A few weeks ago, the LHCb, an experiment at the Large Hadron Collider, announced the discovery of a new particle, the pentaquark. What is a pentaquark? Well…it’s a particle, that’s made of five quarks.

A quark is one of the smallest fundamental building blocks of matter. Quarks have not been observed alone in nature, and are only known to exist as composite particles. Most commonly, they are found in groups of two or three, known respectively as mesons and hadrons. The protons and neutrons that make up atomic nuclei are two well known examples of hadrons.

Similar to the Higgs boson, the pentaquark’s existence was implied by theory decades ago. What is exciting about this discovery is that the mathematical theory that describes quarks is notoriously messy. It is possible to make predictions that are close to what is seen in nature, but are far from exact. Now that researchers have finally seen a pentaquark, further experiments almost certainly will help push the boundaries of our understanding of matter.

The pentaquark’s discovery is also interesting from a historical perspective. The pentaquark’s observation has been announced several times before. In a twist of irony, previous experiments that were actively searching for the pentaquark never yielded conclusive results. At CERN, physicists claim that they weren’t even looking for the particle; it took them by complete surprise.

While this announcement is also much more statistically sound than previous claims, skepticism seems prudent as the paper undergoes peer review. Everyone in particle physics cannot wait to hear more.

Acknowledgements: Many thanks to Baojia (Tony) Tong, a graduate student in the Department of Physics at Harvard University working on the ATLAS Experiment at CERN, for providing his expertise and commentary on the subject.

Original Article: Observation of J/ψ p resonances consistent with pentaquark states in Λ0 b → J/ψK−p decays on the ArXiv