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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 ATLAS collaboration
Phys.Rev. D93 (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

    10.17182/hepdata.75197.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 14 of the paper

    10.17182/hepdata.75197.v1/t5

    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

    10.17182/hepdata.75197.v1/t6

    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

    Observed and expected upper limits at $95\%$ CL in fb on the fiducial cross section $\sigma^{\mathrm{fid.}}_{W^{\pm} Zjj \textrm{-EW} \rightarrow \ell^{'}...

  • Table 9

    Data from Table 7 of the paper

    10.17182/hepdata.75197.v1/t9

    Observed and expected upper limits at $95\%$ CL in fb on the fiducial cross section $\sigma^{\mathrm{fid.}}_{W^{\pm} Zjj \textrm{-EW} \rightarrow \ell^{'}...

  • Table 10

    Data from Table 8 of the paper

    10.17182/hepdata.75197.v1/t10

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

  • Table 11

    Data from Table 9 of the paper

    10.17182/hepdata.75197.v1/t11

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

  • Table 12

    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

    10.17182/hepdata.75197.v1/t35

    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

    10.17182/hepdata.75197.v1/t36

    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

    10.17182/hepdata.75197.v1/t37

    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

    10.17182/hepdata.75197.v1/t41

    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

    10.17182/hepdata.75197.v1/t42

    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

    10.17182/hepdata.75197.v1/t43

    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

    10.17182/hepdata.75197.v1/t44

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

  • Table 45

    Data from Auxiliary Table 44

    10.17182/hepdata.75197.v1/t45

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

  • Table 46

    Data from Auxiliary Table 45

    10.17182/hepdata.75197.v1/t46

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

  • Table 47

    Data from Auxiliary Table 46

    10.17182/hepdata.75197.v1/t47

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

  • Table 48

    Data from Auxiliary Table 47

    10.17182/hepdata.75197.v1/t48

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

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