# Proton Fixed-Target Scintillation Experiment to Search for Minicharged Particles

## TL;DR

The paper proposes a cost-effective, movable detector setup at proton fixed-target facilities to search for minicharged particles with unprecedented sensitivity in the MeV to GeV mass range, leveraging high-intensity proton collisions and existing neutrino detectors.

## Contribution

It introduces the FerMINI detector concept, combining scintillation signatures with existing neutrino infrastructure to enhance sensitivity to minicharged particles in a new experimental approach.

## Key findings

- Potential to detect minicharged particles with fractional charge as low as 10^{-4}
- Design modifications can increase signal yield and detection sensitivity
- Feasible implementation at Fermilab and CERN SPS with high sensitivity in the MeV to GeV range

## Abstract

We propose a low-cost and movable setup to probe minicharged particles (or milli-charged particles) using high-intensity proton fixed-target facilities. This proposal, FerMINI, consists of a milliQan-type detector, requiring multi-coincident (nominally, triple-coincident) scintillation signatures within a small time window, located downstream of the proton target of a neutrino experiment. During the collisions of a large number of protons on the target, intense minicharged particle beams may be produced via meson photo-decays and Drell-Yan production. We take advantage of the high statistics, shielding, and potential neutrino-detector-related background reduction to search for minicharged particles in two potential sites: the MINOS near detector hall and the proposed DUNE near detector hall, both at Fermilab. We also explore several alternative designs, including the modifications of the nominal detector to increase signal yield, and combining this detector technology with existing and planned neutrino detectors to better search for minicharged particles. The CERN SPS beam and associated experimental structure also provide a similar alternative. FerMINI can achieve unprecedented sensitivity for minicharged particles in the MeV to few GeV regime with fractional charge $\varepsilon=Q_{\chi}/e $ between $10^{-4}$ (potentially saturating the detector limitation) and $10^{-1}$.