General bounds on the isovector coupling constants of the weak neutral current

We show that experimental data on inclusive neutrino reactions can be used to obtain general bounds on the coupling constants of the isovector part of the hadronic weak neutral current provided this isovector current is related to the charged current by isospin rotation. These bounds are free from the assumption of a specific model for the neutral current as well as any dynamical assumption on the hadronic structure functions. We derive upper bounds on the coupling constants which involve only the cross sections for isospin-averaged nucleon target as well as lower bounds which require a knowledge of the cross sections for proton and neutron separately.     

Elastic neutrino proton scattering and the structure of the neutral current

Optimal constraints on the structure of a general V, A hadronic neutral current are derived from neutrino proton scattering and compared with corresponding results from inclusive neutrino scattering and single pion production by neutrinos. For an arbitrary axial component of the neutral current, restrictions for the vector coupling constants are obtained. It is shown that the most general neutral current which can be related to charged weak and electromagnetic currents accounts for all existing data on neutrino hadron scattering. The neutral current coupling constants are determined for the pure isovector model, the Salam-Weinberg model and the bottom-quark model. All three models lead to practically the same isovector couplings but they differ in the strength of the isoscalar current.     

Heavy Dirac and Majorana neutrino production ine + e − collisions

The production of heavy Dirac and Majorana neutrinos ine ⁺ e ^? collisions is investigated. The heavy Dirac and/or Majorana neutrinos can be produced in charged and neutral current processes $(e^ + e^ - \to N_1 \bar N_2 )$ . The production of a single heavy neutrino is possible if it mixes with the light neutrino species. The production of heavy neutrinos in Higgs channels is also studied, since in some specific models the Yukawa couplings could be large enough to make the production of heavy neutrinos through Higgs boson exchanges sufficiently large for detection. The most general left-right symmetric model with possibly complexV orA couplings is used in the analytic calculations of the production cross sections, but the numerical examples are given using simplified left-right symmetric model. The interference terms between different production channels have been studied in great detail and in some cases the interference terms are found to be non-negligible in wide range of production spectrum. The pair production cross section is larger in the Dirac case than it is in the Majorana case, but the single heavy Majorana neutrino production cross section is roughly twice as large as that of a Dirac neutrino.     

Topics in the S-matrix theory of massless particles

We discuss how massless particle reactions may be incorporated into standard S-matrix theory. The crucial element for doing so is a low-energy zero. Examples of reactions where such zeros occur are weak interaction processes involving neutrinos, chirally symmetric massless pion scattering, and two-photon exchange between neutral systems. These zeros make two-body unitarity a good approximation for sufficiently low energy despite the coalescence of multiparticle thresholds. Through two-body unitarity, these zeros produce lines of zeros in the absorptive parts and double spectral functions. These lines of zeros are the S-matrix analog of the requirement of an infrared finite field theory. Not only do they produce finite total cross sections at finite energies, but they also allow both upper and lower bounds to be derived for these cross sections at high energies. This upper bound is our main result. If a plausible smoothness assumption is made, we find σ_tot <s^? (where ? is arbitrarily small). In particular, the experimentally observed linear rise of the neutrino proton cross section cannot continue indefinitely.     

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.     

Study of inclusive neutral current interactions of neutrinos and antineutrinos

We report on results from a study of hadron-energy distributions for ν and $\text{ν}$ inclusive neutral current interactions. There is no significant variation of the neutral to charged current total cross-section ratios R_ν and $\text{R}\text{ν}$ with neutrino energy. The space-time structure of neutral currents is dominated by V?A, with a significant admixture of V+A. The Weinberg-Salam model is in agreement with all data if sin²θ_w=0.24±0.02.     

Neutral currents in elastic neutrino-nucleon scattering

We investigate elastic neutrino (antineutrino)-nucleon scattering in the case where some pieces of neutral currents are related to those which appear in electromagnetism and in weak charge-changing reactions. From Gargamelle preliminary results on elastic reactions we get numerical constraints on the parameters which connect the vector parts of neutral currents with the electromagnetic current. Using inclusive neutral current data we give predictions on elastic cross sections in the case of various models of neutral currents.     

On some tests of the basic properties of the neutral weak interaction. I. With massless neutrinos

