Quark Parton Research Articles

Radiative effects in deep inelastic scattering of polarized leptons by polarized nucleons

Low-order electromagnetic corrections to deep inelastic scattering of polarized leptons by polarized nucleons are derived and investigated using a covariant method. Thorough numerical calculations of the corrections to cross sections and to the measured asymmetry are carried out for μp (ep) scattering in the range of lepton energy E = 200–500 GeV (10–16 GeV). The sensitivity of the corrections to the choice of the structure functions is investigated. The electromagnetic corrections to the asymmetry are found to be less than 10% within the greatest part of the kinematical region, but if x ∼ 0, y ∼ 1 they can reach a few tens of percent. The lowest order neutral current contribution to the asymmetry is obtained within the framework of standard electroweak interaction theory and the quark parton model. It is found this effect may be significant, especially in the kinematical range where electromagnetic corrections are negligible.

Is the K factor in the Drell-Yan process necessary?

A simple scale violating quark parton model incorporating only power suppressed correction to scaling is shown to describe simultaneously the deep inelastic lepton scattering, and the Drell-Yan lepton pair production data without the need for the K-factor. In contrast an additional large higher order correction to scaling through the K-factor is considered essential in quantum chromodynamics to explain the Drell-Yan data.

Conventional approach to the problem of the deuteron smearing corrections

A comprehensive analysis of the problem of deuteron smearing corrections is given. Some problems of the usual approach (the conventional approach) are discussed. It is shown that the formalism adopted by this approach leads to (i) the existence of the so-called West $\ensuremath{\beta}$ correction and (ii) the disagreement of the sum rules with the quark parton model expectations in leptonic scattering. It is also shown that in this formalism the electroproduction expression is not inconsistent. Following West for the identification of the wave function, it is found that the smearing correction ${\ensuremath{\sigma}}_{s}$ of the high-energy (50-370 GeV) pion and nucleon process is non-negligible, and hence, in contradiction with the usual expectations. Another test for this approach is suggested.NUCLEAR REACTIONS Deuteron, Fermi motion, smearing correction, West correction.

Charged hadron multiplicities in high energy $$\bar v_\mu n$$ and $$\bar v_\mu p$$ interactions

Charged hadron multiplicity distributions in $$\bar v_\mu n$$ and $$\bar v_\mu p$$ interactions in the energy range $$5< E_{\bar v}< 150GeV$$ GeV are presented. They are obtained from about $$6000\bar v_\mu $$ charged current events produced in BEBC filled with deuterium. Multiplicity moments are studied as a function of the invariant mass of the hadronic systemW. Results on multiplicity distributions in the forward and backward directions in the hadronic c.m.s. are presented and discussed within the framework of the quark parton model. Values for the average charge of the forward jet are also determined and compared with other experimental data.

Diquark fragmentation functions in hadron-nucleon interactions at 19 GeV/c and other energies

New data on pion production in pn interactions at 19 GeV/c are used, together with earlier data on pion production in pn π{su+}n at at other energies, to determine the diquark fragmentation functions\(\mathop D\nolimits_{dd}^{\pi \pm } ( = \mathop D\nolimits_{uu}^{\pi \mp } )\) andDudπ in the neutron and proton fragmentation regions. Typical high-energy data on pion production in pp interactions are also considered. The unfavoured fragmentation function\(\mathop D\nolimits_{dd}^{\pi \pm } (x)\) is found to be much smaller than the favoured fragmentation function\(\mathop D\nolimits_{dd}^{\pi \_} (x)\) and to have a steeperx-dependence. The diquark fragmentation functions agree very well with those from\(\nu (\bar \nu ) - proton\) interaction as expected from quark parton models.

