Studies of the energy dependence of diboson polarization fractions and the Radiation Amplitude Zero effect in WZ production with the ATLAS detector

The ATLAS collaboration
Phys.Rev.Lett. 133 (2024) 101802, 2024.

Abstract (data abstract)
CERN-LHC. This Letter presents the first study of the energy-dependence of diboson polarization fractions in $WZ \rightarrow \ell\nu \ell'\ell'~(\ell, \ell'=e, \mu)$ production. The data set used corresponds to an integrated luminosity of 140 fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector. Two fiducial regions with an enhanced presence of events featuring two longitudinally-polarized bosons are defined. A non-zero fraction of events with two longitudinally-polarized bosons is measured with an observed significance of 5.3 standard deviations in the region with $100<p_T^Z\leq200$ GeV and 1.6 standard deviations in the region with $p_T^Z>200$ GeV, where $p_T^Z$ is the transverse momentum of the $Z$ boson. This Letter also reports the first study of the Radiation Amplitude Zero effect. Events with two transversely-polarized bosons are analyzed for the $\Delta Y(\ell_W Z)$ and $\Delta Y(WZ)$ distributions defined respectively as the rapidity difference between the lepton from the $W$ boson decay and the $Z$ boson and the rapidity difference between the $W$ boson and the $Z$ boson. Significant suppression of events near zero is observed in both distributions. Unfolded $\Delta Y(\ell_W Z)$ and $\Delta Y(WZ)$ distributions are also measured and compared to theoretical predictions. Fiducial phase space definition for the measurement: - $p_{\mathrm{T}}$ of electrons and muons from $Z$ 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 $Z$ boson are separated by $\Delta R(\ell,\ell) > 0.2$ from each other - Leptons from the $Z$ and W bosons are separated by $\Delta R(\ell,\ell) > 0.3$ from each other - |dilepton mass - $Z$ mass| < 10 GeV - $m_{\mathrm{T}}$ of $W^{\pm}$ > 30 GeV. - $p_{\mathrm{T}}$ of jets > 30 GeV - $|\eta|$ of jets < 4.5. In the RAZ measurement, three signal regions are defined: -$p_{\mathrm{T}}^{WZ}$ < 20, 40, 70 GeV. In the $WZ$ polarization fraction measurement, two signal regions are defined: -$p_{\mathrm{T}}^{WZ}$ < 70 GeV && $p_{\mathrm{T}}^{Z}$ > 200 GeV, -$p_{\mathrm{T}}^{WZ}$ < 70 GeV && 100 < $p_{\mathrm{T}}^{Z} \leq$ 200 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.

  • Table 1

    Data from Table 2 of the paper

    10.17182/hepdata.149992.v1/t1

    Polarization fractions in the region with $100<p_T^Z\leq200$ GeV using three unconstrained parameters.

  • Table 2

    Data from Table 2 of the paper

    10.17182/hepdata.149992.v1/t2

    Polarization fractions in the region with $p_T^Z>200$ GeV using three unconstrained parameters.

  • Table 3

    Data from Page 7 of the paper

    10.17182/hepdata.149992.v1/t3

    Fraction of events where both bosons are longitudinally polarized in the region with $100<p_T^Z\leq200$ GeV using two unconstrained parameters.

  • Table 4

    Data from Page 7 of the paper

    10.17182/hepdata.149992.v1/t4

    Fraction of events where both bosons are longitudinally polarized in the region with $p_T^Z>200$ GeV using two unconstrained parameters.

  • Table 5

    Data from Table 1 of the paper

    10.17182/hepdata.149992.v1/t5

    Numbers of observed and expected events in the 00-enhanced signal regions, before the fit. The total uncertainties are quoted.

  • Table 6

    Data from Tables 7 and 8 of the paper

    10.17182/hepdata.149992.v1/t6

    Summary of the relative uncertainties in the measured longitudinal-longitudinal fractions $f_{00}$. The uncertainties are reported as percentages.

  • Table 7

    Data from Auxiliary Table 5

    10.17182/hepdata.149992.v1/t7

    Numbers of observed and expected events in the 00-enhanced signal regions, after the fit. The total uncertainties are quoted.

  • Table 8

    Data from Auxiliary Figure 8

    10.17182/hepdata.149992.v1/t8

    $|\Delta Y(l_{W}Z)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 20$ GeV of the TT state.

  • Table 9

    Data from Auxiliary Figure 8

    10.17182/hepdata.149992.v1/t9

    $|\Delta Y(l_{W}Z)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 40$ GeV of the TT state.

