Model for nucleon gluon and sea quark structure functions at allx and allQ 2 from the correspondence between QCD and DTU

We propose a simple parametrization of the nucleon gluon and sea quark structure functions at allx, and allQ ². We use the DTU parton model to fix the parametrization at a reference point (Q ₀ ² =1.25 GeV² andA ²=0.01 GeV²) and we mimic the QCD evolution by replacing the dimensioned parameters of the DTU parton model by functions depending onQ ².     

Analysis of the G0 Backward Angle experiment

We have measured parity-violating asymmetries in elastic electron?Cproton and quasi-elastic electron?Cdeuteron scattering at Q ²?=?0.22 and 0.63 GeV². They are sensitive to strange quark contributions to currents in the nucleon, and to the nucleon axial current. The results indicate strange quark contributions of ??10% of the charge and magnetic nucleon form factors at these four-momentum transfers. Analysis of the data is summarized.     

The quark compound bag model: Defining the admixture of six-quark bag in the deuteron

The probability of the six-quark bag part of the deuteron is defined within recently formulated quark compound bag (QCB) model. An upper limit of about 1 % for the admixture of the confined bag in the deuteron is found for the QCB potential supplied by the long range Paris interaction. The six-quark bag corrections to the static multipole moments of the deuteron are estimated to be ?1 % forμ _d and ?6% forQ _d .     

Electroproduction of η mesons in the region of the resonanceS 11(1535) at momentum transfers of 2 and 3 GeV2

We report on results of η-electroproduction in the resonance region at momentum transfers ofQ ²=2 GeV² and 3 GeV². The differential cross sections obtained in the region of the second nucleon resonance strongly support the dominance of theS ₁₁(1535) in this channel. The total transverse virtual photoproduction cross section of theS ₁₁(1535) shows a flatQ ²-dependence ～e ^?0.39· Q ². Comparison with the total resonant γ _v p cross section in the second resonance region aroundW=1.5 GeV shows that theD ₁₃(1520) production decreases much faster (～e ^?1.6· Q ²). The data are not compatible with the simple harmonic oscillator quark model with spin and orbit excitation of a quark only.     

Microscopic description of diffractive deuteron breakup by <Superscript>3</Superscript>He nuclei

A microscopic formalism for describing observed cross sections for deuteron breakup by threenucleon nuclei was developed on the basis of the diffraction nuclear model. A general formula that describes the amplitude for the reaction ²H(³He, ³Hep)n and which involves only one adjustable parameter was obtained by using expansions of the integrands involved in terms of a Gaussian basis. This formula was used to analyze experimental data on the exclusive cross sections for deuteron breakup by ³He nuclei at the projectile energy of 89.4MeV. The importance of employing, in calculations, a deuteron wave function that has a correct asymptotic behavior at large nucleon–nucleon distances was demonstrated.     

Resonance-like structure\bar pp annihilation into three π and the ππ correlations

Experimental data of $\bar pp$ annihilation into 3π⁰ and π⁺π⁰π^? are analyzed in the quark pair creation model (³ P ₀ Model) with planar quark diagram topology. There are two form factors depending on whether 1) the two π′s contain a quark or an antiquark that originates from ap or a $\bar p$ respectively, or 2) one π contain a quark and an anti-quark both created from the vacuum. We call the amplitude of the first as a G-type and the latter as the an F-type. The intermediate states in G-type processes which contain correlations of the³ P ₀ vertices in the initial state and those in the final state can be regarded as gluons of 0⁺⁺ and a $\bar qq$ . The two π resonance like structure of 0⁺⁺ (1520) observed in 3π⁰ and 2⁺⁺ observed in π⁺π⁰π^? can be interpreted as the interference of the G-type amplitudes with the F-type amplitudes.     

Gottfried and Bjorken sum rules: The role of vector diquarks

A quark-diquark model of the nucleon is considered and the value of the Gottfried sum ruleS _G , recently measured by the NMC group and found to differ considerably from the quark parton model expectation,S _G =1/3, is computed allowing for both elastic and inelastic contributions from the diquarks. This approach fails to reproduce the data, unless vector diquark contributions persist at very largeQ ² values, contrary to the usual assumptions. The Bjorken sum rule andSU(6) violations due to the quark-diquark structure of the nucleon are also briefly discussed.     

Strangeness in the nucleon: neutrino–nucleon and polarized electron–nucleon scattering

After the EMC and subsequent experiments at CERN, SLAC and DESY on the deep inelastic scattering of polarized leptons on polarized nucleons, it is now established that the Q²=0 value of the axial strange form factor of the nucleon, a quantity which is connected with the spin of the proton and is quite relevant from the theoretical point of view, is relatively large.In this review, we consider different methods and observables that allow one to obtain information on the strange axial and vector form factors of the nucleon at different values of Q². These methods are based on the investigation of the neutral current induced effects such as the P-odd asymmetry in the scattering of polarized electrons on protons and nuclei, the elastic neutrino (antineutrino) scattering on protons and the quasi-elastic neutrino (antineutrino) scattering on nuclei. We discuss in detail the phenomenology of these processes and the existing experimental data.     

