Study of the response of the CALICE Si-W ECAL Physics Prototype to positrons using data taken at the Fermilab test beam facility

The CALICE silicon-tungsten (Si-W) electromagnetic calorimeter (ECAL) physics prototype was tested with electron and positron beams at FNAL. The physics prototype consists of thirty sensitive layers and each layer of $18 \times 18$ cm$^2$ active area is segmented into $1 \times 1$ cm$^2$ cells. We evaluated the response of the prototype to positrons with energies ranging from 4 to 20 GeV in terms of linearity and energy resolution.