R. Aaij, A. S. W. Abdelmotteleb, Carlos Abellán Beteta, C. Abellán Beteta, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. Aidala, Z. Ajaltouni, S. Akar, K. Carvalho Akiba, P. Albicocco, J. Albrecht, R. Aleksiejūnas, F. Alessio, P. Álvarez Cartelle, R. Amalric, S. Amato, S. Amato, Y. Amhis, L. An, L. Anderlini, M. Andersson, P. Andreola, M. Andreotti, Sergio Andres Estrada, Alessia Anelli, D. Ao, C. Arata, F. Archilli, Zaratsyan Areg, Matteo Argenton, S. Arguedas Cuendis, Lisa Arnone, A. Artamonov, M. Artuso, E. Aslanides, R. Ataíde Da Silva, M. Atzeni, B. Audurier, Juliette Authier, D. Bacher, I. Bachiller, S. Bachmann, Marie Bachmayer, J. J. Back, P. Baladrón Rodríguez, V. Balagura, A Balboni, W. Baldini, Z. Baldwin, Luca Balzani, H. Bao, J. Baptista de Souza Leite, C. Barbero Pretel, M. Barbetti, I. R. Barbosa, R. J. Barlow, Mikhail Barnyakov, S. Barsuk, W. Barter, W. Barter, B. Batsukh, B. Batsukh, Piera Battista, A. Bay, A. Beck, A. Beck, F. Bedeschi, I. Bediaga, Noah Albin Behling, S. Belin, Alberto Bellavista, K. Belous, I. Belov, I. Belyaev, E. Ben-Haim, G. Benane, G. Bencivenni, A. Berezhnoy, R. Bernet, H. C. Bernstein, A. Bertolin, F. Betti, J. Bex, O. Bezshyyko, Senjuti Bhattacharya, J. Bhom, M. S. Bieker, N. V. Biesuz, A. Biolchini, M. Birch, F. C. R. Bishop, A. Bitadze, A. Bizzeti, T. Blake, F. Blanc
A bstract A search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a μ ± π ∓ final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb − 1 . The results are interpreted in both lepton-number-conserving and lepton-number-violating scenarios. No significant excess is observed. Constraints are placed on the squared mixing element | U μN | 2 to the active muon neutrino, under the assumption that couplings to other lepton flavours are negligible, in the mass range of 1 . 6–5 . 5 GeV.