Three new exotic particles on the board

Many particles have already been discovered at the Large Hadron Collider (LHC, France-Switzerland). Now physicists say they’ve found evidence of three never-before-seen quark combinations: a pentaquark and a pair of tetraquarks.

The list of particles discovered at Large Hadron Collider (LHC, France-Switzerland) is long. There is the famous Higgs boson, of course. But also some 65 hadrons. And today, there are no less than three new objects exotic which are added to it. A new pentaquark and the very first pair of tetraquarks ever detected.

To understand, remember that the elementary particles what are the quarks have a habit of associating in twos or threes. They thus form hadrons, among which the proton and the neutron which are quite familiar to us. But sometimes – it is much rarer -, the quarks gather by four or even by five. To form exotic hadrons named respectively tetraquarks and pentaquarks.

A pentaquark and a pair of tetraquarks

The pentaquark discovered this time is unique in that it is the first to incorporate an s quark. Understand, a quark of flavor – this is how physicists qualify the different types of quarks that exist; they know six – ” odd “ or s for “strange”. way more “classic”this pentaquark also contains a c quark – for “charm” – and its antiquark, a quark – for “up” – and one d-quark – for “down”.

The two observed tetraquarks form a pair. It is the first time that physicists detect one. One of the tetraquarks in the pair is electrically doubly charged. The other is neutral. Both correspond to what researchers call a tetraquark at charm apparent. Understand that these tetraquarks consist of a c quark – but also of an s antiquark, an u quark and a d antiquark – without its antiquark.

And for those who are wondering, here is what Chris Parkes, the spokesperson for the LHCb collaboration, answers: “Finding new types of tetraquarks and pentaquarks, and measuring their properties will help theorists to develop a unified model of exotic hadrons – as isolated units of tightly bound quarks or as pairs of weakly bound hadrons, similar to molecules -, but also to better understand classical hadrons. »