New physics in singly Cabibbo-suppressed D decays

TL;DR

This paper investigates how new physics operators could affect a precise U-spin relation among D meson decay amplitudes, providing constraints on beyond Standard Model contributions.

Contribution

It demonstrates that the U-spin relation is unaffected by scalar operators but sensitive to certain U=1 operators, refining constraints on new physics in charm decays.

Findings

U-spin relation remains unaffected by scalar operators like QCD penguins.

Relation is sensitive to U=1 operators with a few percent effect.

Combining amplitude relations with CP asymmetries improves constraints on new physics.

Abstract

A U-spin relation among four ratios of amplitudes for $D^0 \to \pi^+K^-$, $K^+\pi^-$, $K^+K^-, \pi^+\pi^-$, including first, second and third order U-spin breaking, has been derived recently with a precision of $10^{-3}$. We study effects of new $|\Delta C|=1$ operators on this relation. We find that it is not affected by U-spin scalar operators, including QCD penguin and chromomagnetic dipole operators occurring in supersymmetric and extra-dimensional models. The relation is modified by new $U=1$ operators with a sensitivity of a few percent characteristic of second order U-spin breaking. Combining this relation with CP asymmetries in $D^0\to K^+K^-, \pi^+\pi^-$ leads to a more solid constraint on $U=1$ operators than from asymmetries alone.