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\title{T1441 --- sPHENIX MAPS Vertex Detector (MVTX)}
%\author{The Author}
\author{Hubert van Hecke$^1$ \and Sanghoon Lim$^1$ \and Ming Liu$^1$ \and Darren McGlinchey$^1$ \and Alex Tkatchev$^1$ \and Sho Uemura$^1$}
\date{%
    $^1$Los Alamos National Laboratory\\[2ex]%
    \today
}

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\section*{Motivation and Goals}

The MAPS Vertex Detector (MVTX) is a proposed upgrade to the sPHENIX experiment planned for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory.
MVTX will consist of three concentric layers of ALPIDE (ALice PIxel DEtector) sensors, developed by the ALICE collaboration at CERN.
Use of the latest Monolithic Active Pixel Sensor (MAPS) technology allows for a compact and thin design with low power consumption and a high degree of segmentation.

The goals for this test beam were to verify the tracking performance of the ALPIDE sensor in various occupancy environments, and prove the detector electronics and readout.
MVTX will use the ALPIDE sensor and frontend FPGA board (``Readout Unit'') developed by ALICE, a backend FPGA board (``FELIX'') developed by ATLAS, and a DAQ system developed by sPHENIX; a test beam would demonstrate successful integration of these components in a working system.

\section*{Setup}
We set up at the downstream end of the MT6.2B area, downstream of the T1439 experiment (sPHENIX silicon strip tracker) and upstream of T1044 (sPHENIX calorimetry).

The system under test consisted of a telescope with four ALPIDE sensors, mounted on carrier PCBs inside a light-tight box (see Figure \ref{fig:t1441_setup}).
We are grateful to the Fermilab SiDet facility for mounting and wirebonding two of the sensors on short notice.
The Readout Unit was set up under the telescope box, and communicated over fiber to FELIX in the control room.

The DAQ was triggered on the FTBF scintillator coincidence (``SC1+SC2+SC3+Spill'').
Most data was taken with a 120 GeV proton beam.
Some runs were taken with lead bricks just upstream of the telescope, to create high-multiplicity shower events.
For the last runs we mounted the telescope on a rotary table for tests of tracking at off-normal incidence.


%Describe where and how your system was setup, including facility instruments. Also, please include a picture of the setup if you have it. 

\begin{figure}[htbp] %  figure placement: here, top, bottom, or page
   \centering
   \includegraphics[height=1.5in]{t1441_telescope} 
   \includegraphics[height=1.5in]{t1441_setup} 
   \caption{(Left) The telescope box, with cover removed. Beam direction is from lower left to upper right. (Right) sPHENIX detectors in the MT6.2 area, beam is left to right.}
   \label{fig:t1441_setup}
\end{figure}


\section*{Results and Publications}
%please include your results and any publication plans. 

The test beam operation successfully characterized the tracking performance of the ALICE ALPIDE sensor and determined that it meets the requirements of the sPHENIX MVTX detector.
We observed excellent spatial resolution as shown in Fig. \ref{fig:t1441_performance} (left) and cluster finding efficiency $>99.5\%$ as shown in Fig. \ref{fig:t1441_performance} (right) for all 4 layers of the telescope, well above the MVTX requirements.
This data is also important for validating the MVTX simulations used in the full sPHENIX tracking configuration, allowing for better understanding of the tracking capabilities and their impact on the physics performance of sPHENIX.

\begin{figure}[htbp] %  figure placement: here, top, bottom, or page
   \centering
   \includegraphics[width=4in]{t1441_performance} 
   \caption{(Left) Displacement between track projection and cluster position in a single sensor. (Right) The cluster finding efficiency per layer for different 3-hit track quality cuts.}
   \label{fig:t1441_performance}
\end{figure}

The successful operation of the full MVTX readout chain in the test beam was a key proof of concept for the MVTX review held at Brookhaven in July 2018.
The review committee was impressed with the progress of the readout systems integration and recommended that MVTX proceed with procurement of the Readout Units.

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%1.       The number of postdocs, number of students, number of faculty/scientists, number of technicians/engineers that came with you to the tests
% 3 postdocs (Sanghoon, Darren, Sho), 2 staff scientists (Hubert, Ming), 1 engineer (Alex)

%2.       Number of people using the data that didn’t come to the actual test beam run (people at home institutions for example)
% 3 in addition to the people above

%3.       Any publications that came out of the test beam data
% none yet - most likely we will do a NIM paper after the next round of sPHENIX test beams

%4.       We need to update our posters around the facility. If anyone has a poster and would like us to display it, we’d be happy to. You can send me the file and I’ll have it printed here.
%QM 2018 poster