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Search for a Nonrelativistic Boson in Two-Body Antimuon Decay
J I Collar1,2, P S Cooper3, C M Lewis1,2
1Enrico Fermi Institute, Kavli Institute for Cosmological Physics, and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA.
Physical Review Letters
|January 5, 2024
Summary
Researchers probed the rare muon decay (μ⁺→e⁺X⁰) for a neutral boson (X⁰). A new limit on this decay suggests X⁰ could be involved in cosmological scenarios, with future detectors promising enhanced sensitivity.
Area of Science:
- Particle Physics
- Cosmology
- Astrophysics
Background:
- Charged lepton flavor violation (CLFV) offers a window into new physics beyond the Standard Model.
- The existence of a neutral, slow-moving boson (X⁰) is hypothesized, potentially interacting gravitationally and participating in cosmological models.
- Probing rare muon decays provides stringent constraints on new particles and interactions.
Purpose of the Study:
- To demonstrate the feasibility of searching for the CLFV decay μ⁺→e⁺X⁰.
- To establish a branching ratio limit for this decay, probing a specific region of the X⁰ phase space.
- To explore the potential cosmological implications of a detected X⁰ boson.
Main Methods:
- Utilizing a short exposure of surface antimuons from the M20 beam line at TRIUMF.
- Analyzing the decay products to set a branching ratio limit for μ⁺→e⁺X⁰.
- Focusing on the kinematic region where the X⁰ boson mass (m<0xE1><0xB5><0xA3>⁰) approaches the muon mass (m<0xE1><0xB5><0xA3>⁺).
Main Results:
- A branching ratio limit of ≲10⁻⁵ was established for the μ⁺→e⁺X⁰ decay.
- This limit is comparable to or surpasses previous searches.
- The search explored a previously unexamined region of the X⁰ phase space near the kinematic limit.
Conclusions:
- The study demonstrates the feasibility of probing for X⁰ bosons via μ⁺→e⁺X⁰ decay.
- The established limit provides constraints on X⁰ properties and its potential role in cosmology.
- Future experiments with enhanced detectors, such as customized germanium detectors, are expected to improve sensitivity.
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