Research

I have been involved in precision muon physics experiments over the last decade, where Muon g-2 experiment at Fermilab and the muEDM experiment at Paul Scherrer Institute my most recent research activities. My research interests are summarized as the following:

  • Physics beyond the Standard Model
  • Anomalous magnetic moments and electric dipole moments
  • Muon production from GeV electron beam
  • Muography
  • Muon cooling and muonium production

Muon g-2 experiment at Fermilab, USA

The Standard Model (SM) of particle physics has been strikingly successful in explaining a wide range of physical phenomena and almost all experimental results. One of the most significant discrepancies at present is the anomalous magnetic moment of the muon (muon g-2), which was measured by the E821 collaboration at BNL in 2004 to be more than three-standard-deviation greater than the SM prediction. This persistent discrepancy between experiment and theory continues to fuel speculative models such as supersymmetry, dark photons, axion-like particles, and beyond. Hence, confirmation of the discrepancy with improved experimental and theoretical uncertainty is one of the priorities in the particle physics community. The Muon g-2 collaboration (E989) at Fermilab aims to measure muon g-2 with a precision goal of 140 parts per billion, a fourfold improvement over BNL’s result. If the central values of the experimental result and the theoretical prediction remain unchanged, the discrepancy will exceed 7 standard deviations – a clear indication of beyond SM physics. Our group is mainly involved in the measurement of the anomalous precession frequency and its beam dynamics corrections.

Aerial view of the Fermilab campus, showcasing its extensive facilities and surrounding landscape. The white building near the top left of the inset is the Muon Campus (MC1) building, where the Muon g-2 experiment is conducted. Inset: Close-up of the superconducting magnetic storage ring, the core of the Muon g-2 experiment.

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Muon Electric Dipole Moment search at Paul Scherrer Institut, Switzerland

The presence of a permanent electric dipole moment (EDM) in any elementary particle implies Charge-Parity (CP) symmetry violation and thus could help explain the matter-antimatter asymmetry observed in our universe. Within the context of the Standard Model (SM), EDMs of SM particles are extremely small. However, in many beyond SM (BSM) theories, EDMs could be within experimental reach in the near future. Recently, the muon EDM is of particular interest due to the tensions in the anomalous magnetic moment of the muon and the electron, and hints of lepton flavor universality violation (LFUV) in B-meson decays. In some of the BSM theories with LFUV, the muon EDM could be as large as 1e-22 e cm. Moreover, the 19 orders of magnitude difference between the current experimental limit (1e-19 e cm) and the SM prediction (1e-38 e cm) means muon EDM is one of the least tested areas of the SM and any detected signal is a strong hint of new physics. At PSI, we plan to perform a sensitive search (1e-23 to 1e-22 e cm) of the muon EDM in the regime predicted by BSM theories. Our group at TDLI is mainly responsible for the muon detection system such as the muon entrance trigger.

Aerial view of the Paul Scherrer Institute (PSI), showcasing its extensive research facilities nestled in the Swiss countryside. The institute is divided into eastern and western sections along the Aare River. Inset: Schematic of the injection and storage scheme for the muEDM experiment at PSI, highlighting the intricate setup used to explore the electric dipole moment of the muon.

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Next-generation muon source based on Shanghai SHINE facility

Muons have been playing important and unique roles in both fundamental physics and applied science; Precise measurements and calculations of the muon magnetic anomaly have revealed a significant discrepancy between the theory and the experiment, hinting at a new physics beyond the Standard Model of particle physics; Muon spin rotation techniques have been widely applied to the study of superconductivity and magnetic materials to probe internal magnetic field and spin dynamics. A muon average lifetime of about 2.2 us and a typical measurement time of 10 lifetimes means that an ideal muon source should operate at around 50 kHz in the pulsed mode. However, current muon sources are either driven by several 10 Hz pulsed proton accelerator (at J-PARC and ISIS) or DC proton accelerator (at PSI and TRIUMF), resulting in low duty cycle for many types of muon experiments. Here we explore the use of high-repetition-rate pulsed electron beam at the Shanghai High repetition rate XFEL and Extreme light facility (SHINE) as a driver for the next-generation muon source. SHINE is a 4th generation light source in Shanghai and it is expected to be commissioned in 2026. It is based on an 8-GeV CW superconducting RF linac, with bunch repetition rate of up to 1 MHz, bunch charge of 100 pC, and an average beam current of 100 uA. Downstream of the undulators producing hard X-rays, the electron beam is deflected and absorbed in a beam dump. The expected number of electrons to be dispatched to the beam dump is of the order of 10^{22} per year.

An aerial view of the SHINE facility, situated close to the Tsung-Dao Lee Institute (TDLI). The accelerator electrons generated at SHINE will be utilized to produce muons, driving advanced research in condensed matter physics, material science, and particle physics.

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Application of Muography to City Underground Surveys

Muon tomography is a powerful, non-invasive imaging technique that uses atmospheric muons to explore hidden structures. It allows us to create detailed two- and three-dimensional images of the internal features of objects or areas that are otherwise inaccessible. This method is typically categorized into two types: muon absorption tomography and muon scattering tomography. At the Tsung-Dao Lee Institute (TDLI), our team is developing next-generation muon detectors, with a focus on applying muography to survey urban underground environments.

Our team members conduct underground muon detector testing as part of a city infrastructure survey, showcasing cutting-edge muography technology in a real-world application.

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Acknowledgment

I would like to acknowledge the funding supports of the following funding agencies for my research work:

  • 2023-2038: MOST National Key R&D Program
  • 2022-2026: Shanghai Pilot Program for Basic Research
  • 2021-2024: NSFC General Program, National Natural Science Foundation of China
  • 2021-2022: The Research Fund for International Young Scientists, NSFC