Optimisation of the vertex detector and measurement of Higgs decays to second-generation quarks at the CEPC

The vertex detector is crucial for precision measurements of the Higgs boson at the electron-positron Higgs factory. Benchmarked with $H\to c\bar{c}$ and $H\to s\bar{s}$ measurements in the $\nu \bar{\nu }H$ channel, we perform an optimisation study on the inner radius and spatial resolution of the vertex detector using the Jet Origin Identification (JOI) framework, which determines the parton flavor of jets using advanced Artificial Intelligence (AI) algorithm. We observe that, compared to the reference detector configuration, halving the inner radius and spatial resolution improves the transverse and longitudinal impact parameter resolution approximately by a factor of two, while increasing the accuracy and significance of the $H\to c\bar{c}\mathrm{/}s\bar{s}$ measurement by 4% and 8%, respectively. Conversely, doubling these parameters results in comparable degradation, with variations in the inner radius being the dominant factor. Our results provide guidance for detector design and highlight promising prospects for identifying the $H\to s\bar{s}$ decay mode at future Higgs factories.