Measurement of shower development and its $\textit{Molière radius}$ with a four-plane LumiCal test set-up

Abstract: A prototype of a luminometer, designed for a future $e<sup>{+}e<sup>{-}$ collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this beam test was to demonstrate a multi-plane operation, to study the development of the electromagnetic shower and to compare it with MC simulations. In addition, the effective $\textit{Moli`ere radius}$ of this configuration is extracted.