Oh, how the mighty have fallen.
Supersymmetry, a theory that predicts the existence of undiscovered "superpartner" particles for every known elementary particle, has dominated particle physics for generations. And for good reason: SUSY, as it's often called, has been widely seen as the best route to new discoveries beyond the standard model of particle physics, offering potential explanations for lingering mysteries like dark matter as well as possible paths forward on vexing problems like quantum gravity.
The trouble is, experimentalists have spent decades searching for SUSY's superpartners using various particle accelerators, only to come up empty. The most damning null results have come from CERN's Large Hadron Collider (LHC), the world's largest and most powerful particle accelerator. That's because production of the lightest superpartner particles predicted by the simplest versions of SUSY should've been within reach of the LHC's collisions after a major upgrade to the facility in 2015. Indeed, searching for evidence of supersymmetry was one of the main justifications for building the LHC in the first place. Yet, once again, no signs of superpartners have emerged from its studies—and particle physicists are recalibrating accordingly.
The latest sign of this is the news that the LHC's two largest SUSY-relevant experiments, ATLAS and CMS, have reorganized their internal working groups so that none now exclusively focus on the theory. You can read all about it in this week's top story. Although this arcane change may seem immaterial, and indeed SUSY research still takes place at the LHC, the dissolution of SUSY-dedicated working groups is a major blow against the once-dominant theory—and a sign that an ever-increasing contingent of the physics community is ready to move on.
Any declaration of SUSY's death would be premature, but the outlook isn't exactly rosy. Then again, neither is the outlook for big-budget particle physics in the absence of a "next big thing" to chase. Supersymmetry has helped fuel major investments in multibillion-dollar physics experiments, so if it's largely abandoned by particle physicists, what comes next? That's a question no shortage of researchers and policymakers are desperately seeking to answer.
—Lee Billings
