Probing flavoured Axions in the Tail of $B_q\to {\mu }^{+}{\mu }^{-}$

Abstract

We discuss how LHC di-muon data collected to study $B_q\to \mu \mu$ 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 $B_q\to \mu \mu a$ and the SM background process $B_q\to \mu \mu \gamma$ near the kinematic endpoint. These rates depend on non-perturbative $B_q\to {\gamma }^{(\ast )}$ 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. With these results, we analyse available LHCb data to obtain the sensitivity on $B_q\to \mu \mu a$ 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 $b\to d$ and $b\to s$ transitions.

37 pages, 6 figures, version to appear in JHEP, added multiple subtracted dispersion relation to extend in resonance region including ancillary Mathematica notebook with Form Factors

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Cited by in corpus (11)

• Flavor probes of axion-like particles
• Quark Flavor Phenomenology of the QCD Axion
• Flavor Violating Axions in the Early Universe
• QCD factorization for the four-body leptonic $B$-meson decays
• Methods for high-precision determinations of radiative-leptonic decay form factors using lattice QCD
• Limits on ALP-neutrino couplings from loop-level processes
• Theoretical analysis of the leptonic decays $B\to \ell \ell {\ell }^{\prime }{\bar{\nu }}_{{\ell }^{\prime }}$
• Dispersion relations for $B^{-}\to {\ell }^{-}{\bar{\nu }}_{\ell }{\ell }^{\prime -}{\ell }^{\prime +}$ form factors
• Resolving Charged Hadrons in QED -- Gauge Invariant Interpolating Operators
• Prospects for detecting the couplings of axion-like particle with neutrinos at the CEPC
• Strange quark mass effect in $B_s\to \gamma \gamma ,\gamma \ell \bar{\ell }$ decays