As the search for the mysterious subatomic particle known as the Higgs boson recently demonstrated, the building blocks of the universe are tricky to find. Now, researchers claim they have observed a whole new subatomic particle.
A false alarm in 2002 led many to believe that particles known as pentaquarks simply did not exist. More than a decade later, physicists involved in CERN's Large Hadron Collider beauty experiment (LHCb) have strong evidence that they've finally observed these exotic subatomic particles, they report in the journal Physical Review Letters.
"The pentaquark is not just any new particle," said LHCb spokesperson Guy Wilkinson in a statement. "It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over 50 years of experimental searches. 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 molecules that make up our world and the universe beyond are composed of atoms — which are in turn made up of protons, neutrons and electrons. Quarks are even smaller still. Three quarks bound together yield a proton or a neutron — depending on the types involved. Five quarks bound together – a pentaquark – was theoretically possible, but until now, there was no solid evidence that they actually existed.
The researchers propose that the five quarks in a pentaquark could be arranged in two different ways. They could be arranged in one group of five quarks tightly bound together (top image), or in a group of two quarks weakly bound to a group of three (shown below). The current data is not sufficient to distinguish between these possibilities.
Discovering the pentaquark was a complete accident, according to a report from Nature, but the researchers are eager to learn more about the elusive subatomic particle that they happened to stumble across. Additional LHC runs are already in the works to collect the data LHCb researchers need to study the two proposed possible states of pentaquarks.
