Combined analysis of double Higgs production via gluon fusion at the HL-LHC in the effective field theory approach

TL;DR

This paper analyzes double Higgs production at the HL-LHC using an effective field theory approach, combining multiple decay channels and advanced analysis techniques to constrain Higgs couplings and self-coupling with improved precision.

Contribution

It performs a combined analysis of double Higgs production in multiple channels at HL-LHC, employing multivariate methods and EFT to improve constraints on Higgs couplings and self-coupling.

Findings

The $b\bar{b}\tau^+\tau^-$ channel outperforms $b\bar{b}\gamma\gamma$ for energy-growing operators.

Adding the $b\bar{b}\tau^+\tau^-$ channel minimally improves Higgs self-coupling measurement.

Projected precision of Higgs self-coupling at HL-LHC ranges from 0.2 to 6.5 times the SM value.

Abstract

We perform the combined analysis of the double Higgs production via gluon fusion in the $b\bar{b} \gamma\gamma$ and $b\bar{b}\tau^+\tau^-$ decay channels at the High-Luminosity LHC (HL-LHC). To validate our analysis, we reproduce the ATLAS result of the $b\bar{b} \gamma\gamma$ process including all contributions from fakes. For the $b\bar{b}\tau^+\tau^-$ decay channel, we perform the similar analysis to the CMS one. As an improvement, we also perform the multivariate analysis employing the boosted decision tree algorithm. Then, we derive 68% probability contours on anomalous Higgs couplings in the effective field theory (EFT) approach for various analyses. We find that the $b\bar{b}\tau^+\tau^-$ process outperforms the $b\bar{b}\gamma\gamma$ for the measurement of energy-growing operators, while adding the $b\bar{b}\tau^+\tau^-$ process is least beneficial for improving the precision of the Higgs self-coupling (mainly set by the $b\bar{b}\gamma\gamma$ process). We illustrate that the double Higgs production alone can be comparable to the single Higgs process in constraining the modification of the top Yukawa coupling in the positive direction. Focusing on the Higgs self-coupling as a special interest, we derive the precision as a function of various improvable parameters such as tag and mistag rates of tau leptons, heavy flavor jets, photon identification, diphoton mass resolution, and jet energy resolution to take into account future phenomenological studies. As an optimistic benchmark scenario, we illustrate that the 68% and 95% probability intervals of the Higgs self-coupling, $\lambda_3/\lambda_{3}^{SM}$, at the HL-LHC can reach $[0.2,\, 2.3]$ and $[-0.1,\, 3.5] \cup [4.0,\, 6.5]$, respectively, where the correlation among the EFT coefficients is taken into account.