Improved anatomy of ε′/ε in the Standard Model

By Andrzej Buras, M. Gorbahn, S. Jäger, M. Jamin. 2015

134 citations recorded by the source corpus.

A bstractWe present a new analysis of the ratio ε′/ε within the Standard Model (SM) using a formalism that is manifestly independent of the values of leading (V − A) ⊗ (V − A) QCD penguin, and EW penguin hadronic matrix elements of the operators Q4, Q9, and Q10, 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 → ππ amplitudes. As a result of this and the high precision now available for CKM and quark mass parameters, to high accuracy ε′/ε depends only on two non-perturbative parameters, B6(1/2) and B8(3/2), and perturbatively calculable Wilson coefficients. Within the SM, we are separately able to determine the hadronic matrix element 〈Q4〉0 from CP-conserving data, significantly more precisely than presently possible with lattice QCD. Employing B6(1/2) = 0.57 ± 0.19 and B8(3/2) = 0.76 ± 0.05, extracted from recent results by the RBC-UKQCD collaboration, we obtain ε′/ε = (1.9 ± 4.5) × 10−4, substantially more precise than the recent RBC-UKQCD prediction and 2.9 σ below the experimental value (16.6 ± 2.3) × 10−4, with the error being fully dominated by that on B6(1/2). Even discarding lattice input completely, but employing the recently obtained bound B6(1/2) ≤ B8(3/2) ≤ 1 from the large-N approach, the SM value is found more than 2 σ below the experimental value. At B6(1/2) = B8(3/2) = 1, varying all other parameters within one sigma, we find ε′/ε = (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.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/6276acc85c86d3f1bcc772fa6fb7f70abc047bfb

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In Nuclear and High Energy Physics

Citations in the corpus

Patterns of flavour violation in models with vector-like quarks (2016, methodology): “These results are supported by upper bounds on the matrix elements of the dominant penguin operators from the large-Nc dual-QCD approach [21, 45], which allows to derive an upper bound on ε′/ε [20], (ε/ε)SM ≤ (8.”
A global likelihood for precision constraints and flavour anomalies (2018, background): “We stress however that we do not make use of the partial cancellations of matrix element uncertainties between the real and imaginary parts of the SM amplitudes [58], so our SM uncertainty is conservative in this respect.”