Position Resolution of the ATLAS Electromagnetic Endcap Calorimeter

The position reconstruction performance of the Electromagnetic Endcap Calorimeter (EMEC) is assessed in terms of its response to electrons. The electromagnetic and hadronic endcap calorimeter modules of the ATLAS detector are exposed to beams of electrons, pions, and muons in the energy range 6 GeV &le; E &le; 200 GeV at several impact positions in the pseudo-rapidity 1.6 &le; |&eta;| &le; 1.8 in a beam test at CERN. The EMEC is a lead-liquid argon sampling calorimeter with a unique accordion structure designed to provide complete hermiticity and excellent energy and position resolution, the attribute on which several physics measurements envisioned at the LHC will depend. Unlike the real ATLAS situation, the beam test setup used a non-pointing geometry in &eta; due to the experimental constraints. Hence, the position resolution of the EMEC is evaluated in the &phi; direction only and found to be at least as good as &sigma; <SUB> &phi; </SUB> = (4.36 &plusmn; 0.10) / &radic; E(GeV) &oplus; (12.64 &plusmn; 0.82) / E &oplus; (0.00 &plusmn; 0.10) in milliradians.