4,621 research outputs found
The structure and kinematics of the the Galaxy thin gaseous disc outside the solar orbit
The rotation curve of the Galaxy is generally thought to be flat. However,
using radial velocities from interstellar molecular clouds, which is common in
rotation curve determination, seems to be incorrect and may lead to incorrectly
inferring that the rotation curve is flat indeed. Tests basing on photometric
and spectral observations of bright stars may be misleading. The rotation
tracers (OB stars) are affected by motions around local gravity centers and
pulsation effects seen in such early type objects. To get rid of the latter a
lot of observing work must be involved. We introduce a method of studying the
kinematics of the thin disc of our Galaxy outside the solar orbit in a way that
avoids these problems. We propose a test based on observations of interstellar
CaII H and K lines that determines both radial velocities and distances. We
implemented the test using stellar spectra of thin disc stars at galactic
longitudes of 135{\degr} and 180{\degr}. Using this method, we constructed the
rotation curve of the thin disc of the Galaxy. The test leads to the obvious
conclusion that the rotation curve of the thin gaseous galactic disk,
represented by the CaII lines, is Keplerian outside the solar orbit rather than
flat.Comment: 33 pages, 18 figures, accepted for publication in Publications of the
Astronomical Society of the Pacific, 2015. February
First operation of a double phase LAr Large Electron Multiplier Time Projection Chamber with a two-dimensional projective readout anode
We have previously reported on the construction and successful operation of
the novel double phase Liquid Argon Large Electron Multiplier Time Projection
Chamber (LAr LEM-TPC). This detector concept provides a 3D-tracking and
calorimetric device capable of adjustable charge amplification, a promising
readout technology for next-generation neutrino detectors and direct Dark
Matter searches. In this paper, we report on the first operation of a LAr
LEM-TPC prototype - with an active area of 1010 cm and 21 cm drift
length - equipped with a single 1 mm thick LEM amplifying stage and a two
dimensional projective readout anode. Cosmic muon events were collected, fully
reconstructed and used to characterize the performance of the chamber. The
obtained signals provide images of very high quality and the energy loss
distributions of minimum ionizing tracks give a direct estimate of the
amplification. We find that a stable gain of 27 can be achieved with this
detector configuration corresponding to a signal-over-noise ratio larger than
200 for minimum ionizing tracks. The decoupling of the amplification stage and
the use of the 2D readout anode offer several advantages which are described in
the text.Comment: 25 pages, 17 figure
Explicit volume-preserving numerical schemes for relativistic trajectories and spin dynamics
A class of explicit numerical schemes is developed to solve for the
relativistic dynamics and spin of particles in electromagnetic fields, using
the Lorentz-BMT equation formulated in the Clifford algebra representation of
Baylis. It is demonstrated that these numerical methods, reminiscent of the
leapfrog and Verlet methods, share a number of important properties: they are
energy-conserving, volume-conserving and second order convergent. These
properties are analysed empirically by benchmarking against known analytical
solutions in constant uniform electrodynamic fields. It is demonstrated that
the numerical error in a constant magnetic field remains bounded for long time
simulations in contrast to the Boris pusher, whose angular error increases
linearly with time. Finally, the intricate spin dynamics of a particle is
investigated in a plane wave field configuration.Comment: 15 pages, 9 figure
THGEM operation in Ne and Ne/CH4
The operation of Thick Gaseous Electron Multipliers (THGEM) in Ne and Ne/CH4
mixtures, features high multiplication factors at relatively low operation
potentials, in both single- and double-THGEM configurations. We present some
systematic data measured with UV-photons and soft x-rays, in various Ne
mixtures. It includes gain dependence on hole diameter and gas purity,
photoelectron extraction efficiency from CsI photocathodes into the gas,
long-term gain stability and pulse rise-time. Position resolution of a 100x100
mm^2 X-rays imaging detector is presented. Possible applications are discussed.Comment: Submitted to JINST, 25 pages, 33 figure
Large-Mass Ultra-Low Noise Germanium Detectors: Performance and Applications in Neutrino and Astroparticle Physics
A new type of radiation detector, a p-type modified electrode germanium
diode, is presented. The prototype displays, for the first time, a combination
of features (mass, energy threshold and background expectation) required for a
measurement of coherent neutrino-nucleus scattering in a nuclear reactor
experiment. The device hybridizes the mass and energy resolution of a
conventional HPGe coaxial gamma spectrometer with the low electronic noise and
threshold of a small x-ray semiconductor detector, also displaying an intrinsic
ability to distinguish multiple from single-site particle interactions. The
present performance of the prototype and possible further improvements are
discussed, as well as other applications for this new type of device in
neutrino and astroparticle physics (double-beta decay, neutrino magnetic moment
and WIMP searches).Comment: submitted to Phys. Rev.
Performance of the Muon Identification at LHCb
The performance of the muon identification in LHCb is extracted from data
using muons and hadrons produced in J/\psi->\mu\mu, \Lambda->p\pi and
D^{\star}->\pi D0(K\pi) decays. The muon identification procedure is based on
the pattern of hits in the muon chambers. A momentum dependent binary
requirement is used to reduce the probability of hadrons to be misidentified as
muons to the level of 1%, keeping the muon efficiency in the range of 95-98%.
As further refinement, a likelihood is built for the muon and non-muon
hypotheses. Adding a requirement on this likelihood that provides a total muon
efficiency at the level of 93%, the hadron misidentification rates are below
0.6%.Comment: 17 pages, 10 figure
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