QCD estimates for associated charm production by weak neutral currents

We give quantitative estimates for associated charm production in neutrino and antineutrino induced neutral current interactions, based on (a) quantum chromodynamics (QCD) and (b) the quark parton model (QPM) and a phenomenological generalization thereof. We emphasize the need for a precise measurement of the ratio σ(v_μN→v_μe⁺X)/σ(v_μN→μ^?X) and the corresponding ratio for antineutrinos, as these can provide clean tests of certain characteristic features of QCD. Bounds are obtained for single charm production by charm-changing neutral currents.     

Nuclear excitation by neutral weak currents

The use of neutrino excitation of nuclear levels to study weak neutral currents is examined.     

Neutral pion production by weak neutral currents in neutrino and antineutrino reactions

A study is presented of single π^o production in neutrino and antineutrino interactions in Gargamelle filled with freon CF₃Br. Limits on the neutral to charged current cross-section ratios $\text{R}{}_{\mathrm{v}}\text{=σ(v}\text{N}\text{→v}\text{N}\text{′π}{}^{\mathrm{o}}\text{)/2 σ(v}\text{N}\text{→ μ}{}^{\mathrm{-}}\text{N}\text{′π}{}^{\mathrm{o}}\text{)}$ and $\text{R}{}_{\mathrm{<mtext>\nu </mtext>}}\text{= σ(}\text{ν}\text{N}\text{→}\text{ν}\text{N}\text{′π}{}^{\mathrm{o}}\text{)/2 σ(}\text{ν}\text{N}\text{→ ω}{}^{\mathrm{+}}\text{N}\text{′π}{}^{\mathrm{o}}\text{)}$ are found to be $\text{0.10 < R}{}_{\mathrm{\nu }}\text{< 0.20}\text{and}\text{0.26 < R}{}_{\mathrm{<mtext>\nu </mtext>}}\text{< 0.44}$ at 68% confidence level.     

Effects of neutral weak currents in annihilation

General cross-sections are given for annihilation via one photon and W⁰ exchange. Effects of the W⁰ in the special cases e⁺e^?→μ⁺μ^? and $\text{p}\text{p}\text{→?}{}^{\mathrm{+}}\text{?}{}^{\mathrm{?}}$ at high energies are discussed. These effects are estimated to be comparable to the effects from one γ exchange at energies accesible in NAL and SPS.     

Pion production by neutral currents in neutrino-nucleon collisions

It is argued that the apparent arbitrariness of the “anomaly” in Fujikawa's approach should be placed into the context of the regularization of the theory not just the regularization of the anomaly. When the theory is regularized at the level of the action the consistent anomaly arises. The converse also holds, namely that if the anomaly is not consistent then the regulator employed does not, by itself, regulate the theory at the level of the action. The criterion that the regularization presription be given at the outset is advocated, and a discussion of results of various two-dimensional models given.     

Analysis of weak neutral currents using light-cone algebra

Using the algebra of light-cone commutators and making some simplifying assumptions, we have attempted to determine the isospin structure of a two-parameter weak hadronic neutral current. We have also computed in the light-cone model, they distributions for inclusive neutrino and antineutrino neutral current deep-inelastic interactions. Contrary to the quark-parton model, we find that both distributions have the same value.     

Energetic stabilization of d-camphor via weak neutral currents

It is shown via a series of numerical tests on the camphor molecule, C10H16O, that the naturally occurring d-enantiomer is energetically stabilized with respect to its mirror image by electroweak force. The calculated energy difference between enantiomers, about 1.5 x 10(-19) hartree, is roughly eight orders of magnitude smaller than the upper bound suggested by available spectroscopic investigations on the frequency of a spectroscopic transition. However, such a difference is about ten times larger than previous estimates of parity-violating energy contributions reported in the literature for other chiral molecules, which makes the idea of electroweak stabilization of one enantiomer more reliable than expected before.     

Testing weak neutral currents in longitudinally polarized colliding beams

We study the effects of a weak neutral current as they show up in longitudinally polarized colliding beams. The reactions considered here are e⁺e^?→μ⁺μ^? and e⁺e^?→π⁺π^?. The electromagnetic background and means to suppress this are also discussed.     

Triangle anomaly free weak interaction with two neutral currents

Considering that the neutral interaction is free of triangle anomalies we derive an expression for the most general neutral interaction with two neutral currents. We show that the Bargers version is a special case. We also determine the interaction wheneverZ, D are mass eigen states and show that this differs from the Barger’s version in an essential way.     

Gauge theories and “elastic” weak neutral currents

For the gauge group O(4) × U(1), the alternatives: left-handed leptons are (a) 4-spinors, (b) 4-vectors are shown to imply (a) possible presence, (b) absence of elastic ν_μ ? e and ν_μ ? nucleon amplitude to O(G). Some properties of the new spinor model are described. In contains a neutral current closely akin to the one in the Salam-Ward-Weinberg model.     

Testing the structure of weak neutral currents by inelastic neutrino scattering from nuclei

By using selected nuclear transitions specific pieces of the weak neutral current may be greatly enhanced, leading to widely different results for different models of the weak neutral current. Predictions for low-energy inelastic neutrino scattering from ¹²C are examined within the framework of a variety of SU(2)_W × U(1) gauge theory models.     

