Physicist: We discovered pentaquarks when physicists were beginning to doubt their existence
LHC. Photo: Fotolia
Our discovery of pentaquark, a new kind of particle, occurred when physicists had lost all hope that these particles would be found. Past observations of these particles turned out to be false, which weakened the morale of physicists - said Prof. Tomasz Skwarnicki.
Prof. Skwarnicki from the University of Syracuse, US was one of the main authors of the paper about the discovery of pentaquarks, which in mid-July was sent to the prestigious journal "Physical Review Letters" (preprint: http://arxiv.org/abs/1507.03414 ) by the so-called. LHCb collaboration, a team working on the experiment at the European Organization for Nuclear Research (CERN).
"In the 1960s there were theories that the previously known particles (protons, neutrons) consisted of something smaller" - Prof. Skwarnicki told PAP. He explained that according to the theory of quarks, particles consist of either three quarks or one quark and one antiquark. "The matter of which we are made is baryons, objects that consist of three quarks. But in experiments we often see other particles, which have one quark and one antiquark. The theory of quarks was supposed to explain that" - explained the researcher. He admitted that theorists had long suspected that there could also be objects arising from assemblies of, for example, two pairs quark-antiquark (tetraquarks) or a pair of quark-antiquark with a triquark object (pentaquarks).
Although models do not exclude the existence of tetra and pentaquarks, for decades scientists had been unable to experimentally show that the particles really existed. In the meantime, there were many reports about the discovery of pentaquarks (for example in 2003-2005), but all these experiments proved wrong - they could not be confirmed in further, more detailed studies. Theories that predicted the existence of pentaquarks remained unconfirmed.
"It\'s an interesting psychological effect: after this series of experimental errors, physicists began to give up. They came to the conclusion that while pentaquarks could exists, for some reason they do not. Our discovery was unexpected, because most physicists had stopped thinking about this topic" - said Prof. Skwarnicki.
However, thanks to experiments carried out at CERN in the LHCb experiment the best tetraquark candidate was finally confirmed (publication of 2014) and a pentaquark found (results sent for publication in mid-July.) .
"I\'m not afraid that someone will invalidate this finding. In our case, the signal indicating that we are dealing with a pentaquark is so clear that it will probably be quickly confirmed as genuine. In all previous, erroneous measurements, similar signals were much weaker - at the level of measurement error - which they then indeed proved to be" - assured the researcher.
Pentaquark has a really short lifespan - only a hundredth part of one sextillionth of a second (10^-23 sec.). The only thing scientists can see in the Large Hadron Collider is what\'s left after the collapse of these objects. The research shows that the observed pentaquarks consist of three light quarks: two up quarks, one down quark, and two heavy quarks: charm quark and charm antiquark. "This is the first measurement that says that such objects exist" - summed up Prof. Skwarnicki.
Scientist has been living in the US for over 20 years, but the beginnings of his scientific career are associated with Poland: he studied physics at the Jagiellonian University, and he did his Ph.D. at the Institute of Nuclear Physics PAS in Kraków. "The fact that I am now successful, is undoubtedly associated with how strong was the physics community in Kraków" - noted the researcher.
PAP - Science and Scholarship in Poland, Ludwika Tomala
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