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Measurement of $W^{\pm}Z$ production cross sections and gauge boson polarisation in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

The collaboration
Eur.Phys.J. C79 (2019) 535, 2019

Abstract (data abstract)
CERN-LHC. This paper presents measurements of $W^{\pm}Z$ production in $pp$ collisions at a center-of-mass energy of $13$ TeV. The data were collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 36.1 fb$^{-1}$. The $W^{\pm}Z$ candidate events are reconstructed using leptonic decay modes into electrons and muons of the gauge bosons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is $\sigma_{W^\pm Z \rightarrow \ell^{'} \nu \ell \ell}^{\textrm{fid.}} = 63.7 \, \pm~1.0~\textrm{(stat.)} \, \pm~2.3~\textrm{(sys.)} \, \pm~0.3~\textrm{(mod.)} \, \pm~1.5~\textrm{(lumi.)}$ fb, in agreement with the next-to-next-to-leading-order Standard Model prediction of $61.5^{+1.4}_{-1.3}$ fb. Cross sections for $W^+Z$ and $W^-Z$ production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of lepton decays of $W$ and $Z$ bosons is performed and integrated helicity fractions in the detector fiducial region are measured for each of the $W$ and $Z$ bosons. The longitudinal polarisation of pair-produced vector bosons is measured for the first time in $pp$ collisions. The cross sections are measured in a fiducial phase space reflecting the detector acceptance, defined by: - $p_{\mathrm{T}}$ of electrons and muons from Z0 decays > 15 GeV - $p_{\mathrm{T}}$ of electrons and muons from the $W^{\pm}$ decays > 20 GeV - $|\eta|$ of muons and electrons < 2.5 - Leptons from the Z0 boson are separated by $\Delta R(\ell,\ell) > 0.2$ from each other - Leptons from the Z0 and W bosons are separated by $\Delta R(\ell,\ell) > 0.3$ from each other - |dilepton mass - Z0 mass| < 10 GeV - $m_{\mathrm{T}}$ of $W^{\pm}$ > 30 GeV. At particle level, the kinematics of final-state prompt electrons and muons is computed including the contributions from final-state radiated photons within a distance in the ($\eta,\phi$) plane of $\Delta R = \sqrt{(\Delta\eta)^2 + (\Delta\phi)^2} = 0.1$ around the direction of the charged lepton. These dressed leptons and the final-state neutrinos that do not originate from hadron or $\tau$ decays are associated with the $W$ and $Z$ boson decay products with an algorithmic approach, called resonant shape''. This algorithm is based on the value of an estimator expressing the product of the nominal line shapes of the $W$ and $Z$ resonances $P = \left| \frac{1}{ m^2_{(\ell^+,\ell^-)} - \left(m_Z^{\textrm{PDG}}\right)^2 + i \; \Gamma_Z^{\textrm{PDG}} \; m_Z^{\textrm{PDG}} } \right|^2 \times \; \left| \frac {1} { m^2_{(\ell',\nu_{\ell'})} - \left(m_W^{\textrm{PDG}}\right)^2 + i \; \Gamma_W^{\textrm{PDG}} \; m_W^{\textrm{PDG}} } \right|^2$ where $m_Z^{\textrm{PDG}}$ ($m_W^{\textrm{PDG}}$) and $\Gamma_Z^{\textrm{PDG}}$ ($\Gamma_W^{\textrm{PDG}}$) are the world average mass and total width of the $Z$ ($W$) boson, respectively, as reported by the Particle Data Group. The input to the estimator is the invariant mass $m$ of all possible pairs ($\ell^+,\ell^-$) and ($\ell',\nu_{\ell'}$) satisfying the fiducial selection requirements. The final choice of which leptons are assigned to the $W$ or $Z$ bosons corresponds to the configuration exhibiting the highest value of the estimator.

• #### Table 1

Data from Table 4 of the paper

10.17182/hepdata.83701.v1/t1

The measured $W^{\pm}Z$ fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined...

• #### Table 2

Data from Table 4 of the paper

10.17182/hepdata.83701.v1/t2

The measured $W^{+}Z$ fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined...

• #### Table 3

Data from Table 4 of the paper

10.17182/hepdata.83701.v1/t3

The measured $W^{-}Z$ fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined...

• #### Table 4

Data from Auxilliary table 1

10.17182/hepdata.83701.v1/t4

The measured fiducial cross sections are corrected to the dressed level. The ratio of $C_{WZ}^{\textrm{dressed}}/C_{WZ}^{\textrm{Born}}$ factors presented in this table...

• #### Table 5

Data from Page 16 of the paper

10.17182/hepdata.83701.v1/t5

Ratio of fiducial cross sections measured for $W^{+} Z$ and $W^{-} Z$ production.

• #### Table 6

Data from Page 16 of the paper

10.17182/hepdata.83701.v1/t6

Cross section extrapolated to total phase space and all W and Z boson decays. The first systematic uncertainty is the...

• #### Table 7

Data from Auxillary material

10.17182/hepdata.83701.v1/t7

The total cross section is measured at dressed level and can also be corrected to Born level use this acceptance...

• #### Table 8

Data from Figure 4 of the paper, Auxiliary Table 6

10.17182/hepdata.83701.v1/t8

• #### Table 11

Data from Auxiliary Table 3

10.17182/hepdata.83701.v1/t11

Correlation matrix for the unfolded cross section.

• #### Table 12

Data from Figure 4 of the paper, Auxiliary Table 4

10.17182/hepdata.83701.v1/t12

• #### Table 15

Data from Auxiliary Table 11

10.17182/hepdata.83701.v1/t15

Correlation matrix for the unfolded cross section.

• #### Table 16

Data from Figure 5 of the paper, Auxiliary Table 8

10.17182/hepdata.83701.v1/t16

• #### Table 19

Data from Auxiliary Table 13

10.17182/hepdata.83701.v1/t19

Correlation matrix for the unfolded cross section.

• #### Table 20

Data from Figure 6 of the paper, Auxiliary Table 14

10.17182/hepdata.83701.v1/t20

• #### Table 23

Data from Auxiliary Table 17

10.17182/hepdata.83701.v1/t23

Correlation matrix for the unfolded cross section.

• #### Table 24

Data from Table 5 of the paper

10.17182/hepdata.83701.v1/t24

5: Measured helicity fractions in the fiducial phase space with Born level leptons, for $W^-$, $W^+Z$ and $W^{\pm}Z$ events. The...