In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved; apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral K mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral B mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of K, D, and B mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model. In the near future, there will be a transition from the current to a new generation of experiments; thus a review of the status of quark flavor physics is timely. This report is the result of the work of physicists attending the 5th CKM workshop, hosted by the University of Rome "La Sapienza", September 9-13, 2008. It summarizes the results of the current generation of experiments that are about to be completed and it confronts these results with the theoretical understanding of the field which has greatly improved in the past decade. (C) 2010 Elsevier B.V. All rights reserved
We present a comprehensive analysis of the contributions to K → πνν decays not described by the leading dimension-six effective Hamiltonian. These include both dimensioneight four-fermion operators generated at the charm scale, and genuine long-distance contributions which can be described within the framework of chiral perturbation theory. We show that a consistent treatment of the latter contributions, which turn out to be the dominant effect, requires the introduction of new chiral operators already at O(G 2 F p 2 ). Using this new chiral Lagrangian, we analyze the long-distance structure of K → πνν amplitudes at the one-loop level, and discuss the role of the dimension-eight operators in the matching between short-and long-distance components. From the numerical point of view, we find that these O(G 2 F Λ 2 QCD ) corrections enhance the SM prediction of B(K + → π + νν) by about ≈ 6%.
The estimation of rare K decay matrix-elements from K ℓ3 experimental data is extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative corrections, are now accounted for. The analysis relies mainly on the cleanness of two specific ratios of form-factors, for which the theoretical control is excellent. As a result, the uncertainties on the K + → π + νν and K L → π 0 νν matrix-elements are reduced by a factor of about 7 and 4, respectively, and similarly for the direct CP-violating contributions to K L → π 0 e + e − and K L → π 0 µ + µ − . They could be reduced even further with better experimental data for the K ℓ3 slopes and the K + ℓ3 branching ratios. As a result, the non-parametric errors for B (K → πνν) and for the direct CP-violating contributions to B K L → π 0 ℓ + ℓ − are now completely dominated by those on the short-distance physics.
We revisit the formulation of the principle of minimal flavor violation (MFV) in the minimal supersymmetric extension of the standard model, both at moderate and large tan β, and with or without new CP-violating phases. We introduce a counting rule which keeps track of the highly hierarchical structure of the Yukawa matrices. In this manner, we are able to control systematically which terms can be discarded in the soft SUSY breaking part of the Lagrangian. We argue that for the implementation of this counting rule, it is convenient to introduce a new basis of matrices in which both the squark (and slepton) mass terms as well as the trilinear couplings can be expanded. We derive the RGE for the MFV parameters and show that the beta functions also respect the counting rule. For moderate tan β, we provide explicit analytic solutions of these RGE and illustrate their behaviour by analyzing the neighbourhood (also switching on new phases) of the SPS-1a benchmark point. We then show that even in the case of large tan β, the RGE remain valid and that the analytic solutions obtained for moderate tan β still allow us to understand the most important features of the running of the parameters, as illustrated with the help of the SPS-4 benchmark point.
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