Abstract
The CP asymmetry in τ→K_{S}πν_{τ}, as measured by the BABAR collaboration, differs from the standard model prediction by 2.8σ. Most nonstandard interactions do not allow for the required strong phase needed to produce a nonvanishing CP asymmetry, leaving only new tensor interactions as a possible mechanism. We demonstrate that, contrary to previous assumptions in the literature, the crucial interference between vector and tensor phases is suppressed by at least 2 orders of magnitude due to Watson's final-state-interaction theorem. Furthermore, we find that the strength of the relevant CP-violating tensor interaction is strongly constrained by bounds from the neutron electric dipole moment and D-D[over ¯] mixing. These observations together imply that it is extremely difficult to explain the current τ→K_{S}πν_{τ} measurement in terms of physics beyond the standard model originating in the ultraviolet.
Highlights
Introduction.—The presence of the baryon asymmetry in the Universe is one clear indication that there has to be physics beyond the standard model (SM) of particle physics [1], since CP violation within the SM, originating solely from the CKM matrix [2], is far too small to explain the observed asymmetry [3,4]
The signs follow from analyzing the quark content: for KL → π−lþνl and τþ → πþKSντ the neutral kaon is produced as K0 1⁄4 sd, while Dþ → πþKS requires K 0 1⁄4 ds
In this paper we demonstrate that this conclusion relies on erroneous assumptions for the πK tensor form factor, provide the corrected expression of the CP asymmetry in terms of the tensor Wilson coefficient, and study the consequences for a possible BSM explanation of (5)
Summary
In the SM the dominant contribution again arises indirectly from K0–K 0 mixing [8], and the same statement holds for the analogous decays of D mesons [9], Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.
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