Coupling QCD-Scale Axionlike Particles to Gluons

We present a novel data-driven method for determining the hadronic interaction strengths of axionlike particles (ALPs) with QCD-scale masses. Using our method, it is possible to calculate the hadronic production and decay rates of ALPs, along with many of the largest ALP decay rates to exclusive final states. To illustrate the impact on QCD-scale ALP phenomenology, we consider the scenario where the ALP-gluon coupling is dominant over the ALP coupling to photons, electroweak bosons, and all fermions for $m_{\pi }\lesssim m_a\lesssim 3\mathrm{GeV}$. We emphasize, however, that our method can easily be generalized to any set of ALP couplings to standard model particles. Finally, using the approach developed here, we provide calculations for the branching fractions of ${\eta }_c\to VV$ decays; i.e., ${\eta }_c$ decays into two vector mesons, which are consistent with the known experimental values.

Figure 1

ALP $U(3)$ representation. Since isospin-violating decays are small above $m_{{\eta }^{\prime }}$, where the isospin-violating component is highly uncertain, we ignore such decays for $m_a>m_{{\eta }^{\prime }}$.

Figure 2

$\mathcal{F}$ from Eq. (13) determined from $e^{+}{e}^{-}$ data [40, 41, 42]. Since we ignore resonance contributions, each result is only valid at masses where narrow resonance contributions are small. We define these as ($\omega$-like) above where the sizable $\omega –\varphi$ interference effect in the $3\pi$ final state becomes negligible, ($\rho$-like) $m_a\gtrsim m_{{\rho }^{*}}+{\mathrm{\Gamma }}_{{\rho }^{*}}$, and ($\varphi$-like) $m_a\gtrsim m_{{\varphi }^{*}}+{\mathrm{\Gamma }}_{{\varphi }^{*}}$.

Figure 3

ALP decay branching fractions to all final states considered; decay widths are given in the Supplemental Material [27].

Figure 4

Constraints on the ALP-gluon coupling.