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\title[]{Precision Muon Tracking Detectors for High-Energy Hadron Colliders}

\author[]{Ph.~Gadow \and O.~Kortner \and H.~Kroha \and S.~Nowak \and R.~Richter}
\institute{Max-Planck-Institut f\"ur Physik, Munich}
\date{14th Vienna Conference on Instrumentation, Vienna, 15-19 February 2016}

\begin{document}
	\begin{frame}
		\begin{block}{Abstract}
			\centering
			\begin{minipage}{0.98\linewidth}
				\small{The experience of the ATLAS muon spectrometer shows that drift-tube chambers provide highly reliable precision muon tracking  over large areas.
					The ATLAS muon chambers are exposed to unprecedentedly high background of photons and neutrons induced by the proton collisions.
					Still higher background rates are expected at future high-energy and high-luminosity colliders beyond HL-LHC.
					Drift-tube detectors with 15 mm tube diameter (30 mm in ATLAS) and improved read-out electronics optimized for high rate operation have been developed for such conditions.
					Tests at the Gamma Irradiation Facility at CERN showed that the rate capability of sMDT chamber is improved by more than an order of magnitude compared to the ATLAS chambers as space charge effects are strongly suppressed and operation with minimal electronics dead time becomes possible. Studies of the new readout electronics are shown.
					Several full-scale chambers have been constructed with unprecedentedly high sense wire positioning accuracy of better than 5 micron. The chamber design and assembly methods have been optimized for large-scale production, reducing considerably cost and construction time while maintaining the high mechanical accuracy and reliability.
					}
			\end{minipage}
		\end{block}
		\vfill
		\begin{columns}
			\begin{column}{0.49\textwidth}
				\parbox[t][\columnheight]{\textwidth}{%
					%MDTs and sMDTs
					\begin{block}{Muon Drift Tube Chambers}
						\small{
							\begin{minipage}{0.96\textwidth}
								\begin{columns}
									\begin{column}{0.47\textwidth}
										\begin{center}
% 											\hspace{-3cm}
											\includegraphics[width=0.9\textwidth]{mdt_and_smdt_tube_end}
										\end{center}
										\hspace{28mm}$\diameter$30\,mm MDT\hspace{30mm}$\diameter$15\,mm sMDT
% 										\vspace{2.5cm} 
										\vfill
									\end{column}
									\hfill
									\begin{column}{0.47\textwidth}
										\textbf{Assembled sMDT chamber for ATLAS}\\
										\vspace{5mm} 
										\includegraphics[width=1.03\textwidth]{sMDT_chamber}
									\end{column}
								\end{columns}
								\vspace{1cm}
								\begin{columns}
									\begin{column}{0.47\textwidth}
										\textbf{Monitored Drift Tube chambers, MDT:}\\ 
										Precision tracking detectors 
									        in the ATLAS Muon Spectrometer with 30\,mm drift tube diameter operated with Ar:CO$_2$ gas at 3 bar
									        and a gas gain of 20000.\\
									        \vfill
									\end{column}
									
									\begin{column}{0.47\textwidth}
										\vbox to 10mm{\vfill}
										\textbf{Small-Diameter MDT chambers, sMDT:}\\ 
										Precision muon tracking detectors with 15\,mm drift tube diameter and \textbf{an order of magnitude 
										higher rate capability} than the MDTs for ATLAS upgrades and future hadron colliders.\\
										
									\end{column}
								\end{columns}
								\vspace{0.5cm}
								\begin{columns}
									\begin{column}{0.01\textwidth}
									\end{column}
								
