Measuring the Higgs boson self-coupling at the LHC using ratios of cross sections

TL;DR

The paper investigates measuring the Higgs trilinear self-coupling $\lambda$ at the LHC by exploiting the ratio $C_{HH} = \sigma_{HH} / \sigma_H$, which reduces theoretical (scale) uncertainties relative to the double-Higgs cross section. They discuss the dependence of the observable on $\lambda$ and the top Yukawa coupling $y_t$ and note that the triangle diagram is subdominant while the interference with the box diagram is destructive and highly sensitive to $y_t$. A counting-based strategy combines channels with final states $b\bar{b}\tau^+\tau^-$, $b\bar{b}W^+W^-$, and $b\bar{b}\gamma\gamma$, with expected signal and background yields provided for current and high-luminosity runs to derive $\delta C_{HH}$. The naive combination yields a projected precision on $\lambda$ of about $+30\% / -20\%$, and the results highlight a strong degeneracy with the top Yukawa $y_t$, underscoring the need for precise $y_t$. The study concludes that the ratio $C_{HH}$ reduces theoretical uncertainties and can constrain the Higgs self-coupling at the HL-LHC, though full detector-level analyses by ATLAS/CMS remain essential.

Abstract

We consider the ratio between the double and single Higgs production cross sections and examine the prospect of measuring the trilinear Higgs self-coupling using this observable. Such a ratio has a reduced theoretical (scale) uncertainty than the double Higgs cross section. We find that with 600/fb, the 14 TeV LHC can constraint the trilinear Higgs self coupling to be positive, and with 3000/fb one could measure it with a +30 % {-20 %}) accuracy.

Figures (2)

• Figure 1: Feynman diagrams for $HH$ production at leading order ($f$ is a generic fermion): (a) triangle and (b) box topologies. (c) Rates (cross section times branching ratios) for $HH$ at the 14 TeV LHC.
• Figure 2: The expected exclusions intervals at one and two standard deviations with 600 fb$^{-1}$ for (a) $\lambda_{\rm true} \ne 1$ and (b) for the SM in the $\lambda- y_t$ plane. (c) Significance for each channel and for their combination.