  • Table 10

    Data from Auxiliary Figure 8

    10.17182/hepdata.149992.v1/t10

    $|\Delta Y(l_{W}Z)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 70$ GeV of the TT state.

  • Table 11

    Data from Auxiliary Figure 9

    10.17182/hepdata.149992.v1/t11

    $|\Delta Y(l_{W}Z)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 20$ GeV of of the sum of all polarization.

  • Table 12

    Data from Auxiliary Figure 9

    10.17182/hepdata.149992.v1/t12

    $|\Delta Y(l_{W}Z)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 40$ GeV of of the sum of all polarization.

  • Table 13

    Data from Auxiliary Figure 9

    10.17182/hepdata.149992.v1/t13

    $|\Delta Y(l_{W}Z)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 70$ GeV of of the sum of all polarization.

  • Table 14

    Data from Auxiliary Figure 8

    10.17182/hepdata.149992.v1/t14

    $|\Delta Y(WZ)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 20$ GeV of the TT state.

  • Table 15

    Data from Auxiliary Figure 8

    10.17182/hepdata.149992.v1/t15

    $|\Delta Y(WZ)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 40$ GeV of the TT state.

  • Table 16

    Data from Auxiliary Figure 8

    10.17182/hepdata.149992.v1/t16

    $|\Delta Y(WZ)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 70$ GeV of the TT state.

  • Table 17

    Data from Auxiliary Figure 9

    10.17182/hepdata.149992.v1/t17

    $|\Delta Y(WZ)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 20$ GeV of of the sum of all polarization.

  • Table 18

    Data from Auxiliary Figure 9

    10.17182/hepdata.149992.v1/t18

    $|\Delta Y(WZ)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 40$ GeV of of the sum of all polarization.

  • Table 19

    Data from Auxiliary Figure 9

    10.17182/hepdata.149992.v1/t19

    $|\Delta Y(WZ)|$ Migration matrix RAZ Region $p_{T}^{WZ}< 70$ GeV of of the sum of all polarization.

  • Table 20

    Data from Auxiliary Figure 11

    10.17182/hepdata.149992.v1/t20

    The $\mathcal{D}$ value for the unfolded $|\Delta Y(l_{W}Z)|$ distributions of the TT polarization state as a function of the $p_T^{WZ}$...

  • Table 21

    Data from Auxiliary Figure 11

    10.17182/hepdata.149992.v1/t21

    The $\mathcal{D}$ value for the unfolded $|\Delta Y(WZ)|$ distributions of the TT polarization state as a function of the $p_T^{WZ}$...

  • Table 22

    Data from Auxiliary Figure 12

    10.17182/hepdata.149992.v1/t22

    Measured normalized differential $|\Delta Y(l_{W}Z)|$ cross-section of the TT state in the RAZ Region $p_{T}^{WZ}< 20$ GeV. The total uncertainties...

  • Table 23

    Data from Auxiliary Figure 12

    10.17182/hepdata.149992.v1/t23

    Measured normalized differential $|\Delta Y(l_{W}Z)|$ cross-section of the TT state in the RAZ Region $p_{T}^{WZ}< 40$ GeV. The total uncertainties...

  • Table 24

    Data from Auxiliary Figure 12

    10.17182/hepdata.149992.v1/t24

    Measured normalized differential $|\Delta Y(l_{W}Z)|$ cross-section of the TT state in the RAZ Region $p_{T}^{WZ}< 70$ GeV. The total uncertainties...

  • Table 25

    Data from Auxiliary Figure 13

    10.17182/hepdata.149992.v1/t25

    Measured normalized differential $|\Delta Y(WZ)|$ cross-section of the TT state in the RAZ Region $p_{T}^{WZ}< 20$ GeV. The total uncertainties...

  • Table 26

    Data from Auxiliary Figure 13

    10.17182/hepdata.149992.v1/t26

    Measured normalized differential $|\Delta Y(WZ)|$ cross-section of the TT state in the RAZ Region $p_{T}^{WZ}< 40$ GeV. The total uncertainties...

  • Table 27

    Data from Auxiliary Figure 13

    10.17182/hepdata.149992.v1/t27

    Measured normalized differential $|\Delta Y(WZ)|$ cross-section of the TT state in the RAZ Region $p_{T}^{WZ}< 70$ GeV. The total uncertainties...

