Publications

The muonium-to-antimuonium conversion experiment (MACE) is proposed to search for charged lepton flavor violation and increase the sensitivity by more than two orders of magnitude compared to the muonium−antimuonium conversion spectrometer (MACS) experiment at PSI in 1999. A clear signature of this conversion is the positron produced from antimuonium decay. This paper presents a near-4π-coverage calorimeter designed for MACE, which can provide an energy resolution of 10.8% at 511 keV, and a signal efficiency of 78.3% for annihilation -ray events. Detailed Monte Carlo simulations using MACE offline software based on Geant4 are performed for geometry optimization, coincidence system design, background estimation, and benchmark detector validation.

Dark matter direct detection experiments are approaching the neutrino floor, with a significant probability of measuring coherent elastic neutrino-nucleus scattering (CEνNS) and exploring potential neutrino-related new physics (νNP). In the present study, the simultaneous presence of dark matter and νNP is emphatically investigated, revealing a response similar to Standard Model neutrino backgrounds in Xenon-based dark matter experiments. Through analyses of three U(1) extension models, it is determined that dark matter signals can be differentiated from an excess or a depletion of neutrino contributions from νNP by applying a statistically defined distinction method to nuclear and electronic recoil spectra. Additionally, an investigation is conducted into how νNP affects the exclusion limits for spin-independent dark matter-nucleon interactions. The present findings could facilitate the identification of new physics in future dark matter experiments.

COMET is a leading experiment to search for coherent conversion of µ−N → e−N with a high-intensity pulsed muon beamline, produced by the innovative slow extraction techniques. Therefore, it is critical to measure the characteristics of the muon beam. We set up a Muon Beam Monitor (MBM), where scintillation fibers (SciFi) weaved in the cross shape are coupled to silicon photomultipliers (SiPM), to measure the spatial profile and timing structure of the extracted muon beam for COMET. The MBM detector has been tested successfully with a proton beamline in China Spallation Neutron Source (CSNS) and taken data with good performance in the commissioning run called COMET Phase-α. Experience of the MBM development, such as the mechanical structure and electronics readout, and its beam measurement results will be shared.

A muonium consists of a positive muon associated with an orbital electron, and the spontaneous conversion to antimuonium serves as a clear indication of new physics beyond the Standard Model in particle physics. One of the most important aspects in muonium-to-antimuonium conversion experiment is to increase the muonium yield in vacuum to challenge the latest limit obtained in 1999. This study focuses on a simulation of the muonium formation and diffusion in the perforated silica aerogel. The independent simulation results can be well-validated by experimental data. By optimizing the target geometry, we find a maximum muonium emission efficiency of 7.92(2)% and a maximum vacuum yield of 1.134(2)% with a typical surface muon beam, indicating a 2.6 times and a 2.1 times enhancement, respectively. Our results will pave the way for muonium experiments.

Observations of suspected coherent elastic neutrino-nucleus scatterings by dark matter direct detection experiments highlight the need for an investigation into the so-called “neutrino floor.” We focus on the discovery limit, a statistical concept to identify the neutrino floor, and analyze the asymptotic behavior of the profile binned likelihood ratio test statistic where the likelihood is constructed by variate from events in each bin and pull terms from neutrino fluxes. To achieve the asymptotic result, we propose two novel methods: (i) the asymptotic-analytic method, which furnishes the analytic result for large statistics, is applicable for more extra nuisance parameters, and enables the identification of the most relevant parameters in the statistical analysis; (ii) the quasi-Asimov dataset, which is analogous to the Asimov dataset but with improved speed. Applying our methods to the neutrino floor, we significantly accelerate the computation procedure compared to the previous literature, and successfully address cases where the Asimov dataset fails. Our derivation on the asymptotic behavior of the test statistic not only facilitates research into the impact of neutrinos on the search for dark matter, but may also prove relevant in similar application scenarios.

The flavour symmetry succeeds in explaining the current global fit results. Focusing on the energy threshold, energy resolution, detection efficiency and background suppression in the analysis of electron-like events, we determine whether using opaque detectors could lead to improvements in the CP violation and light sterile neutrino searches in the future accelerator neutrino experiments. We also identify the minimum requirements for the opaque detectors to reach the designated physics goals in the simulated experiments.

The flavour symmetry succeeds in explaining the current global fit results. Flavour-symmetry models can be tested by the future experiments that improve the precision of neutrino oscillation parameters, such as the MuOn-decay MEdium baseline NeuTrino beam experiment (MOMENT). In this work, we consider tri-direct littlest seesaw (TDLS) models for a case study, and analyze how much MOMENT can extend our knowledge on the TDLS model.

Tetraphenyl butadiene (TPB) is a fluorescent material, acts as a wavelength shifter, and can turn UV light into visible light at a peak wavelength of approximately 425 nm, enabling the light signals to be easily detected during physics studies. Compared with a traditional TPB coating method using vapor deposition, we propose an alternative technique applying a spin-coating procedure to facilitate the development of neutrino and dark matter detectors.

We discuss its sensitivity of measuring the size of nonstandard interactions (NSIs) in matter, which can be described by the parameter ϵ_αβ (α and β are flavors of neutrinos). We find that the CERNPINGU configuration improves ˜ϵ_μμ ≡ ϵ_μμ − ϵ_ττ and ϵ_μτ significantly compared to the next-generation accelerator neutrino experiments. Most of the degeneracy problems in the precision measurements can be resolved, except the one for ˜ϵ_μμ ∼−0.035. Moreover, we point out that this configuration can also be used to detect the CP violation brought by NSIs.

我们用Geant4 软件包实现了对μ 子探测器探 测结果的模拟，并初步讨论了模拟结果的物理含义， 获得了μ 子衰变的谱形，拟合μ 子寿命符合理论预 期值． 该模拟过程不仅可以对探测器的实际搭建起 到指导作用，并为实际探测中的数据提供比对样本， 更能够加深学生对探测器物理过程的理解，具有深 远的教学意义．