Dirt/Detector/Dump: Complementary BSM production at Short-Baseline Neutrino Facilities

TL;DR

This paper explores how beam dumps at Short-Baseline Neutrino facilities can enhance searches for new particles, specifically heavy neutral leptons with magnetic moments, by analyzing their production and decay signatures.

Contribution

It introduces the significance of upstream beam dumps for heavy neutral lepton searches and identifies unique kinematic features to improve signal detection.

Findings

Enhanced sensitivity to HNLs at SBND, MicroBooNE, and ICARUS.

Distinct kinematic features from dump, dirt, and detector production.

Complementary approach to existing anomalies like MiniBooNE.

Abstract

Short-baseline neutrino (SBN) facilities are optimal for new-physics searches, including the possible production of new particles in and along the neutrino beamline. One such class of models considers states that are created by neutrino upscattering that then decay in the neutrino detector -- in the past, such upscattering has often been considered to occur in the detector itself (with a prompt decay) or in the dirt upstream of the detector. In this work, we highlight the importance of the beam dumps, situated even further upstream, for such searches. The Fermilab Booster Neutrino Beam, with its iron dump, provides one such possibility. We focus on sub-GeV heavy neutral leptons (HNLs) with a transition magnetic moment, which allows this upscattering to take advantage of the high-$Z$ iron. We observe that, in addition to increased sensitivity to this model at SBND, MicroBooNE, and ICARUS, there exist distinct features in the signal events' kinematical properties when coming from production in the dump, dirt, and detector which can allow for enhanced signal-to-background separation. We highlight the complementarity of this approach to study parameter space relevant for the MiniBooNE low-energy excess, as well as in models in which the HNLs couple to a light scalar particle.