Electroproduction Data Research Articles

Role of gluons in the neutrino production of charm

We suggest that a sensible and consistent way of treating the associated production of charm and strangeness in $\ensuremath{\nu}N$ or $\overline{\ensuremath{\nu}}N$ collisions is to consider the basic subprocess to be $W^{+}V\ensuremath{\rightarrow}c\overline{s}$ or $W^{\ensuremath{-}}V\ensuremath{\rightarrow}s\overline{c}$, respectively, where $W$ is the virtual weak gauge boson and $V$ denotes a colored gluon. An explicit calculation illustrates how the concept of the sea in the parton model can turn out to be process-dependent in the sense that relative amounts of charm and strangeness in the sea of a nucleon as inferred from neutrino data need not be the same as those inferred from electroproduction data.

Inclusive π0 photoproduction and the quark-parton model

We present measurements on the inclusive structure function for π 0 photoproduction for the incident photon energy range of 2.8–4.8 GeV. Comparisons are made with electroproduction data and it is found that the scaling behaviour already observed for finite q 2 continues to be valid at q 2 = 0.

Information on ΔN axial form factors from low-energy electroproduction of πΔaxial form factors from low-energy electroproduction of πΔ

Low-energy πΔ electroproduction data are analysed in the framework of soft-pion theory, by taking Δ finite-width corrections into account, with the purpose of deriving information on the ΔN axial transition vertex. The numerical results agree with theoretical predictions based on PCAC and on the quark model.

Electroproduction of low hadronic masses

A model satisfying analytic, unitary, and soft-meson requirements is found to account for all electroproduction data in the $\ensuremath{\Delta}(3,3)$ region even at very high photon momentum transfers. The $\ensuremath{\Delta}$, pion, and nucleon axial-vector form factors are discussed within the framework of this simple yet accurate model.

New type of scaling law and the Bloom-Gilman duality

A new scaling law is studied in accommodation with Bloom-Gilman duality, which forces us to use a new scaling variable. We test the new scaling by using electroproduction data and find that it presents a beautiful description of the pattern of scaling violations.

Estimates of production cross sections and distributions forWbosons and hadronic jets in high-energyppandp¯pcollisions

Using the quark-parton model, with structure functions chosen to agree with electroproduction and leptonpair-production data, the cross sections are calculated for the production of charged and neutral $W$ mesons in high-energy $\mathrm{pp}$ collisions. The single- and double-particle distributions for the leptonic and hadronic decays of the $W$ are presented along with leptonic background from electromagnetic pair production. Using the same model, the cross sections for production of single and double hadronic jets are also calculated using both colored-vector-gluon exchange and the Field-Feynman models for the elementary quark-quark scattering. It is concluded that the leptonic decay of the $W$ should be a strong signal well above background, and that the parity violation of the weak interaction leads to characteristically different distributions for leptons and antileptons. The production in proton-antiproton collisions is also studied and found to be only slightly above the proton-proton production. The cross section does not increase rapidly with energy for $\frac{s}{m_{W}^{}{}_{}{}^{2}}\ensuremath{\gtrsim}10$. For hadronic jet production, the vector-gluon and Field-Feynman models lead to significantly different distributions, and if the predictions of the former are true the hadronic jet decay of the $W$, although plentiful, will be difficult to see above background. The effects of transverse motion of the $W$, neglected in the quark model, are found to be unimportant.

A quark-parton description of the deep inelastic scattering processes

A consistent description of various deep inelastic processes in a quark-parton model is presented. The valence quark probability distribution and the form of core quark probability distribution is fixed from the deep inelastic electroproduction data. Langacker and Suzuki prescription is used to fix thep andn quark core distribution. The differential excitation of quark currents similar to the Harari model ofe+e− annihilation process is invoked in deep inelastic electroproduction and neutrino reactions. An effective phenomenological form of the weak currents associated with new quarks and the associated nucleon structure is determined.

Phenomenological Analysis of the Bjorken-Scaling Violation in Electroproductions

A phenomenological analysis of the SLAC large angle electroproduction data is performed on the basis of predictions near x = 1 by field theories with nontrivial fixed points and asymptotically free field theories. It is shown that the data may be reproduced in both cases only if we choose rather unusual values for parameters appearing in these theories. A preliminary test of a new type of scaling proposed by one of the authors is given and it is found that it is consistent with the data in the large x region.

Photon shadowing in nuclei

Photon processes in nuclei are studied using a conventional optical model, interpreted unconventionally. To calibrate the method excellent fits to hadron-nucleus total cross sections are obtained. When applied to photon processes the ''self-absorption'' feature of the model tends to suppress the shadowing from what has previously been predicted. A further suppression is shown to result from the finite width of vector mesons. Reasonable agreement with recent electroproduction data is obtained.

Demythification of electroproduction local duality and precocious scaling

In an effort to develop a quantitative check of asymptotically free color-gauge theories, we analyze the logarithmic corrections to ξ-scaling coming from anomalous dimensions and coefficient functions of twist-two operators and compare with electroproduction data for 1 ⩽ Q 2 ⩽ 16 GeV 2. Excellent agreement is obtained using g 2(2 GeV) 4π 2 = 0.17 for the effective quark-gluon coupling in the color-gauge theory. Effects of higher-twist operators are suppressed by powers of M 0 2 Q 2 . We use data from the resonance region to show M 0 ⋍ 400 MeV , in agreement with theoretical expectations. Our fit to νW 2 in the scaling region also describes the resonance region in the sense of Bloom-gilman local duality. We show that local duality is a consequence of the moment predictions obtained from the operator-product expansion in quantum chromodynamics. We resolve a paradox associated with local duality and spin-zero targets. Present measurements of R = σ L σ T at large x and Q 2 are systematically higher than our predictions.

