Scientists working at CERN's Large Hadron Collider Beauty (LHCb) experiment announced that they have finally figured out the structure of an exotic particle known as the pentaquark, meaning a group of five quarks bound together forming a transient, molecule-like body.
Quarks are the most fundamental building blocks of our universe. Named after the quirky phrases in the contemporary fiction Finnegan’s Wake, the concept of quarks was first theorized by the late Nobel laureate Murray Gell-Mann, as a measure to properly describe the relationships between different subatomic particles in groups. Their existence was later confirmed through particle experiments performed at the Stanford Linear Accelerator Center (SLAC) in 1968.
The LHCb collaboration is one of the seven particle physics experiments that utilize the world's largest accelerator to generate otherwise inaccessible knowledges. With the reliable high-energy particle traffics and consistent collision happening inside the LHC, the research group directs their focus on analyzing data collected by the LHCb detector and interrogating the nature of elementary particles.
Back in 2015, they discovered a signal that corresponded to a combination of five quarks (hence the name "pentaquark"), with a mass approximately 4.5 times heavier than a proton. However, they were unclear how the five quarks arrange themselves inside. Some proposed that they might all occupy a tight space, bound together by the strong nuclear force.
Later on, as the LHC continued with more particle smashing, the LHCb team was able to gain access to 9 times more data as compared to their 2015 work, which allowed them to investigate pentaquark with much higher precision. The original signal masked the two separate pentaquarks of identical masses, according to their analyses. What's more, the masses of the particle twins indicates the pentaquark take the form of baryon-meson pairs, other than having all five quarks lumped together.
This finding is rather intriguing in many perspectives. The atomic nucleus is made of various numbers of protons and neutrons (except for hydrogen-1 which only has one proton), which are the most common baryons. Baryons consist of three quarks, which make them stable. On the other hand, mesons are short-lived subatomic particles that comprise of only two quarks. There were a lot of them at the very beginning of our universe right after the Big Bang, but nowadays we can only find them in physics laboratories as a product of particle bombardment.
The information about the configuration of the pentaquark not only allows scientists to understand better how the strong force holds the quarks together but also provides astrophysicists some useful insights into the origin of our universe and the bizarre formation of quark stars.
The research was published in the journal Physical Review Letters.