									\begin{column}{0.5\textwidth}
									        \includegraphics[width=\textwidth]{dtspectrum_smdt}\\     
										\includegraphics[width=\textwidth]{resolution_curves}\\
										\includegraphics[width=\textwidth]{gaindrop_mdt_smdt_comparison}
									\end{column}
									\begin{column}{0.48\textwidth}
										\begin{itemize}
											\item The high background radiation of neutrons and photons at high energy hadron colliders 
											creates space charge in the muon drift tube detectors  
											due to the slowly drifting ions created in the avalanche near the sense wire 
											and masks muon hits due to finite electronic signal length and dead time.  
											\item Space charge fluctuations deteriorate the drift tube spatial resolution 
											only for large drift radii occuring in MDTs. 
											\item The decrease of gas amplification due shielding of the wire potential by the space charge 
											is proportional to the tube radius $R^3$ for neutron and $\gamma$ radiation, converting predominantly 
											in the aluminum tube walls, and therefore is strongly suppressed in sMDT tubes.\\
											\item The 4 times shorter maximum drift time of sMDTs (185\,ns)compared to MDTs (700\,ns) under the same operating 
											conditions leads, together with the smaller tube cross section, to 8 times lower background 
											occupancy and allows for drastic reduction of the electronics dead time.
											\item Minimimum dead time leads to vast improvement of the muon detection efficiency 
											at high counting rates which is fully exploited by using readout electronics 
											with active baseline restoration.  
										\end{itemize}
									\end{column}
								\end{columns}
							\end{minipage}
						}
					\end{block}
                                \vfill
				\begin{block}{sMDT High-Rate Performance at CERN Gamma Irradiation Facility}
					\small{
						\begin{minipage}{0.96\linewidth}
							\begin{columns}\hspace{-2mm}
								\begin{column}{0.47\textwidth}
									\includegraphics[width=1.085\textwidth]{resolution_vs_rate_smdt_mdt-7}
								\end{column}
								\begin{column}{0.47\textwidth}
									\includegraphics[width=1.085\textwidth]{efficiency_vs_rate_smdt_mdt-7}
								\end{column}
							\end{columns}
     							         Active baseline restoration (BLR) suppresses the obsreved signal pile-up effects promising further improvement 
     							         of spatial resolution and muon efficiency (hit within $3\sigma_{\mathrm resol}$ of the extapolated muon track) at high counting rates.
						\end{minipage}
					}
				\end{block}
				\vfill
				}
				\vfill
			\end{column}
			\hfill
			\begin{column}{0.49\textwidth}
				\parbox[t][\columnheight]{\textwidth}{%
		                                \begin{block}{sMDT Chamber Design}
						\small{
							\begin{minipage}{0.96\linewidth}
								\vspace{0.5cm}
								\begin{columns}[T]
									\begin{column}{0.03\textwidth}
									\end{column}
									\begin{column}{0.65\textwidth}
										\begin{itemize}
												\item sMDT chamber design and assembly optimized for mass production and speed independent of number of tube layers per chamber. 
												\item Simple, low-cost drift tube design  reliability and mechanical precision.
												\item Standard industrial aluminum tubes with 0.4\, mm wall thickness.
												\item Plastic endplug materials selected to prevent outgassing and cracking.\\
												\item No wire aging observed up to 9 $\frac{C}{cm}$ charge on the wire (15 times current ATLAS requirement).
										\end{itemize}
									\end{column}
									\begin{column}{0.35\textwidth}
% 										\textbf{End-plug}
										\vspace{0.5cm}
										\includegraphics[width=1.0\textwidth]{end-plug3}\\
										\vspace{0.5cm}
										\hspace{2cm}
										\tiny{Cross section of an sMDT endplug}
									\end{column}
								\end{columns}
								
							\end{minipage}
						}
					\end{block}
					

						\begin{block}{sMDT Chamber Assembly}
						\small{
							\begin{minipage}{0.96\linewidth}
								\begin{columns}[T]
									\begin{column}{0.32\textwidth}
										\vspace{0.5cm}
										\begin{itemize}
											\item Semi-automated drift-tube production and chamber assembly in an air-conditioned clean room.
											\item Automated measurement of wire tension, gas leak rate and leakage current at nominal operating voltage (2730 V).										\end{itemize}
									\end{column}
									\begin{column}{0.32\textwidth}
										\centering
										\includegraphics[width=1.2\textwidth]{BMG_jig}\\
										\vspace{0.5cm}
										\tiny{sMDT wire positioning by insertion of endplug reference surfaces into precisely machined jigs}
									\end{column}
									\begin{column}{0.34\textwidth}
										\centering
										\vspace{0.3cm}\hspace{2mm}
										\includegraphics[width=0.9\textwidth]{clean-room2}\\
										%\includegraphics[width=0.9\textwidth]{BMG_assembly}\\
										\tiny{sMDT chamber assembly}
									\end{column}
								\end{columns}
								\vspace{0.3cm}
								\begin{itemize}
									\item Assembly of a chamber within one working day.
									\item Measurement of wire positions with coordinate measuring machine with few $\mu$m accuracy. 
									\item \textbf{Sense wire positioning accuracy of better than 5 $\mu$m.}
								\end{itemize}
							\end{minipage}
						}
					\end{block}
					
