Measurement of Higgs-boson self-coupling with single-Higgs and double-Higgs production channels

Abstract

The trilinear self-coupling can be measured directly using the Higgs-boson-pair production cross section, or indirectly through the measurement of single-Higgs-boson production and decay modes. In fact, at next-to-leading order in electroweak interaction, the Higgs-decay partial widths and the cross sections of the main single-Higgs production processes depend on the Higgs-boson self-coupling via weak loops. Measurements of ${\kappa }_{\lambda }$, i.e. the rescaling of the trilinear Higgs self-coupling, are presented in this dissertation. Results are obtained exploiting proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015, 2016 and 2017, corresponding to a luminosity of up to 79.8 fb${}^{-1}$. Constraints on the Higgs self-coupling are presented considering the most sensitive double-Higgs channels (HH), $b\bar{b}{\tau }^{+}{\tau }^{-}$, $b\bar{b}\gamma \gamma$ and $b\bar{b}b\bar{b}$, considering single-Higgs (H) production modes, $ggF$, $VBF$, $ZH$, $WH$ and $t\bar{t}H$, together with $W{W}^{\ast }$, $Z{Z}^{\ast }$, ${\tau }^{+}{\tau }^{-}$, $\gamma \gamma$ and $b\bar{b}$ decay channels, and combining the aforementioned analyses (H+HH) to improve the sensitivity on ${\kappa }_{\lambda }$. Under the assumption that new physics affects only the Higgs-boson self-coupling, the combined H+HH best-fit value of the coupling modifier is: ${\kappa }_{\lambda }=4.6_{-3.8}^{+3.2}$, excluding values outside the interval $-2.3<{\kappa }_{\lambda }<10.3$ at 95% confidence level. Results with less stringent assumptions are also provided, decoupling the Higgs-boson self-coupling and the other Standard Model couplings. The final results of this thesis provide the most stringent constraint on ${\kappa }_{\lambda }$ from experimental measurements to date.

226 pages

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Cited by in corpus (1)

• Off-shell Higgs production at the LHC as a probe of the trilinear Higgs coupling