### Speaker

### Description

Motivated by the long-lasting 3.5σ discrepancy in the anomalous magnetic moment of muon, we consider a new muon-specific force mediated by a light gauge boson, $X$, with mass $m_X < 2 m_\mu$ and the coupling constant $g_X∼(10^{−4},10^{−3})$. We show that the Belle II experiment has a robust chance to probe such a light boson in $e^+e^- \to \mu^+ \mu^- X$ channel and cover the most interesting parameter space explaining the discrepancy with the planned target luminosity, $\int dt \ \mathcal{L} = 50 \ \text{ab}^{−1}$. From the signal of $\mu^- \mu^+ + E_{miss}$ at Belle II, we expect that the (invisibly decaying) muon-philic light ($m_X < 2m_\mu$) gauge boson can be probed down to $g_X \geq 1.5 \times 10^{−4} (4.6 \times 10^{−4}, 2.3 \times 10^{−4})$ for 50 (1, 10) ab$^{−1}$ search.

### Mini-abstract

Light muonic force search at Belle II by using "Dimuon+Missing Energy($\mu^+ \mu^+ + E_{miss}$)".