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\begin{document}

\title{First KLOE results on scalar mesons}

\author{The KLOE Collaboration\lowercase{$^a$} \\ \lowercase{presented by}
  A. Farilla}


\address{INFN - Rome III (Italy)} 



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\maketitle\abstracts{During its first year of data taking in 1999 the KLOE 
experiment\footnote{The full author list can be found in
ref.\cite{osaka}}$^,$\cite{bertolucci}, which is presently running
at Da$\phi$ne in Frascati,  
has collected 2.4 pb$^{-1}$ of integrated luminosity 
corresponding to $\sim$8 Millions $\phi$ decays.
This data sample has been used to study the radiative decays 
$\phi\to f_0\gamma$,$\phi\to a_0\gamma$ .
The preliminary results are reported in this paper and in Ref.2.}

\section{Introduction}
The light scalar mesons $f_0(980)$ and $a_0(980)$ have defied
classification for nearly half a century: they do not conform to the standard
$q\overline{q}$ quark model expectations both
in the total width (predicted
$\Gamma\sim$500 MeV, observed $\Gamma\sim$50 MeV) and in the $\gamma
\gamma$ coupling (predicted $\sim$4.5 keV for $f_0$, $\sim$1.5 keV for
$a_0$, observed $\leq$0.6 keV for $f_0$, $\sim$0.2 keV for $a_0$).
In the last decades many models have been worked out in order to accomodate
their properties as can be seen by other contributions to this working
group \cite{theory}. Since
the branching ratios of $\phi\to f_0\gamma$,$\phi\to a_0\gamma$  
can range from 10$^{-4}$ to 10$^{-6}$, depending on the nature of
$f_0$,$a_0$, their accurate measurement at a $\phi$ factory can help in 
solving the puzzle. Moreover a precise determination of the shape of the 
$\pi\pi$ mass spectrum in
$f_0$ decays and of the $\eta\pi$ mass spectrum in $a_0$ decays can help in
establishing a realistic model for these particles.


\section{$\phi\to f_0\gamma\to\pi^{0}\pi^{0}\gamma$}
The signature for this decay are 5 prompt photons in the detector and no
charged tracks. The main background comes from the non-resonant process
$e^+e^-\to\omega\pi^0$. Other background processes are $\phi\to
\rho\pi^{0},\phi\to a_0 \gamma,\phi\to\eta\gamma$ with only photons in the
final state. A constrained kinematic fit and suitable topological cuts are
applied to reduce the background. The final detection efficiency is
$\sim40\%$. In a data sample of 1.8 pb$^{-1}$ $307\pm18$ $\pi^{0}\pi^{0}\gamma$
events have been selected, with a background of $112\pm11$ (estimated from 
MonteCarlo), corresponding to a Br($\phi\to
f_0\gamma\to\pi^0\pi^0\gamma$)=
(0.81$\pm$0.09$_{stat}\pm$0.06$_{syst}$)$\cdot$10$^{-4}$.
\newline
Different topological cuts have been applied to the same data sample to
select  $\omega\pi^0$ events (detection efficiency $\sim35\%$) resulting in 
529$\pm$23 events  with a background of 93$\pm$10 events (estimated from 
MonteCarlo).
This correspond to a cross section 
$\sigma(e^+e^-\to\omega\pi^0)$=0.67$\pm$0.04$_{stat}\pm$0.05$_{syst}$ nb.

\section{$\phi\to f_0\gamma\to\pi^{+}\pi^{-}\gamma$}
The signature for this decay are two charged tracks from the origin and a
prompt photon. There is high background both from Initial State Radiation 
(I.S.R.) and from Final State Radiation (F.S.R.). The latter process gives
rise to interference (whose sign is  still unknown) with the signal.
\newline
$\pi^{+}\pi^{-}\gamma$ events have been selected in a sample of 1.8 pb$^{-1}$
with an overall efficiency of $\sim50\%$.
Fitting the $M_{\pi\pi}^2$ spectrum in the background region (  $M_{\pi\pi}^2
<0.84 GeV^2$) and extrapolating in the signal region (  $M_{\pi\pi}^2
>0.84 GeV^2$) we obtain the upper limit: Br($\phi\to f_0\gamma\to\pi^+\pi^-\gamma$)$<$
1.6$\cdot$10$^{-4}$ at 90\% C.L.

\section{$\phi\to a_0\gamma\to\eta\pi^{0}\gamma$, with $\eta\to\gamma\gamma$}
The signature for this decay is similar to the 
$\phi\to f_0\gamma\to\pi^{0}\pi^{0}\gamma$  decay, namely  5 prompt 
photons in the detector and no charged tracks. The main  background
processes are $e^+e^-\to\omega\pi^0$ and
$\phi\to f_0\gamma,\phi\to\rho\pi^{0},\phi\to\eta\gamma$ 
with only photons in the final state. A constrained kinematic fit and suitable topological cuts are
applied to reduce the background. The final detection efficiency is
$\sim23\%$. In a data sample of 2.4 pb$^{-1}$ $74\pm9$ $\eta\pi^{0}\gamma$
events have been selected, with a background of $21\pm6$ (estimated from 
MonteCarlo), corresponding to a 
Br($\phi\to\eta\pi^0\gamma$)=
(0.77$\pm$0.15$_{stat}\pm$0.10$_{syst}$)$\cdot$10$^{-4}$
which results in Br($\phi\to a_0\gamma\to\eta\pi^0\gamma$)=
(0.69$\pm$0.15$_{stat}\pm$0.10$_{syst}$)$\cdot$10$^{-4}$ in the $a_0$ region.

\vskip 0.2cm
In conclusion our preliminary measurements seem to favour B.R. O($10^{-4}$)
for $\phi\to f_0\gamma$,$\phi\to a_0\gamma$ and are in agreement with the
latest results of the SND \cite{snd}and the CMD-2 \cite{cmd2}experiments at VEPP-2M.
%The $\eta\pi^0$ invariant mass spectrum is shown in fig.\ref{fig:a0}.

%\begin{figure}[t]
%\epsfxsize150pt
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%   width=0.45\textwidth}                       &
% \epsfig{file=a0.eps,
%   width=0.45\textwidth}  \\
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%\caption{Invariant mass of the $\eta\pi^0$ system, histogram:
%data; shadowed histogram: expected background (MC); points: data-background 
%difference.} 
%\label{fig:a0}
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%\caption{A generalized cactus tree: the confluent
%transfer-matrix $S$ transforms the state function $f(x)$ and
%$f(z)$ into $f(x)$.  \label{fig:radish}}
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\section*{References}
\begin{thebibliography}{99}

\bibitem{bertolucci}S. Bertolucci for the KLOE collaboration, hep-ex/0002030.

\bibitem{osaka} The KLOE collaboration, Contributed paper to ICHEP2000
  (Osaka), hep-ex/0006036.

\bibitem{theory}E. Oset, This proceeding. A. Fariborz, This proceeding.

\bibitem{snd}M.N. Achasov et al., Phys.Lett. B479 (2000) 53. M.N. Achasov et
  al., hep-ex/0005017

\bibitem{cmd2}R.R. Akhmetshin et al., Phys.Lett. B462 (1999) 371. R.R. Akhmetshin 
et al., Phys.Lett. B462 (1999) 380

\end{thebibliography}

\end{document}

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