We consider the Born approximation scattering, by electrons, of neutrinos (and antineutrinos) of the muon and of the electron types; the general Lagrangian respecting lepton locality is used. Throughout, we study only differential cross sections as the experimental observables. Some tests previously proposed for “neutrino identity” or Lorentz structure of the neutral weak interaction are reexamined. We find that, in general, these relations cannot uniquely answer the question of Lorentz structure. Similarly, in general, one cannot estblish whether the final neutral lepton is completely identical with, or “partly identical” with, or completely different from, the initial neutrino; identity allows a difference in helicity. In several experimental situations, one can exclude the possibility of a complete non-identity. In one experimental situation, assuming μe universality, one can establish that the final and the initial neutrinos are completely identical, even in their helicity. “Does an interference between neutral currents and the (V ? A) charged current exist in

e^- scattering?” Certain tests can answer this question completely if μe universality is assumed. Without μe universality, the answer is “destructive interference” if an observable (A_e) turns out to be less than 4; A_e = 4 would exclude a constructive interference. Assuming neutrino identity, time-reversal invariance for the helicity flipping types (S,P,T), and μe universality, certain simple combinations of observables were previously noted to determine the (V,A) neutral interaction couplings of the neutrino to the electron. With our general formalism, that determination is seen not to require the first two assumptions. Also, the couplings concerned are seen to be only the “diagonal” ones—which refer to that part of the final state in which the final neutrino is identical with the iniitial one. Keeping in view a recent experimental situation, the following question is answered: “When will the lack of enough events for $\text{ν}\text{e}{}^{\mathrm{?}}$ scattering (or, similarly, νe^? scattering) become a threat to lepton locality?” Some additional consequences of μe universality are noted.     

Space-time structure of neutral currents and y-distributions

Assuming scaling of the nucleon structure functions, we derive relations for the y-distributions in deep inelastic neutrino scattering for the most general local interaction of neutrinos with hadrons via neutral currents with V, A, S, P and T pieces. In addition, optimal bounds for the y-distributions are presented which follow from positivity requirements for the structure functions and which may serve to discriminate between pure V, A currents and the presence of S, P, T couplings. The influence of the predictions of the $\text{spin}\text{-}\text{1}\text{2}$ parton model on the bounds is investigated. All relations and bounds depend only on the ratio of total neutrino and antineutrino cross sections.     

Experimental study of differential cross sections dσdy in neutral current neutrino and antineutrino interactions

We present differential cross sections dσ/dy corrected for resolution and acceptance, for events induced by both the neutral- and charged-current interactions of neutrinos and antineutrinos. They are based on 8553 neutrino and 3578 antineutrino events obtained using the CHARM fine-grain calorimeter in the CERN 200 GeV narrow-band beam. From these differential cross sections we demonstrate that the coupling strength of the weak neutral current to the strange quark is compatible with being equal to that of the down quark. Assuming this equality we then describe the weak neutral current in terms of one parameter, sin²θ, which we find to be 0.222 ± 0.016. The charged-current differential cross sections yield values of the fractional momentum-weighted content of the nucleon for non-strange (0.12 ± 0.04) and strange (0.06 ± 0.04) sea quarks. Furthermore, from the strength of the allowed y² term in the neutral-current differential cross sections we put a limit of 3% on the presence of scalar or pseudoscalar contributions to the weak neutral current. This can alternatively be expressed in terms of the Callan-Gross violation parameter R, where we find R = 0 .10 ± 0.10.     

Neutrino-excitation of baryon resonances and single pion production

This is an attempt to describe all existing data on neutrino production of single pions in the resonance region up to W = 2 GeV in terms of the relativistic quark model of Feynman, Kislinger and Ravndal (FKR). We considered single pion production to be mediated by all interfering resonances below 2 GeV. A simple noninterfering, nonresonant background of isospin $\text{1}\text{2}$ was added. It improved agreement with experiment, particularly in the ratio of isospin amplitudes in charged current reactions, at the expense of one additional constant. All total cross sections, cross section ratios and W-distributions are well reproduced at low and high energies, with charged and neutral currents (supposing the Salam-Weinberg theory with sin²$\text{θ}{}_{\mathrm{w}}\text{≈}\text{1}\text{4}$ to be correct), and for neutrinos and antineutrinos, giving predictions where data are lacking. New predictions have been made for complex angular distributions in $\text{N}$π channels exhibiting strong interference between neighbouring resonances. These are sensitive (for 1.1 GeV ? W ? 1.5 GeV) to the sign of the Roper resonance P₁₁(1450) which is controversial in photoproduction experiments.     

Scalar and Pseudo-Scalar Form Factors in Electro- and Weak-Production of Pion Near Threshold

We investigated pion production near threshold by the weak current in terms of multipole amplitudes. By exploiting the chiral Ward identity based on the QCD Lagrangian, we derived relevant multipole amplitudes in closed forms and presented their numerical results. In the amplitudes, scalar and pseudo scalar (PS) form factors, which represent the scalar and the PS quark density distributions, manifest by themselves. We applied these amplitudes to the cross sections for the weak- and electro-production near threshold. Both pion and PS form factor contributions are shown to account for the t-channel contribution in the charged pion electro-production near threshold. The asymmetry on the pion production by the neutrino and anti-neutrino is also discussed with their longitudinal and transverse cross sections.     

