At The Large Hadron Collider in Switzerland, the strongest magnetic field ever measured anywhere in the universe has failed to produce detectable magnetic monopoles. These hypothetical particles are predicted by many calculations of possible phenomena beyond the Standard Model of particle physics, but more than a century of searching has still turned up no sign of them.
All magnets that we know today have at least two poles – most commonly a north and south pole, plus and minus. But some models of the universe predict that there should be particles with only one north or one south pole called magnetic monopoles. For example, the existence of magnetic monopoles would explain why electric charge is quantized, meaning it comes in packets of a minimum size.
For the past century or so, scientists have been looking for magnetic monopoles both in space and in the breakdown of particles at colliders, but they have not been found yet. Igor Ostrovskiy at the University of Alabama and his colleagues looked for monopoles produced by a proposed phenomenon called the Schwinger effect, in which extremely powerful magnetic fields could spontaneously produce magnetic particles and their antiparticles.
To look for magnetic monopoles, the team used the largest magnetic field ever measured. This is produced at the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland, when two beams of lead particles are smashed together at extraordinary speeds. That magnetic field measures about 1016 Tesla—about 2 billion billion times stronger than a typical refrigerator magnet, or 100,000 times stronger than the magnetic field of a magnetar, a highly magnetized neutron star.
"Of the searches for magnetic monopoles at accelerators, we are definitely the most sensitive" says Ostrovskiy. "The stronger the magnetic field, the more and the heavier monopoles we can theoretically produce." Nevertheless, the researchers found no monopoles, which set the first strong limits on the mass of these particles: they cannot be less than 70 times the mass of a proton.
"I don't think it's time to give up yet," says Ostrovskiy. He and his team have planned more experiments when the LHC turns on again this year after a three-year hiatus during which the collider was upgraded to reach even higher energy levels.