Measurement of the [Formula: see text] and [Formula: see text] production cross sections in multilepton final states using 3.2 fb[Formula: see text] of [Formula: see text] collisions at [Formula: see text] = 13 TeV with the ATLAS detector

Abstract

A measurement of the [Formula: see text] and [Formula: see text] production cross sections in final states with either two same-charge muons, or three or four leptons (electrons or muons) is presented. The analysis uses a data sample of proton-proton collisions at [Formula: see text] TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015, corresponding to a total integrated luminosity of 3.2 fb[Formula: see text]. The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in [Formula: see text] pb and [Formula: see text] pb, in agreement with the Standard Model predictions.

Fig. 1

The (left) $E_{\text{T}}^{\text{miss}}$ and (right) subleading lepton $p_{\text{T}}$ distributions shown for the b-tagged $2\mathit{\mu }$-SS channel where the signal region requirements on subleading lepton $p_{\text{T}}$, number of b-tags, and $E_{\text{T}}^{\text{miss}}$ are relaxed. The shaded band represents the total uncertainty. The background denoted ‘Other’ contains other SM processes producing two same-sign prompt leptons. The last bin in each of the distributions includes the overflow

Fig. 2

Distributions of (left) the number of electrons and (right) the third-lepton $p_{\text{T}}$ in the 3$\ell$-WZ-CR control region before the fit. The background denoted ‘Other’ contains other SM processes producing three prompt leptons. The shaded band represents the total uncertainty. The last bin of the distribution shown in the right panel includes the overflow

Fig. 3

Distributions of the number of electrons in the (left) $3\ell$-Z-VR and (right) $3\ell$-noZ-VR validation regions, shown before the fit. The background denoted ‘Other’ contains other SM processes producing three prompt leptons. The shaded band represents the total uncertainty

Fig. 4

Distributions of (top left) the number of jets, (top right) the number of b-tagged jets, (bottom left) the missing transverse momentum and (bottom right) the third-lepton $p_{\text{T}}$, for events contained in any of the three signal regions 3$\ell$-Z-1b4j, 3$\ell$-Z-2b3j or 3$\ell$-Z-2b4j. The distributions are shown before the fit. The background denoted ‘Other’ contains other SM processes producing three prompt leptons. The shaded band represents the total uncertainty. The last bin in each of the distributions shown in the bottom panels includes the overflow

Fig. 5

(Top left) Leading lepton $p_{\text{T}}$, (top right) $m_{Z_2}$, (bottom left) missing transverse momentum and (bottom right) jet multiplicity distributions in the 4$\ell$-ZZ-CR control region. The distributions are shown before the fit. The shaded band represents the total uncertainty. The last bin of the distribution shown in the top left panel includes the overflow

Fig. 6

Distributions (left) of the invariant mass of the OSSF lepton pair closest to the Z boson mass, $m_{Z_1}$, and (right) of the number of b-tagged jets, for events in the tetralepton signal regions. The distributions are shown before the fit. The background denoted ‘Other’ contains other SM processes producing four prompt leptons. The shaded band represents the total uncertainty. The first and last bin of the distribution shown in the left panel include the underflow and overflow, respectively

Fig. 7

Expected yields after the fit compared to data for the fit to extract ${\mathit{\sigma }}_{t\overline{t}Z}$ and ${\mathit{\sigma }}_{t\overline{t}W}$ in the signal regions and in the control regions used to constrain the WZ and ZZ backgrounds. The ‘Other’ background summarises all other backgrounds described in Sect. 3. The shaded band represents the total uncertainty

Fig. 8

The result of the simultaneous fit to the $t\overline{t}Z$ and $t\overline{t}W$ cross sections along with the 68 and 95% confidence level (CL) contours. The shaded areas correspond to the theoretical uncertainties in the Standard Model predictions, and include renormalisation and factorisation scale uncertainties as well as PDF uncertainties including ${\mathit{\alpha }}_{\text{S}}$ variations