5,070 research outputs found
Considerations for an Ac Dipole for the LHC
Following successful experience at the BNL AGS, FNAL Tevatron, and CERN SPS,
an AC Dipole will be adopted at the LHC for rapid measurements of ring optics.
This paper describes some of the parameters of the AC dipole for the LHC,
scaling from performance of the FNAL and BNL devices.Comment: proceedings of the 2007 Particle Accelerator Conferenc
Efficient numerical diagonalization of hermitian 3x3 matrices
A very common problem in science is the numerical diagonalization of
symmetric or hermitian 3x3 matrices. Since standard "black box" packages may be
too inefficient if the number of matrices is large, we study several
alternatives. We consider optimized implementations of the Jacobi, QL, and
Cuppen algorithms and compare them with an analytical method relying on
Cardano's formula for the eigenvalues and on vector cross products for the
eigenvectors. Jacobi is the most accurate, but also the slowest method, while
QL and Cuppen are good general purpose algorithms. The analytical algorithm
outperforms the others by more than a factor of 2, but becomes inaccurate or
may even fail completely if the matrix entries differ greatly in magnitude.
This can mostly be circumvented by using a hybrid method, which falls back to
QL if conditions are such that the analytical calculation might become too
inaccurate. For all algorithms, we give an overview of the underlying
mathematical ideas, and present detailed benchmark results. C and Fortran
implementations of our code are available for download from
http://www.mpi-hd.mpg.de/~globes/3x3/ .Comment: 13 pages, no figures, new hybrid algorithm added, matches published
version, typo in Eq. (39) corrected; software library available at
http://www.mpi-hd.mpg.de/~globes/3x3
Phonon-Metamorphosis in Ferromagnetic Manganite Films: Probing the Evolution of an Inhomogeneous State
The analysis of phonon anomalies provides valuable information about the
cooperative dynamics of lattice, spin and charge degrees of freedom.
Significant is the anomalous temperature dependence of the external modes
observed in LaSrMnO (LSMO) films. The two external modes
merge close to the ferromagnetic to paramagnetic transition at and,
moreover, two new modes evolve in this temperature range with strong resonances
at slightly higher frequencies. We propose that this observed phonon
metamorphosis probes the inhomogeneous Jahn-Teller distortion, manifest on the
temperature scale . The analysis is based on the first observation of all
eight phonon modes in the metallic phase of LSMO and on susceptibility
measurements which identify a Griffiths-like phase.Comment: 4 pages, 4 figure
Cosmic-ray propagation properties for an origin in SNRs
We have studied the impact of cosmic-ray acceleration in SNR on the spectra
of cosmic-ray nuclei in the Galaxy using a series expansion of the propagation
equation, which allows us to use analytical solutions for part of the problem
and an efficient numerical treatment of the remaining equations and thus
accurately describes the cosmic-ray propagation on small scales around their
sources in three spatial dimensions and time. We found strong variations of the
cosmic-ray nuclei flux by typically 20% with occasional spikes of much higher
amplitude, but only minor changes in the spectral distribution. The locally
measured spectra of primary cosmic rays fit well into the obtained range of
possible spectra. We further showed that the spectra of the secondary element
Boron show almost no variations, so that the above findings also imply
significant fluctuations of the Boron-to-Carbon ratio. Therefore the commonly
used method of determining CR propagation parameters by fitting
secondary-to-primary ratios appears flawed on account of the variations that
these ratios would show throughout the Galaxy.Comment: Accepted for publication in Ap
EURONU WP6 2009 yearly report: Update of the physics potential of Nufact, superbeams and betabeams
Many studies in the last ten years have shown that we can measure the unknown
angle theta13, discover leptonic CP violation and determine the neutrino
hierarchy in more precise neutrino oscillation experiments, searching for the
subleading channel nue -> numu in the atmospheric range. In this first report
of WP6 activities the following new results are reviewed: (1) Re-evaluation of
the physics reach of the upcoming generation of experiments to measure theta13
and delta; (2) New tools to explore a larger parameter space as needed beyond
the standard scenario; (3) Neutrino Factory: (a) evaluation of the physics
reach of a Nufact regards sterile neutrinos; (b) evaluation of the physics
reach of a Nufact as regards non-standard interactions; (c) evaluation of the
physics reach of a Nufact as regards violation of unitarity; (d) critical
assessment on long baseline tau-detection at Nufact; (e) new physics searches
at a near detector in a Nufact; (4) Beta-beams: (a) choice of ions and location
for a gamma = 100 CERN-based beta-beam; (b) re-evaluation of atmospheric
neutrino background for the gamma = 100 beta-beam scenario; (c) study of a two
baseline beta-beam; (d) measuring absolute neutrino mass with beta-beams; (e)
progress on monochromatic beta-beams; (5) Update of the physics potential of
the SPL super-beam. Eventually, we present an updated comparison of the
sensitivity to theta13, delta and the neutrino mass hierarchy of several of the
different proposed facilities.Comment: 2009 Yearly report of the Working Package 6 (Physics) of the EUROnu
FP7 EU project. 55 pages, 21 figures
Neutrino oscillations: Quantum mechanics vs. quantum field theory
A consistent description of neutrino oscillations requires either the
quantum-mechanical (QM) wave packet approach or a quantum field theoretic (QFT)
treatment. We compare these two approaches to neutrino oscillations and discuss
the correspondence between them. In particular, we derive expressions for the
QM neutrino wave packets from QFT and relate the free parameters of the QM
framework, in particular the effective momentum uncertainty of the neutrino
state, to the more fundamental parameters of the QFT approach. We include in
our discussion the possibilities that some of the neutrino's interaction
partners are not detected, that the neutrino is produced in the decay of an
unstable parent particle, and that the overlap of the wave packets of the
particles involved in the neutrino production (or detection) process is not
maximal. Finally, we demonstrate how the properly normalized oscillation
probabilities can be obtained in the QFT framework without an ad hoc
normalization procedure employed in the QM approach.Comment: LaTeX, 42 pages, 1 figure; v2: minor clarifications, matches
published version; v3: Corrected the discussion of the conditions under which
an oscillation probability can be sensibly defined in the QFT approach (sec.
5.2.4
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