Probing dark matter particles at CEPC

We investigate the capability of the future electron collider CEPC in probing the parameter space of several dark matter models, including millicharged dark matter models, $Z'$ portal dark matter models, and effective field theory dark matter models. In our analysis, the monophoton final state is used as the primary channel to detect dark matter models at CEPC. To maximize the signal to background significance, we study the energy and angular distributions of the monophoton channel arising from dark matter models and from the standard model to design a set of detector cuts. For the $Z'$ portal dark matter, we also analyze the $Z'$ boson visible decay channel which is found to be complementary to the monophoton channel in certain parameter space. The CEPC reach in the parameter space of dark matter models is also put in comparison with Xenon1T. We find that CEPC has the unprecedented sensitivity to certain parameter space for the dark matter models considered; for example, CEPC can improve the limits on millicharge by one order of magnitude than previous collider experiments for ${\cal O}(1)-100$ GeV dark matter.Comment: 21 pages, 31 figure

Explaining the Changes of Income Distribution in China

China has experienced one of the most remarkable increase in inequality over the last decade: the Gini coefficient increasing from 25.7 in 1984 to 37.8 in 1992. Using the recent developments in the theory of income distribution (Benerjee and Newman, 1993; Galor and Zeira, 1993) and a new panel data set about Chinese provincial-urban-level income inequality, this paper finds that inequality increased with the reduction of the share of state-owned enterprises in GDP, high inflation, growth, and (less significantly) the increasing exposure to foreign trade. We also find some evidence for the Director¡¯s Law: income redistribution tends to shift resources from the rich and the poor to the middle class. We do not find schooling and urbanization to be a significant explanatory factor.