Threshold π+ electroproduction at high-momentum transfer: A determination of the nucleon axial vector form factor

Threshold π⁺ electroproduction has been measured at momentum transfers 6k²6 of 0.45, 0.58 and 0.88 (GeV/c)², extending the range of earlier measurements. Using PCAC and current algebra-based models we have deduced the axial vector form factor of the nucleon G_A(k²), and find that the dipole parametrisation is favoured over the monopole. The value of M_A in the dipole parametrisation is, in a weak PCAC model, 0.96 ± 0.03 GeV, in excellent agreement with neutrino measurements. The threshold cross section is also in excellent agreement with the predictions of a fixed-t dispersion relation model.     

Electroweak radiative corrections to neutrino and electron scattering and the value of sin2θw

We describe in detail the calculation of all first-order electroweak radiative corrections to total and differential neutrino cross sections and to the parity-violating asymmetry in ed scattering. We find that leading log approximations agree well with our exact result for the shape, but not necessarily the magnitude, of the corrections to $\text{d}\text{σ}{}^{\mathrm{<mtext>\nu ,</mtext><mtext>\nu </mtext>}}\text{/}\text{d}\text{γ}$ except for γ → 1. Corrections to total neutrino cross sections have also been calculated by Marciano and Sirlin; our results agree with theirs. The corrections to sin²θ_w are experiment dependent. If sin²θ_w is defined in the $\text{MS}$ scheme at a scale M_w, they reduce the average value found from the ratio of charged to neutral current neutrino scattering by 0.012 to 0.215 ± 0.015. They reduce the value obatained from the Paschos Wolfenstein relation by 0.008 to 0.221 ± 0.014. In ed scattering they reduce the value by 0.008 to 0.215 ± 0.015. Using a corrected value of 0.215 ± 0.015 and the first-order corrections to the mass formulae, the SU(2) × U(1) predictions for the vector boson masses are M_w = 83.1_?2.8^+3.1rmGeV and M_z = 93.8_?2.2^+2.5 GeV, about five GeV larger than obtained from the lowest order analysis.     

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.     

Scale breaking in neutrino scattering

We consider two types of scale breaking models—one based on asymptotically free gauge theory and the other phenomenological—which have already been fitted to the electron and muon data. Their predictions for the neutrino scattering are worked out and the sensitivity on the model parameters and the input electron data studied. The effects of scale breaking at very lowQ ² and of a finite longitudinal cross-section are incorporated in analogy withep data. The predictions are compared with the recent neutrino scattering data.     

New results on deep inelastic processes from generalized vector dominance

A formulation of generalized vector dominance (GVD), consistent with the parton model (PM) for deep inelastic electroproduction, is presented. The parton distributions at small x are correctly predicted in terms of the photoabsorption parameters. It is found that no charmed partons exist in the sea of the nucleon. The pomeron ??_c coupling and the ?_c ? photoproduction cross section are negligible. The ratio σ_L/σ_T for deep inelatic and diffractive electroproduction is found to be small. This is related to the prediction that the highest Regge singularity coupled to longitudinal vector mesons is a cut with intercept minus one. In the time-like region it implies that the angular distribution in e⁺e^?→ π + X is ～ (3?cos²Θ), in consistence with experiment and disagreement with PM. Finally the large value of σ(e⁺e^? → hadrons) is attributed to a series of ?_c's.     

Transverse momentum of charmed quarks produced in deep inelastic neutrino scattering

QCD predictions on the transverse momentum of charmed quarks produced in neutrino production are presented and contrasted to similar predictions of the transverse momentum of jets in electroproduction. The effects of including charmed quark mass are also considered and turn out to be significant.     

A measurement of the neutral current electroweak parameters using the fermilab narrow band neutrino beam

We report a measurement of the electroweak parameters sin₂θ ^w and ? based on the ratios of neutral current to charged current events measured in the Fermilab narrow-band neutrino beam at energies of 30–240 GeV. The data are fully corrected for radiative effects, heavy-quark production, and other effects. The best value for sin₂θ ^w obtained, sin₂θ ^w =0.239±0.011, is consistent with the most recent values fromW andZ production, as well as from other neutrino experiments.     