Diffractive production of vector mesons in lepton-nucleon reactions

We calculate cross sections for the production of vector mesons V in reactions if ℓ + N → ℓ' + V + N, ℓ, ℓ' = ν, e, μ, taking into account all presently known information from electroproduction of ϱ's. This leads to considerable differences in results from previous calculations, often more than an order of magnitude. The results for the ϱ are then largely a translation of electroproduction data into ν predictions and they will provide a direct test of the relation of weak and electromagnetic currents. The y or Q 2 distributions for the ϱ are instructive. The prediction for the A 1 provides a direct test of the existence of the A 1 and of whether vector and axial vector currents materialize into particles in the same way. The detection of a B meson would provide direct evidence for second-class currents and a measurement of their strength. We estimate all F ∗ production will account for at most 2% of the total ν cross section at FNAL energies, which must be multiplied by the muon semi-leptonic branching ratio (and possibly a factor of 2 for an axial vector F ∗) to calculate its contribution to the dimuon event rate.

Precocious scaling in field theories

We investigate precocious scaling in the sense of the Wilson operator-product expansion (OPE). We derive expressions for the coefficient functions appearing in such an expansion in terms of moments of the appropriate deep-inelastic structure functions. In these sum rules target-mass terms are treated exactly. Ratios of certain moments of structure functions have a computable deviation from naive scaling results which depends only on the magnitude of the effective charge $g({Q}^{2})$. An analysis of existing electroproduction data indicates that scaling in the OPE sense sets in for ${Q}^{2}$ as low as 2-3 Ge${\mathrm{V}}^{2}$. The charge $g({Q}^{2})$ appears to be small and may have ${Q}^{2}$ dependence only within experimental errors. We consider these results as evidence that the underlying theory of strong interactions is an asymptotically free field theory or a field theory with a small ultraviolet-stable fixed point.

Precocious Scaling: Evidence for Field Theory

Expressions are derived for the Wilson coefficient functions in terms of moments of W/sub 1//sub ,//sub 2/ treating target-mass effects exactly. An analysis of existing electroproduction data indicates that scaling in the Wilson sense sets in for Q/sup 2/ as low as 2--3 GeV/sup 2/. The effective charge sigma/sub s/(Q/sup 2/) appears to be small and may have Q/sup 2/ dependence only within experimental errors. These results are considered as evidence that the underlying theory of strong interactions is a field theory. (AIP)

Production of lepton pairs, J/Ψ and charm with hadron beams

Data for J/Ψ production with nucleon and pion beams are used, together with electro-production data, to extract information about distributions of quarks within hadrons. These distributions are used to make further predictions about J/Ψ production with beams of hadrons of various types, and about the production of lepton pairs. It is argued that, even at SPG or FNAL energies, J/Ψ production does not usually involve the conjont production to charmed particles. The production of charmed particles without the J/Ψ is also considered; the cross section is estimated to be smaller than has been previously predicted.

An improved determination ofG A(x) from single-π+ electroproduction

We analyse recent threshold π+ electroproduction data by combining the current algebra and PCAC approach with a simple model-independent parametrization of the ratio σ L /σ T . Adopting the traditional dipole fit for the nucleon axial-vector form factorG A(x), we findM A=(0.96±0.19) GeV, in agreement with neutrino results.

Inclusive pion production byVandAneutral currents in the quark-parton model

The process of deep-inelastic neutrino-nucleon scattering followed by the fragmentation of the possibly existing neutral current into pions is discussed. The quark-parton model allows for the consideration of characteristic effects of a general $V$ and $A$ neutral current. Charged-pion average multiplicities in $\ensuremath{\nu}$ and $\overline{\ensuremath{\nu}}$ scattering on an isovector target are found to be equal to each other and equal to the corresponding charged-current multiplicites. They are expected to be $x$- and $y$-independent and may be accurately calculated (within 10%) from recent electroproduction data. The structure parameters of the neutral current are related to neutral- to charged-current ratios of ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$ charge asymmetries. The importance of the measurements of these asymmetries is emphasized.

Parton distributions from neutrino data

Quark parton distributions are determined from new Fermilab νN and ḡnN deep inelastic scattering data, with E < 30 GeV. These data are consistent with a zero antiquark contribution, but an appreciable antiquark term is not excluded. The x distributions so determined also agree with the 30 < E < 80 and E > 80 GeV data, so there is no evidence for a breakdown of scaling or new mechanisms in d σ/d x. The neutrino quark distributions differ systematically from forms derived from SLAC electroproduction data, however.

Neutral current cross sections in the deep inelastic region

By considering equal-time commutation relations in the quark model, we are led to derive sum rules for the weak neutral structure functions in the deep inelastic region. By using electroproduction data we can then calculate neutral current cross sections in different gauge models.

Absorptive correction to pion exchange as function of the external mass

π +- n electroproduction data is used to study the dependence of the absorptive correction to pion exchange on the external mass. We find a strong increase of the absorption as the photon becomes more space-like. We argue that this increase is incompatible with present day Regge absorption models.

A modified born term model for π± Δ electroproduction

An electric Born type model is used to describeπ±Δ electroproduction at high energies. The electric pion form factor is taken from VDM; the contact term form factor and theΔ form factor are set equal to the proton form factor (or equal to zero) which is left as an arbitrary parameter, and is determined by a fit of the model to the recentπ+δ0 andπ−Δ++ electroproduction data.