Measurement of Higgs boson production in the diphoton decay channel in $pp$ collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

Abstract: A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 5.4 fb$^{-1}$ of proton-proton collisions data at $\sqrt{s}=7$ TeV and 20.3 fb$^{-1}$ at $\sqrt{s}=8$ TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be $\mu = 1.17 \pm 0.27$ at the value of the Higgs boson mass measured by ATLAS, $m_{H}$ = 125.4 GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of $m_{H}$. They are found to be $\mu_{\mathrm{ggF}} = 1.32 \pm 0.38$, $\mu_{\mathrm{VBF}} = 0.8 \pm 0.7$, $\mu_{{WH}} = 1.0 \pm 1.6 $, $\mu_{{ZH}} = 0.1 ^{+3.7}_{-0.1} $, $\mu_{{t\bar{t}H}} = 1.6 ^{+2.7}_{-1.8} $, for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a $W$ or $Z$ boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.

• The paper measures the Higgs boson signal strength in the diphoton decay channel relative to Standard Model predictions.
• It employs advanced photon calibration techniques to improve the diphoton mass resolution and reduce systematic uncertainties.
• Analysis of production modes such as gluon fusion and vector-boson fusion confirms the robustness of ATLAS measurements.

Measurement of Higgs boson production in the diphoton decay channel in $pp$ collisions with the ATLAS detector

This paper presents an analysis of Higgs boson production in the diphoton decay channel using proton-proton collision data at center-of-mass energies of 7 TeV and 8 TeV, collected by the ATLAS detector at the Large Hadron Collider (LHC). The main objective is to measure the signal strength, defined as the ratio of observed Higgs boson events to those predicted by the Standard Model (SM).

Methodology and Analysis

The dataset includes 4.5 fb$^{-1}$ of collision data at 7 TeV and 20.3 fb$^{-1}$ at 8 TeV. The analysis focuses on the final state with two photons, offering a clean signature against the large background of the LHC. The Higgs boson mass is set at 125.4 GeV, based on previous measurements.

The paper details a sophisticated analysis strategy to disentangle the Higgs signal from the background. The new energy calibration of photons reduces systematic uncertainty on the diphoton mass resolution. This improvement enhances the precision of the signal measurement.

The production processes are meticulously separated into gluon fusion (ggF), vector-boson fusion (VBF), $WH$, $ZH$, and $t\bar{t}H$ channels. Each channel is treated independently to extract signal strengths ($\mu$) for each production mode. The results show no significant deviations from the SM predictions.

Results

The measured signal strength for the combination of all Higgs production modes is consistent with the SM prediction, within the experimental uncertainties. The analysis, leveraging a new calibration procedure, provides increased sensitivity in distinguishing the small Higgs signal from backgrounds through improved diphoton mass resolution.

Implications and Future Outlook

The findings of this study contribute to validating the SM predictions of Higgs boson production. It shows the robustness of the ATLAS detector and analysis techniques in precise measurements at the LHC. The reduction in systematic uncertainties, notably due to the improved photon energy calibration, highlights progress in particle detector technology and analysis methodologies.

These results form the foundation for future analyses at higher luminosities and energies planned in the LHC, where even subtler deviations from the SM might be detected or new physics uncovered. Understanding Higgs production processes continues to be pivotal in particle physics, offering insights into electroweak symmetry breaking and the mass generation mechanism.

This analysis anticipates further refinements in theoretical models and experimental techniques that could enhance the precision and sensitivity of the continued study of the Higgs boson and other possible new phenomena at the LHC.