Constraining off-shell production of axionlike particles with $Z\gamma$ and $WW$ differential cross-section measurements

This article describes a search for low-mass axionlike particles (ALPs) at the Large Hadron Collider (LHC). If ALPs were produced at the LHC via gluon-gluon fusion and decayed to bosons, the energy dependence of the measured diboson cross-sections would differ from the Standard Model expectation. Measurements of $WW$ and $Z\gamma$ differential cross sections by the ATLAS collaboration are interpreted to constrain ALP couplings to $W$-, $Z$-bosons and photons assuming gluon-gluon-fusion production.

Figure 1

Differential cross sections as a function of (top) the leading lepton $p_{\mathrm{T}}$ measured in $WW0j$ events, (bottom) the transverse mass $m_T$ measured in $WW1j$ events. The data is compared to the SM prediction and a hypothetical ALP signal with $m_a=1\mathrm{keV}$, $f_a=1\mathrm{TeV}$, $g_{agg}=1{\mathrm{TeV}}^{-1}$, and $g_{aWW}$ as shown in the legend corresponding to the derived 95% CL upper limit in each analysis. The lower panels show the ratios of the data and of the sum of SM and ALP contribution to the SM prediction.

Figure 2

Differential cross sections as a function of the photon $p_{\mathrm{T}}$ measured in $Z\gamma$ events. The data is compared to the SM prediction and a hypothetical ALP signal with $m_a=1\mathrm{keV}$, $f_a=1\mathrm{TeV}$, $g_{agg}=1{\mathrm{TeV}}^{-1}$, and $g_{aZ\gamma }$ as shown in the legend corresponding to the derived 95% CL upper limit of the analysis. The lower panels show the ratios of the data and of the sum of SM and ALP contribution to the SM prediction.

Figure 3

95% CL constraints on $c_{\tilde{W}}$ and $c_{\tilde{B}}$ from this work ($Z\gamma$ and $WW$) and from Ref. [48] ($ZZ$ and $\gamma \gamma$). Values of $g_{agg}=1{\mathrm{TeV}}^{-1}$, $f_a=1\mathrm{TeV}$ and $m_a=1\mathrm{keV}$ are assumed. The yellow area is still allowed by all analyses.

Figure 4

95% CL constraints on $g_{aWW}$ (top) and $g_{aZ\gamma }$ (bottom). The constraints derived in this work are shown as the hatched area with the assumption $g_{a{V}_1{V}_2}/g_{agg}={\alpha }_{V_1{V}_2}/{\alpha }_s$. Also shown are constraints from other experiments, see text.