Analytical properties of the forward elastic scattering amplitudes following from microcausality

The forward elastic scattering amplitudes T_i(v,q²), (i = 1,2), of the virtual photon with the mass q² are considered in variables σ and ? where σ and ? are related to q² and v by the formulae q² = exp (2σ) and v = exp (σ) ch?. It has been proved that microcausality requirement implies the analyticity of amplitudes in the tube region [Im σ + π/2] + |Im?| < π/2 as a function of both complex variables σ and ?. Formulae are obtained expressing amplitudes T_l(v,q²) at arbitrary v and q² through functions W_l^(?)(v, q²) describing the electroproduction process ?2v < q² < 0.     

Predictions for inclusive reactions based on a parton structure of hadrons

It is proposed that the asymptotic single-particle distributions f(x)=x(dσ/dx) in inclusive reactions should reflect the limiting longitudinal momentum distribution, ∼νW₂(x), of the hypothetical partons constituting a hadron. It is further argued that f(x) becomes, proportional to νW₂(x) as x → 1. Predictions are then made for a large class of inclusive reactions based on our knowledge of νW₂(x) from electroproduction data. For some of these (such as pp → π^±X), in which the predictions differ markedly from the Regge ones, present experiments distinctly favor ours.     

A study of the nuclear-medium influence on transverse momentum of hadrons produced in deep-inelastic neutrino scattering

The influence of nuclear effects on the transverse momentum (p_T) of neutrino-produced hadrons is investigated using the data obtained with the SKAT propane-freon bubble chamber irradiated in the neutrino beam (with E _v =3–30 GeV) at the Serpukhov accelerator. It has been observed that the nuclear effects cause an enhancement of 〈p _T ² 〉 of hadrons produced in the target fragmentation region at low invariant mass of the hadronic system (2 < W < 4 GeV) and at low energies transferred to the hadrons (2 < ν < 9 GeV). At higher W and ν, no influence of nuclear effects on 〈p _T ² 〉 is observed. Measurement results are compared with predictions of a simple model, incorporating secondary intranuclear interactions of hadrons, which qualitatively reproduces the main features of the data.     

Scaling violation in electroproduction at large ω'

The GVD predictions for scaling violation in electroproduction at ω'?5 are presented and agree with data. The effects of charm are included and found negligible in the ω′?q² domain of present experiments, but appreciable at higher ω' and (or)q².     

Hadron production by virtual photons in the quark fragmentation region

We have measured the inclusive electroproduction of positive and negative hadrons in the quark fragmentation region using the streamer chamber at DESY. Data are presented in terms of the variable z_p = p/v in the kinematic region 1.8 < W < 2.8 GeV and 0.3 < Q² < 1.4 GeV². The positive hadron distributions contain a strong proton component. After subtraction of the proton component and elastic rho events, the distribution (1/σ_tot) dσ/dz_p for positive and negative hadrons agrees well with the corresponding distribution from e⁺e^? annihilation (DORIS data). This behaviour supports the validity of the quark-parton model at surprisingly low Q² and W.     

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.     

Electroproduction of single charged pions from deuterons at Q2 ∼0.5 (GeV/c)2

The ratio of π^? to π⁺ electroproduction cross sections from deuterons has been measured in the resonance region at an average four-momentum transfer squared of 0.5 (GeV/c)². Results are presented over a wide range of pion production angles and comparisons are made with theoretical predictions based on SU(6)_w symmetry and the Melosh transformation.     

Final state interaction in pion electroproduction from nuclei near threshold

We have calculated cross sections for pion electroproduction from nuclei near threshold, including the distortion of the pion wave function by the pion-nucleus optical potential. Distortion effects near threshold are found to be significant, changing the ratio σ_π-/σ_π+ for production of 10 MeV pions from ¹⁶O by nearly fifty percent.     

Energy spectrum of photons produced by neutrino (antineutrino) scattering on electrons. Effect of possible neutrino oscillations

The energy spectrum of photons emitted in neutrino (antineutrino) scattering on electrons at E_v ? m_v is calculated with the assumption that the neutral electron flow has an arbitrary (V, A) structure. The result obtained is generalized to the case of possible neutrino oscillations, \(v_e \begin{array}{*{20}c} { - \to } \\ { \leftarrow - } \\ \end{array} v_\mu , \overline v _e \begin{array}{*{20}c} { - \to } \\ { \leftarrow - } \\ \end{array} \overline v _\mu \) , at an arbitrary neutrino mixing angle. Using the Weinberg-Salam model (sin²θ_W = 0.23) estimates of the sections dσ_γ/dω and σ_γ are obtained with consideration of the reactor antineutrino flux \(\bar v_e \) . The contributions from charged and neutral lepton fluxes and their interference to dσ_γ/dω are compared.