Hint of new physics vanishes under scrutiny

An intriguing anomaly in data gathered by the Large Hadron Collider (LHC) that raised hopes of a new elementary particle has turned out to be a fluke. In 2014, LHC scientists at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland, discovered that some massive particles decay more often into electron–positron pairs than into muon–antimuon pairs. This imbalance defied the standard model of physics, which predicts both pairs to occur with roughly the same frequency. The latest measurements and an investigation of confounding factors revealed that the discrepancy was partly the result of misidentifying other particles as electrons.