The existence of a new quark particle was confirmed

For decades physicists have searched in vain for bound states containing more than three quarks. Experiments now show that, in fact, such complex particles do exist in nature.

For decades physicists have searched in vain for bound states containing more than three quarks. Experiments now show that, in fact, such complex particles do exist in nature. The measurements verified the initial results obtained back in 2011 regarding the existence of an exotic particle called a dibarion consisting of six quarks.

Experiments conducted in the particle accelerator at the German research institute Jülich showed that bound states containing more than three quarks do exist in nature. The research findings were recently published in the scientific journal Physical Review Letters. The measurements verify the results obtained back in 2011, when more than 120 scientists from eight different countries discovered, for the first time ever, reliable signs of the existence of an exotic particle called a dibarion (Wikipedia) consisting of six quarks.

For a long time, physicists were able to reliably verify the existence of only two groups of hadrons: unstable particles consisting of one quark and one antiquark and aryons consisting of three quarks. Protons and neutrons, which make up the atomic nucleus, are examples of baryons. However, in recent years, increasing evidence has begun to accumulate for the existence of other types of hadrons, for example - hybrids, glueballs, Wikipedia) and multiquarks (multiquarks). In 1964 the physicist Freeman Dyson was the first to predict the existence of complex situations such as these. However, any reliable verification of these situations proved to be impossible for many years since none of the measurements could be repeated.

Only recently, other research groups - unrelated to each other - managed to find clear signs of the existence of short-lived particles consisting of four quarks, the so-called "tetraquarks" Wikipedia). "The signals we detected confirm that quarks do exist in collections of six units. This discovery could pave the way for a new physical phenomenon," says the group's spokesperson Professor Heinz Clement from the University of Tübingen.

The structure first discovered in 2011 is very short-lived and can only be traced through its decomposition products. The temporary intermediate state - the so-called "resonance state" - exists for only 10-23 seconds before it decays. This duration is so short that, for example, it is sufficient for the passage of a light beam through a distance equal to the diameter of tiny atomic nuclei. It is still not clear if all six quarks make up one compact entity or if they actually constitute a "hadronic molecule". Such a molecule would consist of a number of nuclear building blocks – for example, excited protons and neutrons bound to each other – that are much more tightly bound together than when inside the nucleus of an atom.

"The measurements we conducted at the particle accelerator in 2011 were already very accurate. However, in light of the fact that our experiments could not be repeated at any other particle accelerator in the world, we had to devise another experiment that would confirm our results," explains Professor Hans Ströher, Director of the Institute for Nuclear Physics at the Jülich Research Institute.

In order to obtain further unequivocal evidence regarding the new resonance state, the researchers scanned the range of relevant energies in an elastic scattering experiment. They bombarded a proton target with a polarized beam of heavy hydrogen nuclei called deuterons. Following the collision, the new situation was created. "Our findings are part of a bigger picture - if this particle exists, then the theoretical existence of a full range of other exotic states can be predicted," says one of the directors at the institute.
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