A team of scientists at CERN on 14 July 2015 announced discovery of the exotic subatomic particles pentaquarks which so far had existed in theory only. The discovery amounting to new state of matter was made during Large Hadron Collider beauty (LHCb) experiment at LHC in CERN, Geneva.
The team of scientists who have discovered the pentaquark has submitted a paper reporting these findings to the journal Physical Review Letters.
What are pentaquarks?
Pentaquark is a sub-atomic particle composed of five-quarks (four quarks and an antiquark). These are not new particles but simply aggregation of quarks, the fundamental constituents of ordinary protons and neutrons, similar to baryons wherein protons and neutrons are made up of three quarks.
How pentaquark was discovered?
To discover pentaquark, LHCb researchers examined the decay of Lambda b baryon into three other particles, J-psi meson (or psion), a proton and a charged kaon.
On studying the spectrum of masses of the J-psi and the proton, it was revealed that there exists a transition state with never-seen-before particles Pc(4450)+ and Pc(4380)+.
After the study of the masses of these particles, it was concluded by researchers that it can only be explained with pentaquark states, which more precisely is formed of two up quarks, one down quark, one charm quark and one anti-charm quark.
Why the discovery is significant?
The discovery of pentaquark is a significant development as so far the search for this sub-atomic particle has been proved to be inconclusive.
Further, the LHCb experiment is different from the previous searches in the sense that it has been able to look for pentaquarks from many perspectives, with all pointing to the same conclusion.
Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.
The next step in the analysis will be to study how the quarks are bound together within the pentaquarks.
Background
The term pentaquark was coined by Harry J Lipkin in 1987 and the first evidence for pentaquark was recorded in a lab in Japan.
However, scientists have been looking for pentaquarks since 1964, when two physicists - Murray Gell Mann and George Zweig - independently proposed the existence of quarks.
Although they theorised the existence of the particles known as baryons and mesons but their model allowed the existence of other quark composite states, such as a hypothetical pentaquark.
Zweig coined the term "aces" for the three fractionally charged subatomic particles that constituted protons and neutrons, but it was Gell-Mann's name "quark" that stuck.
Gell-Mann was awarded the Nobel Prize in physics for this work in 1969.
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