Physicists at CERN Discover a New Type of Matter
The LHCb experiment at CERN’s Large Hadron Collider has reported the discovery of a class of particles known as pentaquarks. Formed by five quarks, the new particles will permit better understanding how matter is put together.
Protons and neutrons – the building blocks of atomic nuclei – are composed of fundamental particles called quarks, which come in six different types. While a single quark is never observed in isolation, different arrangements of quarks make up protons, neutrons and other composite particles. Both protons and neutrons are formed by three quarks, the difference between a proton and a neutron being in the types of constituent quarks.
New Particles Composed by Five Quarks
Particle accelerators like the Large Hadron Collider (LHC) at CERN, near Geneva and the border between Switzerland and France, accelerate particles at huge speed and smash them in very high energy collisions, and often the products of the collision unveil new insights on fundamental physics.
The pentaquarks discovered last week are particles consisting of five quarks, a new type of matter not observed in ordinary conditions.
“The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson. “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 fifty 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.
A research paper reporting the findings has been submitted to Physical Review Letters. A preliminary version of the paper is freely available online at the preprint server arXiv.
Pentaquarks had been previously theorized, and previous high energy physics experiments claimed to have observed pentaquarks, but the CERN experiment appears to be the first clear observation. The five quarks might be tightly bonded in a particle (right image) or assembled into a meson (one quark and one antiquark) and a baryon (three quarks), weakly bound together (bottom image).
“The quarks could be tightly bound,” said LHCb physicist Liming Zhang of Tsinghua University, “or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.” More studies are planned to distinguish between these possibilities.
Building and operating high energy particle accelerators like the LHC costs a lot of money, and the wisdom of spending so much money to study exotic forms of matter that doesn’t exist in ordinary conditions is often questioned. But the truth is that new discoveries in fundamental physics often result in practical applications to energy, electronics and new materials.
Images from CERN and LHCb Collaboration.