Measurement of electroweak $Z(\nu\bar{\nu})\gamma jj$ production and limits on anomalous quartic gauge couplings in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration
JHEP 06 (2023) 082, 2023.

Abstract (data abstract)
CERN-LHC. The production of electroweak $Z(\nu\bar{\nu})\gamma$ in association with two jets is studied in a regime with a high transverse momentum photon above 150 GeV using proton-proton collisions at centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb$^{-1}$ collected by the ATLAS detector during the 2015-2018 LHC data taking. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial $Z(\nu\bar{\nu})\gamma jj$ cross section for the electroweak production is measured to be 0.75$^{+0.32}_{-0.28}$ fb and is consistent with the Standard Model prediction. Evidence for the electroweak $Z(\nu\bar{\nu})\gamma jj$ production is found with a significance of 3.2$\sigma$ in the background-only hypothesis, compared with an expected significance of 3.7$\sigma$. Combining this result with the previously published ATLAS observation of electroweak $Z(\nu\bar{\nu})\gamma jj$ production yields in an observed (expected) signal significance of 6.3$\sigma$ (6.6$\sigma$). Limits on anomalous quartic gauge boson couplings are obtained in the framework of Effective Field Theory with dimension-eight operators. The extended fiducial region is defined as: - $p_{T}^{\nu\bar{\nu}} >$ 120 GeV - $N_{phot}$ = 1 - $p_{T}^{\gamma} >$ 150 GeV - $|\eta^{\gamma}| <$ 2.37 - $N_{jets} \geq 2$ - $p_{T}^{jet} >$ 50 GeV - $|\eta^{jet}| <$ 4.5 - $\Delta R(jet,\gamma) >$ 0.3 - $\Delta\phi(\gamma,$p_{T}^{\nu\bar{\nu}})>$ 0.4 - $\Delta\phi(\jet,$p_{T}^{\nu\bar{\nu}})>$ 0.3 - $m_{jj}>$300 GeV - $\gamma$-centrality<0.6.

  • Table 1

    Data from Figure 3a

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    These graphs indicate the effect of the main theory uncertainties, which are associated with the renormalisation and factorisation scales (dashed...

  • Table 2

    Data from Figure 3b

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    These graphs indicate the effect of the main theory uncertainties, which are associated with the renormalisation and factorisation scales (dashed...

  • Table 3

    Data from Figure 4a

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    The $m_{jj}$ distributions for the CRs and the BDT classifier response distribution for the SR after the fit in all...

  • Table 4

    Data from Figure 4b

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    The $m_{jj}$ distributions for the CRs and the BDT classifier response distribution for the SR after the fit in all...

  • Table 5

    Data from Figure 4c

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    The $m_{jj}$ distributions for the CRs and the BDT classifier response distribution for the SR after the fit in all...

  • Table 6

    Data from Figure 4d

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    The $m_{jj}$ distributions for the CRs and the BDT classifier response distribution for the SR after the fit in all...

  • Table 7

    Data from Table 3

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    Observed and expected event yields for the signal and all of the background processes considered in this analysis after the...

  • Table 8

    Data from Figure 5

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    Summary of the event yield for processes in all regions, after the fit over all regions. The dashed line shows...

  • Table 9

    Data from Table 4

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    Impact of different components of systematic uncertainty on the measured cross section, without taking into account the correlations. The impact...

  • Table 10

    Data from Table 5

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    Fitted POI values for this analysis, the previous ATLAS analysis, and their combination. The first and second columns present the...

  • Table 11

    Data from Table 6

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    Observed and expected one-dimensional limits on dimension 8 aQGC parameters. Limits are obtained by setting all aQGCs parameters except one...

  • Table 12

    Data from Table 7

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    Observed and expected one-dimensional limits on dimension 8 aQGC parameters in the region, where unitarity is preserved. Cutoff scales in...

  • Table 13

    Data from Figure 6

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    The $E_{T}^{\gamma}$ distribution in the SR after the fit in the control regions. The red (green) line shows the expected...

  • Table 14

    Data from Figure 7a

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{T0}/\Lambda^4$. The unitarity bound is...

  • Table 15

    Data from Figure 7b

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{T5}/\Lambda^4$. The unitarity bound is...

  • Table 16

    Data from Figure 7c

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{T8}/\Lambda^4$. The unitarity bound is...

  • Table 17

    Data from Figure 7d

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{T9}/\Lambda^4$. The unitarity bound is...

  • Table 18

    Data from Figure 8a

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{M0}/\Lambda^4$. The unitarity bound is...

  • Table 19

    Data from Figure 8b

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{M1}/\Lambda^4$. The unitarity bound is...

  • Table 20

    Data from Figure 8c

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    Evolution of the expected (red line) and observed (blue line) limits versus $E_{c}$ values for $f_{M2}/\Lambda^4$. The unitarity bound is...

  • Table 21

    Data from auxuliary Figure 11

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    Correlation matrix of the parameters for the fit in all regions. Only parameters with absolute value of the correlation coefficient...

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