Estimating epsilon'/epsilon. A Review

Abstract

The real part of epsilon'/epsilon measures direct CP violation in the decays of the neutral kaons in two pions. It is a fundamental quantity which has justly attracted a great deal of theoretical as well as experimental work. Its determination may answer the question of whether CP violation is present only in the mass matrix of neutral kaons (the superweak scenario) or also at work directly in the decays. After a brief historical summary, we discuss the present and expected experimental sensitivities. In the light of these, we come to the problem of estimating epsilon'/epsilon in the standard model. We review the present (circa 1998) status of the theoretical predictions of epsilon'/epsilon. The short-distance part of the computation is now known to the next-to-leading order in QCD and QED and therefore well under control. On the other hand, the evaluation of the hadronic matrix element of the relevant operators is where most of the theoretical uncertainty still resides. We analyze the results of the currently most developed calculations. The values of the B_i parameters in the various approaches are discussed, together with the allowed range of the relevant combination of the Cabibbo-Kobayashi-Maskawa entries Im V_{td}V^*_{ts}. We conclude by summarizing and comparing all up-to-date predictions of epsilon'/epsilon. Because of the intrinsic uncertainties of the long-distance computations, values ranging from 10^{-4} to a few times 10^{-3} can be accounted for in the standard model. Since this range covers most of the present experimental uncertainty, it is unlikely that new physics effects can be disentangled from the standard model prediction. For updates on the review and additional material see http://www.he.sissa.it/review/.

42 pages, 13 figures. To appear in Reviews of Modern Physics

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Cited by in corpus (62)

• Kaon Decays in the Standard Model
• Standard-model prediction for direct CP violation in $K\to \pi \pi$ decay
• Towards the Identification of New Physics through Quark Flavour Violating Processes
• Kaon Matrix Elements and CP-violation from Quenched Lattice QCD: (I) the 3-flavor case
• epsilon'/epsilon and Rare K and B Decays in the MSSM
• $K\to \pi \nu \bar{\nu }$ and ${\epsilon }^{\prime }/\epsilon$ in Simplified New Physics Models
• Improved anatomy of epsilon'/epsilon in the Standard Model
• The Standard Model Prediction for epsilon'/epsilon
• CP Violation in the B System and Relations to $K\to \pi \nu \bar{\nu }$ Decays
• An ${\epsilon }^{\prime }$ improvement from right-handed currents
• Direct CP violation in $K^0\to \pi \pi$: Standard Model Status
• Final State Interactions in Kaon Decays
• Direct CP violation and the $\Delta I=1/2$ rule in $K\to \pi \pi$ decay from the Standard Model
• Constraining models with vector-like fermions from FCNC in K and B physics
• Flavor-Changing Processes in Extended Technicolor
• Kaon CP violation and neutron EDM in the minimal left-right symmetric model
• epsilon'/epsilon at the NLO: 10 Years Later
• CP violation from noncommutative geometry
• New QCD estimate of the kaon penguin matrix elements and epsilon'/epsilon
• An updated analysis of eps'/eps in the standard model with hadronic matrix elements from the chiral quark model
• New Physics Patterns in ${\epsilon }^{\prime }/\epsilon$ and ${\epsilon }_K$ with Implications for Rare Kaon Decays and $\Delta M_K$
• Tree-level FCNC in the B system: from CP asymmetries to rare decays
• Quark Dipole Operators in Extended Technicolor Models
• New physics in ε' from chromomagnetic contributions and limits on Left-Right symmetry
• Gluino-squark contributions to CP violations in the kaon system
• Implications of the possibility that sin(2 beta) is small
• Nonfactorizable contributions to the decay mode D^0 -> K^0 \bar{K^0}
• Exact Chiral Symmetry on the Lattice: QCD Applications
• Analytic Approaches to Kaon Physics
• Soft CP violation in K-meson systems
• Constraints on the Mass and Mixing of the 4th Generation Quark From Direct CP Violation${\epsilon }^{\prime }/\epsilon$ and Rare K Decays
• A gluonic mechanism for B --> D eta'
• Present and Future CP Measurements
• The Strong Isospin-Breaking Correction for the Gluonic Penguin Contribution to epsilon'/epsilon at Next-to-Leading Order in the Chiral Expansion
• A joint analysis of the S-wave in the pi+pi- and pi0pi0 data
• Comment on `Analysis of O(p^2) Corrections to <2pi|Q_{7,8}|K>'
• What is the (epsilon'/epsilon)_exp Telling Us ?
• K to ππ hadronic matrix elements of left-right current-current operators
• epsilon'/epsilon in the Standard Model
• Reanalysis of CP Violation in K_L -> pi^+ pi^- gamma
• V-A hadronic tau decays : a QCD laboratory
• Theoretical status of ${\epsilon }^{\prime }/\epsilon$
• Chiral Limit Prediction for epsilon'/epsilon at NLO in 1/N_c
• CP violation in supersymmetric models with Hermitian Yukawa couplings and A-terms
• Tests of the Standard Model Using Muon Polarization Asymmetries in Kaon Decays
• Instantons and the $\Delta I=1/2$ Rule
• Lattice Matrix Elements and CP Violation in B and K Physics: Status and Outlook
• Estimating eps'/eps in the standard model independently of Im λ_t
• CP violations in the K and B meson systems in the SUSY models with (S_3)^3 flavor symmetry
• New Dipole Penguin Contribution to K --> pi pi decays
• The role of final state interactions in epsilon'/epsilon
• Theoretical overview of kaon decays
• 1/N_c and epsilon'/epsilon
• Theoretical status of epsilon'/epsilon
• Final State Interactions and eps'/eps
• eps'/eps in the standard model
• epsilon'/epsilon and Rare K Decays in the Standard Model and Supersymmetry
• On the Role of FSI in K -> 2πDecay
• CP violation in $K^{\pm }\to {\pi }^0{\pi }^0{\pi }^{\pm }$ decay
• CP Violation and the Cathedral Builders' Paradigm
• Chiral Logarithms in $\Delta S=1$ Kaon Decay Amplitudes in General Effective Flavor Theories
• Chiral loop corrections and isospin violation effects in epsilon'/epsilon