[Paper Review] Minicharged Particles at Accelerators: Progress and Prospects

M. de Montigny, Pierre-Philippe A. Ouimet+3 more|arXiv (Cornell University)|Jul 15, 2023

Dark Matter and Cosmic PhenomenaPhysics and Astronomy3 citations

TL;DR

This paper reviews theoretical frameworks and experimental constraints on minicharged particles (mCPs), hypothetical weakly interacting particles with sub-quantum electric charges. It presents an updated sensitivity analysis for the MoEDAL-MAPP experiment at the LHC, projecting discovery potential for mCPs with masses 0.45–65 GeV and charges as low as 2.5×10⁻³e at 95% CL in Run 3 and future High-Luminosity LHC runs.

ABSTRACT

Minicharged particles (mCPs), hypothetical free particles with tiny electric charges below the elementary charge, $e$, offer a valuable probe of dark sectors and fundamental physics through several clear experimental signatures. Various models of physics beyond the Standard Model predict the existence of such particles, which could help elucidate the ongoing mysteries regarding electric charge quantization and the nature of dark matter. Moreover, a hypothetical scenario involving a small minicharged subcomponent of dark matter has recently been demonstrated as a viable explanation of the anomaly in the 21 cm hydrogen absorption signal reported by the EDGES collaboration. Although several decades of indirect observations and direct experimental searches for mCPs at particle accelerators have led to severe constraints, a substantial window of the mCP mass$\unicode{x2013}$mixing parameter space remains unexplored at the energy frontier accessible to current state-of-the-art accelerators, such as the Large Hadron Collider (LHC). Consequently, mCPs have remained topical over the years, and new experimental searches at accelerators have been gaining interest. In this article, we review the theoretical frameworks in which mCPs emerge and their phenomenological implications, the current direct and indirect constraints on mCPs, and the present state of the ongoing and upcoming searches for mCPs at particle accelerators. Additionally, we present the results of an updated study of the projected sensitivity of the recently approved (and relocated) Phase-1 detector of the MoEDAL's Apparatus for Penetrating Particles (MAPP) experiment to Drell$\unicode{x2013}$Yan pair-produced mCPs at the LHC's Run 3 and the future High-Luminosity LHC.

Motivation & Objective

• To review theoretical models of minicharged particles (mCPs) within hidden sector and vector portal frameworks.
• To summarize current direct and indirect experimental constraints on mCPs across high-energy physics, astrophysics, and cosmology.
• To evaluate the projected sensitivity of the MoEDAL-MAPP experiment to Drell–Yan produced mCPs at the LHC.
• To compare the MAPP-1 detector's sensitivity with other upcoming experiments such as milliQan, FORMOSA, and SHiP.
• To identify the remaining unexplored parameter space for mCPs at the GeV scale accessible to current and future accelerator facilities.

Proposed method

• Employed a background-free assumption to project the sensitivity of the MAPP-1 detector to Drell–Yan pair-produced mCPs at the LHC.
• Used MadGraph5 and FeynRules to simulate mCP production via the Drell–Yan mechanism at a center-of-mass energy of 13.6 TeV.
• Analyzed the detector's response to mCPs based on their ionization energy loss and traversal through the detector material.
• Projected sensitivity over an integrated luminosity of 30 fb⁻¹ for LHC Run 3 and higher luminosities for the High-Luminosity LHC.
• Compared results with existing and planned experiments, including milliQan, FORMOSA, FLArE, and SHiP, to assess complementarity.
• Validated the mCP model implementation using FeynRules and performed model consistency checks with independent simulations.

Experimental results

Research questions

• RQ1 What is the current status of experimental constraints on minicharged particles (mCPs) across high-energy physics, astrophysics, and cosmology?
• RQ2 How sensitive is the MoEDAL-MAPP experiment to mCPs produced via the Drell–Yan mechanism at the LHC’s Run 3?
• RQ3 What range of mCP masses and effective charges can be probed by MAPP-1 at 13.6 TeV with 30 fb⁻¹ of integrated luminosity?
• RQ4 How do the projected sensitivities of MAPP-1, milliQan, FORMOSA, and SHiP compare across the mCP mass–charge parameter space?
• RQ5 What is the potential for discovering mCPs in the GeV mass range with upcoming accelerator experiments at the LHC and SPS?

Key findings

• The MAPP-1 detector is projected to probe mCPs with masses between 0.45 GeV and 65 GeV at 95% confidence level in LHC Run 3.
• The experiment achieves sensitivity to mCPs with effective electric charges as low as 2.5×10⁻³e, significantly below the elementary charge.
• At the High-Luminosity LHC, the sensitivity of MAPP-1 is expected to improve substantially, surpassing current constraints in the GeV mass range.
• The FORMOSA-II detector is projected to exceed the sensitivities of milliQan, MAPP-1, and FerMINI experiments for mCPs.
• The SHiP experiment is expected to achieve sensitivity to mCPs with masses from 0.1 to 5 GeV, improving on current bounds by an order of magnitude.
• The MAPP-1 experiment’s projected sensitivity is competitive with milliQan and FORMOSA-I, and complementary to FLArE and SHiP in the mCP parameter space.