Heavy QCD Axion at Belle II: Displaced and Prompt Signals

Abstract

The QCD axion is a well-motivated addition to the standard model to solve the strong $CP$ problem. If the axion acquires mass dominantly from a hidden sector, it can be as heavy as $O(1)$ GeV, and the decay constant can be as low as $O(100)$ GeV without running into the axion quality problem. We propose new search strategies for such heavy QCD axions at the Belle II experiment, where the axions are expected to be produced via $B\to Ka$. We find that a subsequent decay $a\to 3\pi$ with a displaced vertex leads to a unique signal with essentially no background, and that a dedicated search can explore the range $O(1$-$10)$ TeV of decay-constant values. We also show that $a\to \gamma \gamma$ can cover a significant portion of currently unexplored region of $150\lesssim m_a\lesssim 500$ MeV.

7 pages, 4 figures; Version accepted for publication in PRD Letter, including experimental results published after version-1 that imply new limits on the axion parameters

References in corpus (9)

• A New Flavor of Searches for Axion-Like Particles
• Constraining the Axion-Photon Coupling with Massive Stars
• Search for low mass vector resonances decaying into quark-antiquark pairs in proton-proton collisions at sqrt(s) = 13 TeV
• Consistent treatment of axions in the weak chiral Lagrangian
• Search for Long-Lived Particles in $e^{+}{e}^{-}$ Collisions
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• Long-lived light neutralinos at Belle II
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• Probing $R$-parity violation in $B$-meson decays to a baryon and a light neutralino
• ALP-Pions generalized
• First Evaluation of Meson and $\tau$ lepton Spectra and Search for Heavy Neutral Leptons at ILC Beam Dump
• ALPs and Heavy Hadron Chiral Perturbation Theory