We set constraints and future sensitivity projections on millicharged particles (MCPs) based on electron scattering data in numerous neutrino experiments, starting with MiniBooNE and the Liquid Scintillator Neutrino Detector (LSND). Both experiments are found to provide new (and leading) constraints in certain MCP mass windows: 5–35 MeV for LSND and 100–180 MeV for MiniBooNE. Furthermore, we provide projections for the ongoing Fermilab SBN program, the Deep Underground Neutrino Experiment (DUNE), and the proposed Search for Hidden Particles (SHIP) experiment. In the SBN program, SBND and MicroBooNE have the capacity to provide the leading bounds in the 100–300 MeV mass regime. DUNE and SHIP are capable of probing parameter space for MCP masses in the range of <math><mrow><mn>5</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mi>–</mi><mn>5</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> that is significantly beyond the reach of existing bounds, including those from collider searches and, in the case of DUNE, the SLAC mQ experiment.

Canada

Gabriel Magill

Ryan Plestid

CERN

Maxim Pospelov

United States

Yu-Dai Tsai

Millicharged Particles in Neutrino Experiments

We consider generic neutrino dipole portals between left-handed neutrinos, photons, and right-handed heavy neutral leptons (HNL) with Dirac masses. The dominance of this portal significantly alters the conventional phenomenology of HNLs. We derive a comprehensive set of constraints on the dipole portal to HNLs by utilizing data from LEP, LHC, MiniBooNE, LSND as well as observations of Supernova 1987A and consistency of the standard big bang nucleosynthesis. We calculate projected sensitivities from the proposed high-intensity SHiP beam dump experiment, and the ongoing experiments at the Short-Baseline Neutrino facility at Fermilab. Dipole mediated Primakoff neutrino upscattering and Dalitz-like meson decays are found to be the main production mechanisms in most of the parametric regime under consideration. Proposed explanations of LSND and MiniBooNE anomalies based on HNLs with dipole-induced decays are found to be severely constrained, or to be tested in the future experiments.

Dipole portal to heavy neutral leptons

We investigate the possibility of using neutrino trident production to probe leptophilic charged scalars at future high intensity neutrino experiments. We show that under specific assumptions, this production process can provide competitive sensitivity for generic charged scalars as compared to common existing bounds. We also investigate how the recently proposed mixed-flavor production—where the two oppositely charged leptons in the final state need not be muon flavored—can give a 20%–50% increase in sensitivity for certain configurations of new physics couplings as compared to traditional trident modes. We then categorize all renormalizable leptophilic scalar extensions based on their representation under <math><mi>SU</mi><mo>(</mo><mn>2</mn><mo>)</mo><mo>×</mo><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math>, and discuss the Higgs triplet and Zee-Babu models as explicit UV realizations. We find that the inclusion of additional doubly charged scalars and the need to reproduce neutrino masses make trident production uncompetitive with current bounds for these specific UV completions. Our work represents the first application of neutrino trident production to study charged scalars. Additionally, it is the first application of mixed-flavor trident production to study physics beyond the standard model more generally.