A Time Projection Chamber with GEM-Based Readout

For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.Comment: 22 pages, 19 figure

Track reconstruction for InGrid chips for a Time Projection Chamber

The International Linear Collider (ILC) is one of the best candidates for the future of the high energy physics to explore many unknown phenomena such as dark matter and the physics beyond the Standard Model. The ILC has two detectors. The International Large Detector (ILD) is one of these detectors and a Time Projection Chamber (TPC) is a tracker detector foreseen for the ILD. The main goal of the TPC is to measure the momentum of tracks and the energy loss of charged particles in order to reach high precision physics observables. Many different technologies are considered for this purpose. GridPix, i.e. a combination of a micropattern gaseous detector and pixelized readout, one of the candidate readouts for the ILD TPC, is under investigation in this thesis. The result of this combination is that there are many hits along a track causing a better spatial resolution compared with other readout systems. This property is essential to measure the momentum more precisely. In addition, the huge amount of the hits along a track improves the energy loss measurement. However, the pattern recognition (track finding) for the GridPix is very challenging due to a large number of hits and diffusion effects in the TPC in addition to the noise in the readout system. A novel algorithm for the track finding has been developed to solve this difficulty. This algorithm first tries to find a segment of a track in a small area, called tracklet, based on the Hough Transform and using a bivariate normal distribution to improve collecting relevant hits of a tracklet. After finding all tracklets in all regions, the relevant tracklets are merged in order to have the full track. A successful performance of this algorithm for both simulated and experimental data shows that it is promising for the future.Der International Linear Collider (ILC) ist einer der besten Kandidaten für die Zukunft der Hochenergiephysik, um viele unbekannte Phänomene wie Dunkle Materie und die Physik jenseits des Standardmodells zu erforschen. Der ILC hat zwei Detektoren. Der International Large Detector (ILD) ist einer dieser Detektoren, für den eine Time Projection Chamber (TPC) als Spurdetektor vorgesehen ist. Das Hauptziel einer TPC ist es, gleichzeitig den Impuls und den Energieverlust geladener Teilchen anhand ihrer Spuren zu messen, um hochpräzise physikalische Observablen zu erhalten. Zu diesem Zweck werden viele verschiedene Technologien in Betracht gezogen. GridPix, d.h. die Kombination eines Mikrostruktur-Gasdetektors und eines Pixel- Auslesesystems, ist ein Kandidat für die Auslesetechnologie der TPC und wird in dieser Arbeit untersucht. Das Ergebnis dieser Kombination ist, dass es viele Treffer entlang einer Spur gibt, die zusammen eine bessere räumliche Auflösung im Vergleich zu anderen Auslesesystemen bewirken. Diese Eigenschaft ist für eine präzisere Messung des Impulses wesentlich. Darüber hinaus verbessert die große Anzahl an Treffern entlang einer Spur die Messung des Energieverlusts. Die Mustererkennung (Spurbestimmung) für GridPix ist allerdings sehr schwierig aufgrund der großen Zahl an Treffern und Diffusionseffekten in der TPC zusätzlich zum elektronischen Rauschen im Auslesesystem. Es wurde ein neuer Algorithmus zur Spurbestimmung entwickelt, um diese Schwierigkeiten aufzulösen. Der Algorithmus versucht zuerst, auf der Grundlage der Hough-Transformation ein Spursegment (Tracklet) zu finden, wobei zur besseren Identifikation für das Tracklet relevanter Treffer eine bivariate Normalverteilung verwendet wird. Nachdem alle Tracklets in allen Regionen gefunden wurden, werden die relevanten Tracklets zur vollständigen Spur zusammengefügt. Die erfolgreiche Anwendung dieses Algorithmus sowohl auf simulierte als auch auf experimentelle Daten zeigt, dass er für die Zukunft vielversprechend ist

Bivariate normal distribution for finding inliers in Hough space for a Time Projection Chamber

