Lorentz angle measurements as part of the sensor R\&D for the CMS Tracker upgrade

The CMS detector is one of the main experiments at the LHC accelerator at CERN. Its $200 m^2$ silicon strip tracker was designed to withstand the radiation of 10 years of LHC operation. The foreseen high luminosity upgrade of the LHC imposes even higher demands on the radiation tolerance and thus requires the construction of a new tracking detector. To determine the properties of different silicon materials and production processes, a campaign has been started by the CMS Tracker Collaboration to identify the most promising candidate material for the new CMS tracker. The silicon sensors of the CMS tracker are operated in a 3.8 T magnetic field. Charges created by traversing ionizing particles inside the active sensor volume are deflected by the Lorentz force. The Lorentz angle, under which the charge drifts through the sensor, is strongly dependent on the mobility, which in turn depends on the electric field and may depend on the radiation damage created by the particles produced by the LHC. Studying this is part of the campaign mentioned above. This contribution summarizes the Lorentz angle measurements at magnetic fields of up to 8 T performed on small strip sensors after mixed irradiation with protons and neutrons to fluences of up to $5.8\times10^{15} n_{eq}/cm^2$ and gives a comparison to a simple simulation model.