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%\title[GEANT4/EGS5]{GEANT4/EGS5}

\title{SVT readout latency and burst-mode noise}

\author{Sho Uemura}
\institute{SLAC}
\date[June 3, 2015]

\begin{document}

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

\begin{frame}{Latency}
	\begin{columns}
		\column{0.6\textwidth}
		\begin{itemize}
			\item On trigger, SVT readout chip outputs 6 samples (24 ns apart) from pipeline; readout latency determines which 6 get output
			\item We are picky about our latency:
				\begin{itemize}
					\item For pileup fitting, need 2 samples before hits
					\item To pass DAQ cuts, need 3 samples above threshold (after hits)
					\item 24 ns jitter in hit time relative to readout (trigger comes at random phase relative to SVT clock)
				\end{itemize}
		\end{itemize}
		\column{0.4\textwidth}
		\includegraphics[width=\textwidth]{linfit}
	\end{columns}
\end{frame}

\begin{frame}{Losing hits (and 1/4 of tracks) to DAQ cuts}
	\begin{itemize}
		\item Losing all tracks for one trigger phase, 50\% of tracks for another
	\end{itemize}
	\begin{center}
		\includegraphics[width=0.5\textwidth]{5639_tracktime}
		\includegraphics[width=0.5\textwidth]{5640_tracktime}

		\includegraphics[width=0.5\textwidth]{5698_clustertimes}
		\includegraphics[width=0.5\textwidth]{5795_clustertimes}
	\end{center}
\end{frame}

\begin{frame}{Summary: latency problem}
	\begin{itemize}
		\item We ``timed in'' our latency on April 19
		\item We realized our latency might not be optimal and we might be losing hits; dropped the ball (travel, shifts)
		\item Hesitant to move latency by a full 24 ns (would put us in danger of losing pileup rejection)
		\item Hoped to make DAQ changes to allow 8 ns latency steps; fell through the cracks (other priorities for SLAC SVT group), then didn't work (May 11 test)
		\item Didn't realize until the last week that a small loss in hit efficiency for one trigger phase causes a big loss of track efficiency
		\item Tested 24 ns shift (May 13), too busy to look closely at data
		\item Looked at data May 15, realized this was a big deal, changed production config
		\item Logbook entries: 3340722 (studies) 3341153 (decision to change production config)
	\end{itemize}
\end{frame}

\begin{frame}{Burst mode noise}
	\begin{itemize}
		\item APV25 readout chip puts analog and digital signals on the same output line: 128 clocks of analog data, 12 clocks of digital data
		\item Preamp crosstalk from large currents/voltage swings: events coinciding with digital output will have extra noise
		\item ``Burst mode'' (allowing a trigger while the APV25 is still sending data) increases noise in the SVT (only in a subset of events)
			\begin{itemize}
				\item Noisy events can be identified by looking for noise hits in the SVT (normally 0-2; noisy events have up to 100), and are correlated with time between triggers
				\item From TI timestamps, we can identify all events where hits overlapped with digital output
				\item Noisy events are 4-6\% of data: just discard these
			\end{itemize}
	\end{itemize}
	\begin{center}
		\includegraphics[width=0.6\textwidth]{apv_analogdata}
		\includegraphics[width=0.4\textwidth]{smallHitFracVsReadoutDt}
	\end{center}
\end{frame}

\begin{frame}{Impact and plans}
	\begin{itemize}
		\item Latency:
			\begin{itemize}
				\item Impact: lost (rough estimate) 25\% of events in all runs before 5722; last 2 days of run have better latency setting
				\item For next run: get 8 ns latency shift working so we have more control, get 35 ns shaping time so we have more margin for error in setting latency
			\end{itemize}
		\item Burst-mode noise:
			\begin{itemize}
				\item Impact: 4-6\% of events have extra noise hits, degraded time resolution, low hit efficiency
				\item For existing data: may be possible to subtract out noise from noisy events
				\item For next run: change hybrid voltages/preamp setpoints to reduce impact of crosstalk
			\end{itemize}
	\end{itemize}
\end{frame}

\end{document}
