Everything you see around you, is composed of elementary particles — quarks and leptons, which can be combined with the formation of larger particles, such as protons or atoms. But not limited to: these subatomic particles can also connect exotic way what we never saw. Collaboration CERN LHCb announced the discovery of a new particle which was called “pentaquarks”. The results of their work can help us to discover the many mysteries of the theory of quarks, the most important part of the Standard model.
TANK found pentaquark: what is it?
Quarks was first proposed to explain the oddities of a new particle discovered in cosmic rays and in experiments at colliders in the mid-20th century. This growing “zoo” apparently fundamental particles caused confusion in the ranks of the physicists, who adore the simplicity and order — and it is not like to produce the basic principles. The famous Italian physicist Enrico Fermi noticed the mood of his colleagues and said: “Young man, if I could remember the names of all these particles, I’d be a botanist”.
Fortunately, in the 1960s, the American physicist Murray Gell-Mann noticed in the particle zoo patterns similar to those noted by Dmitri Mendeleev, making the periodic table of chemical elements. Just as the periodic table means that there are things smaller than atoms, the theory of Gell-Man assumed the existence of a new class of fundamental particles. Particle physics was eventually able to explain that hundreds of the particles in the zoo consist of a much smaller number of truly fundamental particles called quarks.
In the Standard model there are six types of quarks — top, bottom, strange, charmed, beautiful and true. They also have satellites in the form of antimatter, it is considered that each particle has an antimatter version, almost identical, but with opposite charge. Quarks and antiquark together with the creation of particles, known as hadrons.
According to the model Gell-Mann, there are two broad classes of hadrons. One particle consists of three quarks — baryons (which include protons and neutrons that comprise the atomic nucleus) and other particles consisting of a quark and an antiquark, i.e. mesons.
Until recently, the baryons and mesons were the only types of hadrons that have been observed experimentally. But in the 1960-ies of the Gell-Mann also brought forth the possibility of more exotic combinations of quarks, such as tetraquarks (two quark and two antiquark) and pentaquarks (four quark and one antiquark).
In 2014, the LHCb is one of four giant experiments at the Large hadron Collider at CERN, have published results showing that the particle Z(4430)+ was tetraquarks. This gave rise to a flood of interest in new exotic hadrons. Then, in 2015, LHCb has announced the opening of the first ever pentaquark, which added a whole new class of particles in the family of hadrons.
The results presented LHCb today, expanded after first opening of pentaquarks due to the additional detection of such particles. It became possible thanks to the flood of new data recorded during the second run of the Large hadron Collider. Liming Zhang, Professor of Tsinghua University in Beijing and one of the physicists who conducted the measurements, said that “now we have ten times more data than in 2015, allowing us to see more interesting and subtle structure than before.” When Liming and his colleagues studied the original pentaquark, discovered in 2015, they were surprised to learn that it was divided into two parts. Original pentaquark represented two separate particles-pentaquark that were so similar masses that they are taken for one particle.
But pentaquark two for the price of one is not all that interesting news. LHCb also found a third pentaquark with a mass smaller than the first two. All three pentaquarks consist of a single bottom quark, the top two, a charmed quark and a charmed antiquark.
The big question is this: what is the exact internal structure of these pentaquarks? One of the options is that they do consist of five quarks, and mixed evenly in a single hadron. Another possibility is that pentaquark actually represent the baryon and the meson, which melted together with the formation of weakly bound molecules, like protons and neutrons bind together in the atomic nucleus.
Tomas Skwarnicki, Professor of physics at Syracuse University in new York, who also worked on the measure, said that the new state has “mass, which gives clues about the internal structure of pentaquarks”. The most likely option is that these are pentaquark baryon-meson molecules, he adds. To be absolutely sure, physicists will need to perform additional experiments and develop theory. This means that the history of pentaquarks is still far from complete.
These results conclude the week of exciting announcements LHCb, including the discovery of a new type of asymmetry of matter and antimatter. The TANK has not yet detected any particles beyond the Standard model, which could help explain mysteries like dark matter, the invisible and unknown substance that comprises the bulk of matter in the Universe.
However, these exciting measurements show that much remains to learn about the particles and forces of the Standard model. Perhaps our best chance to find answers to the big questions facing fundamental physics, is in a more detailed study of the particles, which we already know, rather than opening a new one. In any case, much remains to be open.
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