%Abstract file for Israel Physical Society Meeting
%This is an example of the Latex file of the abstract to be submitted
%for oral or poster presentation at the 1997 Annual Meeting of the
%Israel Physical Society. Please replace the abstract title,
%names of authors, adresses and the text of the abstract.
%Also, please specify the session your contribution is designated to.
%Only files using this format will be accepted!
\documentstyle[12pt]{article}
\textheight=20.0cm
\textwidth=15.0cm
\renewcommand{\refname}{}
\newcommand{\vsp}{\vspace*{-0.6\baselineskip}}
\pagestyle{empty}
\begin{document}
% The session the contribution is designated to:
% Lasers and Plasma Physics
% Oral  preferred
\begin{center}
{\bf The $pp \to pp \pi^0$ Reaction at Energies Close to 
Threshold} 

\bigskip

{E. Gedalin,  A. Moalem and L. Razdolskaja}

\bigskip

{\it Department of Physics\\
Ben Gurion University, 84105 Beer Sheva, Israel}
\end{center}

\bigskip

Total cross section measurements for the $pp \to pp \pi^0$ reaction, 
at energies near the $\pi$ production threshold, are analysed using 
a coherent formalism, based on a covariant one boson exchange model.
By taking into account the nucleon-nucleon and meson-nucleon
final state interactions (FSI) coherently, we reproduced the scale and
energy dependence of the total cross section.

The main contributions to the transition amplitude are due to $\rho$ and
$\omega$ meson exchanges. The transition amplitudes for the elementary
processes $\rho p \to \pi^0 p$ and $\omega p \to \pi^0 p$ are
calculated using vector meson dominance and the usual approximation for 
$\pi^0$ electroproduction  off the proton. This stands in marked difference 
with Horowitz et al. \cite{horowitz} where the scale of the cross section
is determined to a large extent by $\sigma$ meson exchange. 
However, vector meson exchanges in our model
play a similar role to $\pi^0$ production through axial current in 
Lee and  Riska analysis\cite{riska}.

The energy dependence is determined almost solely by the FSI correction factor
which we identify with the on-shell elastic scattering amplitude for the
$pp \pi^0 \to pp \pi^0$ ( 3 particles to 3 particles) transition. 
This amplitude can be calculated from solving the Faddeev equations, 
or otherwise, it can be estimated using $\pi$N and NN elastic scattering 
data. 

It is shown that the effects due to the isoscalar and isovector 
$\pi^0$-N interactions
are significant but, their overall contribution to the FSI factor almost
cancels out. This is in marked difference with the results from a similar
analysis of the $pp \to pp \eta$ data, where the $\eta$N interaction
plays an essential role in reproducing the energy dependence of the total
cross section\cite{moalem}. Our analysis is basically parameter free as 
all of the coupling constants and scattering lengths are determined 
independently from NN and meson-N scattering data. 
\vspace*{-3\baselineskip}
\begin{thebibliography}{99}
\bibitem {horowitz} C. J. Horowitz et al. , Phys. Rev. ${\bf C49}$, 
1337(1994).\vsp
\bibitem {riska} T. -S. H. Lee and D. O. Riska, Phys. Rev. Lett.
${\bf 70}$, 2237(1993).\vsp 
\bibitem {moalem} A. Moalem et al., Nucl. Phys. ${\bf A589}$,
649 (1995); and refs. therein.
\end{thebibliography}


\end{document}
\end


