S-wave contribution to rare D^0 →π^+ π^- ℓ^+ ℓ^- decays in the Standard Model and sensitivity to New Physics
arxiv(2023)
摘要
Physics of the up-type flavour offers unique possibilities of testing the
Standard Model (SM) compared to the down-type flavour sector. Here, we discuss
SM and New Physics (NP) contributions to the rare charm-meson decay D^0 →π^+ π^- ℓ^+ ℓ^-. In particular, we discuss the effect of including
the lightest scalar isoscalar resonance in the SM picture, namely, the f_0
(500), which manifests in a big portion of the allowed phase space. Other than
showing in the total branching ratio at an observable level of about 20%,
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, that we analyse in view of the inclusion of vector resonances.
We propose the measurement of alternative observables which are sensitive to
the S-wave and are straightforward to implement experimentally. This leads to
a new set of null observables, that vanish in the SM due to its gauge and
flavour structures. Finally, we study observables that depend on the SM
interference with generic NP contributions from semi-leptonic four-fermion
operators in the presence of the S-wave.
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