Combined Measurement of the Higgs Boson Mass in $pp$ Collisions at $\sqrt{s}=7$ and 8 TeV with the ATLAS and CMS Experiments

A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the $H\to \gamma \gamma$ and $H\to ZZ\to 4\ell$ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is $m_H=125.09\pm 0.21(\text{stat})\pm 0.11(\text{syst})\mathrm{GeV}$.

Figure 1

Scans of twice the negative log-likelihood ratio $-2\ln \mathrm{\Lambda }(m_H)$ as functions of the Higgs boson mass $m_H$ for the ATLAS and CMS combination of the $H\to \gamma \gamma$ (red), $H\to ZZ\to 4\ell$ (blue), and combined (black) channels. The dashed curves show the results accounting for statistical uncertainties only, with all nuisance parameters associated with systematic uncertainties fixed to their best-fit values. The 1 and 2 standard deviation limits are indicated by the intersections of the horizontal lines at 1 and 4, respectively, with the log-likelihood scan curves.

Figure 2

Summary of Higgs boson mass measurements from the individual analyses of ATLAS and CMS and from the combined analysis presented here. The systematic (narrower, magenta-shaded bands), statistical (wider, yellow-shaded bands), and total (black error bars) uncertainties are indicated. The (red) vertical line and corresponding (gray) shaded column indicate the central value and the total uncertainty of the combined measurement, respectively.

Figure 3

The impacts $\delta m_H$ (see text) of the nuisance parameter groups in Table 1 on the ATLAS (left), CMS (center), and combined (right) mass measurement uncertainty. The observed (expected) results are shown by the solid (empty) bars.

Figure 4

Summary of likelihood scans in the 2D plane of signal strength $\mu$ versus Higgs boson mass $m_H$ for the ATLAS and CMS experiments. The 68% C.L. confidence regions of the individual measurements are shown by the dashed curves and of the overall combination by the solid curve. The markers indicate the respective best-fit values. The SM signal strength is indicated by the horizontal line at $\mu =1$.