Standard-Model Tests with Superallowed β-Decay: An Important Application of Very Precise Mass Measurements

Superallowed β-decay provides a sensitive means for probing the limitations of the Electroweak Standard Model. To date, the strengths (ft-values) of superallowed 0⁺→0⁺ β-decay transitions have been determined with high precision from nine different short-lived nuclei, ranging from ¹⁰C to ⁵⁴Co. Each result leads to an independent measure for the vector coupling constant G _V and collectively the nine values can be used to test the conservation of the weak vector current (CVC). Within current uncertainties, the results support CVC to better than a few parts in 10,000 - a clear success for the Standard Model! However, when the average value of G _V, as determined in this way, is combined with data from decays of the muon and kaon to test another prediction of the Standard Model, the result is much more provocative. A test of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix fails by more than two standard deviations. This result can be made more definitive by experiments that require extremely precise mass measurements, in some cases on very short-lived (≤100 ms) nuclei. This talk presents the current status and future prospects for these Standard-Model tests, emphasizing the role of precise mass, or mass-difference measurements. There remains a real challenge to mass-measurement technique with the opportunity for significant new results. This revised version was published online in July 2006 with corrections to the Cover Date.     

The spectrum of the 4-generation Dirac–Kähler extension of the SM

We compute the mass spectrum of the fermionic sector of the Dirac–Kähler extension of the SM (DK-SM) by showing that there exists a Bogoliubov transformation that transforms the DK-SM into a flavor U(4)$U(4)$ extension of the SM (SM-4) with a particular choice of masses and mixing textures. Mass relations of the model allow determination of masses of the 4th generation. Tree level prediction for the mass of the 4th charged lepton is 370 GeV. The model selects the normal hierarchy for neutrino masses and reproduces naturally the near tri-bimaximal and quark mixing textures. The electron neutrino and the 4th neutrino masses are related via a see-saw-like mechanism.     

Leading order one-loop CP and P violating effective action in the Standard Model

The fermions of the Standard Model are integrated out to obtain the effective Lagrangian in the sector violating P and CP   at zero temperature. We confirm that no contributions arise for operators of dimension six or less and show that the leading operators are of dimension eight. To assert this we explicitly compute one such non-vanishing contribution, namely, that with three Z⁰$Z^0$, two W⁺$W^{+}$ and two W⁻$W^{-}$. Terms involving just gluons and W?s are also considered, however, they turn out to vanish in the P-odd sector to eighth order. The analogous gluonic term in the CP-odd and P-even (C-odd) sector is non-vanishing and it is also computed. The expressions derived apply directly to massive Dirac neutrinos. All CP-violating results display the infrared enhancement already found at dimension six.     

Flavour democracy calls for the fourth generation

It is argued with the help of an illustrative model, that the inter species hierarchy among the fermion masses and the quark mixing angles can be accommodated naturally in the standard model with (approximate) flavor democracy provided there are three exactly massless neutrinos and four families of sequential quark-leptons with all members of the fourth family having roughly equal masses. The special problem of light neutrino masses (if any) and possible solutions are also discussed.     

Hermitian quark matrices

Assuming a relation between the quark mass matrices of the two sectors a unique solution can be obtained for the CKM flavor mixing matrix. A numerical example is worked out which is in excellent agreement with experimental data.     

Precision flavour physics and supersymmetry

We review the salient features of a comparative study of the profile of the CKM unitarity triangle, and the resulting CP-violating phases , β and γ in B decays, in the standard model and in several variants of the minimal supersymmetric standard model (MSSM), reported recently by us. These theories are characterized by a single phase in the quark flavour mixing matrix and give rise to well-defined contributions in the flavour-changing-neutral-current transitions in K and B decays. We analyse the supersymmetric contributions to the mass differences in the B_d⁰– and B_s⁰– systems, ΔM_d and ΔM_s, respectively, and to the CP-violating quantity || in K decays. Our analysis shows that the predicted ranges of β in the standard model and in MSSM models are very similar. However, precise measurements at B-factories and hadron machines may be able to distinguish these theories in terms of the other two CP-violating phases and γ.     

“Could charm (& τ ) transitions be the ‘poor princess’ providing a deeper understanding of fundamental dynamics ?” or: “Finding novel forces”

We know that our Universe is composed of only ～4.5% “known” matter; therefore, our understanding is incomplete. This can be seen directly in the case of neutrino oscillations (without even considering potential other universes). Charm quarks have had considerable impact on our understanding of known matter, and quantum chromodynamics (QCD) is the only local quantum field theory to describe strong forces. It is possible to learn novel lessons concerning strong dynamics by measuring rates around the thresholds of [QˉQ] states with Q = b, c. Furthermore, these states provide us with gateways towards new dynamics (ND), where we must transition from “accuracy” to “precision” eras. Finally, we can make connections with τ transitions and, perhaps, with dark matter. Charm dynamics acts as a bridge between the worlds of light- and heavy-flavor hadrons (namely, beauty hadrons), and finding regional asymmetries in many-body final states may prove to be a “game changer”. There are several different approaches to achieving these goals: for example, experiments such as the Super Tau-Charm Factory, Super Beauty Factory, and the Super Z⁰ Factory act as gatekeepers – and deeper thinking regarding symmetries.     

First lattice QCD calculation of semileptonic decays of charmed-strange baryonsΞc

While the standard model is the most successful theory to describe all the interactions and constituents of elementary particle physics,it has been constantly scrutinized for over four decades.Weak decays of charm quarks can be used to measure the coupling strength between quarks in different families and serve as an ideal probe for CP violation.As the lowest charm-strange baryons with three different flavors,Ξ;baryons(composed of csu or csd)have been extensively studied in experiments.In this study,we use state-of-the-art lattice QCD techniques to generate 2+1 clover fermion ensembles with two lattice spacings,a=(0.108,0.080 fm).Then,we present the first ab-initio lattice QCD calculation of the Ξ;→Ξ form factors.Our theoretical results for the Ξc→Ξl;v;decay widths are consistent with and approximately two times more precise than the latest measurements by the ALICE and Belle collaborations.Based on the latest experimental measurements,we independently obtain the quark-mixing matrix element |V;|,which is in good agreement with results from other theoretical approaches.     

Charm hadronic decays and quantum correlations at CLEO-c

Several recent CLEO-c results on hadronic decays of charm mesons are reviewed.Topics include measurements of precision branching fractions for exclusive modes,investigations of inclusive rates,and analyses of Dalitz plots.In addition,the quantum correlations of the D pairs produced at the ψ(3770) are exploited to measure phase information that is of current interest for both D and B physics.     

Mass mixing,the fourth generation,and the kinematic Higgs mechanism

We describe how to construct explicit chiral fermion mass terms using Dirac–Kähler (DK) spinors. Classical massive DK spinors are shown to be equivalent to four generations of Dirac spinors with equal mass coupled to a background U(2,2)$U(2,2)$ gauge field. Quantization breaks U(2,2)$U(2,2)$ to U(2)×U(2)$U(2)\times U(2)$, lifts mass spectrum degeneracy, and generates a non-trivial CKM mixing.