Unique solution for the weak neutral current coupling constants in purely leptonic interactions

By combining results from the MARK-J at PETRA on Bhabha scattering, μ⁺μ^- and τ⁺τ^- production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants g_V and g_A in the framework of electroweak models containing a single Z⁰. In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ? U (1) model of Glashow, Weinberg and Salam, we find sin²θ_W=0.24±0.11.     

Determination of neutral current couplings from neutrino-induced semi-inclusive pion and inclusive reactions

We show that by looking at data from neutrino-induced semi-inclusive pion and inclusive reactions on isoscalar targets alone, one can determine completely the neutral current couplings. Predictions for various models are also presented.     

Note on the QED corrections to leptonic decays of the neutral vector boson

An exact calculation of the lowest-order QED corrections to leptonic decay rates of the neutral vector boson is presented and the origin of a discrepancy between two recent results is explained.     

Study of the V,a structure of the charged leptonic current

Although the charged weak interactions of leptons are conventionally described by pure V - A currents, several recent models have mechanisms which admit components of other structures. It is therefore becoming increasingly important to know the experimentally allowed amounts of V + A (as well as S, P, and T) admixture.In this paper the structure of the charged leptonic weak currents is studied in the framework of two models, the fermion-mirror fermion mixing model connected with many grand unification schemes, and the left-right symmetric SU(2)_L × SU(2)_R × U(1) flavor model. Both of these models allow more general V, A structure of the currents. We fit the parameters of these models to experimental data from pseudoscalar meson decay, muon decay, nuclear β-decay, and inverse muon decay. We find that substantial departure from pure V - A is allowed, the best fit values of the parameters being within one standard deviation from their V - A values.In the mixing model, different mass configurations of the mirror neutrinos are considered. The case with a heavy (>m_K) electron mirror neutrino and a light (⪡m_e) muon mirror neutrino is disfavored by the fit.The lower limit of the mass of the right-handed gauge boson W_R in the SU(2)_L × SU(2)_R × U(1) model is m(W_R) >3.4m(W_L) (68.3% c.l.). The left-right symmetric model fits slightly better than the mixing model. The only data explicitly disagreeing with the V - A model is the ξ-parameter in muon decay. It would be of great importance to have this parameter remeasured.     

A determination of quark weak couplings at petra energies

Data on hadron production by e⁺e^? annihilation at c.m. energies between 12 and 36.6 GeV have been collected using the JADE detector. They have been analysed in terms of single-photon and weak neutral-current exchange assuming production of quark-antiquark pairs with only d, u, s, c and b quarks to produce values for the quark weak neutral-current couplings. A further analysis in terms of the Glashow-Salam-Weinberg theory produced the result, sin²θ_{W = 0.22 ± 0.08}. The theory has therefore been tested in a new energy domain and within the context of the neutral weak couplings of the first, second and third generation quarks.     

Charged current couplings in the six-quark model

New values for the V_cd and V_cs couplings are determined from opposite sign dimuon data. These results together with the V_ud and V_us couplings give restrictive bounds for other elements of the Kobayashi-Maskawa matrix.     

Unified QCD determination of all pseudoscalar leptonic decay constants

Leptonic decay constants of all pseudoscalar mesons are determined in QCD by means of a new QCD sum-rule method. In the light meson and heavy quark limit the results are very similar and also agree with the well-known PCAC and scaling predictions respectively. The corrections to light meson pole dominance are generally small while those to the heavy quark limit are found to be sensitive to the binding energy (i.e. meson and quark mass differences). For standard values of quark masses we obtainf =132 MeV,f _k=161 MeV,f _B=128±28 MeV,f _D=175±13 MeV,f _Bs=144±30 MeV andf _Ds=193±12 MeV.Work supported by Bundesministerium für Forschung und Technologie (BMFT) under contract No. 06MZ758     

A novel approach to probing new physics with neutral Gauge Boson couplings

Even before reaching the energy threshold for producing any new elementary particle beyond the Standard Model(SM)[1],new physics effects can be systematically described by effective operators with mass-dimensions higher than 4.These new operators together with the SM form the so-called SM effective theory(SMEFT).Most analyses consider only dimension-6 operators.     

Non-Hermitian weak hadronic current and the Σ→λ leptonic decay

It is shown that an antihermitian contribution to the isotriplet of weak hadronic strangeness-conserving currents leads to a charge asymmetry. The existence of such currents with “wrong” G-parity is neither established nor refuted by existing experimental data. A deviation of Γ(Σ^?→Λe^?v)/Γ(Σ⁺→Λe⁺v) from the phase space ratio by more than ≈2 percent strongly suggests the presence of an antihermitian weak hadronic current, irrespective of time reversal invariance or CVC being valid or not.     

Relations among neutral current couplings to test the SU(2) ⊗ U(1) gauge group structure

The experimental implications of neutral heavy leptons N in e⁺e^? annihilation are examined. We calculate the production rate of both right-handed and left-handed N's at SPEAR and PEP/PETRA energies and show that observation of the process $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→}\text{ν}\text{?}\text{N}\text{,}\text{N}\text{→}\text{e}$ (or μ)π allows the determination of both the mass and handedness of N.     

Universality and the weak neutral current

We consider the possibility that the weak neutral current displays both muon-electron and quark-lepton universality. Such a model contains three parameters which we determine, within limits, from existing data on deep inelastic scattering of neutrinos off nucleons and elastic scattering of neutrinos off leptons. We show that such a model is consistent with other results on elastic neutrino-nucleon scattering and neutrino-induced production of single pions.     

The neutral weak current of the nucleon

A brief review of the structure of the nucleon as determined through parity-violating electron scattering is presented. The relationship between the electromagnetic and neutral weak currents is developed in a pedagogical introduction. Recent results and present measurements are discussed.     

The Hypothesis of theV−A fermion current dominance and neutral current interactions

The hypothesis of theV–A fermion current dominance is expressed through an appropriate hypercharge partitioning criterion. The application of this criterion to the standard electroweak model imposes on the Weinberg mixing angle a bound which is in excellent agreement with experiments.