Did CERN really discover the new baryon

Large Hadron Collider: CERN physicists identify new particle

The physicists at CERN have made a new find: As they report in a preliminary study that has not yet been assessed, they have discovered a particle that consists of four identical and, above all, noticeably heavy charm quarks. So far, researchers have not observed such a combination - two quarks and two antiquarks of the same kind in one compound.

Quarks normally appear either in combinations of two, or when three of them form a so-called baryon, such as a proton or a neutron. Exactly which particle, a so-called hadron, is created depends on the type of quarks and antiquarks. Because there are actually six types that differ in their mass, among other things: Up, Down, Top, Bottom, Charm and Strange Quarks, with their respective counterparts. Particles composed of more than three quarks have only been observed in experiments so far. But even such hadrons made up of four, five or six quarks (penta-, tetra- and hexaquarks) never forge communities with particles of the same kind. The recently discovered particle now contradicts this rule and may provide evidence of a new class.

The "bump" is the decisive factor

The large research group around Roel Aaji came across the new particle by sifting through the data from past experiments of the LHCb detector at CERN, which date from 2009 to 2013 and 2015 to 2018. In doing so, they concentrated on events in which a noticeably high number of collisions in the accelerator were detected. They are literally represented in the data as so-called "bumps" (elevations) that should exceed the standard value of five sigma. If this value is reached, the results can be considered significant and not random, because the probability that it is a chance find is one in 3.5 million. That was the case for the new particle, named by the researchers as X (6900). According to the physicists, the data show that it is a very unusual combination of four heavy charm quarks. Usually, as mentioned, even multi-part hadrons contain at least two different types of quarks.

In addition to the peculiarity of the tetraquark, such exotic particles are interesting for physicists for another reason: They try to find out more about the so-called strong interaction from them. Quarks are fundamental building blocks of matter. They are in protons and neutrons, which in turn form the atomic nuclei. The particles are held together by the interaction, also known as the strong nuclear force. It represents one of the four basic forces in physics.