Speaker
Description
It is crucial to explore physics beyond the Standard Model (BSM) because the Standard Model is incomplete in explaining questions that arise from cosmological observations, such as the existence of dark matter and the matter-antimatter asymmetry in our universe. Precise spectroscopy of muonium is a powerful way to search for BSM because of muonium’s simple energy structure. Muonium is a purely leptonic atom that consists of a positive muon and an electron, both of which can be viewed as point charges. The absence of internal structure provides stringent tests of the Standard Model by comparing theoretical predictions of the energy levels with precise measurements. For these tests, it is crucial to reduce the muon mass uncertainty, which currently dominates the uncertainty in the energy level calculation. The muon mass can be precisely determined from the transition frequency of the 1S-2S levels using laser spectroscopy. We have developed a suitable environment for the precision laser experiment at J-PARC, and performed the Doppler-free two-photon laser spectroscopy of the 1S-2S transition in muonium. We developed a narrowlinewidth, pulsed 244 nm laser system, a highly efficient muonium generation target made by laser-ablated silica aerogel [1], and a detection system (Fig. 1) with a high detection efficiency and low background noise. With these improvements, we achieved a laser excitation rate of 1S-2S (𝐹 = 1 → 𝐹′ = 1) transition more than 300 times higher than that of the previous experiment [2]. We also observed, for the first time, the transition of 1S-2S (𝐹 = 0 → 𝐹′ = 0), where 𝐹 is the total angular momentum. Such a high signal rate enables us to reduce the muon mass uncertainty in the future experiment. [1] J. Beare et al., PTEP 2020, 123C01 (2020) [2] V. Mayer et al., Phys. Rev. Lett. 84, 1136 (2000)
