Open Questions in Charm Decays Deserving an Answer

Abstract

A list is given of those open questions concerning the dynamics of charm decays where there exists a strong need for an answer. Such a need is based on lessons to be learnt about QCD -- either in their own right or for a better understanding of $B$ physics -- or on searches for New Physics with a small background from the Standard Model. The major items on this list are: lifetimes of the $Ξ_c^{0,+}$ baryons; semileptonic branching ratios of $D_s$, $Λ_c$ and $Ξ_c$ hadrons and absolute branching ratios for those states; radiative decays $D\rightarrow γK^*,\, γρ/ω, \, D_s \rightarrow γϕ/ω,\, D\rightarrow l^+l^-K/K^*$; $D^0-\bar D^0$ oscillations down to a sensitivity below $10^{-4}$ and CP asymmetries in non-leptonic $D$ decays down to 0.1\%. Ongoing and already approved experiments will produce important new insights, which are unlikely to provide sufficient answers to all these questions yet. It is discussed how a third-generation fixed-target experiment like CHARM2000 or a $τ$-charm factory can fill the bill.