  • Table 28

    Data from Auxiliary Figure 12

    10.17182/hepdata.149992.v1/t28

    Measured normalized differential $|\Delta Y(l_{W}Z)|$ cross-section of the sum of polarization states in the RAZ Region $p_{T}^{WZ}< 20$ GeV. The...

  • Table 29

    Data from Auxiliary Figure 12

    10.17182/hepdata.149992.v1/t29

    Measured normalized differential $|\Delta Y(l_{W}Z)|$ cross-section of the sum of polarization states in the RAZ Region $p_{T}^{WZ}< 40$ GeV. The...

  • Table 30

    Data from Auxiliary Figure 12

    10.17182/hepdata.149992.v1/t30

    Measured normalized differential $|\Delta Y(l_{W}Z)|$ cross-section of the sum of polarization states in the RAZ Region $p_{T}^{WZ}< 70$ GeV. The...

  • Table 31

    Data from Auxiliary Figure 13

    10.17182/hepdata.149992.v1/t31

    Measured normalized differential $|\Delta Y(WZ)|$ cross-section of the sum of polarization states in the RAZ Region $p_{T}^{WZ}< 20$ GeV. The...

  • Table 32

    Data from Auxiliary Figure 13

    10.17182/hepdata.149992.v1/t32

    Measured normalized differential $|\Delta Y(WZ)|$ cross-section of the sum of polarization states in the RAZ Region $p_{T}^{WZ}< 40$ GeV. The...

  • Table 33

    Data from Auxiliary Figure 13

    10.17182/hepdata.149992.v1/t33

    Measured normalized differential $|\Delta Y(WZ)|$ cross-section of the sum of polarization states in the RAZ Region $p_{T}^{WZ}< 70$ GeV. The...

  • Table 34

    Data from Auxiliary Table 9

    10.17182/hepdata.149992.v1/t34

    Summary of the relative uncertainties in the measured depth of the TT state in the RAZ Region $p_{T}^{WZ}<20$ GeV using...

  • Table 35

    Data from Auxiliary Table 10

    10.17182/hepdata.149992.v1/t35

    Summary of the relative uncertainties in the measured depth of the TT state in the RAZ Region $p_{T}^{WZ}<40$ GeV using...

  • Table 36

    Data from Auxiliary Table 11

    10.17182/hepdata.149992.v1/t36

    Summary of the relative uncertainties in the measured depth of the TT state in the RAZ Region $p_{T}^{WZ}<70$ GeV using...

  • Table 37

    Data from Auxiliary Table 9

    10.17182/hepdata.149992.v1/t37

    Summary of the relative uncertainties in the measured depth of the TT state in the RAZ Region $p_{T}^{WZ}<20$ GeV using...

  • Table 38

    Data from Auxiliary Table 10

    10.17182/hepdata.149992.v1/t38

    Summary of the relative uncertainties in the measured depth of the TT state in the RAZ Region $p_{T}^{WZ}<40$ GeV using...

  • Table 39

    Data from Auxiliary Table 11

    10.17182/hepdata.149992.v1/t39

    Summary of the relative uncertainties in the measured depth of the TT state in the RAZ Region $p_{T}^{WZ}<70$ GeV using...

  • Table 40

    Data from Auxiliary Table 9

    10.17182/hepdata.149992.v1/t40

    Summary of the relative uncertainties in the measured depth of the sum of polarization states in the RAZ Region $p_{T}^{WZ}<20$...

  • Table 41

    Data from Auxiliary Table 10

    10.17182/hepdata.149992.v1/t41

    Summary of the relative uncertainties in the measured depth of the sum of polarization states in the RAZ Region $p_{T}^{WZ}<40$...

  • Table 42

    Data from Auxiliary Table 11

    10.17182/hepdata.149992.v1/t42

    Summary of the relative uncertainties in the measured depth of the sum of polarization states in the RAZ Region $p_{T}^{WZ}<70$...

  • Table 43

    Data from Auxiliary Table 9

    10.17182/hepdata.149992.v1/t43

    Summary of the relative uncertainties in the measured depth of the sum of polarization states in the RAZ Region $p_{T}^{WZ}<20$...

  • Table 44

    Data from Auxiliary Table 10

    10.17182/hepdata.149992.v1/t44

    Summary of the relative uncertainties in the measured depth of the sum of polarization states in the RAZ Region $p_{T}^{WZ}<40$...

  • Table 45

    Data from Auxiliary Table 11

    10.17182/hepdata.149992.v1/t45

    Summary of the relative uncertainties in the measured depth of the sum of polarization states in the RAZ Region $p_{T}^{WZ}<70$...

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