The New Physics Reach of Null Tests with $D \to \pi \ell \ell$ and $D_s \to K \ell \ell $ Decays

TL;DR

This paper explores the potential of null tests in rare charm meson decays to uncover new physics beyond the Standard Model, highlighting signatures of supersymmetry, leptoquarks, and $Z'$ models with significant effects.

Contribution

It provides a comprehensive analysis of null test observables in $D o \pi \, ext{and} \, D_s o K$ decays, identifying large room for new physics signals.

Findings

Large room for new physics above SM predictions.

Explicit examples of supersymmetry, leptoquarks, and $U(1)'$ models.

Potential sizable effects from $Z'$-mediated transitions.

Abstract

$|\Delta c|=|\Delta u|=1$ processes are unique probes of flavor physics in the up-sector within and beyond the Standard Model (SM). SM tests with rare semileptonic charm meson decays are based on an approximate CP--symmetry, a superior GIM--mechanism, angular distributions, lepton-universality and lepton flavor conservation. We analyze the complete set of null test observables in $D \to \pi \ell \ell^{(\prime)}$ and $D_s \to K \ell \ell^{(\prime)}$ decays, $\ell^{(\prime)}=e, \mu$, and find large room for new physics safely above the SM contribution. We identify signatures of supersymmetry, leptoquarks and anomaly-free $U(1)^\prime$-models with generation-dependent charges, for which we provide explicit examples. $Z^\prime$-effects in $c \to u \ell \ell^{(\prime)}$ transitions can be sizable if both left-handed and right-handed couplings to quarks are present.