Old and new anomalies in charm

Abstract

The recent LHCb determination of the direct CP asymmetries in the decays $D^0\to K^{+}{K}^{-},{\pi }^{+}{\pi }^{-}$ hints at a sizeable breaking of two approximate symmetries of the SM: CP and U-spin. We aim at explaining the data with BSM physics and use the framework of flavorful $Z^{\prime }$ models. Interestingly, experimental and theoretical constraints very much narrow down the shape of viable models: Viable, anomaly-free models are electron- and muon-phobic and feature a light $Z^{\prime }$ of 10-20 GeV coupling only to right-handed fermions. The $Z^{\prime }$ can be searched for in low mass dijets or at the LHC as well as dark photon searches. A light $Z^{\prime }$ of $\sim$ 3 GeV or $\sim$ 5-7 GeV can moreover resolve the longstanding discrepancy in the $J/\psi ,{\psi }^{\prime }$ branching ratios with pion form factors from fits to $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ data, and simultaneously explain the charm CP asymmetries. Smoking gun signatures for this scenario are ${\rm Y}$ and charmonium decays into pions, taus or invisbles.

Comments: 2 pages, 4 figures