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Search for Higgs bosons decaying into new spin-0 or spin-1 particles in four-lepton final states with the ATLAS detector with 139 fb<sup> −1</sup> of pp collision data at √s = 13 TeV

G Aad, B Abbott, DC Abbott, A Abed Abud, K Abeling, DK Abhayasinghe, SH Abidi, A Aboulhorma, H Abramowicz, H Abreu, Y Abulaiti, AC Abusleme Hoffman, BS Acharya, B Achkar, L Adam, C Adam Bourdarios, L Adamczyk, L Adamek, SV Addepalli, J Adelman, A Adiguzel, S Adorni, T Adye, AA Affolder, Y Afik, C Agapopoulou, MN Agaras, J Agarwala, A Aggarwal, C Agheorghiesei, JA Aguilar-Saavedra, A Ahmad, F Ahmadov, WS Ahmed, X Ai, G Aielli, I Aizenberg, S Akatsuka, M Akbiyik, TPA Åkesson, AV Akimov, K Al Khoury, GL Alberghi, J Albert, P Albicocco, MJ Alconada Verzini, S Alderweireldt, M Aleksa, IN Aleksandrov, C Alexa, T Alexopoulos, A Alfonsi, F Alfonsi, M Alhroob, B Ali, S Ali, M Aliev, G Alimonti, C Allaire, BMM Allbrooke, PP Allport, A Aloisio, F Alonso, C Alpigiani, E Alunno Camelia, M Alvarez Estevez, MG Alviggi, Y Amaral Coutinho, A Ambler, L Ambroz, C Amelung, D Amidei, SP Amor Dos Santos, S Amoroso, KR Amos, CS Amrouche, V Ananiev, C Anastopoulos, N Andari, T Andeen, JK Anders, SY Andrean, A Andreazza, S Angelidakis, A Angerami, AV Anisenkov, A Annovi, C Antel, MT Anthony, E Antipov, M Antonelli, DJA Antrim, F Anulli, M Aoki, JA Aparisi Pozo, MA Aparo, L Aperio Bella, N Aranzabal, V Araujo Ferraz, C Arcangeletti
OAI: oai:www.repository.cam.ac.uk:1810/338510 DOI: 10.17863/CAM.85923
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Abstract

Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass $125$ GeV decays into four leptons ($\ell =$ $e$,$\mu$). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons: $H \rightarrow XX/ZX \rightarrow 4\ell$, where the new boson $X$ has a mass between 1 and 60 GeV. The search uses $pp$ collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb$^{-1}$ at a centre-of-mass energy $\sqrt{s}=13$ TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay into $XX/ZX$, improving those from previous publications by a factor between two and four. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where $X$ is interpreted to be a dark boson.