Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC

Abstract

A search for the Standard Model Higgs boson in proton–proton collisions with the ATLAS detector at the LHC is presented. The datasets used correspond to integrated luminosities of approximately 4.8 fb−1 collected at √s=7 TeV in 2011 and 5.8 fb−1 at √s=8 TeV in 2012. Individual searches in the channels H→ZZ(⁎)→4ℓ, H→γγ and H→WW(⁎)→eνμν in the 8 TeV data are combined with previously published results of searches for H→ZZ(⁎), WW(⁎), bb and τ+τ− in the 7 TeV data and results from improved analyses of the H→ZZ(⁎)→4ℓ and H→γγ channels in the 7 TeV data. Clear evidence for the production of a neutral boson with a measured mass of 126.0±0.4(stat)±0.4(sys) GeV is presented. This observation, which has a significance of 5.9 standard deviations, corresponding to a background fluctuation probability of 1.7×10−9, is compatible with the production and decay of the Standard Model Higgs boson

Preserving the validity of the two-Higgs-doublet model up to the Planck scale

“…With the recent discovery of a Higgs-like particle with a mass of about 125 GeV by both the ATLAS [1] and CMS [2] collaborations, the focus has now turned to deciphering the properties of this particle and determining whether it is the Standard Model (SM) Higgs particle, or part of an extended Higgs sector. Analyses performed by ATLAS and CMS collaborations have shown that the couplings of the newly discovered particle are consistent with a SM-like Higgs boson, within the accuracy of their measurements.…”

“…[16] has shown that the SM scalar potential becomes unstable at a value of Λ well below the Planck scale, if the Higgs boson mass is smaller than 129.6 ± 1.5 GeV. 1 Taken at face value, these results would further imply that we live in a metastable vacuum that will eventually (and catastrophically) decay via tunneling into the true vacuum. However, the lifetime of the metastable vacuum is many orders of magnitude larger than the age of the universe [16,17].…”

Beam polarization effects on top-pair production at the ILC

“…The discovery of the Higgs boson [1,2] in 2012 showed the standard theory of particle physics to be well established. Even though the standard theory can describe the microscopic nature at a subatomic level very precisely [3], it cannot be the most fundamental theory of nature because, for instance, it includes many parameters (e.g., particle masses and couplings, number of generations) that are not determined within the theory.…”

“…While experiments at the Large Hadron Collider continue to search for signals beyond the standard model (BSM), none have been reported to date. 1 Besides discovering new particles, pursuing the BSM also involves precise measurements of the properties of known particles. Milestones along this direction must surely be the Higgs boson and the top quark.…”

Higgs Boson Decays to Tau Pairs at the ILC with the ILD Detector

“…After the discovery of the Higgs boson [1,2], the investigation of that particle has become one of the most important problems for the particle physics, especially the verification of the mass generation mechanism. In the Standard Model (SM), the Yukawa coupling of matter fermions with the Higgs boson is proportional to the fermion mass.…”