3,517 research outputs found
The MEGA Advanced Compton Telescope Project
The goal of the Medium Energy Gamma-ray Astronomy (MEGA) telescope is to
improve sensitivity at medium gamma-ray energies (0.4-50 MeV) by at least an
order of magnitude over that of COMPTEL. This will be achieved with a new
compact design that allows for a very wide field of view, permitting a
sensitive all-sky survey and the monitoring of transient and variable sources.
The key science objectives for MEGA include the investigation of cosmic
high-energy particle accelerators, studies of nucleosynthesis sites using
gamma-ray lines, and determination of the large-scale structure of galactic and
cosmic diffuse background emission. MEGA records and images gamma-ray events by
completely tracking both Compton and pair creation interactions in a tracker of
double-sided silicon strip detectors and a calorimeter of CsI crystals able to
resolve in three dimensions. We present initial laboratory calibration results
from a small prototype MEGA telescope.Comment: 7 pages LaTeX, 5 figures, to appear in New Astronomy Reviews
(Proceedings of the Ringberg Workshop "Astronomy with Radioactivities III"
Development of Silicon Strip Detectors for a Medium Energy Gamma-ray Telescope
We report on the design, production, and testing of advanced double-sided
silicon strip detectors under development at the Max-Planck-Institute as part
of the Medium Energy Gamma-ray Astronomy (MEGA) project. The detectors are
designed to form a stack, the "tracker," with the goal of recording the paths
of energetic electrons produced by Compton-scatter and pair-production
interactions. Each layer of the tracker is composed of a 3 x 3 array of 500
micron thick silicon wafers, each 6 cm x 6 cm and fitted with 128 orthogonal p
and n strips on opposite sides (470 micron pitch). The strips are biased using
the punch-through principle and AC-coupled via metal strips separated from the
strip implant by an insulating oxide/nitride layer. The strips from adjacent
wafers in the 3 x 3 array are wire-bonded in series and read out by 128-channel
TA1.1 ASICs, creating a total 19 cm x 19 cm position-sensitive area. At 20
degrees C a typical energy resolution of 15-20 keV FWHM, a position resolution
of 290 microns, and a time resolution of ~1 microsec is observed.Comment: 9 pages, 13 figures, to appear in NIM-A (Proceedings of the 9th
European Symposium on Semiconductor Detectors
Tests of the Equivalence Principle with Neutral Kaons
We test the Principle of Equivalence for particles and antiparticles, using
CPLEAR data on tagged K0 and K0bar decays into pi^+ pi^-. For the first time,
we search for possible annual, monthly and diurnal modulations of the
observables |eta_{+-}| and phi_{+-}, that could be correlated with variations
in astrophysical potentials. Within the accuracy of CPLEAR, the measured values
of |eta_{+-}| and phi_{+-} are found not to be correlated with changes of the
gravitational potential. We analyze data assuming effective scalar, vector and
tensor interactions, and we conclude that the Principle of Equivalence between
particles and antiparticles holds to a level of 6.5, 4.3 and 1.8 x 10^{-9},
respectively, for scalar, vector and tensor potentials originating from the Sun
with a range much greater than the distance Earth-Sun. We also study
energy-dependent effects that might arise from vector or tensor interactions.
