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\title{Status Report on the RadPhi Experiment}

\author{P. Rubin}

\address{Department of Physics, University of Richmond \\ Richmond, VA 23173,
USA \\
E-mail:  prubin@richmond.edu}

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\maketitle

\abstracts{
We report on Jefferson Laboratory Experiment 94-016 (RadPhi),
a search for rare, radiative decays of the $\phi(1020)$ meson.  We provide
a motivation, description of the detector, and summary of status.
With regard to the latter, the experiment is in the midst of its data run,
expected to end 31 July, 2000, having
collected an event sample equivalent to that at Novosibirsk and
Frascati (1999 run), but with substantially different backgrounds and
systematics.}

\section{Motivation}

High energy photon beams are in some ways equivalent to vector meson
factories.  The tagged photon beam in Hall B at Thomas Jefferson National
Accelerator Facility, with its continuous wave acceleration of electrons
to an end-point energy of nearly 6 GeV, thus provides an excellent means
for precision studies of $\rho$, $\omega$, and $\phi$ mesons.  At the time
of the proposal for Experiment 94-016 (RadPhi)\footnote{The RadPhi
collaboration includes the following institutions:  Catholic University
of America, University of Connecticut, Indiana University, Thomas Jefferson
National Accelerator Facility, University of Notre Dame, Rensselaer
Polytechnic Institute, University of Richmond, University of Virginia, and
College of William and Mary.}, very little was known about
radiative decays of the $\phi$.  Of its seven two-body radiative channels,
only two had been observed.  The two-body radiative rate of vector meson to 
(pseudo)scalar is damped as $E_{\gamma}^3$ .

Measuring the remaining undetected channels would not only determine the
radiative width of the $\phi$---an important consideration for $\phi$-factories
intending to study kaon CP-violation---but also provide insights into a number
of outstanding spectroscopic questions and examples of symmetry violations.
In particular, such measurements might illuminate the nature of the $a_0(980)$
and $f_0(980)$ mesons (assigned originally to the scalar nonet but perhaps
four-quark or molecular $(K\overline{K})$ rather than $q\overline{q}$
states)\cite{{ja},{we},{cl}} as well as the gluonic and strangeness content of
the $\eta'$ versus the $\eta$.

Two energetically allowed decays, $\phi \rightarrow \rho \gamma$ and
$\phi \rightarrow \omega \gamma$ are C-violating;
experimental limits on the branching ratios are quite high.  In addition,
RadPhi is capable of investigating $\rho$ and $\omega$ decays as well as
looking for exotics.

\section{RadPhi Detector}

The bachelor photon in $\phi$ radiative decay is low in
energy and so difficult to detect.  When the $\phi$ is formed in a tagged
photon beam with 6 GeV endpoint electrons, this photon is boosted by as much as
a factor of 12.

To detect all-neutral final states, RadPhi's primary component is a
650-channel lead-glass wall assembled octogonally around the beamline.
In front of the wall sits a 30-channel scintillator array, which
will identify offline charged particles in
the final state.  The original JETSET barrel array surrounds a 2.5cm
beryllium target, providing nearly full angular coverage.  Its
lead-scintillating fiber calorimeter should reconstruct
$\eta$'s.  It readily  detects wide-angle
photons which miss the lead-glass.  Such ``broken'' events comprise RadPhi's
primary
background.  A steel wall and
veto-counter system upstream of the target block
beamline-related backgrounds.

The first-level trigger consists of a coincidence (from the recoil proton) in
the barrel's three
scintillator planes with
a signal in the high-energy portion of the photon tagger.  A feature of the
custom-built ADCs used in the experiment provides fast analog descrimination
for large energy deposition in any given lead-glass block, and this feature
is employed as a second-level trigger.  A custom-built memory look-up
unit computes total energy in the glass from ADC readouts and serves
as the third-level trigger.

\section{Status}

Radphi is presently collecting data at approximately the rate requested in
its proposal.  By the end of its run (31 July 2000), it expects
statistics comparable to those of Novosibirsk and KLOE (1999).
With analysis already underway, first results should
be announced before Spring, 2001.

\section*{Acknowledgments}
The author's participation in the RadPhi experiment has been supported by
the National Science Foundation, Research Corporation, and the Thomas F.
Jeffress and Kate Miller Jeffress Memorial Trust.

\begin{thebibliography}{99}

\bibitem{ja}R. L. Jaffe, \Journal{\PRD}{19}{267}{1977}.

\bibitem{we}J. Weinstein and N. Isgur, \Journal{\PRL}{48}{659}{1982}.

\bibitem{cl}F. Close, N. Isgur, and S. Kumano, \Journal{\NPB}{389}{513}{1993}.

\end{thebibliography}

\end{document}

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