# Flavoured axions in the tail of B$_{q}$ → μ$^{+}$ μ$^{-}$ and B → γ$^{*}$ form factors

Albrecht, Johannes; Stamou, Emmanuel; Ziegler, Robert 1; Zwicky, Roman
1 Institut für Theoretische Teilchenphysik (TTP), Karlsruher Institut für Technologie (KIT)

## Abstract:

We discuss how LHC di-muon data collected to study B$_{q}$ → μμ can be used to constrain light particles with flavour-violating couplings to b-quarks. Focussing on the case of a flavoured QCD axion, a, we compute the decay rates for B$_{q}$ → μμa and the SM background process Bq → μμγ near the kinematic endpoint. These rates depend on non-perturbative Bq → γ($^{*}$) form factors with on- or off-shell photons. The off-shell form factors — relevant for generic searches for beyond-the-SM particles — are discussed in full generality and computed with QCD sum rules for the first time. This includes an extension to the low-lying resonance region using a multiple subtracted dispersion relation. With these results, we analyse available LHCb data to obtain the sensitivity on B$_{q}$ → μμa at present and future runs. We find that the full LHCb dataset alone will allow to probe axion-coupling scales of the order of 10$^{6}$ GeV for both b → d and b → s transitions. As a spin-off application of the off-shell form factors we further analyse the case of light, Beyond the Standard Model, vectors.

 Zugehörige Institution(en) am KIT Institut für Theoretische Teilchenphysik (TTP) Publikationstyp Zeitschriftenaufsatz Publikationsjahr 2021 Sprache Englisch Identifikator ISSN: 1029-8479, 1126-6708, 1127-2236 KITopen-ID: 1000138930 Erschienen in Journal of High Energy Physics Verlag Scuola Internazionale Superiore di Studi Avanzati (SISSA) Band 2021 Heft 9 Seiten Art.-Nr.: 139 Bemerkung zur Veröffentlichung Gefördert durch SCOAP3 Nachgewiesen in arXivDimensionsScopusWeb of Science
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