Speaker
Description
Physics of the up-type flavour offers unique possibilities of testing the Standard Model (SM) compared to the down-type flavour sector. Here, I discuss SM and New Physics (NP) contributions to the rare $D$-meson decays $ D^0 \to \pi^+ \pi^- \ell^+ \ell^- $. In particular, I discuss the effect of including the lightest scalar isoscalar resonance in the SM picture, namely, the $f_0 (500)$. Other than showing in the total branching ratio at an observable level, the $f_0 (500)$ resonance manifests as interference terms with the vector resonances, such as at high invariant mass of the leptonic pair in distinct angular observables. Recent data from LHCb optimize the sensitivity to $P$-wave contributions. I point out that a different definition of the observables used therein is sensitive to the $S$-wave. Finally, I study which observables are sensitive to the interference of the $S$-wave with generic NP contributions in semi-leptonic four-fermion operators.
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