Publicação
Search for tt¯H/A→tt¯tt¯ production in proton–proton collisions at s=13 TeV with the ATLAS detector
| Resumo: | A search is presented for a heavy scalar (H) or pseudo-scalar (A) predicted by the two-Higgs-doublet mod els, where the H/A is produced in association with a topquark pair(\( t\overline{t} H/A \)), and with the H/A decaying into a \( t\overline{t} \) ¯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. Data driven corrections are applied to improve the modelling of the \( t\overline{t} \)+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 \( t\overline{t} H/A \rightarrow t\overline{t}t\overline{t} \) 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 \( t\overline{t}t\overline{t} \) cross-section, tan \( \beta \) 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 \( t\overline{t} \) pair. |
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| Autores principais: | Castro, Nuno Filipe |
| Outros Autores: | Onofre, A.; ATLAS Collaboration |
| Assunto: | Ciências Naturais::Ciências Físicas |
| Ano: | 2025 |
| País: | Portugal |
| Tipo de documento: | artigo |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | A search is presented for a heavy scalar (H) or pseudo-scalar (A) predicted by the two-Higgs-doublet mod els, where the H/A is produced in association with a topquark pair(\( t\overline{t} H/A \)), and with the H/A decaying into a \( t\overline{t} \) ¯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. Data driven corrections are applied to improve the modelling of the \( t\overline{t} \)+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 \( t\overline{t} H/A \rightarrow t\overline{t}t\overline{t} \) 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 \( t\overline{t}t\overline{t} \) cross-section, tan \( \beta \) 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 \( t\overline{t} \) pair. |
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