Axionlike Particles at Future Neutrino Experiments: Closing the Cosmological Triangle

Axionlike particles (ALPs) provide a promising direction in the search for new physics, while a wide range of models incorporate ALPs. We point out that future neutrino experiments, such as DUNE, possess competitive sensitivity to ALP signals. The high-intensity proton beam impinging on a target can not only produce copious amounts of neutrinos, but also cascade photons that are created from charged particle showers stopping in the target. Therefore, ALPs interacting with photons can be produced (often energetically) with high intensity via the Primakoff effect and then leave their signatures at the near detector through the inverse Primakoff scattering or decays to a photon pair. Moreover, the high-capability near detectors allow for discrimination between ALP signals and potential backgrounds, improving the signal sensitivity further. We demonstrate that a DUNE-like detector can explore a wide range of parameter space in ALP-photon coupling $g_{a\gamma }$ vs ALP mass $m_a$, including some regions unconstrained by existing bounds; the “cosmological triangle” will be fully explored and the sensitivity limits would reach up to $m_a\sim 3–4\mathrm{GeV}$ and down to $g_{a\gamma }\sim {10}^{-8}{\mathrm{GeV}}^{-1}$.

Figure 1

Tree-level ALP production through the Primakoff process (top left), ALP scattering through the inverse Primakoff process (top right), and ALP decays (bottom).

Figure 2

Left: Opening angle $\mathrm{\Delta }{\theta }_{\gamma \gamma }$ from $a\to \gamma \gamma$ decays for representative ALP masses in the decay-dominated signal regime for a fixed lifetime. Middle: Decaying ALP fluxes as a function of the angle with respect to the beam axis. The black dotted line represents the geometric acceptance for the GAr-detector solid angle. Right: Normalized energy spectra for the decay-dominated ($a\to \gamma \gamma$) region of parameter space for a fixed ALP lifetime.

Figure 3

The 90% C.L. sensitivity reaches in the $(m_a,g_{a\gamma })$ plane expected for a DUNE-like GAr detector with 1 and 7 year exposures ($a\to \gamma \gamma$ decays) and at a LAr detector for 1 and 7 year exposures (inverse Primakoff scattering, $a+A\to \gamma +A$). Existing laboratory limits [49, 50, 51] are shown in gray, while astrophysical limits [52, 53, 54, 55, 56] are shown in tan.