				

					\begin{block}{Limitations of Present MDT Read-Out Electronics at High Rates}
						\small{
							\begin{minipage}{0.96\linewidth}
								\vspace{0.5cm}
								\begin{columns}
									\begin{column}{0.48\textwidth}
										\begin{itemize}
											\item Bipolar shaping used to guarantee baseline stability at high rates.
											\item Disadvantage: long undershoot following the shaped signal pulse.
											\item[$\Rightarrow$] For desired operation at short dead time: \
									                amplitude of secondary muon pulses effectlively reduced and 
											jitter of discriminator threshold crossing time increased. 
										\end{itemize}
									\end{column}
									\begin{column}{0.48\textwidth}
										\textbf{Signal Pile-Up of Closely Spaced Hits}\\
										\vspace{0.5cm}
										\includegraphics[width=1.0\textwidth]{pile_up}\\
										\begin{tikzpicture}[overlay]
											\node[text width=15cm, color=red] at (20,6.5) {Muon};
											\node[text width=25cm, color=blue] at (14,2.8) {$\gamma$-background};
										\end{tikzpicture}
									\end{column}
								\end{columns}										
							\end{minipage}
						}
				\end{block}
				
				\begin{block}{Signal Shaping Circuit With Optional Active Baseline Restoration}
					\small{
						\begin{minipage}{0.96\linewidth}
							%\begin{columns}
							%	\begin{column}{0.35\textwidth}
							%		\begin{itemize}
							%			\item High bandwidth (700 MHz) transimpedance preamplifier 
							%			\item Discrete bipolar shaping circuit (2 filter stages) with baseline restoration (BLR)
							%		\end{itemize}
							%	\end{column}
							%	\begin{column}{0.63\textwidth}
							%		\centering
							%		\includegraphics[width=1.03\textwidth]{ASBC}\\
							%		\tiny{Photograph of discrete preamplifier, shaper with two-stage filter and BLR circuit, and comparator circuits}
							%	\end{column}
							%\end{columns}
							%\vspace{0.5cm}
							\textbf{Principle of active baseline restoration (according to L.B.Robinson, Rev.Sci.Instr.\ 32 (1961) 1057):}
							\begin{columns}
								\begin{column}{0.1\textwidth}
								\end{column}
								\begin{column}{0.23\textwidth}
									\includegraphics[width=1.0\textwidth]{blr_diode}
								\end{column}
								\begin{column}{0.63\textwidth}
									\begin{itemize}
										\item Diode slightly conducting at working point with $I_{Base}\neq 0$.
										\item Diode non-conducting for positive signal polarity.
										$\Rightarrow$ signal stays unchanged.
										\item Diode conducting for negative polarity (undershoot) restoring baseline by draining current to ground. 
									\end{itemize}
								\end{column}
							\end{columns}
						\end{minipage}
					}
				\end{block}
		
			\begin{block}{Effect of Active Baseline Restoration}
				\small{
					\begin{minipage}{0.96\linewidth}
						\begin{columns}
							\begin{column}{0.65\textwidth}
								\includegraphics[width=1.00\textwidth]{muon_elec_shaped_blr}
							\end{column}
							\begin{column}{0.33\textwidth}
								\begin{itemize}
									\item Signals recorded before and after shaping with and without baseline restoration (BLR). 
									\item BLR circuit clearly suppresses the bipolar undershoot.																	
								\end{itemize}
							\end{column}
						\end{columns}
					\end{minipage}
					}
				\end{block}
				}
			\end{column}
		\end{columns}
	\end{frame}
\end{document}

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