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

CMS Collaboration

Accepted by Phys. Lett. B
CMS-HIG-12-028
CERN-PH-EP-2012-220
CDS record 1471016
arXiv:1207.7235

Abstract:

Results are presented from searches for the standard model Higgs boson in proton-proton collisions at √s=7 and 8 TeV in the CMS experiment at the LHC, using data samples corresponding to integrated luminosities of up to 5.1 inverse femtobarns at 7 TeV and 5.3 inverse femtobarns at 8 TeV. The search is performed in five decay modes: γγ, ZZ, WW, τ+τ−, and bbˉ. An excess of events is observed above the expected background, 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, γγ 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.

Figures:

Image File links Description
png pdf Figure 1: Expected local p-values for a SM Higgs boson as a function of mH, for the decay modes γγ, ZZ, WW, ττ, and bb and their combination.
png pdf Figure 2: The local p-value as a function of mH in the γγ decay mode for the combined 7 and 8 TeV data sets. The additional lines show the values for the two data sets taken individually. The dashed line shows the expected local p-value for the combined data sets, should a SM Higgs boson exist with mass mH.
png pdf Figure 3: The diphoton invariant mass distribution with each event weighted by the S/(S+B) value of its category. The lines represent the fitted background and signal, and the coloured bands represent the 1 and 2 standard deviation uncertainties in the background estimate. The inset shows the central part of the unweighted invariant mass distribution.
png pdf Figure 4: Distribution of the four-lepton invariant mass for the ZZ→4l analysis. The points represent the data, the filled histograms represent the background, and the open histogram shows the signal expectation for a Higgs boson of mass mH = 125 GeV, added to the background expectation. The inset shows the m4l distribution after selection of events with KD > 0.5.
png pdf Figure 5: The distribution of events selected in the 4l subchannels for the kinematic discriminant KD versus m4l. Events in the three final states are marked by filled symbols (defined in the legend). The horizontal error bars indicate the estimated mass resolution. In the upper plot the colour-coded regions show the background expectation; in the lower plot the colour-coded regions show the event density expected from a SM Higgs boson (mH = 125 GeV) (both in arbitrary units).
png pdf
png pdf Figure 6: The observed local p-value for the ZZ decay mode as a function of the SM Higgs boson mass. The dashed line shows the expected local p-values for a SM Higgs boson with a mass mH.
png pdf Figure 7: Distribution of mll for the zero-jet eμ category in the H→WW search at 8 TeV. The signal expected from a Higgs boson with a mass mH = 125 GeV is shown added to the background.
png pdf Figure 8: The 95% CL limit on σ/σSM for a Higgs boson decaying, via a W boson pair, to two leptons and two neutrinos, for the combined 7 and 8 TeV data sets. The symbol σ/σSM denotes the production cross section times the relevant branching fractions, relative to the SM expectation. The background-only expectations are represented by their median (dashed line) and by the 68% and 95% CL bands. The dotted curve shows the median expected limit for a SM Higgs boson with mH = 125 GeV.
png pdf Figure 9: Distribution of mττ in the combined 7 and 8 TeV data sets for the μτh VBF category of the H→ττ search. The signal expected from a SM Higgs boson (mH = 125 GeV) is added to the background.
png pdf Figure 10: The 95% CL limit on the signal strength σ/σSM for a Higgs boson decaying to τ pairs, for the combined 7 and 8 TeV data sets. The symbol σ/σSM denotes the production cross section times the relevant branching fractions, relative to the SM expectation. The background-only expectations are represented by their median (dashed line) and by the 68% and 95% CL bands. The dotted curve shows the median expected limit for a SM Higgs boson with mH = 125 GeV.
png pdf Figure 11: Distribution of BDT scores for the high-pT subchannel of the Z(νν)H(bb) search in the 8 TeV data set after all selection criteria have been applied. The signal expected from a Higgs boson (mH = 125 GeV), including W(lν)H events where the charged lepton is not reconstructed, is shown added to the background and also overlaid for comparison with the diboson background.
png pdf Figure 12: The 95% CL limit on the signal strength σ/σSM for a Higgs boson decaying to two b quarks, for the combined 7 and 8 TeV data sets. The symbol σ/σSM denotes the production cross section times the relevant branching fractions, relative to the SM expectation. The background-only expectations are represented by their median (dashed line) and by the 68% and 95% CL bands. The dotted curve shows the median expected limit for a SM Higgs boson with mH = 125 GeV.
png pdf Figure 13: The CLs values for the SM Higgs boson hypothesis as a function of the Higgs boson mass in the range 110--145 GeV. The background-only expectations are represented by their median (dashed line) and by the 68% and 95% CL bands.
png pdf Figure 14: The observed local p-value for 7 TeV and 8 TeV data, and their combination as a function of the SM Higgs boson mass. The dashed line shows the expected local p-values for a SM Higgs boson with a mass mH.
png pdf Figure 15: The observed local p-value for the five decay modes and the overall combination as a function of the SM Higgs boson mass. The dashed line shows the expected local p-values for a SM Higgs boson with a mass mH.
png pdf Figure 16: The observed local p-value for decay modes with high mass-resolution channels, γγ and ZZ, as a function of the SM Higgs boson mass. The dashed line shows the expected local p-values for a SM Higgs boson with a mass mH.
png pdf Figure 17: The 68% CL contours for the signal strength σ/σSM versus the boson mass mX for the untagged γγ, γγ with VBF-like dijet, 4l, and their combination. The symbol σ/σSM denotes the production cross section times the relevant branching fractions, relative to the SM expectation. In this combination, the relative signal strengths for the three decay modes are constrained by the expectations for the SM Higgs boson.
png pdf Figure 18: The observed best-fit signal strength σ/σSM as a function of the SM Higgs boson mass in the range 110--145 GeV for the combined 7 and 8 TeV data sets. The symbol σ/σSM denotes the production cross section times the relevant branching fractions, relative to the SM expectation. The band corresponds to the 1 standard deviation uncertainty in σ/σSM.
png pdf Figure 19: Values of σ/σSM for the combination (solid vertical line) and for individual decay modes (points). The vertical band shows the overall σ/σSM value 0.87 0.23. The symbol σ/σSM denotes the production cross section times the relevant branching fractions, relative to the SM expectation. The horizontal bars indicate the 1 standard deviation uncertainties in the σ/σSM values for individual modes; they include both statistical and systematic uncertainties.
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