Implications of mass-dependent renormalization group parameters for conventional QCD phenomenology

The effects of quark mass dependence in the momentum-subtracted beta function and anomalous dimensions of quantum chromodynamics are investigated. We examine the sensitivity of predicted quark and gluon moments for deep inelastic scattering to changes in the prescriptions used in defining the mass-dependent renormalization group parameters and we discuss interpretations of the resulting differences. Simple algorithms are presented in which the mass-dependent evolution of parton moments and the effective coupling can be approximated by massless formulae with carefully chosen thresholds for exciting additional quark flavors. We examine the expected nature of heavy quark components in the nucleon's sea, with particular attention given to the strange and charmed sea. The inherent scheme dependence in the definition of heavy quark parton distributions is also discussed.

Gluons in the hadronicS matrix

We derive a theoretical explanation of the similarities which have been experimentally observed between final state distributions in soft processes (K−p interactions andpp collisions at ISR) and hard processes (e+e− annihilations and deep inelastic scattering). The theoretical framework is the correspondence between QCD and dual topological unitarization (DTU), which expresses confinement as the equivalence of the hadron and parton bases to account for unitarity. Starting from the interpretation of the zero handle topology in DTU in terms of the naive quark parton model, we show how to characterize gluons in the hadron basis: primordial gluons are associated with the one handle topology, and the cascading of hard gluons is related to the sum of all higher topologies in DTU. We get this way a QCD interpretation of the reggeon calculus which is the theoretical framework of soft hadronic processes at asymptotic energies.

On a covariant quark parton model with confinement

We examine the standard-parton-model unitarity relations in the context of a covariant quark parton model which incorporates confinement in a very naive way. We also make a deeper analysis than was made in recent papers by the same authors about the sensitivity of the baryonic structure functions to the confinement mechanism. This new analysis shows that, contrarily to what was stated in those papers, one can expect, because of the confinement, changes in the behaviour of the baryonic structure functions similar to those already found for the meson structure functions. However, because of the different quark content of mesons and baryons, we have not found any connection between the size of these changes for mesons and baryons.

Hadron Production in Lepton-Nucleon Scattering

Contents: Kinematic variables, cross-sections and data--(Kinematics of lepton scattering, kinematics of annihilation, definition of cross-sections); Theoretical models--(Quark-parton model, Quantum chromodynamics, fragmentation models, applicability of quark parton model, Other theoretical models); Multiplicity; Experimental evidence for jets; Longitudinal distributions--(Charge distributions, fragmentation functions, Tests of factorization and scaling, Quark fragmentation function results, Charmed particle fragmentation, fragmentation to baryons, moments of fragmentation functions); Transverse momentum--(Experimental properties of transverse momentum, transverse momentum and QCD predictions, searches for planar events, intrinsic transverse momentum).

On Ψ production inPP collisions

The inclusive production cross section, σ(pp → ψX), of the narrow state ψ is investigated in proton proton collisions in the context of theDrell—Yan mechanism and the quark parton distribution functions obtained from the modifiedKuti—Weisskopf model. Results are compared with the available experimental data.

Parton models of high momentum transfer electron-nuclear scattering

High-energy electron-nuclear scattering processes are discussed from the point of view of a parton model description. The light-cone formalism is introduced in a schematic presentation emphasizing: (i) the connection to relativistic dynamics, (ii) the phenomenological construction of the far off-shell components of wave functions, and (iii) asymptotic scaling laws. A survey is made of some of the recent calculations based on a nucleon constituent parton model and their comparison with data for momentum transfers Q 2 ≲ 6(GeV/ c) 2. A prospective discussion is also made on multiquark nuclear components and the quark parton model in QCD.

Multiplicity distributions in neutrino-hydrogen interactions

Multiplicity distributions of charged hadrons produced in νp interactions are studied using a sample of 7850 charged current interactions in BEBC. Multiplicity moments are studied as functions of the invariant mass of the hadronic system, W, and a comparison is made with other lepton- and hadron-induced reactions. The mean charged multiplicity 〈 n ch〉 is found to increase linearly with ln W 2. The other multiplicity moments indicate a close similarity between the neutrino scattering and the class of annihilation processes. A study of the multiplicity distributions in the forward and backward directions in the hadronic c.m.s. gives results in qualitative agreement with the quark parton model.

