Abstract
We discuss the impact of physics beyond the Standard Model on direct CP violation in charm. On general grounds, models in which the primary source of flavor violation is linked to the breaking of chiral symmetry (left-right flavor mixing) are natural candidates to explain this effect, via enhanced chromomagnetic operators. In the case of super-symmetric models, we identify two motivated scenarios: disoriented A-terms and split families. Non-supersymmetric models with Z-mediated and scalar-mediated FCNC are also discussed.
Highlights
Models in which the flavor hierarchies are explained without invoking the hypothesis of minimal flavor violation [4]
To the case of supersymmetry with split families, if we assume that the transition between the first two generations is induced only as a result of 1–3 and 2–3 mixings, the couplings necessary to generate |∆aCP | ≈ 10−2 lead to effects in D0 − D 0 mixing well below the current experimental bounds
It is not easy to assess whether new physics is necessary to explain the evidence for CP violation in charm, observed by LHCb through the difference in the time-integrated asymmetries in the decays D0 → K+K− and D0 → π+π− [5]
Summary
The singly-Cabibbo-suppressed decay amplitude Af (Af ) of D0 (D 0) to a CP eigenstate f can be decomposed as [10]. A detailed translation of these bounds into corresponding constraints on the coefficients of dimension-six ∆C = 2 effective operators, obtained under the assumption that nonstandard contributions can at most saturate the above experimental bounds, can be found in ref. The time-integrated CP asymmetry for neutral D meson decays into a CP eigenstate f , defined in eq (1.2), receives both direct and indirect CP-violating contributions. This cancellation is not exact in eq (1.1) because of different propertime cuts in the two decay modes [5] This effect, as well as similar corrections in the previous measurements of time-integrated CP asymmetries [6,7,8], have been taken into account by HFAG [9] in obtaining the averages reported in (1.3) and (2.13)
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