27 research outputs found

### Nonpartonic components in the nucleon structure functions at small Q^2 in a broad range of x

We construct a simple two-phase model of the nucleon structure functions
valid for both small and large Q^2 and in the broad range of Bjorken x. The
model incorporates hadron dominance at small x and Q^2 and parton model at
large Q^2. The VDM contribution is modified for small fluctuation times of the
hadronic state of the photon. With two free parameters we describe SLAC, CERN
NMC, Fermilab E665 and CERN BCDMS data for both proton and deuteron structure
functions. Our model explains some phenomenological higher-twist effects
extracted from earlier analyses. A good description of the NMC F_2^p(x) -
F_2^n(x) data is obtained in contrast to other models in the literature. We
predict faster vanishing of the partonic component at low Q^2 than previously
expected and strong Q^2 dependence of the Gottfried Sum Rule below Q^2 ~ 4
GeV^2.Comment: 22 pages, LaTeX with 8 eps and 1 table (2 figures and dicussion
added

### \bar u - \bar d asymmetry - a few remarks

We make a few remarks on possible sources of uncertainties of the $\bar d -
\bar u$ asymmetry obtained by different methods and comment on its possible
verification in the future. In addition we comment on its present
understanding.Comment: 3 pages, a talk at the 7th International Workshop on Deep Inelastic
Scattering and QCD (DIS99), Zeuthen, April 199

### Exclusive channels in semi-inclusive production of pions and kaons

We investigate the role of exclusive channels in semi-inclusive
electroproduction of pions and kaons. Using the QCD factorization theorem for
hard exclusive processes we evaluate the cross sections for exclusive
pseudoscalar and vector meson production in terms of generalized parton
distributions and meson distribution amplitudes. We investigate the
uncertainties arising from the modeling of the nonperturbative input
quantities. Combining these results with available experimental data, we
compare the cross sections for exclusive channels to that obtained from quark
fragmentation in semi-inclusive deep inelastic scattering. We find that rho^0
production is the only exclusive channel with significant contributions to
semi-inclusive pion production at large z and moderate Q^2. The corresponding
contribution to kaon production from the decay of exclusively produced phi and
K^* is rather small.Comment: 33 pages, 18 figure

### $\bar d - \bar u$ asymmetry and semi-inclusive production of pions in DIS

We investigate unambiguities in the extraction of the $\bar d - \bar u$
asymmetry from semi-inclusive production of pions in DIS. The role of several
effects beyond the quark-parton model (QPM) which lead to $N_p^{\pi^+} \ne
N_n^{\pi^+}$ and $N_p^{\pi^-} \ne N_n^{\pi^-}$ and may therefore cloud such an
extraction is studied. The results are discussed in the context of the recent
HERMES data. We find that the interaction of the resolved photon with the
nucleon significantly modifies the observed $\bar d - \bar u$ asymmetry. The
exclusive elastic production of $\rho$ mesons plays a similar role for the
large-$z$ data sample. Our estimate shows a rather small effect of the
spectator mechanism. Nuclear effects in the deuteron also look potentially
important but are difficult to estimate quantitatively.
Throughout the paper we make in addition several general remarks concerning
semi-inclusive and exclusive production of mesons.Comment: 47 pages, LaTeX with 19 eps figure