Opposite side quantum number correlations ine + e −-annihilation

We claim that double moments of twoparticle distributions are very sensitive quantities for testing the opposite side quantum number correlations ine+e−-annihilation predicted by the quark parton model. In particular it is found that kaon correlations are extremely transparent in these quantities. This feature survives when the QCD predictedQ2-dependence is taken into account. We also stress the importance of establishing the higher meson resonance content in quark jets in order to make a sensible QCD-analyses of the fragmentation functions.

Charge radii of nucleons

Charge radii of nucleons are studied in the context of a quark parton model by using Sehgal's hypothesis of nonfactorizable transverse distribution of partons. It is shown that the observed negative sign and the finite magnitude of the squared neutron charge radius, =−(0.16÷0.11) fm2, can be reconciled if different, spatial distributions are assumed for the u and d quarks inside a nucleon.

Role of parton transverse momenta in polarized deep inelastic scattering

The transverse momenta of quark partons are shown to significantly dilute the moderate- Q 2 broken-SU (6) constraints on the leading spin-dependent deep inelastic electromagnetic structure function of the proton. A realistic calculation of the latter is performed incorporating these effects as well as those of the quantum chromodynamic evolution to higher Q 2.

The reaction e +e −→ γ+hadrons at high energy

Contributions to the reaction e +e −→ γ+hadrons due to lepton radiation and central emission (expressed in terms of photon structure functions) are described in their most general form including weak neutral currents and polarization effects. The photon structure functions are calculated with the quark parton model. Applications to cross sections, photon spectra, asymmetries and polarizations are given for the LEP energy range.

Polarised electron-hadron scattering and weak interaction theory

It is shown that the naive valence quark parton model assumptions used to calculate the parity violation in polarisede-d scattering are not needed in order to extract informations from the experimental data about the neutral current couplings. Much more general assumptions which can be justified within the QCD approach are sufficient in order to arrive at essentially the same conclusions for the neutral current coupling parameters

Quark parton model with large partonk T

The quark-parton model is generalized to allow for large partonk T subject to mass shell restrictions. Since it is expected that <k T > will rise withQ 2 in (highly virtual) photon mediated processes, this generalization is necessary to restore the applicability of the quark-parton model. By treatingk T as an essential kinematical variable, we have been led to the introduction of a new scaling variablez. Together with Bjorken'sx variable, we give a unified kinematical description of the four distribution functions: hadron structure functions and jet decay functions for spacelike and timelike photons. Possibility of a simple interpolating universal function is considered. Phenomenological determination of that function is examined in detail. Predictions onR, parton <k T >, hadron <p T > in jets, etc., are made with the dimuon <q T > being used as an input. The usual relation $$\left\langle {q_T } \right\rangle = \sqrt 2 \left\langle {k_T } \right\rangle$$ is shown to be false in the region wherek T is not small compared tok L , a situation which prevails in the production of dileptons recently measured. Thek T distributions for timelike and spacelike cases are shown to be not identical. The model is consistent with nearly all relevant data on virtual photon processes.

Ypsilons and Jets at DORIS

The production of the Y(9.46)- and Y'(10.02)-resonances in e+e--annihilation has been observed in three, respectively two, different experiments at DORIS. The observed leptonic decay widths are consistent with Y and Y' being the ground and the first excited state of a bound bb̄ system, where b represents a heavy quark with charge - 1/3. The event topology at energies outside the Y resonances clearly exhibit 2-jet structure in good agreement with the quark parton model. The characteristics of the Y direct hadronic decays are consistent with the 3 gluon model.

Formula omitted]μp and [formula omitted]μn charged-current interactions unfolded from high energy [formula omitted]μ interactions in neon

We have developed a method to separate ν n and ν p interactions from antineutrino-neon interactions by using the final state electric charge. We present the distributions of the scaling variables x and y for ν n and ν p interactions separately , along with the ν n and ν p cross section ratios as a function of x and y. We obtain a total ν n to ν p cross section ratio of 0.45± 0.08. Our results are consistent with the predictions of the simple quark parton model.