M³: a new muon missing momentum experiment to probe (g – 2)_μ and dark matter at Fermilab

Journal Article · 26 September 2018 · Journal of High Energy Physics (Online)

DOI: https://doi.org/10.1007/JHEP09(2018)153 · OSTI ID:1439466

Kahn, Yonatan ^[1]; Krnjaic, Gordan ^[2]; Tran, Nhan ^[2]; Whitbeck, Andrew ^[2]

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1. Princeton Univ., Princeton, NJ (United States)
2. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

Here, new light, weakly-coupled particles are commonly invoked to address the persistent $$\sim 4\sigma$$ anomaly in $$(g-2)_\mu$$ and serve as mediators between dark and visible matter. If such particles couple predominantly to heavier generations and decay invisibly, much of their best-motivated parameter space is inaccessible with existing experimental techniques. In this paper, we present a new fixed-target, missing-momentum search strategy to probe invisibly decaying particles that couple preferentially to muons. In our setup, a relativistic muon beam impinges on a thick active target. The signal consists of events in which a muon loses a large fraction of its incident momentum inside the target without initiating any detectable electromagnetic or hadronic activity in downstream veto systems. We propose a two-phase experiment, M$^3$ (Muon Missing Momentum), based at Fermilab. Phase 1 with $$\sim 10^{10}$$ muons on target can test the remaining parameter space for which light invisibly-decaying particles can resolve the $$(g-2)_\mu$$ anomaly, while Phase 2 with $$\sim 10^{13}$$ muons on target can test much of the predictive parameter space over which sub-GeV dark matter achieves freeze-out via muon-philic forces, including gauged $$U(1)_{L_\mu - L_\tau}$$.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: AC02-07CH11359
• OSTI ID: 1439466
• Report Number(s): arXiv:1804.03144; FERMILAB-PUB-18-087-A; 1667037; TRN: US1900618
• Journal Information: Journal of High Energy Physics (Online), Vol. 2018, Issue 9; ISSN 1029-8479
• Publisher: Springer BerlinCopyright Statement
• Country of Publication: United States
• Language: English