nuSTORM as a Precision Probe of the Standard Model and New Physics

TL;DR

nuSTORM presents a precisely characterized neutrino beam from stored muons and pions, enabling percent-level flux knowledge and a broad physics program. The paper details the experimental design, simulations, event-rate estimates, and a statistical framework to quantify sensitivity to SM measurements (notably a low-$Q^2$ determination of the weak mixing angle and neutrino trident production) and to BSM scenarios including sterile neutrinos, large extra dimensions, lepton-flavour violation, and heavy QCD axions/ALPs produced in kaon decays. The findings show nuSTORM can deliver competitive SM tests and, in several BSM channels, surpass or complement existing bounds, highlighting its role as a powerful, complementary probe alongside long-baseline experiments and collider searches. Overall, nuSTORM offers significant opportunities to reduce systematic uncertainties in neutrino physics, test foundational SM structure, and explore new light hidden-sector particles, with potential synergy toward future muon-collider technology.

Abstract

The Neutrinos from Stored Muons (nuSTORM) facility will generate neutrino beams from both muon and meson decays in a storage ring, providing a neutrino flux known to the percent level. This unprecedented precision enables a rich physics programme, including high-precision tests of the Standard Model and searches for new phenomena. In this paper we demonstrate nuSTORM's sensitivity to key Standard Model processes such as, measurements of the weak mixing angle at low $Q^2$ and the rare process of neutrino trident production. We also show its powerful reach for a diverse range of beyond-the-Standard-Model scenarios, including eV-scale sterile neutrinos, Kaluza-Klein excitations from large extra dimensions and lepton flavour violation. Furthermore, nuSTORM can place significant constraints on heavy QCD axions and other axion-like particles produced in rare kaon decays. These capabilities establish nuSTORM as a powerful and complementary probe to long baseline experiments and collider searches.

Figures (10)

• Figure 1: Schematic of the nuSTORM Experiment: Pions generated from a target and focusing horn are injected into a racetrack-shaped muon storage ring with a detector placed downstream of the production straight. nuSTORM:2022div
• Figure 2: Neutrino fluxes for four representative nuSTORM running conditions given four different muon beam energies.
• Figure 3: Running of the weak mixing angle $\sin^2\theta_W$ with the momentum transfer $Q$ (green curve), compared against existing measurements (orange points). The projected sensitivities from nuSTORM, SBND Alves:2024twb, and DUNE-PRISM deGouvea:2019wav are shown in purple. The DUNE-PRISM point corresponds to an electron angular resolution of $\sigma_\theta = 1^\circ$, and SBND-PRISM corresponds to an optimistic benchmark of $10^{22}$ POT with $5\%$ correlated systematics. The data points from Tevatron, SLC, and LHC have been slightly shifted from $Q= M_Z$ for improved visibility.
• Figure 4: Feynman diagrams contributing to the neutrino trident process Ballett:2018uuc
• Figure 5: Cross-section for diffractive (top row) and coherent (bottom row) trident production. The normalization $\sigma_0$ for the top row is $\sigma_0 = 10^{-44} \text{cm}^2$ and that for the bottom row is $\sigma_0 = \text{Z}^2\, 10^{-44} \text{cm}^2$ where Z here would be 18.