Measurements of four-lepton production in $pp$ collisions at $\sqrt{s}=$ 8 TeV with the ATLAS detector

TL;DR

This paper measures the production cross section of four-lepton events in proton-proton collisions at 8 TeV using the ATLAS detector, providing detailed results on the cross section and the gluon-fusion signal strength.

Contribution

It presents the first detailed measurement of four-lepton production cross sections at 8 TeV, including differential distributions and the gluon-fusion signal strength, with a large dataset and comprehensive analysis.

Findings

Observed 476 signal events with low background.

Measured the gluon-fusion signal strength as 2.4 ± 1.0 (stat) ± 0.5 (syst) ± 0.8 (theory).

Provided differential cross sections as functions of invariant mass and transverse momentum.

Abstract

The four-lepton ($4\ell$, $\ell = e, \mu$) production cross section is measured in the mass range from 80 to 1000 GeV using 20.3 fb$^{-1}$ of data in $pp$ collisions at $\sqrt{s}=8$ TeV collected with the ATLAS detector at the LHC. The $4\ell$ events are produced in the decays of resonant $Z$ and Higgs bosons and the non-resonant $ZZ$ continuum originating from $q\bar q$, $gg$, and $qg$ initial states. A total of 476 signal candidate events are observed with a background expectation of $26.2 \pm 3.6$ events, enabling the measurement of the integrated cross section and the differential cross section as a function of the invariant mass and transverse momentum of the four-lepton system. In the mass range above $180$ GeV, assuming the theoretical constraint on the $q\bar q$ production cross section calculated with perturbative NNLO QCD and NLO electroweak corrections, the signal strength of the gluon-fusion component relative to its leading-order prediction is determined to be $\mu_{gg}=2.4 \pm 1.0 (stat.) \pm 0.5 (syst.)\pm 0.8 (theory)$.