6,039 research outputs found
A triple GEM detector with two dimensional readout
The triple GEM detector is a micropattern gas detector which consists of a
primary ionisation gap and three consecutive gas electron multiplier (GEM)
foils. A printed circuit board with readout strips detects the current induced
by the drifting electron cloud originating from the last GEM stage. Thus the
gas amplification and the signal readout are completely separated. Triple GEM
detectors are being developed as a possible technology for the inner tracking
in the LHCb experiment.
In an earlier note we have reported first experience with such a detector in
a test beam at PSI. Here we describe the construction of an improved version
(thinner transfer gaps, segmented GEM foils, two dimensional readout). Results
from performance measurements are presented using intense hadronic beams as
well as cosmic ray data.Comment: 20 pages, 24 figure
Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection
The equations for fully compressible rotating magnetoconvection are
numerically solved in a Cartesian box assuming conditions roughly suitable for
the geodynamo. The mean electromotive force describing the generation of mean
magnetic flux by convective turbulence in the rotating fluid is directly
calculated from the simulations, and the corresponding alpha-coefficients are
derived. Due to the very weak density stratification the alpha-effect changes
its sign in the middle of the box. It is positive at the top and negative at
the bottom of the convection zone. For strong magnetic fields we also find a
clear downward advection of the mean magnetic field. Both of the simulated
effects have been predicted by quasi-linear computations (Soward, 1979;
Kitchatinov and Ruediger, 1992). Finally, the possible connection of the
obtained profiles of the EMF with mean-field models of oscillating
alpha^2-dynamos is discussed.Comment: 17 pages, 9 figures, submitted to Phys. Earth Planet. Inte
Two-component Bose gas in an optical lattice at single-particle filling
The Bose-Hubbard model of a two-fold degenerate Bose gas is studied in an
optical lattice with one particle per site and virtual tunneling to empty and
doubly-occupied sites. An effective Hamiltonian for this system is derived
within a continued-fraction approach. The ground state of the effective model
is studied in mean-field approximation for a modulated optical lattice. A
dimerized mean-field state gives a Mott insulator whereas the lattice without
modulations develops long-range correlated phase fluctuations due to a
Goldstone mode. This result is discussed in comparison with the superfluid and
the Mott-insulating state of a single-component hard-core Bose.Comment: 11 page
Charm Baryon Studies at BABAR
The authors present a precision measurement of the mass of the {Lambda}{sub c}{sup +} and studies of the production and decay of the {Omega}{sub c}{sup 0} and {Xi}{sub c}{sup 0} charm baryons using data collected by the BABAR experiment. To keep the systematic uncertainty as low as possible, the {Lambda}{sub c}{sup +} mass measurement is performed using the low Q-value decays, {Lambda}{sub c}{sup +} {yields} {Lambda}{sup 0} K{sub S}{sup 0}K{sup +} and {Lambda}{sub c}{sup +} {yields} {Sigma}{sup 0} K{sub S}{sup 0}K{sup +}. Several hadronic final states involving an {Omega}{sup -} and a {Xi}{sup -} hyperon are analyzed to reconstruct the {Xi}{sub c}{sup 0} and the {Omega}{sub c}{sup 0}
Shearingbox-implementation for the central-upwind, constraint-transport MHD-code NIRVANA
We describe the implementation of the shearingbox approach into the
Godunov-type central-upwind/constraint-transport magnetohydrodynamics code
NIRVANA. This will allow for applications which require sheared-periodic
boundary conditions as typically used in local Cartesian simulations of
differentially rotating systems. We present the algorithm in detail and discuss
necessary modifications in the numerical fluxes in order to preserve conserved
quantities and to fulfill other analytical constraints as good as seem feasible
within the numerical scheme. We check the source terms which come with the
shearingbox formulation by investigating the conservation of the epicyclic mode
energy. We also perform more realistic simulations of the magneto-rotational
instability with initial zero-net-flux vertical magnetic field and compare the
obtained stresses and energetics with previous non-conservative results
exploring the same parameter regime.Comment: 17 pages, 4 figures, to be published in CP
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