Nepedia
Back to Discover
Advanced Reader
⚛️

Pentaquark

physical science Maturity 11-13 Next article →

A pentaquark is a unique type of subatomic particle. It is made of four quarks and one antiquark bound together. Most particles made of quarks are very common. These common particles are called hadrons. Hadrons can be mesons, which have one quark and one antiquark. They can also be baryons, which usually have three quarks. Because a pentaquark has five quarks, it is called an exotic baryon. Understanding these particles helps scientists learn about the fundamental forces of nature.

Pentaquark
Pentaquark

Quarks are the tiny building blocks of matter. They have mass, electric charge, and a property called colour charge. They also have a property called flavour. Flavour describes the specific type of quark, such as up, down, strange, charm, top, or bottom. Quarks are never found alone because of a rule called colour confinement. They must group together so their colour charges cancel out. In a pentaquark, the quarks are held together by the strong force. This force ensures the total colour charge is neutral.

PQ EB ape hyp geom5 B 3D
PQ EB ape hyp geom5 B 3D

There are different ways a pentaquark might be structured. Scientists are still studying exactly how these five pieces stay bound. One theory is that they are five quarks tightly packed together. Another idea is that they form a "meson-baryon molecule." In this version, a three-quark baryon and a two-quark meson interact weakly. They might connect through pion exchange, which is the same force that binds atomic nuclei. To identify the specific quarks, physicists use notation like qqqq̅. For example, a particle with two up quarks, one down quark, one charm quark, and one charm antiquark is written as uudc̅.

Pentaquark
Pentaquark

The history of the pentaquark is a long and difficult journey. Murray Gell-Mann first suggested that five-quark particles could exist in 1964. Later, in 1987, Claude Gignoux and Harry J. Lipkin coined the name "pentaquark." For many years, scientists could not find proof of them. In 2003, a group in Japan called LEPS reported finding a pentaquark. However, other scientists could not replicate those results. Many early claims were eventually dismissed due to poor data or statistical errors. This made the search for pentaquarks a famous mystery in the scientific community.

In 2015, the mystery finally began to resolve at CERN. The LHCb collaboration studied the decay of bottom lambda baryons. A decay happens when a particle breaks down into other particles. On July 13, 2015, they reported results that showed pentaquark states. These specific particles were charmonium-pentaquarks. They were made of two up quarks, one down quark, one charm quark, and one anti-charm quark. The statistical significance of this discovery was very high, reaching 15 sigma. This was enough to claim a formal discovery.

Pentaquark-Feynman
Pentaquark-Feynman

Since that major breakthrough, the LHCb team has found even more particles. On March 26, 2019, they announced a new pentaquark called Pc(4312)+. This particle has a mass of about 4312 MeV. The team also discovered that a previous observation was actually two different resonances. These were named Pc(4440)+ and Pc(4457)+. Most recently, on July 5, 2022, the team found a third pentaquark. This one is named PψsΛ(4338)0. It is the first confirmed pentaquark to contain a strange quark.

J-psi p pentaquark mass spectrum
J-psi p pentaquark mass spectrum

Studying pentaquarks has many important connections to the wider universe. These particles allow physicists to study the strong force in great detail. This helps them understand quantum chromodynamics, which is the study of how quarks interact. Beyond small laboratories, pentaquarks might exist in deep space. Some theories suggest that very large stars produce them during collapse. This could provide vital clues about the physics of neutron stars. By looking at these tiny particles, we can learn about the largest objects in the cosmos.

612 words

Where will your curiosity go next?

Keep exploring at your chosen reading level.

🖼️ Images & Media (4)
File:Pentaquark.svg
Pentaquark.svg
File:Pentaquark-Feynman.svg
Pentaquark-Feynman.svg
File:J-psi p pentaquark mass spectrum.svg
J-psi p pentaquark mass spectrum.svg
File:PQ EB ape hyp geom5 B 3D.jpg
PQ EB ape hyp geom5 B 3D.jpg
More to explore

🔬 Go deeper

More advanced topics to explore

🪜 Step back

Simpler topics to build understanding

What is Nepedia?

A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.