Scientists have used a novel approach merging quantum mechanics and general relativity to identify the legendary “glueball,” a particle theorized to be made of pure nuclear force.
The Standard Model of particle physics, developed in the 1970s, theorized a whole host of subatomic particles that should exist based on electromagnetic, weak, and strong nuclear interactions. So far, particle physicists have confirmed the existence of quarks, tau neutrinos, and the Higgs boson, earning the Standard Model the nickname “theory of almost everything.” Now physicists believe they have pinned down another elusive member of the Standard Model clique: the glueball.
The particle takes its whimsical name from its composition of gluon particles. Gluons are like fancier versions of photons (light particles), except they carry a “strong nuclear force” instead of electromagnetic radiation. During their day job, gluons glue quarks together to form larger particles like protons and neutrons. The Standard Model hypothesizes that gluons can also autonomously assemble into larger exotic particles called glueballs. Since gluons have no mass, these mythical glueballs would be made purely of strong nuclear force.
In the past few decades, particle accelerator experiments have found possible candidates for glueballs, but no one ever agreed on the discoveries. The tricky thing is that, while gluons themselves are massless, their interactions with each other end up endowing glueballs with mass that can then decay into quarks and antiquarks. Physicists have recently focused on two particles called f0(1500) and f0(1710), which are subatomic particles called mesons, each composed of one quark and one antiquark.
But the only way to definitively identify one or both of these candidates as a glueball was by studying their decay. Physicists used to believe f0(1500) was a stronger candidate because f0(1710)’s decay patterns didn’t match the predictions for glueball behavior. When it decayed, it only produced the heavier “strange” quarks, and everything scientists knew about gluon interactions up to that point declared that they didn’t differentiate between heavy or light quarks.
Anton Rebhan and Frederic Brunner from the Vienna University of Technology have devised new calculations that show f0(1710) could indeed be a glueball. They took a new approach that incorporated theories about gravitational forces, which many assume to act on too large of a scale to govern subatomic particles. By applying the gravitational forces to glueball behavior, they found that it is possible for glueballs to decay into strange quarks — in exactly the way that f0(1710) exhibits.
Luckily, they don’t have to wait much longer to confirm f0(1710)’s identity as a true glueball — the Large Hadron Collider’s second, higher-energy run should yield new data within the next few months. If the measurements taken at the LHC agree with these calculations, it will provide robust evidence for the legendary glueball. This discovery also forges a bond between the long-sundered physics theories of quantum mechanics and general relativity. If these two could just get along, who knows what breakthroughs we could make?