Measuring the ATLAS ITk pixel detector material via multiple scattering of positrons at the CERN PS

The ITk is a new silicon tracker for the ATLAS experiment designed to increase detector resolution, readout capacity, and radiation hardness, in preparation for the larger number of simultaneous proton-proton interactions at the High Luminosity LHC. This paper presents the first direct measurement of the material budget of an ATLAS ITk pixel module, performed at a testbeam at the CERN Proton Synchrotron via the multiple scattering of low energy positrons within the module volume. Using a four plane telescope of thin monolithic pixel detectors from the MALTA Collaboration, scattering datasets were recorded at a beam energy of $$ . Kink angle distributions were extracted from tracks derived with and without information from the ITk pixel module, and were fit to extract the RMS scattering angle, which was converted to a fractional radiation length $$ . The average $$ across the module was measured as $$ , which agrees within uncertainties with an estimate of $$ derived from material component expectations.