Mr Jan-Hendrik Arling (DESY) Ms Michaela Queitsch-Maitland (DESY)
The ATLAS Phase-II Inner Tracker (ITk) Strip Detector is an upgrade for the current ATLAS tracking detector designed for the challenges of the high-luminosity LHC. A key point in the design stage of a tracking detector is to minimise the amount of material and therefore radiation lengths (X0) associated with the detector. As local support for the silicon strip sensors in the forward region (the end-caps) wedge-shaped structures called petals are foreseen. These petals are built dominantly out of light-weight carbon-fibre composite materials to address the tracker design goals. For such composite materials in the petal or new adhesives for gluing the sensors on the petal, only rough estimations of the radiation length can be calculated. To validate these estimations, which are taken into account in detector simulations, one can measure the radiation length directly in a testbeam experiment. In this case, electrons with energies between 1 and 5 GeV from the DESY testbeam traversing the inserted device will be scattered inside the material. The amount of scattering is dependent on the radiation lengths traversed. By using the provided EUDET-type beam telescopes it is possible to reconstruct the particle tracks with high positional and angular resolution and to evaluate the angular scattering distribution. The reconstruction is performed in EUTelescope using General Broken Lines (GBL) track fitting. Applying theoretical scattering models (e.g. Highland formula) allows the radiation length of the material to be extracted. One goal of these studies is to provide an infrastructure of X0 measurements for DESY testbeam users in the future by exploring now the details of this direct X0 measurement method. This talk will show the used X0 calibration targets as well as validation tests of the method. Moreover, dedicated measurements of ATLAS ITk specific materials will be presented.