Detector R&D towards realistic luminosity measurement at the forward region of future $e^{+}e^{-}$ linear colliders.

The luminosity measurement at a future $e^{+}e^{-}$ linear collider will be preformed with a specialized compact calorimeter foreseen in the very forward region. The design of the luminosity calorimeter (LumiCal) is based on a tungsten-silicon sandwich calorimeter. The R&D effort by the FCAL collaboration aims towards the assembly of the full calorimeter prototype, that will serve as a realistic demonstrator for the final detector. Two methods for silicon sensor automated testing were used for the characterization of LumiCal sensor prototypes. In these measurements the total capacitance, depletion voltage, donor density and the pad dark current were measured for each pad in the sensor. A first LumiCal prototype consisting of four planes was tested at the CERN PS accelerator T9 beam. An improved compact prototype, utilizing new thin detector modules, was tested at DESY with an electron beam of $1~GeV - 6~GeV$. In the tests, the sensor performance was measured, the development of the electromagnetic shower was studied and the prototype energy and position reconstruction resolution were determined. The effective Moliere radii of the two prototypes were also extracted using a parameterization of the lateral shower shape. For the first prototype it was determined to be $24.0 \pm 0.6 (stat.) \pm 1.5 (syst.)~mm$, while for the more compact prototype it was determined to be significantly lower, $8.2 \pm 0.1 (stat) \pm 0.3 (syst)~mm$. Very good agreement was obtained between data and MC simulations. The smaller effective Moliere radius reached by the compact prototype indicate that the full LumiCal will be capable, in due time, to preform the luminosity measurement with the desired precision.