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Large-area silicon detector systems for tracking and vertex detection are of central importance to frontier precision hadron physics experiments. Examples are the CBM and the PANDA projects planned at the international accelerator facility FAIR. Their physics with rare probes (e.g. D mesons and L_c baryons) demands for unprecedented silicon detector performance. One of the key requirements is an ultra-light-weight construction of the detector systems as a whole, essential for high-resolution determination of the particles momenta and the vertex identification of short-lived decays. This is particularly challenging because in the new experiments high particle multiplicities (up to 1000 per event) and high nuclear interaction rates (up to 10 million per second) require a large number of fine-pitch detector channels equipped with fast and thus power dissipating front-end electronics. The necessary cooling infrastructure would introduce an excessive material budget in the tracking system aperture, making the required high-resolution momentum and vertex measurements impossible if the detector systems were built similar to current state-of-the-art designs realized e.g. in tracking detectors of LHC experiments at CERN.

In this research activity we propose to explore new innovative technologies and system concepts to demonstrate that high-performance, ultra-low-mass detector systems for tracking and vertex detection can be built compatible with the large-area requirement. This will be addressed in three R&D projects each focusing on a different system challenge:

1. An innovative thin microstrip tracking detector system for large-area coverage:   
   Microstrip detectors are ideally suited for low-mass tracking applications as the sensors themselves are thin and passive. In large state-of-the-art tracking systems, however, the material budget from the readout electronics, traditionally attached directly to the microstrip detectors, reduces significantly the advantages of the thin sensors. The goal of this R&D task is to develop the demonstrator of a novel ultra-low-mass microstrip detector module that can be used to build up a light-weight planar tracking station of up to about 1 m² size. We will focus on exploring frontier ultra-low-mass Aluminum-Kapton flat-cable technology to route on a very light mechanical support the signals of existing, thin microstrip detectors to fast readout electronics located at the periphery of the module, thus avoiding excessive material budget in the active detector area.
2. A thin fast hybrid pixel detector system for tracking in high particle densities:       
   In detector regions with very high track densities the unambiguous two-dimensional coordinate measurement capabilities of pixel detectors will be required. However, current hybrid pixel detector technologies are too massive. In this R&D task we will address the design and realization of an advanced light-weight hybrid pixel system optimized for the conditions in hadron physics experiments. The focus is on developing very-low power front-end electronics with high-resolution position, energy loss and timing measurements, and on achieving a minimum system thickness with thinned readout chips connected with advanced bump-bonding or frontier 3D-integration techniques to very thin epitaxial pixel detectors.
3. An ultra-thin monolithic pixel detector system for decay vertex identification:       
   The object of the research task is a novel ultra-thin charged particle detection system for precision decay vertex identification, composed of thinned CMOS monolithic pixel detectors supported by a thin thermal conductor. The material budget of the system is of central concern, since conventional technologies based on carbon fibre supports will hardly meet the challenging CBM vertex detection requirements, taking into account the cooling needs of the detectors in a vacuum environment. Several materials, including thin-film polymers, allow for the integration of read-out and power lines, thus assuring minimum system thickness. This is culminated with the application of industrial CVD diamond, due to its excellent material properties regarding flexural stiffness and, in particular, heat conduction.     
   For the assembly of such very thin devices, the mastering of novel processing techniques and advanced handling skills are key aspects of the challenge. In this activity, we focus on exploring 3D or vertical integration technologies that are currently vividly emerging in fore-front semiconductor research labs and industry. These technologies allow for stacking very thin layers of heterogeneous, micro-structured circuitry. We will explore how to condition and to manipulate thin CMOS sensors and how to fix and align them with high precision on thin support layers. A prototype module will be assembled and characterized in particular for thermal stability. The research will end with a decision on the way how to elaborate for the final deliverable, a high-precision ultra-thin vertex detection system with built-in thermal management and an overall material budget below the current record (which is between 0.3% and 0.4% radiation length in ambient atmosphere), in a possible extension of the research project beyond 2011.

Thin Aluminum-Kapton cables with high line density are one of the key components for constructing innovative new types of low-mass microstrip tracking detector systems for large-area coverage. This includes advanced interconnection technologies required to attach the cables to detectors and electronics components. Industry and research institutes in Europe do not offer or dispose of production technologies for such cables readily. We expect that our developments, conducted in close collaboration with aerospace research laboratories, and the demonstration of the construction and successful operation of the building block of such a system, will meet wide interest in the instrumentation sector of both nuclear and particle physics communities. New challenging experiments will become possible with the availability of such particle tracking system.

Thin pixel detector tracking systems realized with bump-bonded (or 3D-integrated) hybrid components will be the necessary complement to thin microstrip detector based tracking systems when the experimental conditions involve very high track densities. Such situations may not be handled any more with microstrip detectors as they unavoidably present false combinatorial hits to the tracking algorithms. Hybrid pixel detectors, the current state-of-the-art for best true space point measurement, provide the best performance where good timing, high resolution and high radiation tolerance must be combined. There is considerable interest in the detector community towards the developments of new hybrid pixel detector modules with reduced material budget and lower cost. We envisage hybrid pixel detector modules with a thickness well below 1% of radiation length, advanced read-out capability (charge/timing information + triggerless read-out) and pixels of at least half the size with respect to present implementations. These detectors will be attractive tools for future hadron physics experiments, in particular for the planned experiments at FAIR, but also for the upgrades of ALICE and for new fixed target experiments with heavy ions presently under study at the CERN SPS.

The project is pioneering a fully novel detector system technique based on CMOS monolithic pixel sensors on a thin mechanical support with integrated electrical supply and readout bus, ultimately with excellent thermal management as in CVD diamond substrates. It is expected to have spin-offs in a wide variety of applications, ranging from subatomic physics to beta-imaging. It exploits the collaborative effort of research institutions and industrial partners which have outstanding expertise in key domains underlying the project (CMOS sensor design, thin support substrate fabrication with integrated electrical lines, 3D assembly techniques). One of the partners (CNRS) develops simultaneously the technology for other applications: ILC vertex detector, beta-imaging for bio-medical research. A wide community of potential users will be kept in contact with the development evolution.