Another difference between matter and antimatter has been found

 Finding the difference between matter and antimatter may be a bit like the scientific equivalent of playing “find 10 differences between pictures”. There is a lot at stake in this task: it is the answer to the question of why we exist. Now, in the LHCb experiment at CERN, the researchers have found another (though not yet the last) difference.

Shortly after the Big Bang — as it can be assumed — equal numbers of particles of matter and antimatter should be formed. The particle has the opposite charge and is a mirror image of its antiparticle. And when these two meet — it is annihilated. It would seem that all particles and antiparticles should immediately turn into energy in the processes of annihilation. But it didn’t, because we, the Universe, and the rest do exist. And we are made of matter. Antimatter is much rarer.

Mesons are unstable particles — but live long enough for their properties to be studied. The first mesons (pions) were observed in the first half of the 20th century in cosmic rays. Today we know that they are composed of a pair of a quark and an antiquark, and since there are 6 types of quarks themselves (physicists talk about six smells, which has absolutely nothing to do with the olfactory sensations of everyday life!), The combinations leading to different mesons really are many. Of course, each meson also has its own antiparticle, in which the respective quarks and antiquarks are turned into their antiparticles.

The breaking of CP symmetry in the decays of neutral kaons, i.e. mesons with a quark and an upper and a strange antiquark, was observed over half a century ago and was awarded the Nobel Prize. Twenty years ago, symmetry breaking was also noticed among mesons containing a beautiful quark. The mystery was, among others, the mesons with the charm quark, which in terms of mass is between the strange and the beautiful quark.

- Until now, we have not been able to measure directly and with the appropriate precision how the breaking of CP symmetry manifests itself in the decays of charm mesons. The results of the analyzes presented at the recently completed ICHEP conference of high energy physics in Bologna perfectly fill this gap — says Prof. Wojciech Wiślicki from the National Center for Nuclear Research (NCBJ), quoted in a statement from his institute. The results are available on the LHCb website.

The latest results are the result of detailed analyzes of about fifty million cases with the decay of D0 charm mesons into positively and negatively charged kaons. These decays were recorded over several years during proton collisions in the LHCb detector operating at the Large Hadron Collider at the CERN facility near Geneva. Part of the calculations related to data processing were carried out in the Świerk IT Center.

- In fact, breaking the space-charge symmetry in the decays of charm mesons was first noticed in the LHCb experiment three years ago — explains Dr. Artur Ukleja (NCBJ) in a release. — Contrary to the current measurement, however, the contemporary one did not suggest so clearly possible different matter-antimatter asymmetries between the decays of charm mesons into kaon-anti-kaon pairs and decays into pawn-antimatter pairs — he adds.

Physicists comment that the latest results from the LHCb detector experiments provide a key complement to our understanding of the difference between matter and antimatter. The Standard Model imposes restrictions on breaking the symmetry between matter and antimatter. If too many such phenomena were observed, the result would be inconsistent with the predictions of the Standard Model, signaling the existence of a new physics.

- The data presented in Bologna show that breaking the CP symmetry is rare in the case of charm mesons — concludes Prof. Wiślicki. Rarely enough that these results do not contradict the Standard Model describing elementary particles and their interactions.

However, physicists explain that the discrepancy between the amount of matter observed in the universe and the predictions of our cosmological models remains visible even after taking into account the latest results. So it is not yet the last difference between matter and antimatter. However, the mystery still does not have a complete answer. “More clues to unravel this mystery may be seen in the next stage of particle collisions in the LHC accelerator that has just begun,” physicists hope.