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 $10^{-1}$.
Highlights
The quantization of electric charge has been one of the longest-standing mysteries in particle physics
minicharged particles (MCP) may be a member of a dark sector [17] that couples to the Standard Model via a massless dark photon through kinetic mixing [18], and these or other dark sector particles may constitute the relic abundance of dark matter
We propose a Fermilab-based experiment to probe minicharged particles, FerMINI, that combines the techniques of dedicated searches at SLAC [5,7] and the Large Hadron Collider (LHC) [13] with the advantages of neutrino facility sites [16]
Summary
The quantization of electric charge has been one of the longest-standing mysteries in particle physics. The favored range of masses of these MCP is below roughly a hundred MeV, which is a region that could be explored in proton fixed-target experiments. Probes of MCP and other weakly-interacting MeV-GeV particles have been under intense study, due in large part to the fact that many dark matter and dark sector hypotheses fall into these categories. We propose a Fermilab-based experiment to probe minicharged particles, FerMINI, that combines the techniques of dedicated searches at SLAC [5,7] and the LHC [13] with the advantages of neutrino facility sites [16]. FerMINI serves as an example to demonstrate that the proton-fixed target facilities could be natural habitats for the dedicated low-cost detectors to search for weakly interacting and long-lived particles. Accelerator-based experiments like FerMINI that directly produce dark matter particles with high energy that can survive the attenuation through the propagation are needed to explore this parameter regime
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