Search for a long-lived spin-0 mediator in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>s</mml:mi></mml:math> transitions at the Belle II experiment
I. Adachi, K. Adamczyk, L. Aggarwal, H. Aihara, Н. Акопов, A. Aloisio, N. Anh Ky, D. M. Asner, H. Atmacan, T. Aushev, V. Aushev, M. Aversano, V. Babu, H. Bae, S. Bahinipati, P. Bambade, Sw. Banerjee, M. Barrett, J. Baudot, M. Bauer, A. Baur, A. Beaubien, Jürgen Becker, P. K. Behera, J. V. Bennett, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, B. Bhuyan, F. Bianchi, T. Bilka, D. Biswas, A. Bobrov, D. Bodrov, A. E. Bolz, A. Bondar, J. Borah, A. Bożek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, M. Campajola, L. Cao, G. Casarosa, C. Cecchi, J. Cerasoli, M.-C. Chang, P. Chang, R. Cheaib, P. Cheema, V. Chekelian, B. G. Cheon, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, J. Cochran, L. Corona, L. Cremaldi, S. Das, F. Dattola, E. De La Cruz–Burelo, S. A. De La Motte, G. De Nardo, M. De Nuccio, G. De Pietro, R. de Sangro, M. Destefanis, S. Dey, A. De Yta-Hernandez, R. Dhamija, A. Di Canto, F. Di Capua, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, M. Dorigo, K. Dort, S. Dreyer, S. Dubey, G. Dujany, P. Ecker, M. Eliachevitch, D. Epifanov, P. Feichtinger, T. Ferber, D. Ferlewicz, T. Fillinger, C. Finck, G. Finocchiaro
Abstract
Additional spin-0 particles appear in many extensions of the standard model. We search for long-lived spin-0 particles $S$ in $B$-meson decays mediated by a $b\ensuremath{\rightarrow}s$ quark transition in ${e}^{+}{e}^{\ensuremath{-}}$ collisions at the $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance at the Belle II experiment. Based on a sample corresponding to an integrated luminosity of $189\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, we observe no evidence for signal. We set model-independent upper limits on the product of branching fractions $\mathcal{B}({B}^{0}\ensuremath{\rightarrow}{K}^{*}(892{)}^{0}(\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})S)\ifmmode\times\else\texttimes\fi{}\mathcal{B}(S\ensuremath{\rightarrow}{x}^{+}{x}^{\ensuremath{-}})$ and $\mathcal{B}({B}^{+}\ensuremath{\rightarrow}{K}^{+}S)\ifmmode\times\else\texttimes\fi{}\mathcal{B}(S\ensuremath{\rightarrow}{x}^{+}{x}^{\ensuremath{-}})$, where ${x}^{+}{x}^{\ensuremath{-}}$ indicates ${e}^{+}{e}^{\ensuremath{-}},{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}},{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, or ${K}^{+}{K}^{\ensuremath{-}}$, as functions of $S$ mass and lifetime at the level of ${10}^{\ensuremath{-}7}$.