There could be not one superpartner, but two appearing in LHC collisions, both of roughly similar masses - say, around 550 and 500 protons. There is one way in which Muon g – 2 could resurrect supersymmetry and also provide evidence for dark matter, Stöckinger says. “If you look at it in comparison to any other ideas, it’s not worse than the others,” he says. But he still sees it as a plausible way to explain his experiment’s findings.

“Many people would say supersymmetry is almost dead,” says Dominik Stöckinger, a theoretical physicist at the Dresden University of Technology in Germany, who is a member of the Muon g – 2 collaboration. The data that the LHC has produced so far suggest that typical superpartners, if they exist, cannot weigh less than 1,000 protons (the bounds can be higher depending on the type of superparticle and the flavour of supersymmetry theory). Many expected that the collisions at the Large Hadron Collider (LHC) outside Geneva, Switzerland, would produce a plethora of these new particles, but so far none has materialized. Until ten years ago, various lines of evidence had suggested that a superpartner weighing as much as a few hundred protons could constitute dark matter. If so, these particles could solve two mysteries at once: muon magnetism and dark matter, the unseen stuff that, through its gravitational pull, seems to keep galaxies from flying apart. Superpartners could be among the ‘virtual particles’ that constantly pop in and out of the empty space surrounding the muon, a quantum effect that would help to explain why this particle’s magnetic field is stronger than expected. Supersymmetry comes in many variants, but in general, it posits that every particle in the standard model has a yet-to-be-discovered heavier counterpart, called a superpartner. Take supersymmetry, or SUSY, a theory that many physicists once thought was the most promising for extending the current paradigm, the standard model of particle physics. The result is that researchers have to perform the theoretical-physics equivalent of a triple somersault to make an explanation work.

And additional anomalies in the muon’s behaviour, reported in March 2 by a collider experiment, only make that task harder. It seems maddeningly hard to explain it in a way that is compatible with everything else physicists know about elementary particles. If the discrepancy pans out, it would be the first time that the theory has failed to account for observations since its inception five decades ago - and there is nothing physicists love more than proving a theory wrong.īut rather than pointing to a new and revolutionary theory, the result - announced on 7 April 1 by the Muon g – 2 experiment near Chicago, Illinois - poses a riddle. Taken at face value, the surprisingly strong magnetism of the elementary particles called muons, revealed by an experiment this month, suggests that the established theory of fundamental particles is incomplete. The Large Hadron’s Collider LHCb detector, pictured, reported anomalies in the behaviour of muons, two weeks before the Muon g – 2 experiment announced a puzzling finding about muon magnetism.

Standard model particles