A search is presented for a heavy scalar (H) or pseudo-scalar (A) predicted by the two-Higgs-doublet models, where the H/A is produced in association with a topquark pair(tt H¯ /A), and with the H/A decaying into a tt ¯pair. The full LHC Run 2 proton–proton collision data collected by the ATLAS experiment is used, corresponding to an integrated luminosity of 139 fb−1. Events are selected requiring exactly one or two opposite-charge electrons or muons. Datadriven corrections are applied to improve the modelling of the tt ¯+jets background in the regime with high jet and b-jet multiplicities. These include a novel multi-dimensional kinematic reweighting based on a neural network trained using data and simulations. An H/A-mass parameterised graph neural network is trained to optimise the signal-to-background discrimination. In combination with the previous search performed by the ATLAS Collaboration in the multilepton final state, the observed upper limits on the tt H¯ /A → ttt¯ t ¯ production cross-section at 95% confidence level range between 14 fb and 5.0 fb for an H/A with mass between 400 GeV and 1000 GeV, respectively. Assuming that both the H and A contribute to the ttt¯ t ¯ cross-section, tan β values below 1.7 or 0.7 are excluded for a mass of 400 GeV or 1000 GeV, respectively. The results are also used to constrain a model predicting the pair production of a colour-octet scalar, with the scalar decaying into a tt ¯ pair.

Null, N., Aad, G., Aakvaag, E., Abbott, B., Abdelhameed, S., Abeling, K., et al. (2025). Search for tt¯ H/A → tt¯ tt¯ production in proton–proton collisions at √s = 13 TeV with the ATLAS detector. EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS, 85(5), 1-36 [10.1140/epjc/s10052-025-14041-z].

Search for tt¯ H/A → tt¯ tt¯ production in proton–proton collisions at √s = 13 TeV with the ATLAS detector

Alberghi, G. L.;Alfonsi, F.;Ballabene, E.;Bellagamba, L.;Bianco, G.;Boscherini, D.;Bruni, A.;Carratta, G.;Cremonini, D.;De Castro, S.;Fabbri, F.;Fabbri, L.;Franchini, M.;Gabrielli, A.;Giacobbe, B.;Levrini, G.;Nechaeva, S.;Polini, A.;Rinaldi, L.;Romano, M.;Sanzani, E.;Sbarra, C.;Sbrizzi, A.;Semprini-Cesari, N.;Sioli, M.;Todome, K.;Valentinetti, S.;Villa, M.;Vittori, C.;Vivarelli, I.;Zoccoli, A.;
2025

Abstract

A search is presented for a heavy scalar (H) or pseudo-scalar (A) predicted by the two-Higgs-doublet models, where the H/A is produced in association with a topquark pair(tt H¯ /A), and with the H/A decaying into a tt ¯pair. The full LHC Run 2 proton–proton collision data collected by the ATLAS experiment is used, corresponding to an integrated luminosity of 139 fb−1. Events are selected requiring exactly one or two opposite-charge electrons or muons. Datadriven corrections are applied to improve the modelling of the tt ¯+jets background in the regime with high jet and b-jet multiplicities. These include a novel multi-dimensional kinematic reweighting based on a neural network trained using data and simulations. An H/A-mass parameterised graph neural network is trained to optimise the signal-to-background discrimination. In combination with the previous search performed by the ATLAS Collaboration in the multilepton final state, the observed upper limits on the tt H¯ /A → ttt¯ t ¯ production cross-section at 95% confidence level range between 14 fb and 5.0 fb for an H/A with mass between 400 GeV and 1000 GeV, respectively. Assuming that both the H and A contribute to the ttt¯ t ¯ cross-section, tan β values below 1.7 or 0.7 are excluded for a mass of 400 GeV or 1000 GeV, respectively. The results are also used to constrain a model predicting the pair production of a colour-octet scalar, with the scalar decaying into a tt ¯ pair.
2025
Null, N., Aad, G., Aakvaag, E., Abbott, B., Abdelhameed, S., Abeling, K., et al. (2025). Search for tt¯ H/A → tt¯ tt¯ production in proton–proton collisions at √s = 13 TeV with the ATLAS detector. EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS, 85(5), 1-36 [10.1140/epjc/s10052-025-14041-z].
Null, Null; Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboelela, M.; Aboulhorma, A.; Abramowicz, H.;...espandi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/1042382
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