Finally, we compile upper limits on the gravitational coupling difference
between K0 and K0bar as a function of the scalar, vector and tensor interaction
range.Comment: 15 pages latex 2e, five figures, one style file (cernart.csl)
incorporate
Test of CPT Symmetry and Quantum Mechanics with Experimental data from CPLEAR
We use fits to recent published CPLEAR data on neutral kaon decays to
and to constrain the CPT--violation parameters
appearing in a formulation of the neutral kaon system as an open
quantum-mechanical system. The obtained upper limits of the CPT--violation
parameters are approaching the range suggested by certain ideas concerning
quantum gravity.Comment: 9 pages of uuencoded postscript (includes 3 figures
Performance of a spaghetti calorimeter prototype with tungsten absorber and garnet crystal fibres
A spaghetti calorimeter (SPACAL) prototype with scintillating crystal fibres was assembled and tested with electron beams of energy from 1 to 5 GeV. The prototype comprised radiation-hard Cerium-doped GdAlGaO (GAGG:Ce) and YAlO (YAG:Ce) embedded in a pure tungsten absorber. The energy resolution was studied as a function of the incidence angle of the beam and found to be of the order of 10%/E⊕1%, in line with the LHCb Shashlik technology. The time resolution was measured with metal channel dynode photomultipliers placed in contact with the fibres or coupled via a light guide, additionally testing an optical tape to glue the components. Time resolution of a few tens of picosecond was achieved for all the energies reaching down to (18.5 ± 0.2) ps at 5 GeV.We acknowledge support by the CERN Strategic Programme on Technologies for Future Experiments, https://ep-rnd.web.cern.ch/, by the MCIN/AEI, GenCat and GVA (Spain), and by the NSFC (China) under grant Nos. 12175005, 12061141007. The measurements were performed at the Test Beam Facility at DESY Hamburg (Germany), a member of the Helmholtz Association (HGF). The authors would like to thank T. Schneider, H. Gerwig, N. Siegrist, and D. Deyrail (CERN) for their help in designing and assembling the prototype and the set-up, A. Barnyakov, Budker Institute of Nuclear Physics (BINP), Novosibirsk, for kindly providing the MCPs, and the ITEP ATLAS group for the DWCs
First-forbidden mirror beta-decays in A=17 mass region
The first-forbidden beta-decay of 17Ne into the 'halo' state J=1/2+ of 17F
presents one of the largest measured asymmetries for mirror beta-decay feeding
bound final states. This asymmetry is studied in the framework of the Shell
Model Embedded in the Continuum (SMEC). The spatial extent of single particle
orbits is constrained by the proton capture cross-section 16O(p,gamma)17F
calculated in SMEC . This allows to estimate the mirror symmetry breaking in
17F/17O and 17Ne/17N nuclei.Comment: 23 pages, 7 figures Misprints correcte
The role of advance directives in end-of-life decisions in Austria: survey of intensive care physicians
<p>Abstract</p> <p>Background</p> <p>Currently, intensive care medicine strives to define a generally accepted way of dealing with end-of-life decisions, therapy limitation and therapy discontinuation.</p> <p>In 2006 a new advance directive legislation was enacted in Austria. Patients may now document their personal views regarding extension of treatment. The aim of this survey was to explore Austrian intensive care physicians' experiences with and their acceptance of the new advance directive legislation two years after enactment (2008).</p> <p>Methods</p> <p>Under the aegis of the OEGARI (Austrian Society of Anaesthesiology, Resuscitation and Intensive Care) an anonymised questionnaire was sent to the medical directors of all intensive care units in Austria. The questions focused on the physicians' experiences regarding advance directives and their level of knowledge about the underlying legislation.</p> <p>Results</p> <p>There were 241 questionnaires sent and 139 were turned, which was a response rate of 58%. About one third of the responders reported having had no experience with advance directives and only 9 directors of intensive care units had dealt with more than 10 advance directives in the previous two years. Life-supporting measures, resuscitation, and mechanical ventilation were the predominantly refused therapies, wishes were mainly expressed concerning pain therapy.</p> <p>Conclusion</p> <p>A response rate of almost 60% proves the great interest of intensive care professionals in making patient-oriented end-of-life decisions. However, as long as patients do not make use of their right of co-determination, the enactment of the new law can be considered only a first important step forward.</p
Study of Z Boson Pair Production in e+e- Collisions at LEP at \sqrt{s}=189 GeV
The pair production of Z bosons is studied using the data collected by the L3
detector at LEP in 1998 in e+e- collisions at a centre-of-mass energy of 189
GeV. All the visible final states are considered and the cross section of this
process is measured to be 0.74 +0.15 -0.14 (stat.) +/- 0.04 (syst.) pb. Final
states containing b quarks are enhanced by a dedicated selection and their
production cross section is found to be 0.18 +0.09 -0.07 (stat.) +/- 0.02
(syst.) pb. Both results are in agreement with the Standard Model predictions.
Limits on anomalous couplings between neutral gauge bosons are derived from
these measurements
Search for Low Scale Gravity Effects in e+e- Collisions at LEP
Recent theories propose that quantum gravity effects may be observable at LEP
energies via gravitons that couple to Standard Model particles and propagate
into extra spatial dimensions. The associated production of a graviton and a
photon is searched for as well as the effects of virtual graviton exchange in
the processes: e+e- -> gamma gamma, ZZ, WW, mu mu, tau tau, qq and ee No
evidence for this new interaction is found in the data sample collected by the
L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1
TeV on the scale of this new scenario of quantum gravity are set
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