Freiburg 1999 – scientific programme
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HK: Physik der Hadronen und Kerne
HK 13: Elektromagnetische und hadronische Proben III
HK 13.1: Group Report
Monday, March 22, 1999, 16:30–17:00, E
Do the E866 Drell Yan data change our picture of chiral structure of the nucleon ? — •W. Schäfer1, N.N. Nikolaev1,2, A. Szczurek3, and J. Speth1 — 1Institut für Kernphysik, Forschungszentrum Jülich, D-52425 Jülich — 2L.D. Landau Inst. for Theor. Phys., Moscow — 3Institute of Nuclear Physics, PL-31-342 Kraków
We revisit the evaluation of the pionic mechanism of the
ū−d–
asymmetry in the proton structure function.
Our analysis is based on the extended AGK unitarity relation
between contributions of different mechanisms
to the inclusive particle production and the total
photoabsorption cross-section (i.e. the proton structure function).
We reanalyze the role of isovector reggeons in inclusive production of
nucleons and Delta isobars in hadronic reactions. We find rather
large contribution of reggeon-exchange induced production of Delta isobars.
This leaves much less room for the pion-exchange induced mechanism of
Δ production and provides a constraint on the π N Δ form
factor.
The production of leading pions in proton-proton collisions at ISR
puts additional constraints on the π NN vertex form factors.
An extension of the AGK-rules to reggeon exchange suggests
a negligible contribution to the proton structure function from
DIS off the exchanged ρ,a2 reggeons.
All these constraints are used then to estimate the pion content
of the nucleon and allow to calculate parameter-free the x-dependence
of d − ū.
We discuss the violation of the Gottfried Sum Rule and d-ū
asymmetry and compare to the one obtained from the E866 experiment
at Fermilab. The limitation from hadronic reactions allow to understand
unexpectedly small d-ū asymmetry at intermediate x as
obtained from the E866 Fermilab experiment. We estimate the background
to the pion structure function being determined by the ZEUS and H1
collaborations at HERA from leading neutron experiments.