New bounds on axion-like particles from MicroBooNE

TL;DR

This paper derives new constraints on axion-like particles using MicroBooNE data, focusing on ALP production and decay via effective operators, and shows potential for improved bounds over existing experiments.

Contribution

It introduces novel bounds on ALPs from MicroBooNE, considering higher-dimensional operators and decay channels, and compares these with previous limits.

Findings

MicroBooNE sets competitive bounds for ALPs with 100-200 MeV mass.

Potential to improve constraints on ALP-W coupling with future data.

Analysis of decay channels enhances understanding of ALP phenomenology.

Abstract

Neutrino experiments lie at the edge of the intensity frontier and therefore can be exploited to search for new light particles weakly coupled to the visible sector. In this work we derive new constraints on axion-like particles (ALPs) using data from the MicroBooNE experiment, from a search for $e^+ e^-$ pairs pointing in the direction of the NuMI absorber. In particular, we consider the addition of higher-dimensional effective operators coupling the ALP to the electroweak gauge bosons. These would induce $K\to \pi a$ from kaon decay at rest in the NuMI absorber, as well as ALP decays into pairs of leptons or photons. We discuss in detail and compare various results obtained for the decay width $K\rightarrow \pi a$ in previous literature. For the operator involving the Higgs, MicroBooNE already sets competitive bounds (comparable to those of NA62) for ALP masses between 100 and 200 MeV. We also compute the expected sensitivities from the full NuMI dataset recorded at MicroBooNE. Our results show that a search for a $a\to\gamma\gamma$ signal may be able to improve over current constraints from beam-dump experiments on the operator involving the ALP coupling to the $W$.