4 research outputs found
Relativistic Heavy--Ion Collisions in the Dynamical String--Parton Model
We develop and extend the dynamical string parton model. This model, which is
based on the salient features of QCD, uses classical Nambu-Got\=o strings with
the endpoints identified as partons, an invariant string breaking model of the
hadronization process, and interactions described as quark-quark interactions.
In this work, the original model is extended to include a phenomenological
quantization of the mass of the strings, an analytical technique for treating
the incident nucleons as a distribution of string configurations determined by
the experimentally measured structure function, the inclusion of the gluonic
content of the nucleon through the introduction of purely gluonic strings, and
the use of a hard parton-parton interaction taken from perturbative QCD
combined with a phenomenological soft interaction. The limited number of
parameters in the model are adjusted to and -- data. Utilizing
these parameters, the first calculations of the model for -- and
-- collisions are presented and found to be in reasonable agreement with
a broad set of data.Comment: 26 pages of text with 23 Postscript figures placed in tex
QCD Form Factors and Hadron Helicity Non-Conservation
Recent data for the ratio shocked the
community by disobeying expectations held for 50 years. We examine the status
of perturbative QCD predictions for helicity-flip form factors. Contrary to
common belief, we find there is no rule of hadron helicity conservation for
form factors. Instead the analysis yields an inequality that the leading power
of helicity-flip processes may equal or exceed the power of helicity conserving
processes. Numerical calculations support the rule, and extend the result to
the regime of laboratory momentum transfer . Quark orbital angular
momentum, an important feature of the helicity flip processes, may play a role
in all form factors at large , depending on the quark wave functions.Comment: 25 pages, 5 figure