= Higgs boson discovery in 2012
{c}
The <ATLAS experiment> and <CMS experiment> searched <proton>-<proton> collisions at the <Large Hadron Collider> at collision <energies> of $7$ and $8\,\mathrm{TeV}$. The <ATLAS experiment> used <silicon> tracking, a $2\,\mathrm T$ solenoid, liquid-argon <electromagnetic calorimeters> and an external <muon> spectrometer. Its July 2012 paper reported a combined local <statistical significance> of $6.0$ <standard deviations> near $126.5\,\mathrm{GeV}$; this paper result is distinct from the initial 4 July announcement.<Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC by ATLAS Collaboration>[abstract; Section 2; Section 9.2 and Table 7]{ref}
The <CMS experiment> used <silicon> tracking in a $3.8\,\mathrm T$ solenoid, lead-tungstate <electromagnetic calorimeters> and external <muon> chambers. <Electrons> combine tracks and <particle showers>; <muons> combine tracking and chamber hits; <photons> supply shower <energies> and directions. Selected $H\to\gamma\gamma$ and $H\to ZZ^*\to4\ell$ candidates, with $\ell=e,\mu$, yielded <invariant mass> peaks. It checked lepton efficiencies with <Z boson> decays, estimated fake-lepton backgrounds from control samples with relaxed identification, and fitted the smooth diphoton background from data. Its combined local <statistical significance> was $5.0$ <standard deviations> near $125\,\mathrm{GeV}$.<Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC by CMS Collaboration>[abstract; Sections 2, 5.1–5.2 and 7.1]{ref}
The <ATLAS experiment> compared signal-plus-background and background-only hypotheses with a <profile likelihood>, accounting for systematic uncertainties and correlations between <decay channels>. Diphoton and four-lepton candidates gave precise <invariant masses>; $WW^*$ decays supplied additional evidence with poorer mass reconstruction because of escaping <neutrinos>. A local <p-value> concerns one specified mass; scanning masses requires a <look-elsewhere effect> correction.<Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC by ATLAS Collaboration>[Sections 6–7 and 9.2]{ref}
Two-<photon> decay excludes <spin> one under the usual assumptions, but does not prove <spin> zero. A mass peak does not determine every <Higgs boson> coupling. Production rates, <branching fractions> and angular correlations require additional tests.<Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC by CMS Collaboration>[Sections 7.1–7.3 and Summary]{ref}
Back to article page
