A Higgs particle has been spotted

Fifty years ago a number of theoretical physicists suggested a way of augmenting the developing standard model of particle physics with a new mechanism that involved a particle since dubbed the Higgs boson. That particle interacts not only with gauge bosons, as in its original formulation, but also with quarks and other fundamental fermions, endowing those entities with mass. A half-century after its proposal, the elusive Higgs, or something much like it, has now been observed. In a symposium and press conference held Wednesday at CERN, ATLAS and CMS collaboration scientists affirmed that they had seen the particle at a mass of about 125 GeV. At the end of 2011, the two groups had announced tantalizing hints of the Higgs—resonance peaks three standard deviations above background (see Physics Today, February 2012, page 16). In the intervening months, the groups have doubled their data and now report peaks of five sigma above background. On Monday of this week, the CDF and D0 groups at Fermilab announced that their experiments—lower in energy and with different detection capabilities—are consistent with CERN results. Now CERN physicists need to check the particulars of the particle’s production and decay rates (one particular decay is shown here), which are well predicted by the standard model. They may find that they have discovered a novel particle that gives mass as the standard model Higgs does, but that heralds physics beyond the standard paradigm. (ATLAS collaboration, “Latest results from ATLAS Higgs search”; CMS collaboration, “Observation of a new particle with a mass of 125 GeV.” )—Steven K. Blau