The Higgs boson was discovered at the LHC in 2012 by the ATLAS and CMS experiments, with a mass of 125.1 GeV. Its production and decay rates are consistent with Standard Model predictions: it is a spin-0, CP-even scalar whose couplings to other particles are proportional to their masses. Measuring the Higgs couplings with increasing precision is the central goal of the LHC program and future colliders.
The discovery of the Higgs boson on July 4, 2012, by the ATLAS and CMS experiments at the LHC was the culmination of a nearly 50-year search. The particle was predicted in 1964 by Brout, Englert, and Higgs as a consequence of the mechanism that gives mass to the W and Z bosons. Its mass of 125.1 GeV, while not predicted by the Standard Model, turns out to be in a theoretically interesting range: heavy enough to be discovered at the LHC but light enough to leave the Standard Model perturbative up to very high energy scales.
The production mechanisms at the LHC reflect the Higgs coupling structure. Gluon fusion (gg -> H via a top loop) dominates because of the large gluon luminosity and the strong top Yukawa coupling. Vector boson fusion (qq -> qqH via W/Z exchange) has a distinctive signature of two forward jets with a rapidity gap. Associated production (WH, ZH, ttH) provides direct access to the HWW, HZZ, and Htt couplings. Each production mode has been observed and measured, confirming the expected coupling pattern.
The decay modes span a wide range of branching ratios. The dominant decay is H -> bb (58%), followed by H -> WW* (21%), H -> gg (8.2%), H -> tau tau (6.3%), H -> cc (2.9%), H -> ZZ* (2.6%), H -> gamma gamma (0.23%), H -> Z gamma (0.15%), and H -> mu mu (0.02%). The hierarchy of branching ratios directly reflects the mass-proportional coupling: the Higgs decays predominantly to the heaviest particles that are kinematically accessible. The rare decays H -> gamma gamma and H -> Z gamma are loop-induced (like gg -> H) and are sensitive to virtual particles in the loop, including potential new charged particles beyond the Standard Model.
The future Higgs program aims to measure all couplings at the percent level or better and to observe the Higgs self-coupling (the trilinear HHH coupling, which determines the shape of the Higgs potential). The HL-LHC (High-Luminosity LHC, starting ~2029) will collect 20 times more data, enabling 3-5% coupling measurements and a first look at Higgs pair production. Proposed future colliders -- the FCC-ee (e+e- at 240 GeV), ILC, CLIC, CEPC, and the FCC-hh (100 TeV pp) -- could measure couplings to sub-percent precision and determine the Higgs self-coupling to 5-10%. Any deviation from the Standard Model prediction would point to new physics in the Higgs sector, such as additional scalar fields, compositeness, or supersymmetry.