Effect of Reducing Atmosphere on the Magnetism of Zn1-xCoxO Nanoparticles

We report the crystal structure and magnetic properties of Zn1-xCoxO nanoparticles synthesized by heating metal acetates in organic solvent. The nanoparticles were crystallized in wurtzite ZnO structure after annealing in air and in a forming gas (Ar95%+H5%). The X-ray diffraction and X-ray photoemission spectroscopy (XPS) data for different Co content show clear evidence for the Co+2 ions in tetrahedral symmetry, indicating the substitution of Co+2 in ZnO lattice. However samples with x=0.08 and higher cobalt content also indicate the presence of Co metal clusters. Only those samples annealed in the reducing atmosphere of the forming gas, and that showed the presence of oxygen vacancies, exhibited ferromagnetism at room temperature. The air annealed samples remained non-magnetic down to 77K. The essential ingredient in achieving room temperature ferromagnetism in these Zn1-xCoxO nanoparticles was found to be the presence of additional carriers generated by the presence of the oxygen vacancies.Comment: 11 pages, 6 figures, submitted to Nanotechnology IO

Construction, assembly and tests of the ATLAS electromagnetic end-cap calorimeters

The construction and the assembly of the two end-caps of the ATLAS liquid argon electromagnetic calorimeter as well as their test and qualification programs are described. The work described here started at the beginning of 2001 and lasted for approximately three years. The results of the qualification tests performed before installation in the LHC ATLAS pit are given. The detectors are now installed in the ATLAS cavern, full of liquid argon and being commissioned. The complete detectors coverage is powered with high voltage and readout

Study of e+e−→ppˉe^+e^- \rightarrow p\bar{p} in the vicinity of ψ(3770)\psi(3770)

Using 2917 $\rm{pb}^{-1}$ of data accumulated at 3.773~$\rm{GeV}$, 44.5~$\rm{pb}^{-1}$ of data accumulated at 3.65~$\rm{GeV}$ and data accumulated during a $\psi(3770)$ line-shape scan with the BESIII detector, the reaction $e^+e^-\rightarrow p\bar{p}$ is studied considering a possible interference between resonant and continuum amplitudes. The cross section of $e^+e^-\rightarrow\psi(3770)\rightarrow p\bar{p}$, $\sigma(e^+e^-\rightarrow\psi(3770)\rightarrow p\bar{p})$, is found to have two solutions, determined to be ($0.059\pm0.032\pm0.012$) pb with the phase angle $\phi = (255.8\pm37.9\pm4.8)^\circ$ ($<$0.11 pb at the 90% confidence level), or $\sigma(e^+e^-\rightarrow\psi(3770)\rightarrow p\bar{p}) = (2.57\pm0.12\pm0.12$) pb with $\phi = (266.9\pm6.1\pm0.9)^\circ$ both of which agree with a destructive interference. Using the obtained cross section of $\psi(3770)\rightarrow p\bar{p}$, the cross section of $p\bar{p}\rightarrow \psi(3770)$, which is useful information for the future PANDA experiment, is estimated to be either ($9.8\pm5.7$) nb ($<17.2$ nb at 90% C.L.) or $(425.6\pm42.9)$ nb

Very High Energy Gamma Ray Astronomy and Cosmic Ray Physics with the ARGO-YBJ experiment

Gamma ray astronomy at energies 1011 1013 eV, which are strictly related to the identication and study of the cosmic ray acceleration sites, is the main scientic goal of the ARGO-YBJ experiment. The detector, which is now being assembled in Tibet (China) at 4300 m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers covering a surface of about 7000 m2. The high altitude ( atmospheric depth 600 g/cm2 ) and the full coverage ensure a very low primary photon energy threshold at few hundreds GeV (close to the limits of the satellite technology), while the detector time resolution st 1ns gives a good pointing accuracy, thus allowing a high sensitivity to g -ray sources. Moreover the large eld of view and the high duty-cycle ensure the continuous monitoring of the sky in the declination band 20 d 80 . The detector layout, performance and location, offer a unique possibility to make also a deep study of several characteristics of the hadronic component of the cosmic ray ux up to energies of hundreds of TeV. In particular, the structure of the shower core, the lateral distribution, the energy spectra and the angular (e.g. anisotropies) and time (e.g. solar ares) ux modulations can be measured with high sensitivity. Moreover, the use of a full coverage detector with a high space granularity gives detailed images of the shower front, that can be used to test different hypotheses on the cosmic ray interactions, the shower development in the atmosphere and particle physics at very high energies. In this work the general layout of the detector and its performance will be described, together with some of the rst results coming from the data analysis of a relevant fraction of the apparatus that is already operating

Search for emission of gamma-ray bursts with the ARGO-YBJ detector

The ARGO-YBJ experiment has been designed to decrease the energy threshold of tipical Extensive Air Shower arrays by exploiting the high altitude location (Tibet P.R. China, 4300 m a.s..l.) and the full coverage. The lower energy limit of the detector (a few GeV) is reached with the single particle technique, recording the counting rate at fixed time intervals. We present the first results concerning the search for emission from Gamma-Ray Bursts in coincidence with satellite detections

First results on the angular resolution of the ARGO-YBJ detector

We present the first results on the angular resolution of the ARGO-YBJ detector in data taking at the Yangbajing Laboratory (Tibet, P.R. China, 4300 m a.s.l.)

Status of the ARGO-YBJ experiment

The ARGO-YBJ experiment, under construction at the Yangbaijing Laboratory (P.R. China, 4300 m a.s.l.), is a full coverage detector of dimension 74£78 m2 made by a single layer of Resistive Plate Counters. About 10% of the final active area (» 700 m2) is in stable operation to check the detector performance and the reconstruction algorithms. In this paper the status of the experiment and the analysis of the first data are presented