2,275 research outputs found
A GaAs-based self-aligned stripe distributed feedback laser
We demonstrate operation of a GaAs-based self-aligned stripe (SAS) distributed feedback (DFB) laser. In this structure, a first order GaInP/GaAs index-coupled DFB grating is built within the p-doped AlGaAs layer between the active region and the n-doped GaInP opto-electronic confinement layer of a SAS laser structure. In this process no Al-containing layers are exposed to atmosphere prior to overgrowth. The use of AlGaAs cladding affords the luxury of full flexibility in upper cladding design, which proved necessary due to limitations imposed by the grating infill and overgrowth with the GaInP current block layer. Resultant devices exhibit single-mode lasing with high side-mode-suppression of >40 dB over the temperature range 20 °C–70 °C. The experimentally determined optical profile and grating confinement correlate well with those simulated using Fimmwave
Rim inertial measuring system
The invention includes an angular momentum control device (AMCD) having a rim and several magnetic bearing stations. The AMCD is in a strapped down position on a spacecraft. Each magnetic bearing station comprises means, including an axial position sensor, for controlling the position of the rim in the axial direction; and means, including a radial position sensor, for controlling the position of the rim in the radial direction. A first computer receives the signals from all the axial position sensors and computes the angular rates about first and second mutually perpendicular axes in the plane of the rim and computes the linear acceleration along a third axis perpendicular to the first and second axes. A second computer receives the signals from all the radial position sensors and computes the linear accelerations along the first and second axes
Flavor independent systematics of excited baryons and intra-band transition
Transitions among excited nucleons are studied within a non-relativistic
quark model with a deformed harmonic oscillator potential. The transition
amplitudes are factorized into the -th moment and a geometrical factor. This
fact leads to an analogous result to the ``Alaga-rule'' for baryons.Comment: 4 Pages, 2 figures, Talk given at XVI International Conference on
Particles and Nuclei (PaNic02), Osaka, Japan, Sep.30 - Oct.4, 200
A 25 Input Pulse Height Recording System
A general description is given of a data recording system which provides a link between counter experiments in high-energy physics and a high-speed digital computer. The instrument described can accept as many as 25 simultaneous photomultiplier tube signals and pulse height analyze them into 100 channels each. Six bits of digital data may be substituted for any unused pulse height input. The usual output is perforated paper tape with a binary coded decimal format for use with a Burroughs 220 computer. Identification words can be set up and recorded on the tape. The speed of the paper tape perforator limits the rate of analysis to one event per second. If the output data is fed directly into a computer memory, then the recording rate can be increased to 60 events per second. The instrument has been in operation since December 1961, and results obtained with it using both particles produced by the Caltech Synchrotron and pulsers are given. Only solid state components have been used, including nearly 1700 transistors and an equal number of diodes
A method to polarise antiprotons in storage rings and create polarised antineutrons
An intense circularely polarised photon beam interacts with a cooled
antiproton beam in a storage ring. Due to spin dependent absorption cross
sections for the reaction gamma+antiproton > pi- + antineutron a built-up of
polarisation of the stored antiprotons takes place. Figures-of-merit around 0.1
can be reached in principle over a wide range of antiproton energies. In this
process antineutrons with Polarisation > 70% emerge. The method is presented
for the case of 300 MeV/c cooled antiproton beam
Exotic mesons from quantum chromodynamics with improved gluon and quark actions on the anisotropic lattice
Hybrid (exotic) mesons, which are important predictions of quantum
chromodynamics (QCD), are states of quarks and anti-quarks bound by excited
gluons. First principle lattice study of such states would help us understand
the role of ``dynamical'' color in low energy QCD and provide valuable
information for experimental search for these new particles. In this paper, we
apply both improved gluon and quark actions to the hybrid mesons, which might
