CKM Mixing Matrix Research Articles

W pair production cross-section and W branching fractions in e+e− interactions at 183 GeV

The cross-section for the process e + e −→ W + W − has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 182.65 GeV and corresponding to an integrated luminosity of 53 pb −1. Based on the 770 events selected as WW candidates, the cross-section for the doubly resonant process σ(e +e −→W +W −)=15.86 ±0.69 (stat) ±0.26 (syst) pb has been measured and found to be in good agreement with the Standard Model expectation. The branching fractions of the W decay were also measured. From these a value of the CKM mixing matrix element |V cs|=0.985±0.073 (stat)±0.025 (syst) was derived. Our previously published WW cross-section measurements and the derived measurement of m W have been revised and updated with the present cross-section measurement to yield m W=80.49±0.43 (stat)±0.09( syst)±0.03( LEP) GeV/c 2 .

Breaking of the flavor permutational symmetry: Mass textures and the CKM matrix

Different Ans\"atze for the breaking of flavor permutational symmetry according to ${S}_{L}(3)\ensuremath{\bigotimes}{S}_{R}(3)\ensuremath{\supset}{S}_{L}(2)\ensuremath{\bigotimes}{S}_{R}(2)$ give different Hermitian mass matrices of the same modified Fritzsch type, which differ in the symmetry breaking pattern. In this work we obtain a clear and precise indication on the preferred symmetry breaking scheme from a fit of the predicted $|{\mathbf{V}}^{\mathrm{th}}|$ to the experimentally determined absolute values of the elements of the CKM matrix. The preferred scheme leads to simple mass textures and allows us to compute the CKM mixing matrix, the Jarlskog invariant $J$, and the three inner angles of the unitarity triangle in terms of four quark mass ratios and only one free parameter: the $\mathrm{CP}$ violating phase $\ensuremath{\Phi}$. Excellent agreement with the experimentally determined absolute values of the entries in the CKM matrix is obtained for $\ensuremath{\Phi}=90\ifmmode^\circ\else\textdegree\fi{}$. The corresponding computed values of the Jarlskog invariant and the inner angles are $J=3.00\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5},$ $\ensuremath{\alpha}=84\ifmmode^\circ\else\textdegree\fi{},$ $\ensuremath{\beta}=24\ifmmode^\circ\else\textdegree\fi{}$, and $\ensuremath{\gamma}=72\ifmmode^\circ\else\textdegree\fi{}$ in very good agreement with current data on $\mathrm{CP}$ violation in the neutral kaon-antikaon system and oscillations in the ${B}_{s}^{0}\ensuremath{-}{B}_{s}^{0}$ system.

Light quark masses and CKM matrix elements from lattice QCD

I give a brief overview of recent results from lattice QCD calculations which are relevant for the phenomenology of the Standard Model. I discuss, in particular, the lattice determination of light quark masses and the calculation of those hadronic quantities, such as semileptonic form factors, decay constants and B-parameters, which are of particular interest for the analysis of the CKM mixing matrix and the origin of CP violation.

Charming-penguin enhanced B decays

Long-distance contributions of operators of the effective non-leptonic weak Hamiltonian containing charmed currents have been recently studied. Penguin-like contractions of these operators, denoted as charming penguins, have been shown to be relevant for several B decays into two pseudoscalar mesons. In particular, they are expected to give large enhancements to processes which would be otherwise Cabibbo-suppressed. Their contributions easily lead to values of BR( B + → K 0 π +) and BR( B d → K + π −) of about 1 × 10 −5, as recently found by the CLEO collaboration. In this paper, we show that such large branching fractions cannot be obtained without charming penguins. This holds true irrespective of the model used to compute the non-leptonic amplitudes and of the relevant parameters of the CKM mixing matrix. We use the experimental measurements of the B + → K 0 π + and B d → K + π − decay rates to constrain the charming-penguin amplitudes and to predict BR's for a large set of other two-body decay channels where their contributions are also important. These include several pseudoscalar-vector and vector-vector channels, such as B → ϱK and B → ϱK ∗ , which have not been measured yet.

Electroweak baryogenesis and standard model CP violation.

We analyze the mechanism of electroweak baryogenesis proposed by Farrar and Shaposhnikov in which the phase of the CKM mixing matrix is the only source of $CP$ violation. This mechanism is based on a phase separation of baryons via the scattering of quasiparticles by the wall of an expanding bubble produced at the electroweak phase transition. In agreement with the recent work of Gavela, Hern\'andez, Orloff and P\`ene, we conclude that QCD damping effects reduce the asymmetry produced to a negligible amount. We interpret the damping as quantum decoherence. We compute the asymmetry analytically. Our analysis reflects the observation that only a thin, outer layer of the bubble contributes to the coherent scattering of the quasiparticles. The generality of our arguments rules out any mechanism of electroweak baryogenesis that does not make use of a new source of $CP$ violation.

Single top quark production and Vb CKM matrix element measurement in high energy e+e− collisions

A new method for the determination of the CKM mixing matrix element V tb has been proposed. It has been shown, that at future colliders one will measure the tb-mixing element with an accuracy 12–28%.

New approach for the construction of fermion mass matrices in SO(10) supersymmetric grand unified theories.

A new procedure is developed which enables one to start from the quark and lepton mass and mixing data at the low scale and construct mass matrices which exhibit simple SO(10) structure at the SUSY GUT scale. This approach is applied to the present data involving quark and charged lepton masses, the CKM mixing matrix and the MSW solar neutrino and atmospheric neutrino depletion effects. In terms of just 12 model parameters suggested by the procedure for the 5 mass matrices, we can reproduce 15 masses and 8 mixing parameters remarkably consistent with the input starting values.