A Time Projection Chamber (TPC) is foreseen as the main tracking detector for the International Large Detector (ILD), one of the two detectors for the next candidate collider named International Linear Collider (ILC) [1]. GridPix, a combination of a micropattern gaseous detector with a pixelized readout, is one of the candidate readout systems for the TPC [2] [3]. One of the challenges in the track reconstruction is the large number of individual hits along a track (around 100 per cm). Due to the small pixel size of 55 x 55 μm2, the distance between the individual ionization processes in the gas is larger than the size of the pixels. Consequently, the hits in the GridPix are not contiguous. This leads to the challenge of assigning the individual hits to the correct track. Hits within a given distance from a reconstructed track are called inliers. Consequently, finding inliers within the large number of hits and in the presence of noise is difficult for pattern recognition. This difficulty is increased by diffusion effects in the TPC. One of the current algorithms which are utilized for track finding is the Hough transform. Using a bivariate normal distribution based on the covariance matrix calculated from the diffusion effect improves collecting inliers in the Hough space directly [5]

Bivariate normal distribution for finding inliers in Hough space for a Time Projection Chamber

A Time Projection Chamber (TPC) is foreseen as the main tracking detector for the International Large Detector (ILD), one of the two detectors for the next candidate collider named International Linear Collider (ILC) [1]. GridPix, a combination of a micropattern gaseous detector with a pixelized readout, is one of the candidate readout systems for the TPC [2] [3]. One of the challenges in the track reconstruction is the large number of individual hits along a track (around 100 per cm). Due to the small pixel size of 55 x 55 μm2, the distance between the individual ionization processes in the gas is larger than the size of the pixels. Consequently, the hits in the GridPix are not contiguous. This leads to the challenge of assigning the individual hits to the correct track. Hits within a given distance from a reconstructed track are called inliers. Consequently, finding inliers within the large number of hits and in the presence of noise is difficult for pattern recognition. This difficulty is increased by diffusion effects in the TPC. One of the current algorithms which are utilized for track finding is the Hough transform. Using a bivariate normal distribution based on the covariance matrix calculated from the diffusion effect improves collecting inliers in the Hough space directly [5]

Bivariate normal distribution for finding inliers in Hough space for a Time Projection Chamber

A Time Projection Chamber (TPC) is foreseen as the main tracking detector for the International Large Detector (ILD), one of the two detectors for the next candidate collider named International Linear Collider (ILC) [1]. GridPix, a combination of a micropattern gaseous detector with a pixelized readout, is one of the candidate readout systems for the TPC [2] [3]. One of the challenges in the track reconstruction is the large number of individual hits along a track (around 100 per cm). Due to the small pixel size of 55 x 55 μm2, the distance between the individual ionization processes in the gas is larger than the size of the pixels. Consequently, the hits in the GridPix are not contiguous. This leads to the challenge of assigning the individual hits to the correct track. Hits within a given distance from a reconstructed track are called inliers. Consequently, finding inliers within the large number of hits and in the presence of noise is difficult for pattern recognition. This difficulty is increased by diffusion effects in the TPC. One of the current algorithms which are utilized for track finding is the Hough transform. Using a bivariate normal distribution based on the covariance matrix calculated from the diffusion effect improves collecting inliers in the Hough space directly [5]

A time projection chamber with GEM-based readout

International audienceFor the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1T solenoidal field and read out with three independent Gas Electron Multiplier (GEM) based readout modules, are reported. The TPC was exposed to a 6GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented

A time projection chamber with GEM-based readout

International audienceFor the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1T solenoidal field and read out with three independent Gas Electron Multiplier (GEM) based readout modules, are reported. The TPC was exposed to a 6GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented

Double-hit separation and dE/dx resolution of a time projection chamber with GEM readout

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at theplanned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC wasplaced in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx

Double-hit separation and dE/dx resolution of a time projection chamber with GEM readout

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx

Double-hit separation and dE/dx resolution of a time projection chamber with GEM readout

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.Comment: 28 pages, 27 figure