be much more efficient than the previous works in reducing lattice spacing
error and finite volume effect. Quenched simulations were done at
and on a anisotropic lattice using our PC cluster. We
obtain MeV for the mass of the hybrid meson
in the light quark sector, and Mev in the
charm quark sector; the mass splitting between the hybrid meson in the charm quark sector and the spin averaged S-wave charmonium mass
is estimated to be MeV. As a byproduct, we obtain MeV for the mass of a P-wave or
meson and MeV for the mass of a P-wave meson, which are comparable to their experimental value 1426 MeV for the
meson. The first error is statistical, and the second one is
systematical. The mixing of the hybrid meson with a four quark state is also
discussed.Comment: 12 pages, 3 figures. Published versio
Structure and texture of the quark mass matrix
Starting from a weak basis in which the up (or down) quark matrix is
diagonal, we obtain an exact set of equations for the quark mass matrix
elements in terms of known observables. We make a numerical analysis of the
down (up) quark mass matrix. Using the data available for the quark masses and
mixing angles at different energy scales, we found a numerical expression for
these matrices. We suggest that it is not possible to have an specific texture
from this analysis. We also examine the most general case when the complex
phases are introduced in the mass matrix. We find the numerical value for these
phases as a function of , the CP-violationg phase.Comment: 7 pages, we use the macros of Elsevie
Evidence for Neutrinoless Double Beta Decay
The data of the Heidelberg-Moscow double beta decay experiment for the
measuring period August 1990 - May 2000 (54.9813 kg y or 723.44 molyears),
published recently, are analyzed using the potential of the Bayesian method for
low counting rates. First evidence for neutrinoless double beta decay is
observed giving first evidence for lepton number violation. The evidence for
this decay mode is 97% (2.2\sigma) with the Bayesian method, and 99.8% c.l.
(3.1\sigma) with the method recommended by the Particle Data Group. The
half-life of the process is found with the Bayesian method to be T_{1/2}^{0\nu}
= (0.8 - 18.3) x 10^{25} y (95% c.l.) with a best value of 1.5 x 10^{25} y. The
deduced value of the effective neutrino mass is, with the nuclear matrix
elements from [Sta90,Tom91] = (0.11 - 0.56) eV (95% c.l.), with a best
value of 0.39 eV. Uncertainties in the nuclear matrix elements may widen the
range given for the effective neutrino mass by at most a factor 2. Our
observation which at the same time means evidence that the neutrino is a
Majorana particle, will be of fundamental importance for neutrino physics.
PACS. 14.69.Pq Neutrino mass and mixing; 23.40.Bw Weak-interaction and lepton
(including neutrino) aspects 23.40.-s Beta decay; double beta decay; electron
and muon capture.Comment: 14 pages, psfile, 7 figures, Published in Modern Physics Letters A,
Vol. 16, No. 37 (2001) 2409-2420, World Scientific Publishing Company, Home
Page: http://ejournals.wspc.com.sg/mpla/16/1637/S0217732301005825.html, Home
Page of Heidelberg Non-Accelerator Particle Physics Group:
http://www.mpi-hd.mpg.de/non_acc
Consistent analysis of the reaction and
The production of mesons in the reactions and
is described consistently within a relativistic meson exchange
model of hadronic interactions. The photoproduction can be described quite well
over the entire energy range of available data by considering an and a
resonance, in addition to the -channel mesonic current. The
observed angular distribution is due to the interference between the
-channel and the nucleon resonance - and -channel contributions. Our
analysis yields positions close to 1650 MeV and 1870 MeV for the and
resonances, respectively. We argue that, at present, identifying these
states with the known resonance and the missing
resonance predicted at 1880 MeV, respectively, would be premature. It is found
that the nucleonic current is relatively small and that the
coupling constant cannot be much larger than . As for the
reaction, different current contributions are
constrained by a combined analysis of this and the photoproduction reaction.
Difficulties to simultaneously account for the 47-MeV and 144-MeV angular
distributions measured by the COSY-11 and DISTO collaborations, respectively,
are addressed.Comment: minor revision, scheduled to a appear in Phys. Rev. C 69 (May 2004),
revtex, 17 pages, 10 figures, 3 table
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
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