Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector (1806.00425v2)

Abstract: The observation of Higgs boson production in association with a top quark pair ($t\bar{t}H$), based on the analysis of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb$^{-1}$, and considering Higgs boson decays into $b\bar{b}$, $WW^*$, $\tau\tau$, $\gamma\gamma$, and $ZZ^*$, the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the $t\bar{t}H$ searches using a dataset corresponding to integrated luminosities of 4.5 fb$^{-1}$ at 7 TeV and 20.3 fb$^{-1}$ at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total $t\bar{t}H$ production cross section at 13 TeV is measured to be 670 $\pm$ 90 (stat.) $^{+110}_{-100}$ (syst.) fb, in agreement with the Standard Model prediction.

• The paper reports the first direct observation of Higgs boson production with top quark pairs, demonstrating a 5.8σ significance that confirms the top Yukawa coupling.
• Advanced methods, including boosted decision trees and enhanced photon and lepton reconstruction, were applied to a combined data set of up to 79.8 fb⁻¹ at 13 TeV.
• The measured cross-sections match Standard Model predictions, paving the way for further studies to reduce uncertainties and explore potential new physics.

Observation of Higgs Boson Production in Association with a Top Quark Pair at the LHC with the ATLAS Detector

This paper reports on the observation of the production of the Higgs boson in association with a top quark pair ($t\bar{t}H$) at the Large Hadron Collider (LHC) using the ATLAS detector. The paper uses proton-proton collision data collected at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of up to 79.8 fb$^{-1}$. The analysis focuses on various decay channels of the Higgs boson, including $H \rightarrow b\bar{b}$, $H \rightarrow WW^{*}$, $H \rightarrow \tau\tau$, $H \rightarrow \gamma\gamma$, and $H \rightarrow ZZ^{*}$.

Methodology and Analysis

The analysis incorporates datasets from different periods and energies: 36.1 fb$^{-1}$ at $\sqrt{s} = 13$ TeV, includes earlier datasets at 7 TeV and 8 TeV. An improved photon and lepton reconstruction algorithm and analysis techniques have been utilized to enhance the sensitivity of the measurements compared to prior analyses. The significance of each channel is assessed using a variety of techniques, including Boosted Decision Trees (BDTs), which are employed in specific decay channels like $H \rightarrow \gamma\gamma$ to discriminate between signal and background efficiently.

Results and Significance

The analysis reveals an observed significance of $\sigma$ standard deviations for the $t\bar{t}H$ signal, which surpasses the expected significance based on background-only hypotheses. The observed significance becomes even more pronounced when combining data from different energy datasets. The results indicate a good agreement between the measured cross-sections and the predictions of the Standard Model (SM).

The paper reports an observed significance for the combined analysis from datasets at 7, 8, and 13 TeV. Specifically, the significance of the $t\bar{t}H$ production is $5.8$ standard deviations, thus confirming the direct observation of the Higgs boson couplings with the top quark.

Implications

The results have significant implications for the field of particle physics, as they provide a direct test of the Yukawa coupling between the Higgs boson and the top quark, the heaviest particle in the SM. This process serves as a crucial test for the SM and offers potential insights into new physics beyond the SM by examining any deviations in the observed values from theoretical predictions.

Future Prospects

Future investigations could focus on reducing systematic uncertainties and improving the detection of secondary decay channels to refine measurements further. Additionally, ongoing data collection at higher luminosities will help improve the precision of the coupling measurements, potentially allowing for the discovery of deviations that may hint at new physics phenomena.

The paper presents robust evidence of Higgs boson production in association with top quark pairs and sets a strong foundation for further exploration in the probing of fundamental particle interactions using advanced detector technologies at high-energy colliders like the LHC.