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\begin{document}

\title{Prospects and Status of ZEUS at HERA II}

\author{R. Yoshida}

\address{Argonne National Laboratory\\
9700 S Cass Ave.\\ 
Argonne, IL, 60439   USA\\ 
E-mail: rik.yoshida@anl.gov}


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\maketitle

\abstracts{Selected physics topics of the HERA II program are 
briefly reviewed. An outlook for data taking as of October 2003
and estimated luminosity requirements for some physics
topics are given.}

\section{Physics of HERA II}
Some physics topics of HERA II were covered by the previous speaker\cite{max}.
Here I briefly outline some of the remaining topics.
\subsection{Structure Functions}
The HERA Collider experiments H1 and ZEUS have made measurements\cite{f2}
of the proton lstructure function $F_2$ spanning five orders of magnitude in 
both the Bjorken variable $x$ and the virtuality of the photon $Q^2$, 
from the data taken in the period 1992-2000.
Below $Q^2$ of 500 GeV$^2$, these measurements have a 2-3\% precision,
which is dominated by systematic effects.  In this kinematic region, these 
measurements will most likely be the most precise for the foreseeable future.

For higher $Q^2$, and so for high $x$ ($x > 0.1$), the statistical 
uncertainties dominate the current $F_2$ measurements. Studies\cite{wksp1}
have shown that with an integrated luminosity of 1 fb$^{-1}$ planned at
HERA II, the precision measurements at high $x$ will be such that, for
example, the strong coupling constant $\alpha_s(M_Z)$ can be 
constrained to 0.002, in experimental uncertainties, 
and the gluon to 3\% when these data are used in a QCD fit.

\subsection{Electroweak Studies}

The sensitivity of polarized 
Neutral Current (NC) and Charged Current (CC) DIS cross-sections to electroweak
parameters means that there will be a rich spectrum of Electroweak results
from HERA II.  Again most of these are discussed in detail 
elsewhere\cite{wksp2}.

An example of such a result is the determination of the NC couplings of 
the light quarks\cite{wksp3}.  Depending on the polarization
and integrated luminosity achieved, these can be determined to approximately
10\%, and provide a result complementary to the heavy quark
couplings at LEP.

Another example is the use of measured electron-proton
cross-sections, both NC and CC, to determine the
consistency of the electroweak description\cite{wksp4}.  The results can be
expressed in terms of the $W$ mass and the top mass.  A precise
measurement of the top mass at the Tevatron or the LHC at the 5 GeV
level would enable the HERA $W$ mass to be constrained at the 50 MeV
level.  This would be a stringent test of the electroweak sector.

\subsection{Exotics and Anomalies}

There are intriguing anomalies observed in HERA I.  H1 has observed
excess of isolated electrons(and positrons) and muons accompanied by
missing $P_T$; also an excess of di- and tri-electrons at high
masses was seen\cite{h1ex}.  
While ZEUS does not see these excesses\cite{znoex}, 
it observes more than the expected number of 
isolated $\tau$ leptons accompanied 
by missing $P_T$, not
associated with the $\tau$ decay\cite{isotau}.  All of these anomalies are
at a level where more data are  needed to study these effects.
Since the HERA I data are based on an integrated luminosity of about
 100 pb$^{-1}$,
we would need something in the same order of magnitude in luminosity
to start to make progress.

Also, there are new-physics channels, including R-parity violating
SUSY and leptoquarks where HERA II remains 
competitive with the Tevatron\cite{wksp5}.
In any case, the sign of the lepton beam and polarization are important
for understanding any new physics that may emerge.

\section{Prospects for data}

\subsection{HERA performance}
Through 2002, the HERA machine has demonstrated its readiness for
the high luminosity operation.  The specific luminosity goal for HERA II of
$1.8\times 10^{30} cm^{-2}s^{-1}mA^{-2}$ has already been reached 
in November 2001.  After a period of improvements to background
conditions due to synchrotron radiation and aperture limitations, a HERA record luminosity of
$2.7\times 10^{31} cm^{-2}s^{-1}$ was reached in February 2003.  This
is to be compared to the design goal of $7.0\times 10^{31} cm^{-2}s^{-1}$.
Polarization of 50\% during luminosity runs was also achieved in February 2003.
However, the maximum beam current storable in HERA was limited by the
severe backgrounds encountered at H1 and ZEUS; this has severely limited
the luminosity at which the machine could be operated practically.

\subsection{Background}

Throughout 2002 and early 2003, 
H1 and ZEUS could not effectively take data due to the
background rates.  
To a very good approximation, they can be equated with the
current being drawn in the central tracking detector, which is too high 
so that it  cannot be operated safely.  
Many measures against the background were taken during the HERA shutdown
of 2003 in time for beam operation in September 2003.

