Electron and Photon Identification Performance in ATLAS

The understanding of the reconstruction and calibration of electrons and photons is one of the key steps at the start-up of data-taking with ATLAS at the LHC (Large Hadron Collider). The calorimeter cells are electronically calibrated before being clustered. Corrections to local position and energy measurements are applied to take into account the calorimeter geometry. Finally, longitudinal weights are applied to correct for energy loss upstream of the calorimeter. As a last step the Z -> ee events will be used for in-situ calibration using the Z boson mass. The electron identification is based on the shower shape in the calorimeter and relies heavily on the tracker and combined tracker/calorimeter information to achieve the required rejection of 10^5 against QCD jets for a reasonably clean inclusive electron spectrum above 20-25 GeV. For photon identification, in addition to the shower shape in the calorimeter, recovery of photon conversions is an essential ingredient given the large amount of material in the inner tracker. The electron and photon identification methods (cuts and multivariate analysis) will be discussed.Comment: Poster write-up at ICHEP08, Philadelphia, USA, July 2008. 4 pages, LaTeX, 7 eps figures, 2 rtx files, 1 sty file and 1 cls fil

Electronic structures of Zn1−x_{1-x}Cox_xO using photoemission and x-ray absorption spectroscopy

Electronic structures of Zn$_{1-x}$Co$_x$O have been investigated using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The Co 3d states are found to lie near the top of the O $2p$ valence band, with a peak around $\sim 3$ eV binding energy. The Co $2p$ XAS spectrum provides evidence that the Co ions in Zn$_{1-x}$Co$_{x}$O are in the divalent Co$^{2+}$ ($d^7$) states under the tetrahedral symmetry. Our finding indicates that the properly substituted Co ions for Zn sites will not produce the diluted ferromagnetic semiconductor property.Comment: 3 pages, 2 figure

A Note on the Unsteady Cavity Flow in a Tunnel

The unsteady internal cavitating flow such as the one observed in a pump or a turbine is studied for a simple two-dimensional model of a base-cavitating wedge in an infinite tunnel and it is shown how the cavitation compliance can be calculated using the linearized free streamline theory. Numerical values are obtained for the limiting case of a free jet. Two important features are: First, the cavitation compliance is found to be of complex form, having additional resistive and reactive terms beyond the purely inertial oscillation of the whole channel in "slug flow." Second, the compliance has a strong dependence on frequency