Open Questions in Charm Decays Deserving an Answer

TL;DR

This paper lists key open questions in charm decays related to QCD and New Physics, emphasizing the need for future experiments like CHARM2000 or a tau-charm factory to address these unresolved issues.

Contribution

It highlights specific unresolved questions in charm decay dynamics and discusses how upcoming experiments can provide crucial insights beyond current capabilities.

Findings

Identifies major open questions in charm decay physics.

Suggests future experiments can address these questions.

Highlights the importance of improved measurements for understanding QCD and New Physics.

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 $\Xi _c^{0,+}$ baryons; semileptonic branching ratios of $D_s$, $\Lambda _c$ and $\Xi _c$ hadrons and absolute branching ratios for those states; radiative decays $D\rightarrow \gamma K^*,\, \gamma \rho /\omega , \, D_s \rightarrow \gamma \phi /\omega ,\, D\rightarrow l^+l^-K/K^*$; $D^0-\bar D^0$ 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 $\tau$-charm factory can fill the bill.