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Search for type-II seesaw mechanism processes with same charge leptons in the final states with the ATLAS detector
ID Leban, Blaž (Author), ID Kerševan, Borut Paul (Mentor) More about this mentor... This link opens in a new window, ID Maček, Boštjan (Co-mentor)

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Abstract
A search for pair production of doubly charged Higgs bosons (\(H^{\pm \pm}\)), each decaying into a pair of prompt, isolated, and highly energetic leptons with the same electric charge, is presented. The search uses a proton-proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb\(^{-1}\) recorded by the ATLAS detector during Run 2 of the Large Hadron Collider (LHC). This analysis focuses on same-charge leptonic decays, \(H^{\pm \pm} \rightarrow \ell^{\pm} \ell^{\prime \pm}\), where \(\ell, \ell^{\prime} = e, \mu, \tau\), in two-, three- and four-lepton channels but only considers final states, which include electrons or muons. No evidence of a signal is observed. Assuming that the branching ratios to each possible leptonic final state are equal, \(\mathcal{B}(H^{\pm \pm} \rightarrow e^{\pm} e^{\pm} / e^{\pm} \mu^{\pm} / \mu^{\pm} \mu^{\pm} / e^{\pm} \tau^{\pm} / \mu^{\pm} \tau^{\pm} / \tau^{\pm} \tau^{\pm}) = 1/6\), the corresponding upper limits on the pair production cross-section of doubly charged Higgs bosons are derived as a function of its mass, \(m_{H^{\pm \pm}}\), at a 95% confidence level. The limits, which are the strongest produced by the ATLAS Collaboration to date, are obtained for the left-right symmetric type-II seesaw model. Additionally, this work provides the first direct test of the Zee-Babu neutrino mass model at the LHC.

Language:English
Keywords:ATLAS, CERN, LHC Run 2, left-right symmetry, type-II seesaw, Zee-Babu model, machine learning, boosted decision trees, neural networks, same-charge leptons, doubly charged Higgs, lepton flavour violation
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FMF - Faculty of Mathematics and Physics
Year:2023
PID:20.500.12556/RUL-152826 This link opens in a new window
COBISS.SI-ID:167238147 This link opens in a new window
Publication date in RUL:08.12.2023
Views:373
Downloads:22
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Secondary language

Language:Slovenian
Title:Iskanje procesov gugalničnega mehanizma tipa II s pari enako nabitih leptonov v končnih stanjih z detektorjem ATLAS
Abstract:
V doktorskem delu je predstavljeno iskanje nastanka para dvojno nabitih Higgsovih bozonov (\(H^{\pm \pm}\)), izmed katerih vsak razpade na par neposrednih, izoliranih in visokoenergijskih leptonov z enakim električnim nabojem. V analizi so uporabljeni podatki, zabeleženi z detektorjem ATLAS med drugim obratovalnim ciklom (Run 2) velikega hadronskega trkalnika (LHC), kar ustreza integrirani luminoznosti 139 fb\(^{-1}\). Zajeti so bili med trki protonov pri težiščni energiji 13 TeV. Analiza se osredotoča na razpade delca (\(H^{\pm \pm}\)) v par leptonov z enakim nabojem, \(H^{\pm \pm} \rightarrow \ell^{\pm} \ell^{\prime \pm}\), pri čemer je \(\ell, \ell^{\prime} = e, \mu, \tau\). Posebej so obravnavana končna stanja z dvema, tremi in štirimi leptoni, vendar so upoštevana le ta, ki vključujejo elektrone ali mione. Statistična obdelava podatkov ne kaže znatnih odstopanj od napovedi Standardnega modela. Ob predpostavki, da so razvejitvena razmerja v vsa možna leptonska končna stanja enaka, \(\mathcal{B}(H^{\pm \pm} \rightarrow e^{\pm} e^{\pm} / e^{\pm} \mu^{\pm} / \mu^{\pm} \mu^{\pm} / e^{\pm} \tau^{\pm} / \mu^{\pm} \tau^{\pm} / \tau^{\pm} \tau^{\pm}) = 1/6\), so izpeljane ustrezne zgornje meje produkcijskih sipalnih presekov dvojno nabitih Higgsovih bozonov kot funkcija njihove mase \(m_{H^{\pm \pm}}\), pri stopnji zaupanja 95 %. Meje, ki so najstrožje, kar jih je doslej objavila kolaboracija ATLAS, so določene za gugalnični mehanizem tipa II znotraj levo-desno simetričnega modela. Poleg tega je to delo prvi neposredni preizkus modela Zee-Babu na LHC.

Keywords:ATLAS, CERN, LHC Run 2, levo-desna simetrija, gugalnični mehanizem tipa II, model Zee–Babu, strojno učenje, pospešena odločevalna drevesa, nevronske mreže, enako nabiti leptoni, dvojno nabiti Higgsov bozon, kršitev leptonskega okusa

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