Performance of an endcap prototype of the ATLAS accordion electromagnetic calorimeter

The design and construction of a lead-liquid-argon endcap calorimeter prototype using an accordion geometry and conceived as a sector of the inner wheel of the endcap calorimeter of the future ATLAS experiment at the LHC is described. The performance obtained using electron beam data is presented. The main results are energy resolution with a sampling term below 11%/√E(GeV) and a small local constant term, good linearity of the response with the incident energy and a global constant term of 0.8% over an extended area in the rapidity range 2.2 < η < 2.9. These properties make the design suitable for the ATLAS electromagnetic endcap calorimeter.