There are three components to the background:
\begin{itemize}
\item{Backscattered synchrotron radiation.  This background, 
up to early 2003, was worse in ZEUS than in H1.  
This was reduced with improved synchrotron
masks at the experiments.  At ZEUS, the reduction is estimated to
amount to a factor of ten.}
\item{Lepton-beam-related particle background.  This was reduced by
reducing the thickness of some collimators and making provisions for
better vacuum such as additional pumps or improvement in existing pumps.
A reduction of a factor of two in this background is expected.}
\item{Proton-beam-related particle background.  This is the dominant
background after the improvements above.  This is also the background
that is the least understood quantitatively.  The vacuum improvements,
better vacuum conditioning and collimators redesigned to reduce 
higher-order-mode heating will certainly reduce this background.
The aimed-for reduction for this background is a factor of two.}
\end{itemize}

As of the date of this report, only sizable positron
together with small proton currents hadve been stored in HERA.  
However, studies
at ZEUS of the synchrotron background showed that the improvement
was as expected.  Also the positron background showed steady improvement
over several days.  

Since no significant proton currents have been stored, the situation
with respect to the proton background was not known\footnote{As of January 2004,
the background had been reduced to such an extent that it no longer limited 
the performance of the machine.}.

\section{Luminosity requirements and constraints}

An estimate of the integrated luminosity required for the main physics
topics for HERA II is shown in Figure 1.  
It is clear that the expected
integrated luminosity for HERA II of 1 fb$^{-1}$ is enough to cover
a large portion, but not all, of the topics listed.  The default plan
of 250 pb$^{-1}$ appears to be a relatively good compromise.  Obviously,
the actual operation of the machine and developing physics interests
as the run progresses will determine the character of the data actually
taken.
\begin{figure}[ht]
\centerline{\epsfxsize=4.2in\epsfbox{yoshida.fig1.eps}}   
\caption{A table of estimated integrated luminosities needed for HERA II
physics topics.}
\end{figure}

\begin{thebibliography}{0}
\bibitem{max} M.Klein in these proceedings.
\bibitem{f2} 
H1 Coll., C.Adloff et al., Nucl. Phys. B {\bf 470}, 3 (1996).\\
H1 Coll., C.Adloff et al., Nucl. Phys. B {\bf 497}, 3 (1997).\\
ZEUS Coll., J.Breitweg et al., Eur. Phys. J. C {\bf 11}, 427 (1999).\\
H1 Coll., C.Adloff et al., Eur. Phys. J. C {\bf 13}, 609 (2000).\\
H1 Coll., C.Adloff et al., Eur. Phys. J. C {\bf 19}, 269 (2001).\\
H1 Coll., C.Adloff et al., Eur. Phys. J. C {\bf 21}, 33 (2001).\\
ZEUS Coll., S.Chekanov et al., Eur. Phys. J. C {\bf 21}, 443 (2001).\\
ZEUS Coll., S.Chekanov et al., Eur. Phys. J. C {\bf 28}, 175 (2003).\\
H1 Coll., C.Adloff et al., Eur. Phys. J. C {\bf 30}, 1 (2003).\\
ZEUS Coll., S.Chekanov et al., DESY-03-218, submitted to Phys. Rev. D.
\bibitem{wksp1} 
M.Botje, M.Klein and C.Pascaud,
{\it Proceedings of the Workshop on Future Physics at HERA}, 
G.Ingelman, A.DeRoeck and R.Klanner (eds.), Vol. 1, p. 33.
Hamburg, Germany, DESY (1996).
\bibitem{wksp2} R.Cashmore et al., ibid., Vol. 1, p. 129.
\bibitem{wksp3} R.Cashmore et al., ibid., Vol. 1, p. 163.
\bibitem{wksp4} S.Beyer et al., ibid., Vol. 1, p. 140.
\bibitem{h1ex} 
H1 Coll., C.Adloff et al., Eur. Phys. J. C {\bf 5}, 575 (1998).\\
H1 Coll., C.Adloff et al., Phys. Lett. B {\bf 561}, 241 (2003).\\
H1 Coll., C.Adloff et al., Eur. Phys. J. C {\bf 31}, 17 (2003).
\bibitem{znoex} 
ZEUS Coll., S.Chekanov et al., Phys. Lett. B {\bf 471}, 411 (2000).\\
ZEUS Coll., S.Chekanov et al., Phys. Lett. B {\bf 559}, 153 (2003).\\
ZEUS Coll., S.Chekanov et al., contributed paper to XXXIst International
Conference on High Energy Physics, Amsterdam, (2000). Abs. no. 910.
\bibitem{isotau} 
ZEUS Coll., S. Chekanov et al., DESY-03-182, accepted by Phy. Lett. B.
\bibitem{wksp5} 
M.Dreiner et al.,
{\it Proceedings of the Workshop on Future Physics at HERA}, 
G.Ingelman, A.DeRoeck and R.Klanner (eds.), Vol. 1, p. 239.
Hamburg, Germany, DESY (1996).
\end{thebibliography}
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