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\title{Initial Plans for the A' Vertex Search}

\author{Sho Uemura}
\institute{SLAC}
\date[January 23, 2014]

\begin{document}

\begin{frame}
	\titlepage
\end{frame}

\begin{frame}{The search}
	\begin{itemize}
		\item Event sample: $e^+e^-$ pairs with 2-track vertex and invariant mass
			\begin{itemize}
				\item Event quality cuts, blinding
			\end{itemize}
		\item Signal: small number of events with detached vertices and a single mass
			\begin{itemize}
				\item Parameters: mass, production cross-section, lifetime
				\item In minimal model, cross-section and lifetime are both determined by $\alpha'/\alpha$
			\end{itemize}
		\item Background: QED tridents with finite vertex resolution and smooth mass distribution
	\end{itemize}
	\begin{center}
		\includegraphics[width=0.5\textwidth]{toy}
	\end{center}
\end{frame}

\begin{frame}{Event cuts}
	\begin{itemize}
		\item Many cuts are common to all analyses:
			\begin{itemize}
				\item Calibration, data quality: not relevant for MDC
				\item Track quality (track fit and time $\chi^2$, ECal track match)
				\item Pair quality: (vertex fit $\chi^2$, $E_++E_-\approx E_{beam}$)
				\item Kinematic cuts to be developed
			\end{itemize}
		\item Important to reduce vertex tails (may or may not be useful for other analyses):
			\begin{itemize}
				\item Track quality: layer 1 isolation cut (mishits), kink cut (large-angle multiple scattering)
			\end{itemize}
	\end{itemize}
\end{frame}

\begin{frame}{Blinding}
	\begin{itemize}
		\item Hidden signal box: cut out events with vertex Z above some limit
			\begin{itemize}
				\item Box should be looser than expected signal region, but tight enough that background can be characterized before unblinding
			\end{itemize}
		\item Before unblinding:
			\begin{itemize}
				\item Measure vertex resolution as a function of mass, compare to expected value
				\item Measure trident rate as a function of mass, compare to MC
			\end{itemize}
	\end{itemize}
\end{frame}

\begin{frame}{Fitting the signal}
	\begin{itemize}
		\item Use a mass window larger than mass resolution (to capture all signal events), but small enough that background (i.e. trident rate and vertex resolution as function of mass) can be fit well; step the window across the search range
		\item At each step, do a (probably unbinned) fit to the cross section and lifetime, either as independent parameters or both dependent on $\alpha'/\alpha$ 
			\begin{itemize}
				\item Cross section computed from signal event count using relationship to radiative trident cross section
				\item Get a limit on $\alpha'/\alpha$
			\end{itemize}
	\end{itemize}
\end{frame}

\end{document}