Pion production by fragmentation of weak currents in Weinberg theory

The Feynman quark parton model is used to study inclusive single-pion production by the fragmentation of the neutral and charged weak currents of Weinberg theory. The structure functions for the neutral current-induced reactions are related to those for the electromagnetic and charged weak current processes. Analogues of inclusive deep-inelastic sum rules are derived. The ratios of neutral current to charged current cross sections for semi-inclusive pion production are studied. In the approximation of neglect of “core” partons, these ratios are given in terms of average pion multiplicities in the charged current-induced reaction. We finally specialise to the quark parton distributions of McElhaney and Tuan to calculate these ratios as functions of the Weinberg angle.     

Experimental limits on the strength of weak neutral currents in lepton pair production at PETRA energies

The processes e⁺e^? → e⁺e^? and μ⁺μ^? have been studied at PETRA using the JADE detector. The data, which were collected at s-values of up to 1300 GeV² have been analysed in terms of an electro-weak extension of QED to obtain values for the weak vector and axial vector couplings in the lepton sector. The values obtained agree with the predictions of the standard Salam-Weinberg model and the data are further analysed in terms of this model to obtain the limits 0.10 < sin²?_w < 0.40 (68% CL). The mass of the neutral weak gauge boson is deduced to be greater than 51 GeV/c².     

Information on neutral weak currents from circular polarization of bremsstrahlung

Bremsstrahlung of unpolarized electrons is analysed for information on neutral weak interactions. The coupling of axial lepton and polar hadron neutral currents should cause a circular polarization of about 10^?6 at electron and photon energies of a few hundred MeV and forward angles. The specific nuclear structure is of modest importance.     

Effects of neutral weak currents in e+-e− annihilation

The effects of neutral weak currents are discussed in e⁺e^? annihilation into final states such as μ⁺μ^?, e⁺e^?, π⁺π^?, many hadrons and also in the one particle inclusive production. According to current gauge models these weak effects which are manifested as various asymmetries, turn out to be around 10% in the energy range of PEP and PETRA. In identifying weak effects polarized incident beams are advantageous, in particular, the longitudinally polarized beams select parity violating asymmetries.     

Space-time structure of weak neutral currents: (II). Elastic scattering

The elastic scattering of neutrinos and antineutrinos on nucleons in which the initial and final nucleon polarizations are measured, is studied from the point of view of the space-time properties of the currents. Structure functions are defined and experimentally measurable quantities which can be usual to disentangle the Lorentz structure of the currents are given. Second class current effects are also examined.     

Chiral U(1) symmetry and weak neutral currents at high energy

If chiral U(1) symmetry is a gauge symmetry, CP is automatically conserved despite the instanton effects, and the weak neutral currents have a definite structure. A realistic SU(2) _L ?U(1)?U(1) _R model contains an axion which is consistent with present data. Furthermore the neutrino interactions to lowest order are identical to the Weinberg-Salam model. Implications for the chiral U(1) currents are discussed.     

Semi-leptonic weak and electromagnetic interactions in nuclei:: Parity violations in electron scattering and weak neutral currents

A general result for the difference in differential cross sections for electron scattering between any two nuclear levels with incident longitudinally polarized right- and left-handed electrons is derived. This difference must involve the parity-violating weak interaction at least linearly and can be used to study weak neutral currents as pointed out by Feinberg. A V — A structure for the weak neutral currents is assumed with a semi-leptonic current-current interaction, and the electromagnetic interaction is treated in the one-photon-exchange approximation. The result is expressed in terms of the same set of reduced matrix elements of the multipoles of the nuclear currents which govern all electromagnetic and weak transitions between these levels. A previously developed unified analysis of semi-leptonic weak and electromagnetic interactions in nuclei which determines one-body transition densities, including their spin and spatial dependences, through electron scattering provides nuclear transitions to serve as known analyzers in testing the structure of this part of the weak interaction. Examples are given using Weinberg's model of the weak neutral currents. Feinberg's result for elastic scattering from spin-0 nuclei is rederived and two new examples using previously determined one-body densities are discussed : the 1⁺0 → 0⁺1 (3.56 MeV) transition in ⁶Li and the 0⁺0 → 1⁺ 1(15.1 MeV) transition in ¹²C.     

Inclusive muon production reactions as a test of neutral currents

With right and left handed polarized muons scattering on an unpolarized target we discuss possible asymmetries of inclusive cross sections induced by neutral weak currents. Using general positivity arguments we derive rigorous upper bounds to the asymmetries. Numerical estimates of the bounds are already possible if use is made of the branching ratios NC/CC)_ν, $\text{v}$ observed in the CERN Gargamelle bubble chamber. Upper and lower bounds to the asymmetries, specific to the Weinberg-Salam model, are also discussed.     

Single-pion production and the structure of the weak neutral current

We investigate the restrictions on the structure of the weak neutral current imposed by single pion production cross sections on single nucleons. A general vector (V), axial-vector (A) neutral current with |ΔI|?1 is assumed, where the isovector V,A neutral currents are the neutral members of the isotriplets containing the charged weak currents. From neutrino cross sections alone we derive bounds for the neutral current coupling constants. These bounds supplement the known constraints from inclusive scattering in a very useful way. More specific assumptions about the isoscalar neutral current are also considered. We discuss the resulting bounds using the existing neutrino data. Finally, it is shown that with the advent of antineutrino data for single pion production the neutral current coupling constants will be determined uniquely.