Charming synergies: the role of charm-threshold studies in the search for physics beyond the Standard Model

TL;DR

Charm-threshold studies at the $ ext{ψ}(3770)$ resonance provide crucial quantum correlation data that enhance flavour physics research, including measurements of $CP$ violation and meson oscillations, with future larger datasets needed for further progress.

Contribution

This paper reviews the importance of charm-threshold measurements in flavour physics and highlights the potential benefits of larger datasets for advancing beyond the Standard Model.

Findings

Quantum correlations enable access to strong-phase information.

Recent measurements of $CP$-violating phase $oldsymbol{ extgamma}$ and $D^0-ar{D}^0$ oscillations.

Larger threshold data samples can significantly benefit flavour physics studies.

Abstract

Measurements performed with pairs of charm mesons produced at threshold from the decay of the $\psi(3770)$ resonance are of great value in flavour physics. The quantum correlation that exists between the two mesons allows unique access to strong-phase information, which is essential input to flavour-physics studies conducted in other environments. An excellent example from the BESIII collaboration is a recent determination of the strong-phase difference between $D^0$ and $\bar{D}^0$ mesons in the decay $D^0 \to K^0_S\pi^+\pi^-$, which has enabled recent measurements to be performed of the $C\!P$-violating phase $\gamma$ and $D^0-\bar{D}^0$ oscillations by the LHCb experiment at CERN. These $\psi(3770)$ data, and also those collected just above the thresholds for $D_s^+$ and $\Lambda_c^+$ production, can also be exploited in many other ways that are of benefit to flavour-physics studies. These synergies are reviewed, and the need for larger threshold data samples in the near future is emphasised.