Parity violation in electron-deuteron scattering. II. Break-up channels

Parity violation in electron-deuteron inelastic scattering is decribed. An impulse approximation, modified to incorporate gauge invariance, is employed. Additional meson-exchange currents are included. Normal-parity and abnormal-parity wave function components are generated numerically with a Reid soft-core potential for the former and a general parity-violating weak potential with adjustable coupling constants for the latter. Numerical results for parity-conserving differential cross sections are in good agreement with existing data. For low n?p excitation energies and medium-energy electrons, we find that parity-violating asymmetries are dominated by contributions from neutral weak currents so that the Weinberg-Salam theory can be tested. For low-energy electrons, 5 MeV ? E_e ? 50 MeV, our results indicate that the asymmetry caused by nuclear parity violation is roughly as important as that due to neutral weak currents. The pion-nucleon parity-violating coupling, f_π, as well as the rho- and omega-nucleon parity-violating couplings, may be determinable from such experiments. Further, it is possible to check the experiment of Lobashov et al., which detects circular polarization in the thermal-neutron capture reaction.     

Pion distributions in inelastic neutrino interactions

Using data on semi-inclusive pion electroproduction as input we calculate in the framework of the quark parton model the distribution of pions in the current fragmentation region for inelastic neutrino interactions. Results for the π⁺/π^? asymmetry are presented for both charged and neutral currents. These provide stringent tests of the parton fragmentation hypothesis and the Weinberg-Salam gauge model.     

Cross-section measurements of single pion production in charged current neutrino and antineutrino interactions

All six exclusive single pion production processes from neutrino and antineutrino charged current interactions are studied in the energy range between 3 and 30 GeV. Using a quark model for single pion production from Rein and Sehgal we fitted the aximal mass parameter from total cross sections and compare the results with values from other experiments and the world-averages.     

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.     

Pion and K meson production in the multiperipheral model

A simple multiperipheral model, that utilizes only three parameters, two coupling constants and exponential damping for each momentum transfer is developed and applied to the calculation of inclusive distributions. The pion rapidity and p_⊥² distributions are successfully predicted; as are the energy dependences of strange particle production cross sections. The development of inclusive distributions with increasing energy and possible improvements to the model are discussed.     

A calculation of semileptonic neutral currents assuming partons and Weinberg's renormalizable theory

The Weinberg renormalizable theory of weak and electromagnetic interactions and its simple extension to hadron interactions are applied to a simple parton model. Strange partons are neglected. Inelastic neutrino and antineutrino cross sections for charged and neutral currents are expressed as functions of the parton charges, the Weinberg angle and the parton distributions in the Feynman variable x. Using the experimental charged current results, the neutral current to charged current total-cross section ratios are given as a function of the Weinberg angle for both integral and fractionally charged partons. Comparing these ratios with the experimental limits we conclude (a) that integral charges are excluded, and (b) that, given fractional charges, the Weinberg angle is constrained to be 40° ± 5°. It is shown that this result is not inconsistent with other published limits.     

Analysis of a six-quark model with right-handed currents

A model for the weak interactions using the six-quark model of Harari, right-handed currents, and heavy leptons which was proposed previously by some of us is analyzed in considerable detail. The model is one of a class of “vector-like” theories that are free of gauge theory anomalies. The neutral current is pure vector, which leads to predictions for diffractive production of vector mesons by neutrinos that are different from the predictions of the standard Weinberg-Salam model; the A₁ uncouples and the fractions of ? and ω are enhanced. It is also predicted that relative production of $\text{I =}\text{1}\text{2}$ final states is larger than $\text{I =}\text{3}\text{2}$ final states in vN → vNπ in contrast to the Weinberg-Salam model. The non-leptonic decays of hyperons and mesons and the restrictions imposed by chiral symmetry are discussed. The decays of the charmed mesons are shown to be very rich due to the presence of both V ? A and V + A interactions. The y-anomalies in neutrino interactions are discussed and calculations of $\text{d}\text{σ}\text{d}\text{x}\text{and}\text{d}\text{σ}\text{d}\text{y}$ for both neutrinos and antineutrinos using modified Kuti-Weisskopf distributions are presented. Cross sections and ratios of neutrino and a neutrino cross sections are shown along with available experimental data. The v-distribution of dimuon events is also presented and compared with experiment. It is concluded that the model is not inconsistent with the currently available data.     

Neutrino absorption cross sections in the supernova environment

We study charged-current neutrino cross sections on neutron-rich nuclei in the mass A∼60 region. Special attention is paid to environmental effects, i.e., finite temperature and density, on the cross sections. As these effects are largest for small neutrino energies, it is sufficient to study only the Gamow–Teller (GT) contributions to the cross sections. The relevant GT strength distributions are derived from large-scale shell model calculations. We find that the low-energy cross sections are enhanced at finite temperatures. However, for (ν_e,e⁻) reactions Pauli blocking of the electrons in the final state makes the cross sections for low-energy neutrinos much smaller than for the competing inelastic scattering on electrons at moderate and large densities. Absorption cross sections for low-energy antineutrinos are strongly enhanced at finite temperatures.