Measurements of Higgs boson production and couplings in the four-lepton channel in $pp$ collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

TL;DR

This paper reports precise measurements of the Higgs boson production and couplings in the four-lepton decay channel using ATLAS data at 7 and 8 TeV, confirming the Higgs signal with high significance and comparing production rates to the Standard Model.

Contribution

First detailed measurement of Higgs couplings in the four-lepton channel at 7 and 8 TeV with combined ATLAS data, including signal strength in various production modes.

Findings

Higgs signal observed with 8.1 sigma significance

Measured signal strength is 1.44 with uncertainties

Production mode signals are consistent with Standard Model expectations

Abstract

The final ATLAS Run 1 measurements of Higgs boson production and couplings in the decay channel $H\to ZZ^{*}\to\ell^+\ell^-\ell^{'+}\ell^{'-}$, where $\ell,\ell^{'}=e$ or $\mu$, are presented. These measurements were performed using $pp$ collision data corresponding to integrated luminosities of 4.5 fb$^{-1}$ and 20.3 fb$^{-1}$ at center-of-mass energies of 7 TeV and 8 TeV, respectively, recorded with the ATLAS detector at the LHC. The $H\to ZZ^{*}\to 4\ell$ signal is observed with a significance of 8.1 standard deviations, with an expectation of 6.2 standard deviations, at $m_{H}$ = 125.36 GeV, the combined ATLAS measurement of the Higgs boson mass from the $H\to \gamma\gamma$ and $H\to ZZ^{*}\to 4\ell$ channels. The production rate relative to the Standard Model expectation, the signal strength, is measured in four different production categories in the $H\to ZZ^{*}\to 4\ell$ channel. The measured signal strength, at this mass, and with all categories combined, is 1.44 $^{+0.40}_{-0.33}$. The signal strength for Higgs boson production in gluon fusion or in association with $t\bar{t}$ or $b\bar{b}$ pairs is found to be 1.7 $^{+0.5}_{-0.4}$, while the signal strength for vector-boson fusion combined with $WH/ZH$ associated production is found to be 0.3 $^{+1.6}_{-0.9}$.