Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC

Jul 3, 2026

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Search results for the Standard Model Higgs boson are presented using proton-proton collision data from the CMS experiment at the LHC at center-of-mass energies of 7 and 8 TeV, totaling up to 5.1 fb−1 and 5.3 fb−1. The analysis targets five Higgs decay modes: gg, ZZ, WW, tt, and bb. A statistically significant excess of events over the expected background is observed near 125 GeV, with local significance 5.0 standard deviations and expected 5.8. Fits to high-resolution channels yield a mass of 125.3±0.4(stat)±0.5(syst) GeV, and the diphoton decay supports bosonic spin distinct from one.

LanguageEnglish

CategoryResearch & Report

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Pages42

Reading Time1 h 46 min

Abstract

Introduction

arXiv : 1207 .7235v2 [hep-ex] 28 Jan 2013 EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-PH-EP/2012-220 2013/01/29 CMS-HIG-12-028 Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC The CMS Collaboration Abstract Results are presented from searches for the standard model Higgs boson in protonproton collisions at ps = 7 and 8 TeV in the Compact Muon Solenoid experiment at the LHC, using data samples corresponding to integrated luminosities of up to 5.1 fb 􀀀1 at 7 TeV and 5.3 fb 􀀀1 at 8 TeV. The search is performed in ﬁve decay modes: gg, ZZ, W+ W 􀀀 , t+ t 􀀀 , and bb. An excess of events is observed above the expected background, with a local signiﬁcance of 5.0 standard deviations, at a mass near 125 GeV, signalling the production of a new particle. The expected signiﬁcance for a standard model Higgs boson of that mass is 5.8 standard deviations. The excess is most signiﬁcant in the two decay modes with the best mass resolution, gg and ZZ; a ﬁt to these signals gives a mass of 125.3 􀀆 0.4 (stat.) 􀀆 0.5 (syst.) GeV. The decay to two photons indicates that the new particle is a boson with spin different from one. Submitted to Physics Letters B 1 Introduction The standard model (SM) of elementary particles provides a remarkably accurate description of results from many accelerator and non-accelerator based experiments. The SM comprises quarks and leptons as the building blocks of matter, and describes their interactions through the exchange of force carriers: the photon for electromagnetic interactions, the W and Z bosons for weak interactions, and the gluons for strong interactions. The electromagnetic and weak interactions are uniﬁed in the electroweak theory. Although the predictions of the SM have been extensively conﬁrmed, the question of howtheWandZ gauge bosons acquire mass whilst the photon remains massless is still open. Nearly ﬁfty years ago it was proposed [1–6] that spontaneous symmetry breaking in gauge theories could be achieved through the introduction of a scalar ﬁeld. Applying this mechanism to the electroweak theory [7–9] through a complex scalar doublet ﬁeld leads to the generation of the W and Z masses, and to the prediction of the existence of the SM Higgs boson (H) . The scalar ﬁeld also gives mass to the fundamental fermions through the Yukawa interaction. The mass m H of the SM Higgs boson is not predicted by theory. However, general considerations [10–13] suggest that mH should be smaller than 􀀘 1 TeV, while precision electroweak measurements imply that mH < 152 GeV at 95% conﬁdence level (CL) [14] . Over the past twenty years, direct searches for the Higgs boson have been carried out at the LEP collider, leading toa lower bound of mH > 114.4 GeV at 95% CL [15], and at the Tevatron proton-antiproton collider, excluding the mass range 162–166 GeV at 95% CL [16] and detecting an excess of events, recently reported in [17–19], in the range 120–135 GeV. The discovery or exclusion of the SM Higgs boson is one of the primary scientiﬁc goals of the Large Hadron Collider (LHC) [20] . Previous direct searches at the LHC were based on data from proton-proton collisions corresponding to an integrated luminosity of 5 fb 􀀀1 collected at a centre-of-mass energy ps = 7 TeV. The CMS experiment excluded at 95% CL a range of masses from 127 to 600 GeV [21] . The ATLAS experiment excluded at 95% CL the ranges 111.4–116.6, 119.4–122.1 and 129.2–541 GeV [22] . Within the remaining allowed mass region, an excess of events near 125 GeV was reported by both experiments. In 2012 the proton-proton centre-ofmass energy was increased to 8 TeV and by the end of June an additional integrated luminosity of more than 5 fb 􀀀1 had been recorded by each of these experiments, thereby enhancing significantly the sensitivity of the search for the Higgs boson. This paper reports the results of a search for the SM Higgs boson using samples collected by the CMS experiment, compri

FAQs

What experimental data and energies were used in the CMS Higgs search?

The CMS analysis uses proton-proton collision data at 7 TeV and 8 TeV, with integrated luminosities up to 5.1 fb−1 at 7 TeV and 5.3 fb−1 at 8 TeV.

Which Higgs decay modes were studied?

Five decay modes are analyzed: gg, ZZ, WW, tt, and bb.

What is the reported mass and significance of the observed excess?

An excess over expected background is observed near 125 GeV with a local significance of 5.0 standard deviations (expected 5.8). A fit gives a mass of 125.3±0.4(stat)±0.5(syst) GeV.

Jul 3, 2026

Upload by Jiven