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Measurements of $W^\pm Z$ production cross sections in $pp$ collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings

The collaboration
Phys.Rev.D 93 (2016) 092004, 2016.

Abstract (data abstract)
CERN-LHC. This paper presents measurements of $W^\pm Z$ production in $pp$ collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 20.3 fb$^{-1}$. The measured inclusive cross section in the detector fiducial region is $\sigma_{W^\pm Z \rightarrow \ell^{'} \nu\ \ell \ell} = 35.1 \pm$ 0.9 (stat.) $\pm 0.8$ (sys.) $\pm 0.8$ (lumi.) fb, for one leptonic decay channel. In comparison, the next-to-leading-order Standard Model expectation is 30.0 $\pm$ 2.1 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. Limits on anomalous triple gauge boson couplings are derived from the transverse mass spectrum of the $W^\pm Z$ system. From the analysis of events with a $W$ and a $Z$ boson associated with two or more forward jets an upper limit at 95% confidence level on the $W^\pm Z$ scattering cross section of 0.63 fb, for each leptonic decay channel, is established, while the Standard Model prediction at next-to-leading order is 0.13 fb. Limits on anomalous quartic gauge boson couplings are also extracted The cross sections are measured in a fiducial phase space reflecting the detector acceptance, defined below. Fiducial phase space definition: - $p_{\mathrm{T}}$ 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~\cite{Agashe:2014kda}. 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 defined in the next paragraph. 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. The inclusive cross section is also extrapolated to the total phase space and all W and Z boson decay modes. This result is model-dependent and includes phase space that was not experimentally accessible, so it should be used with caution. Whenever possible, the fiducial cross sections should be used instead, since they are only minimally model-dependent. Fiducial phase space for VBS measurement: additional criteria to the above Fiducial phase space definition - at least 2 jets - $p_{\mathrm{T}}$ of jets > 30 GeV - $|\eta|$ of jets < 4.5 - invariant mass of the 2 leading jets > 500 GeV - leptons and jets separated by $\Delta R(\ell,jet) > 0.3$ where jets are particle level jets with anti-kt R=0.4. Fiducial phase space for aQGC measurement: additional criteria to the above VBS phase space definition - difference in azimuthal angle between W and Z bosons directions $|\Delta \phi(W,Z)| > 2$ - scalar sum of the transverse momenta of the three charged leptons associated with W and Z bosons $\sum |p_{\mathrm{T}}^{\ell}| > 250$ GeV.

• #### Table 1

Data from Table 6 of the paper

10.17182/hepdata.75197.v1/t1

The measured fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined systematic...

• #### Table 2

Data from Table 6 of the paper

10.17182/hepdata.75197.v1/t2

The measured fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined systematic...

• #### Table 3

Data from Table 6 of the paper

10.17182/hepdata.75197.v1/t3

The measured fiducial cross section in the four channels and their combination. The first systematic uncertainty is the combined systematic...

• #### Table 4

Data from Auxilliary table 10

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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...

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Data from Page 14 of the paper

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

• #### Table 6

Data from Auxillary table 10

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

• #### Table 7

Data from Page 13 of the paper

10.17182/hepdata.75197.v1/t7

Ratio of fiducial cross sections measured for $W^{+} Z$ and $W^{-} Z$ production. The first systematic uncertainty is the combined...

• #### Table 8

Data from Table 7 of the paper

10.17182/hepdata.75197.v1/t8

• #### Table 10

Data from Table 8 of the paper

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Expected and observed one-dimensional 95% Confidence Level intervals on the anomalous couplings parameters. Anomalous couplings are introduced as form factors...

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Data from Table 9 of the paper

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Expected and observed one-dimensional intervals at 95% Confidence Level on the Effective Field Theory (EFT) parameters.

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Data from Figure 4 of the paper, Auxiliary Table 11

10.17182/hepdata.75197.v1/t12

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 13

Data from Auxiliary Table 12

10.17182/hepdata.75197.v1/t13

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 14

Data from Auxiliary Table 13

10.17182/hepdata.75197.v1/t14

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 15

Data from Figure 4 of the paper, Auxiliary Table 14

10.17182/hepdata.75197.v1/t15

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 16

Data from Auxiliary Table 15

10.17182/hepdata.75197.v1/t16

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 17

Data from Auxiliary Table 16

10.17182/hepdata.75197.v1/t17

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 18

Data from Figure 5 of the paper, Auxiliary Table 17

10.17182/hepdata.75197.v1/t18

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 19

Data from Auxiliary Table 18

10.17182/hepdata.75197.v1/t19

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 20

Data from Auxiliary Table 19

10.17182/hepdata.75197.v1/t20

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 21

Data from Figure 6 of the paper, Auxiliary Table 20

10.17182/hepdata.75197.v1/t21

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 22

Data from Auxiliary Table 21

10.17182/hepdata.75197.v1/t22

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 23

Data from Auxiliary Table 22

10.17182/hepdata.75197.v1/t23

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 24

Data from Figure 6 of the paper, Auxiliary Table 23

10.17182/hepdata.75197.v1/t24

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 25

Data from Auxiliary Table 24

10.17182/hepdata.75197.v1/t25

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 26

Data from Auxiliary Table 25

10.17182/hepdata.75197.v1/t26

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 27

Data from Figure 10 of the paper, Auxiliary Table 26

10.17182/hepdata.75197.v1/t27

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 28

Data from Figure 11 of the paper, Auxiliary Table 27

10.17182/hepdata.75197.v1/t28

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 29

Data from Auxiliary Table 28

10.17182/hepdata.75197.v1/t29

Measured fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell^-$ channels combined, where $\ell, \ell' = e, \mu$. The first...

• #### Table 30

Data from Auxiliary Table 29

10.17182/hepdata.75197.v1/t30

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 31

Data from Auxiliary Table 30

10.17182/hepdata.75197.v1/t31

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 32

Data from Auxiliary Table 31

10.17182/hepdata.75197.v1/t32

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 33

Data from Auxiliary Table 32

10.17182/hepdata.75197.v1/t33

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 34

Data from Auxiliary Table 33

10.17182/hepdata.75197.v1/t34

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 35

Data from Auxiliary Table 34

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Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 36

Data from Auxiliary Table 35

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Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 37

Data from Auxiliary Table 36

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Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 38

Data from Auxiliary Table 37

10.17182/hepdata.75197.v1/t38

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 39

Data from Auxiliary Table 39

10.17182/hepdata.75197.v1/t39

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 40

Data from Auxiliary Table 38

10.17182/hepdata.75197.v1/t40

Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 41

Data from Auxiliary Table 40

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Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 42

Data from Auxiliary Table 41

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Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 43

Data from Auxiliary Table 42

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Measured normalised fiducial cross section in all $\ell'^\pm \nu \ell^+ \ell^-$ channels combined, where $\ell, \ell' = e, \mu$. The...

• #### Table 44

Data from Auxiliary Table 43

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• #### Table 46

Data from Auxiliary Table 45

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• #### Table 48

Data from Auxiliary Table 47

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Ratio of $W^{+}Z$ over $W^{-}Z$ differential fiducial cross sections measured in all $\ell'^\pm \nu \ell^+ \ell'^-$ channels combined, where \$\ell,...