A study of π− charge-exchange reactions on nuclei at 48 GeV/c

The charge-exchange cross sections were measured for π^? on Li, C, Al and Cu nuclei at momentum 48 GeV/c. By comparing the data obtained for nuclei with those for hydrogen under the same conditions the effective numbers of protons are defined. The conclusion is made that η⁰ mesons are absorbed in nuclei weaker then π⁰. The total cross section of η⁰ interactions with the nucleon is determined to be σ_tot(η⁰ N) = 15 ± 5 mb in agre ement with the quark model.     

Higher-Twist Effects on the Nucleon Spin Structure Functions in the Small Q2 Range

Based on the quark model, the Q² evolution of the nucleon spin structure functions in the small Q² region is calculated. The higher-twist effects a₂(Q²) and d₂(Q²) are investigated. Comparison with other model calculations is also proceeded.     

Axial exchange currents and nucleon spin

We calculate the axial couplings g_A⁸(0) and g_A⁰(0) related to the spin of the nucleon in a constituent quark model. In addition to the standard one-body axial currents, the model includes two-body axial exchange currents. The latter are necessary to satisfy the Partial Conservation of Axial Current (PCAC) condition. For both axial couplings we find significant corrections to the standard quark model prediction. Exchange currents reduce the valence quark contribution to the nucleon spin and afford an interpretation of the missing nucleon spin as orbital angular momentum carried by nonvalence quark degrees of freedom.     

Gottfried sum rule from maximum entropy method quark distributions with DGLAP evolution and with DGLAP evolution with GLR-MQ-ZRS corrections

A new method to test the valence quark distribution of nucleons obtained from the maximum entropy method using the Gottfried sum rule by performing the DGLAP equations with GLR-MQ-ZRS corrections and the original leading-order/next-to-leading-order(LO/NLO) DGLAP equations is outlined. The test relies on knowledge of the unpolarized electron–proton structure function F_2~(ep) and the electron–neutron structure function F_2~(en) and the assumption that Bjorken scaling is satisfied. In this work, the original Gottfried summation value obtained by the integrals of the structure function at different Q~2 is in accordance with the theoretical value of 1/3 under the premise of light-quark flavor symmetry of the nucleon sea, whether it results from dynamical evolution equations or from global quantum chromodynamics fits of PDFs. Finally, we present the summation value of the LO/NLO DGLAP global fits of PDFs under the premise of light-quark flavor asymmetry of the nucleon sea. According to analysis of the original Gottfried summation value with two evolution equations at different Q~2, we find that the valence quark distributions of nucleons obtained by using the maximum entropy method are effective and reliable.     

Determination of the internal structure of valons

We determine the internal structure functions of the valons introduced by Hwa and coworkers, using low-p _t data and Regge model constraints. Our calibration reaction is the fragmentation processp→π^? observed in 70 GeV/cK ⁺ p interactions. The fitted valon structure parameters are used to make successful predictions for various other fragmentation processes (p→π⁺ andp→K ⁺). A comparison with experimental data of the DISvW ₂ (x)-values implied by this same fit, indicates that soft processes probe the nucleon typically at aQ ²-value of ～1 GeV². This finding supports the hypothesis that soft hadronic reactions are useful (and often unique) tools to learn about hadron quark structure.     

The role of screening corrections in smallx-behaviour of structure functions

We consider the influence of shadowing effects on the proton structure function in the small-x interval. The gluon-gluon shadowing are noticeable in the HERA kinematical region while the screening of the quark component of the structure function effects negligibly the gluon distribution. The only noticeable effect is the decreasing of sea quark densities at small-x. The explicit form of the gluon distribution in the proton depends significantly on the form of used boundary condition atQ ²=Q ₀ ² . We consider also difference of results obtained with the help of Kuraev-Lipatov-Fadin and Altarelli-Parisi evolution equations.     

Anomalous parity-violating coupling of photon to nucleon

It is pointed out that in the naive quark model the weak-interaction-induced parity-violating coupling of transverse photons to the nucleon does not vanish atq ²=0. The presence of this nonvanishing anomalous parity-violatingNN couplingg _ais a direct consequence of thecomposite nature of hadrons: gauge invariance requires the vanishing ofg _aonly if the nucleon can be described by a Dirac spinor depending on asingle spacetime point. Nonvanishing ofg _ain the quark model makes precise measurements of weak radiative hyperon decays particularly important.On leave of absence from the Department of Theoretical Physics, Institute of Nuclear Physics, Cracow, Poland.     

Model for nucleon valence structure functions at allx,allp ⊥ and allQ 2 from the correspondence between QCD and DTU

We propose a simple parametrization of the nucleon valence structure functions at allx, allp _⊥ and allQ ². We use the DTU parton model to fix the parametrization at a reference point (Q ₀ ² =3 GeV²) and we mimic the QCD evolution by replacing the dimensioned parameters of the DTU parton model by functions depending onQ ². Excellent agreement is obtained with existing data.