 and 2013 and between 2015 and 2018 respectively.

This bump has a statistical significance of more than five standard deviations, which is the usual threshold to claim the discovery of a new particle, explain the authors of the study. And it turns out that the latter also corresponds to the predicted mass of the charmed quark particles.

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