Hints of the Higgs heighten anticipation

The Higgs boson is the only remaining undiscovered particle required by the standard model (SM) of particle theory. It’s the neutral, spinless quantum of the Higgs field, which serves to break the SM’s underlying symmetry between the electromagnetic and weak interactions. The field bestows mass on the spin-1 bosons that mediate the weak interaction, and on the quarks and leptons. The SM doesn’t predict the Higgs mass M _H, but precision measurements of electroweak parameters and null results of searches at various colliders have restricted its range to 115–156 GeV. (The proton’s mass is about 1 GeV.) Now the ATLAS and CMS detector collaborations at CERN’s Large Hadron Collider (LHC) have reported tantalizing—but still statistically marginal—evidence of the Higgs near 125 GeV. Because the Higgs would live only 10^–22 seconds, one could find and weigh it only by measuring the energies of its decay products in many collision events. A particularly useful decay mode ends with four high-energy muons (the red tracks in the display of one event’s collision products in ATLAS). Though each team’s sighting could easily be a two-standard-deviation statistical fluke, the fact that the two teams saw very similar peaks near the same mass in several decay modes heightens the anticipation of experimenters and theorists. The teams have already excluded M _H greater than 130 GeV, and by the end of this year’s LHC run they should have enough data for a statistically robust discovery, or exclusion, of a standard-model Higgs in the remaining mass range. Either result would be momentous. (ATLAS collaboration, http://cdsweb.cern.ch/record/1406358/files/ATLAS-CONF-2011-163.pdf ; CMS collaboration, http://cdsweb.cern.ch/record/1406347/files/HIG-11-032-pas.pdf .)—Bertram Schwarzschild