V. Garde

We report test beam studies of 11% of the production ATLAS Tile Calorimeter modules. The modules were equipped with production front-end electronics and all the calibration systems planned for the final detector. The studies used muon, electron and hadron beams ranging in energy from 3 to 350 GeV. Two independent studies showed that the light yield of the calorimeter was ∼70pe/GeV, exceeding the design goal by 40%. Electron beams provided a calibration of the modules at the electromagnetic energy scale. Over 200 calorimeter cells the variation of the response was 2.4%. The linearity with energy was also measured. Muon beams provided an intercalibration of the response of all calorimeter cells. The response to muons entering in the ATLAS projective geometry showed an RMS variation of 2.5% for 91 measurements over a range of rapidities and modules. The mean response to hadrons of fixed energy had an RMS variation of 1.4% for the modules and projective angles studied. The response to hadrons normalized to incident beam energy showed an 8% increase between 10 and 350 GeV, fully consistent with expectations for a noncompensating calorimeter. The measured energy resolution for hadrons of σ/E=52.9%/E⊕5.7% was also consistent with expectations. Other auxiliary studies were made of saturation recovery of the readout system, the time resolution of the calorimeter and the performance of the trigger signals from the calorimeter.

We measured angular distributions of recoil-polarization response functions for neutral pion electroproduction for $W=1.23\text{ }\text{ }\mathrm{GeV}$ at ${Q}^{2}=1.0\text{ }\text{ }(\mathrm{GeV}/c{)}^{2}$, obtaining 14 separated response functions plus 2 Rosenbluth combinations; of these, 12 have been observed for the first time. Dynamical models do not describe quantities governed by imaginary parts of interference products well, indicating the need for adjusting magnitudes and phases for nonresonant amplitudes. We performed a nearly model-independent multipole analysis and obtained values for $\mathrm{Re}\text{ }({S}_{1+}/{M}_{1+})=\ensuremath{-}(6.84\ifmmode\pm\else\textpm\fi{}0.15)%$ and $\mathrm{Re}\text{ }({E}_{1+}/{M}_{1+})=\ensuremath{-}(2.91\ifmmode\pm\else\textpm\fi{}0.19)%$ that are distinctly different from those from the traditional Legendre analysis based upon ${M}_{1+}$ dominance and ${\ensuremath{\ell}}_{\ensuremath{\pi}}\ensuremath{\le}1$ truncation.