Search for Majorana neutrinos in same-sign WW scattering events from pp collisions at √s=13 TeV

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jats:titleAbstract</jats:title>jats:pA search for Majorana neutrinos in same-sign jats:italicWW</jats:italic> scattering events is presented. The analysis uses jats:inline-formulajats:alternativesjats:tex-math$$\sqrt{s}= 13$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:msqrt mml:mis</mml:mi> </mml:msqrt> mml:mo=</mml:mo> mml:mn13</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> TeV proton–proton collision data with an integrated luminosity of 140 fbjats:inline-formulajats:alternativesjats:tex-math$$^{-1}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msup <mml:mrow /> mml:mrow mml:mo-</mml:mo> mml:mn1</mml:mn> </mml:mrow> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> recorded during 2015–2018 by the ATLAS detector at the Large Hadron Collider. The analysis targets final states including exactly two same-sign muons and at least two hadronic jets well separated in rapidity. The modelling of the main backgrounds, from Standard Model same-sign jats:italicWW</jats:italic> scattering and jats:italicWZ</jats:italic> production, is constrained with data in dedicated signal-depleted control regions. The distribution of the transverse momentum of the second-hardest muon is used to search for signals originating from a heavy Majorana neutrino with a mass between 50 GeV and 20 TeV. No significant excess is observed over the background expectation. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. In addition, the sensitivity to the Weinberg operator is investigated. Upper limits at the 95% confidence level are placed on the squared muon-neutrino–heavy-neutrino mass-mixing matrix element jats:inline-formulajats:alternativesjats:tex-math$$\vert V_{\mu N} \vert ^{2}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mrow mml:mo|</mml:mo> </mml:mrow> mml:msub mml:miV</mml:mi> mml:mrow mml:miμ</mml:mi> mml:miN</mml:mi> </mml:mrow> </mml:msub> mml:msup mml:mrow mml:mo|</mml:mo> </mml:mrow> mml:mn2</mml:mn> </mml:msup> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> as a function of the heavy Majorana neutrino’s mass jats:inline-formulajats:alternativesjats:tex-math$$m_N$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:msub mml:mim</mml:mi> mml:miN</mml:mi> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula>, and on the effective jats:inline-formulajats:alternativesjats:tex-math$$\mu \mu $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:miμ</mml:mi> mml:miμ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> Majorana neutrino mass jats:inline-formulajats:alternativesjats:tex-math$$|m_{\mu \mu }|$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mrow mml:mo|</mml:mo> </mml:mrow> mml:msub mml:mim</mml:mi> mml:mrow mml:miμ</mml:mi> mml:miμ</mml:mi> </mml:mrow> </mml:msub> mml:mrow mml:mo|</mml:mo> </mml:mrow> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>.</jats:p>

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Acknowledgements: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; Minciencias, Colombia; MEYS CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRI, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MEiN, Poland; FCT, Portugal; MNE/IFA, Romania; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DSI/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TENMAK, Türkiye; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, Compute Canada and CRC, Canada; PRIMUS 21/SCI/017 and UNCE SCI/013, Czech Republic; COST, ERC, ERDF, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; Investissements d’Avenir Labex, Investissements d’Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and MINERVA, Israel; Norwegian Financial Mechanism 2014-2021, Norway; NCN and NAWA, Poland; La Caixa Banking Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resources are listed in Ref. [86].

Keywords
5106 Nuclear and Plasma Physics, 5107 Particle and High Energy Physics, 51 Physical Sciences
Journal Title
European Physical Journal C
Conference Name
Journal ISSN
1434-6044
1434-6052
Volume Title
83
Publisher
Springer Science and Business Media LLC