Scientists working at the Large Hadron Collider (LHC, its acronym in English) – an accelerator massive particles which straddles the border between France and Switzerland – have announced the discovery of a new particle, called of pentaquark.
An illustration of a possible configuration of quarks in a particle pentaquark
Photo: CERN
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The first prediction of the existence of pentaquark was made in the 1960s, but as well as the Higgs boson (or “God particle”), scientists failed to detect the pentaquark for decades.
In 1964, two physicists, Murray Gell-Mann and George Zweig, proposed separately the existence of subatomic particles known as quarks.
their theories said the most important properties of particles known as baryons and mesons could be best explained if, in fact, they were made up of even smaller particles. Zweig called these under “aces” particles, a name that was not very popular.
Gell-Mann called them “quark”, the name by which they are known today.
The model proposed by the scientists also allowed the discovery of other states of quarks, as the pentaquark. This particle – before purely theoretical – is made up of four quarks and an antiquark (the antimatter equivalent of an ordinary quark).
The announcement is the equivalent to discovering a new form of matter, and was published in the journal Physical Review Letters .
Discovery
During the first decade of the 2000s, several teams of scientists claimed to have detected the pentaquarks, but these findings were questioned by other experiments .
“There’s quite a story with pentaquarks, so we are being very careful in presenting this research,” he told BBC Patrick Koppenburg, physical LHC coordinator at CERN, the European laboratory nuclear research, the Franco-Swiss border.
“It’s just the word ‘pentaquark’, which seems to be cursed in some way because they were made many discoveries that then were overcome by new results showing that the former were actually fluctuations, and no real signs (the existence of the particle), “he added.
An alternative configuration for the pentaquark, showing a particle meson (a quark and an antiquark) and a baryon (three quarks)
Photo : CERN
Physicists have studied how a subatomic particle, the Lambda b, turned into three other particles within the Large Hadron Collider. The analysis showed that intermediate states were involved in some occasions, in the production of three particles.
These intermediate states were called Pc (4450) and Pc + (4380) +.
“We examined all the possibilities for these signs and concluded that they can only be explained (the existence) of the states (of matter) pentaquark” said physicist LHC Tomasz Skwarnicki, the Syracuse University in the United States.
Previous experiments had only measured the so-called mass distribution, in which a statistical peak may appear against the background noise, a possible sign of the existence of a new particle.
But the collider allowed the researchers to analyze data from other perspectives, especially the four corners defined by the different directions of the trajectories of the particles within the LHC.
“We are turning this problem (a problem) of a dimension in a five-dimensional … we were able to describe everything that happens in transforming (the Lambda particle b),” he said Koppenburg, which identified the first signs in 2012.
“There’s no way we’ve seen to be due to anything other than the addition of a new particle that had not been observed before. ”
“The pentaquark is not only a new particle any … It represents a way to add quarks, the main components of protons and neutrons common, in a pattern that has never been observed before in more than 50 years of experimental search, “said Guy Wilkinson, spokesman for the LHC.
“Studying their properties may provide a better understanding of how ordinary matter, protons and neutrons are made.”
The Large Hadron Collider was switched on again in April after a shutdown that lasted two years to complete a repairs and upgrades program.
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