Improved anatomy of ε′/ε in the Standard Model


Buras, Andrzej J, Gorbahn, Martin, Jäger, Sebastian and Jamin, Matthias (2015) Improved anatomy of ε′/ε in the Standard Model. Journal of High Energy Physics, 2015 (11). pp. 1-32.

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Abstract

We present a new analysis of the ratio epsilon'/epsilon within the Standard Model (SM) using a formalism that is manifestly independent of the values of leading (V-A)x(V-A) QCD penguin, and EW penguin hadronic matrix elements of the operators Q_4, Q_9, and Q_10, and applies to the SM as well as extensions with the same operator structure. It is valid under the assumption that the SM exactly describes the data on CP-conserving K -> pi pi amplitudes. As a result of this and the high precision now available for CKM and quark mass parameters, to high accuracy epsilon'/epsilon depends only on two non-perturbative parameters, B_6^(1/2) and B_8^(3/2), and perturbatively calculable Wilson coefficients. Within the SM, we are separately able to determine the hadronic matrix element <Q_4>_0 from CP-conserving data, significantly more precisely than presently possible with lattice QCD. Employing B_6^(1/2) = 0.57+-0.19 and B_8^(3/2) = 0.76+-0.05, extracted from recent results by the RBC-UKQCD collaboration, we obtain epsilon'/epsilon = (1.9+-4.5) 10^-4, substantially more precise than the recent RBC-UKQCD prediction and 2.9 sigma below the experimental value (16.6+-2.3) 10^-4, with the error being fully dominated by that on B_6^(1/2). Even discarding lattice input completely, but employing the recently obtained bound B_6^(1/2) <= B_8^(3/2) <= 1 from the large-N approach, the SM value is found more than 2 sigma below the experimental value. At B_6^(1/2) = B_8^(3/2) = 1, varying all other parameters within one sigma, we find epsilon'/epsilon = (8.6+-3.2) 10^-4. We present a detailed anatomy of the various SM uncertainties, including all sub-leading hadronic matrix elements, briefly commenting on the possibility of underestimated SM contributions as well as on the impact of our results on new physics models.

Item Type: Article
Additional Information: 32 pages, 2 figures, systematic uncertainty for lattice B_6^(1/2) included, treatment of isospin breaking improved; some remarks added, version to appear in JHEP
Uncontrolled Keywords: CP violation, Kaon Physics, QCD
Depositing User: Symplectic Admin
Date Deposited: 03 Mar 2017 11:41
Last Modified: 19 Jan 2023 07:14
DOI: 10.1007/JHEP11(2015)202
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3006202
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