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Abstract:

A search for quantum black holes in electron+jet or muon+jet final states with high invariant mass is performed. The analysis uses data from s = 13.6 TeV pp collisions recorded by the ATLAS detector between 2022 and 2024 during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of 164 fb − 1 . This search is strongly motivated by a dramatic increase of the production cross-section by up to an order of magnitude for the highest masses considered, thanks to the small increase of 0.6 TeV in centre-of-mass energy between Run 2 and Run 3. No significant excess above the Standard Model background is observed, and 95% CL upper limits are set on the production cross-section times branching ratio in several benchmark models, reaching a mass scale of 9.4 TeV. These represent the strongest exclusion limits to date on quantum black hole production.

Abstract:

This Letter presents the first evidence of the simultaneous production of two $Z$ bosons and one photon with the ATLAS detector at the Large Hadron Collider. The measurement is performed using the full Run-2 dataset, recorded from 2015 to 2018, of proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $140{\mathrm{fb}}^{-1}$ . The fully leptonic final state with four leptons and one photon is analyzed, $pp\to ZZ\gamma \to {\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}\gamma$ with $\ell ,{\ell }^{\prime }=e$ or $\mu$ . This final state is measured in a fiducial region where photon final-state radiation is minimized, and the photon has a transverse momentum of $p_{\mathrm{T}}^{\gamma }>20\mathrm{GeV}$ . Eight events are selected, with a background estimate of $0.92\pm 0.15$ . This results in an observed (expected) significance of the $ZZ\gamma$ final state of $4.4\sigma$ ( $4.0\sigma$ ). The measured cross section for $pp\to ZZ\gamma \to {\ell }^{+}{\ell }^{-}{\ell }^{\prime +}{\ell }^{\prime -}\gamma$ in the fiducial region is ${\sigma }_{ZZ\gamma }=0.144_{-0.051}^{+0.065}{(\mathrm{stat})}_{-0.004}^{+0.008}(\mathrm{syst})\mathrm{fb}$ , in agreement with the standard model prediction of ${\sigma }_{\mathrm{fid}}^{\mathrm{SM}}=0.130\pm 0.006\mathrm{fb}$ .