Eighty years ago an Italian physicist called Ettore Majorana predicted the existence of a subatomic particle that could effectively cancel itself out.
Months later Majorana vanished during a voyage from Palermo to Naples. Some said he had taken his own life; others, that he had run away to a monastery, or to Buenos Aires, or to take up the life of a nameless beggar. The curious case of the disappearing scientist has never been solved and for the best part of a century his self-negating particle has proved no less elusive. Now, however, researchers in California say they have found the first compelling evidence that it exists.
The findings, published in the journal Science, are a window into a strange mathematical universe. We know that the world around us is made up of fermions, particles such as protons and electrons that carry a small electrical charge and derive their mass from the field that gathers around the Higgs boson — the so-called God particle whose existence was hypothesised by the British physicist Peter Higgs in the 1960s but not confirmed until 2012. We also know that each of these particles is mirrored by an anti-matter particle with the opposite charge, such as the anti-proton and the positron.
In the 1930s a brilliant young student of Enrico Fermi — the physicist who gave the fermion its name — came up with a third and even stranger kind of object. Majorana, described by his boss as a genius in the same class as Galileo and Newton, drew up the equations for a theoretical phenomenon that was both particle and anti-particle, matter and anti-matter, at the same time.
Like the Higgs boson, the Majorana fermion has been fiendishly tricky to pin down in practice. However, physicists at Stanford University and the University of California, Los Angeles, have spotted the shadow of Majorana’s particle in the quantum behaviour of electrons around the edge of a superconductor, a two-dimensional material that carries electricity with no resistance.
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Shoucheng Zhang, the Stanford physics professor who designed the test, said: “Our team predicted exactly where to find the Majorana fermion and what to look for as its ‘smoking gun’ experimental signature. This discovery concludes one of the most intensive searches in fundamental physics.” He has called his find the “angel particle” after the plot to drop an anti-matter bomb in the Dan Brown thriller Angels and Demons.
Tom Devereux, director of the Stanford Institute for Materials and Energy Sciences, hailed the paper as the first solid vindication of Majorana’s theory and a “landmark in the field”.
However, Stefan Söldner-Rembold, head of the University of Manchester’s particle physics group, said that while the mathematics in the experiment closely resembled those of the Majorana fermion, they were not direct evidence for the particle itself.
That evidence could turn up in the next few years thanks to several international projects that are attempting to work out whether the neutrino, a mysterious fundamental particle with almost no mass that zips through the universe at close to the speed of light, could be what Majorana had in mind.