B. Yağmur Zubaroğlu

arXiv2026

A Standard Model analysis of $D^0 \to π^- π^+, K^- K^+, K_{\rm S}^0 K_{\rm S}^0$

We investigate the Standard Model (SM) description of the singly Cabibbo-suppressed charm decays $D^0\to π^-π^+$, $D^0\to K^-K^+$ and $D^0\to K_{\rm S}^0K_{\rm S}^0$. Using factorisation together with isospin symmetry, we constrain non-factorisable effects and the associated $U$-spin breaking required by the measured branching fractions. We find that corrections of order $50\%$ are sufficient to describe all modes, which although sizeable, are not unexpected for hadronic charm decays. Using the constraints from the branching fractions, we derive SM predictions for the direct CP asymmetry in $D^0\to K_{\rm S}^0K_{\rm S}^0$, finding it to be at most at the per-mille level in our benchmark scenario, providing motivation for future precision measurements.

hep-ph↗

arXiv2025

Standard Model Benchmarks for $D^0\to K^- K^+, π^-π^+, K^0_{\rm S} K^0_{\rm S}$ Decays

The non-leptonic $D^0\to K^- K^+$ and $D^0\to π^-π^+$ decays are powerful probes of the Standard Model and are related to each other through the $U$-spin symmetry of the strong interaction. Using lattice QCD inputs we calculate the corresponding colour-allowed tree amplitudes in factorisation and demonstrate that non-factorisable contributions and $U$-spin-breaking effects at the level of 50% allow us to accommodate the measured branching ratios in the Standard Model. An exciting direct probe of such non-factorisable and $U$-spin breaking effects is provided by the $D^0\to K^0_{\rm S} K^0_{\rm S}$ channel. This decay is governed by non-factorisable exchange topologies and essentially vanishes in the $U$-spin limit, although it is experimentally well established with a prominent branching ratio. Extrapolating our $D^0\to K^- K^+$ results using the isospin symmetry, we find a consistent benchmark picture. Specifically, we can accommodate the measured $D^0\to K^0_{\rm S} K^0_{\rm S}$ branching ratio with $U$-spin-breaking effects at the 50% level and exchange amplitudes at the level of 50% of the colour-allowed $D^0\to K^- K^+$, $D^0\to π^-π^+$ tree contributions. Finally, we explore the resulting range for direct CP violation in $D^0\to K^0_{\rm S} K^0_{\rm S}$, obtaining upper bounds in our benchmark scenarios of a few per mille, offering an exciting target for future measurements.

hep-ph↗