Performance of a large scale prototype of the ATLAS accordion electromagnetic calorimeter

A 2 m long prototype of a lead-liquid argon electromagnetic caloriemeter with accordion-shaped electrodes, conceived as a sector of the barrel calorimeter of the future ATLAS experimentat the LHC, has been tested with electron and pion beams in the energy range 10 to 287 GeV. A sampling term of 10%√E(GeV) was obtained for electrons in the rapidly range 0 < η < 1, while the constant termmeasured over an area of about 1 m2 is 0.69%. With a cell size of 2.7 cm the position resolution is about 4 mm√E(GeV).