In 2010, an international team of researchers at PSI used negative muons to perform a new measurement of the proton and found that its radius is significantly smaller than previously thought: 0.84184 femtometers instead of 0.8768. According to press reports, this result was not only surprising, it could also call previous models in physics into question. The measurements were only possible with PSI's 590 MeV proton accelerator HIPA because its secondarily generated muon beam is the only one worldwide that is intense enough to conduct the experiment.