A consistent picture for large penguins in D -> pi+ pi-, K+ K-

TL;DR

This paper explains the large difference in decay rates and CP asymmetries between D0 -> K+ K- and D0 -> pi+ pi- in charm physics through Standard Model penguin contractions, linking two longstanding puzzles.

Contribution

It demonstrates that the observed decay rate differences and CP asymmetries can be simultaneously explained by penguin contractions within the Standard Model, considering SU(3) breaking.

Findings

Large penguin contractions naturally explain Delta A_CP.

A U-spin fit supports the Standard Model explanation.

Expectations for individual CP asymmetries are discussed.

Abstract

A long-standing puzzle in charm physics is the large difference between the D0 -> K+ K- and D0 -> pi+ pi- decay rates. Recently, the LHCb and CDF collaborations reported a surprisingly large difference between the direct CP asymmetries, Delta A_CP, in these two modes. We show that the two puzzles are naturally related in the Standard Model via s- and d-quark "penguin contractions". Their sum gives rise to Delta A_CP, while their difference contributes to the two branching ratios with opposite sign. Assuming nominal SU(3) breaking, a U-spin fit to the D0 -> K+ pi-, pi+ K-, pi+ pi-, K+ K- decay rates yields large penguin contractions that naturally explain Delta A_CP. Expectations for the individual CP asymmetries are also discussed.