
%\section{{Introduction}}

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We conclude with a brief comparison between the physics capabilities of \superb\ and SuperKEKB.  Any such comparison is perforce difficult, especially when provided by the proponents of one of the proposed projects. to  improve the precision of the comparison, let us list a few of the salient characteristics of the two collider projects as proposed

\begin{itemize}
\item \superb\ has an initial luminosity of \hbox{$10^{36}$ cm$^{-2}$s$^{-1}$}, and can therefore integrate 15 ab$^{-1}$ in a Snowmass Year of $10^7$ seconds. SuperKEKB, as embodied in the KEK Roadmap, will have a luminosity of $2\times 10^{35}$ cm$^{-2}$s$^{-1}$ and can thus integrate approximately 2 ab$^{-1}$ in the 200 days of running specified, assuming the same overall efficiency.
\item
\superb\ has a proposed upgrade path that can raise the peak luminosity to $2.5\times 10^{36}$ cm$^{-2}$s$^{-1}$. \hbox{SuperKEKB}  has the potential of reaching \hbox{$8 \times 10^{35}$ cm$^{-2}$s$^{-1}$} by 2027, but this is not included in the KEK Roadmap.
\item
The power consumption of \superb is 17 MW. The power consumption of SuperKEKB, which uses much higher beam currents to produce smaller luminosity, is much higher. We can find no documentation on the SuperKEKB  power consumption at $2\times 10^{35}$, but the consumption at $4 \times 10^{35}$ is quoted as 60 MW for RF alone.
\item
These higher currents produce very difficult detector backgrounds at SuperKEKB. As the currents at \superb\ are comparable to those at \pep2, backgrounds are a much less difficult issue. There are luminosity-associated backgrounds as well as current-associated backgrounds; these are currently under detailed study.
\item
It appears that $\tau$ physics will assume great importance as a probe of physics beyond the Standard Model. \superb\ includes in the baseline design an 85\% longitudinally polarized electron beam and spin rotators to facilitate the production of polarized $\tau$ pairs. This polarization is the key to the study of the structure of lepton-flavor-violating couplings in $\tau$ decay, as well as the search for a $\tau$ EDM, or for $\CP$ violation in $\tau$ decay. SuperKEKB cannot incorporate a polarized beam.
\item
The recent observation of large \DzDzb mixing raises the exciting prospect of finding $\CP$ violation in charm decay, which would almost certainly indicate physics beyond the Standard Model. \superb can attack this problem in a comprehensive manner, with high luminosity data sample in the \FourS region and at the $\psi(3770)$ resonance, as the collider is designed to run at lower center-of-mass energies, at reduced luminosity. With very short duration low energy runs, a data sample an order of magnitude greater than that of the final BESIII sample can readily be obtained. SuperKEKB cannot run at low energies.
\end{itemize}

