Mu2e Run I Sensitivity Projections for the Neutrinoless μ− → e− Conversion Search in Aluminum

Abstract

The Mu2e experiment at Fermilab will search for the neutrinoless μ−→e− conversion in the field of an aluminum nucleus. The Mu2e data-taking plan assumes two running periods, Run I and Run II, separated by an approximately two-year-long shutdown. This paper presents an estimate of the expected Mu2e Run I search sensitivity and includes a detailed discussion of the background sources, uncertainties of their prediction, analysis procedures, and the optimization of the experimental sensitivity. The expected Run I 5σ discovery sensitivity is Rμe=1.2×10−15, with a total expected background of 0.11±0.03 events. In the absence of a signal, the expected upper limit is Rμe<6.2×10−16 at 90% CL. This represents a three order of magnitude improvement over the current experimental limit of Rμe<7×10−13 at 90% CL set by the SINDRUM II experiment.

Theory introduction to Lepton Flavour Violation

“…The SINDRUMII collaboration sets the upper limit Γ(𝜇 𝐴𝑢 → 𝑒 𝐴𝑢)/Γ 𝑐𝑎 𝑝𝑡 < 7 × 10 −13 [10] on the rate of 𝜇 → 𝑒 conversion with respect to the flavour conserving muon capture (on a gold target). Upcoming searches led by the Mu2e and COMET collaboration aim at sensitivities of order 𝐵𝑟 (𝜇𝐴𝑙 → 𝑒 𝐴𝑙) ∼ 10 −17 , using Aluminum as a target [11,12]. The calculation of the 𝜇 → 𝑒 conversion rate can be found in [1].…”

The Mu2e experiment

“…An intense simulation and analysis campaign has been performed to evaluate the sensitivity for muon conversions corresponding to 6 • 10 16 stopped muons, that is the expected amount of data collected in Run 1, and using a realistic description of the experimental conditions based of the latest understanding of the accelerator and detector performances [5].…”

“…The These cuts have been otpimized to achieve the best 5𝜎 discovery sensitivity. The final single event sensitivity and background levels are summarized in Tab.1 [5].…”

Search for R-Parity-Violation-Induced Charged Lepton Flavor Violation at Future Lepton Colliders

“…For the reasons above, the search for CLFV has attracted great interest in recent decades. Numerous experiments have been performed or will be constructed with different approaches, including muon-based experiments, such as µ − N → e − N at Mu2e [13,14] and COMET [15], µ → eγ at MEG-II [16,17], µ → eee at Mu3e [18,19], and high energy colliders like LEP and LHC looking for CLFV decays of mesons [20][21][22][23], µ, τ [24], Z bosons [25][26][27], and Higgs bosons [28][29][30]. In the next decades, several proposed lepton colliders, such as the Circular Electron Positron Collider (CEPC) [31], the Future Circular Collider (FCC)-ee [32], the International Linear Collider (ILC) [33], the Compact Linear Collider (CLIC) [34] and the Muon Collider [35], will be ideal facilities to further probe CLFV processes [36][37][38][39][40] since they have cleaner environments with low backgrounds and higher luminosity than hadron colliders.…”