1,091 research outputs found
Recurrence Spectroscopy: Observation and Interpretation of Large-Scale Structure in the Absorption Spectra of Atoms in Magnetic Fields
Measurements were made of the absorption spectrum of hydrogen atoms to levels near the ionization threshold in a strong magnetic field. Taking advantage of a classical scaling law, we varied the photon energy and the magnetic-field strength simultaneously, and measured absorption versus B−1/3 at fixed scaled energy, ɛ=E/(B/Bo)2/3. The absorption rate has sinusoidal fluctuations which are correlated with closed classical orbits of the electron. Fourier transformation of this signal gives peaks, which we interpret as ‘‘recurrence strength,’’ as a function of the classical action of the closed orbit. Closed-orbit theory gives formulas for these recurrence strengths. We find that the formulas are in good agreement with the measurements. As the scaled energy is increased, observed recurrences proliferate, consistent with a change from orderly to chaotic motion of the electron. Bifurcation theory provides organizing principles for understanding this proliferation and for interpreting the data. New ‘‘exotic’’ orbits suddenly appear through saddle-node bifurcations. The ‘‘main sequence’’ of orbits is produced from an orbit parallel to B through a sequence of pitchfork and period-doubling bifurcations. Other recurrences are created by period-tripling and higher-order bifurcations of existing orbits. These bifurcations can have ‘‘generic’’ structure, or sometimes the structures are modified by symmetries of the system. Focusing effects associated with these bifurcations cause some recurrences to be particularly strong
Detecting the Neutrino Mass Hierarchy with a Supernova at IceCube
IceCube, a future km^3 antarctic ice Cherenkov neutrino telescope, is highly
sensitive to a galactic supernova (SN) neutrino burst. The Cherenkov light
corresponding to the total energy deposited by the SN neutrinos in the ice can
be measured relative to background fluctuations with a statistical precision
much better than 1%. If the SN is viewed through the Earth, the matter effect
on neutrino oscillations can change the signal by more than 5%, depending on
the flavor-dependent source spectra and the neutrino mixing parameters.
Therefore, IceCube together with another high-statistics experiment like
Hyper-Kamiokande can detect the Earth effect, an observation that would
identify specific neutrino mixing scenarios that are difficult to pin down with
long-baseline experiments. In particular, the normal mass hierarchy can be
clearly detected if the third mixing angle is not too small, sin^2 theta_13 <
10^-3. The small flavor-dependent differences of the SN neutrino fluxes and
spectra that are found in state-of-the-art simulations suffice for this
purpose. Although the absolute calibration uncertainty at IceCube may exceed
5%, the Earth effect would typically vary by a large amount over the duration
of the SN signal, obviating the need for a precise calibration. Therefore,
IceCube with its unique geographic location and expected longevity can play a
decisive role as a "co-detector" to measure SN neutrino oscillations. It is
also a powerful stand-alone SN detector that can verify the delayed-explosion
scenario.Comment: 19 pages, 6 Figs, final version accepted by JCAP, some references
adde
Symmetry breaking in crossed magnetic and electric fields
We present the first observations of cylindrical symmetry breaking in highly
excited diamagnetic hydrogen with a small crossed electric field, and we give a
semiclassical interpretation of this effect. As the small perpendicular
electric field is added, the recurrence strengths of closed orbits decrease
smoothly to a minimum, and revive again. This phenomenon, caused by
interference among the electron waves that return to the nucleus, can be
computed from the azimuthal dependence of the classical closed orbits.Comment: 4 page REVTeX file including 5 postscript files (using psfig)
Accepted for publication in Physical Review Letters. Difference from earlier
preprint: we have discovered the cause of the earlier apparent discrepancy
between experiment and theory and now achieve excellent agreemen
The Hydrogen Atom in Combined Electric and Magnetic Fields with Arbitrary Mutual Orientations
For the hydrogen atom in combined magnetic and electric fields we investigate
the dependence of the quantum spectra, classical dynamics, and statistical
distributions of energy levels on the mutual orientation of the two external
fields. Resonance energies and oscillator strengths are obtained by exact
diagonalization of the Hamiltonian in a complete basis set, even far above the
ionization threshold. At high excitation energies around the Stark saddle point
the eigenenergies exhibit strong level repulsions when the angle between the
fields is varied. The large avoided crossings occur between states with the
same approximately conserved principal quantum number, n, and this
intramanifold mixing of states cannot be explained, not even qualitatively, by
conventional perturbation theory. However, it is well reproduced by an extended
perturbation theory which takes into account all couplings between the angular
momentum and Runge-Lenz vector. The large avoided crossings are interpreted as
a quantum manifestation of classical intramanifold chaos. This interpretation
is supported by both classical Poincar\'e surfaces of section, which reveal a
mixed regular-chaotic intramanifold dynamics, and the statistical analysis of
nearest-neighbor-spacingComment: two-column version, 10 pages, REVTeX, 10 figures, uuencoded,
submitted to Rhys. Rev.
Lowering IceCube's energy threshold for point source searches in the Southern Sky
Observation of a point source of astrophysical neutrinos would be a "smoking gun" signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current ν μ interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (~100 TeV) starting event in the sample found that this event alone represents a 2.8σ deviation from the hypothesis that the data consists only of atmospheric background.Fil: Aartsen, M. G.. University of Adelaide; AustraliaFil: Abraham, K.. Technische Universität München; AlemaniaFil: Ackermann, M.. Deutsches Elektronen-Synchrotron; AlemaniaFil: Adams, J.. University Of Canterbury; Nueva ZelandaFil: Aguilar, J. A.. Université Libre de Bruxelles; BélgicaFil: Golup, Geraldina Tamara. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Wallace, A.. University of Adelaide; AustraliaFil: Wallraff, M.. Rwth Aachen University; AlemaniaFil: Wandkowsky, N.. University of Wisconsin; Estados UnidosFil: Weaver, Ch.. University of Alberta; CanadáFil: Wendt, C.. University of Wisconsin; Estados UnidosFil: Westerhoff, S.. University of Wisconsin; Estados UnidosFil: Whelan, B. J.. University of Adelaide; AustraliaFil: Whitehorn, N.. University of California at Berkeley; Estados UnidosFil: Wickmann, S.. Rwth Aachen University; AlemaniaFil: Wiebe, K.. Johannes Gutenberg Universitat Mainz; AlemaniaFil: Wiebusch, C. H.. Rwth Aachen University; AlemaniaFil: Wille, L.. University of Wisconsin; Estados UnidosFil: Williams, D. R.. University of Alabama at Birmingahm; Estados UnidosFil: Wills, L.. Drexel University; Estados UnidosFil: Wissing, H.. University of Maryland; Estados UnidosFil: Wolf, M.. Stockholms Universitet; SueciaFil: Wood, T. R.. University of Alberta; CanadáFil: Woschnagg, K.. University of California at Berkeley; Estados UnidosFil: Xu, D. L.. University of Wisconsin; Estados UnidosFil: Xu, X. W.. Southern University; Estados UnidosFil: Xu, Y.. Stony Brook University; Estados UnidosFil: Yanez, J. P.. Deutsches Elektronen-Synchrotron; AlemaniaFil: Yodh, G.. University of California at Irvine; Estados UnidosFil: Yoshida, S.. Chiba University; JapónFil: Zoll, M.. Stockholms Universitet; Sueci
The AMANDA Neutrino Telescope
With an effective telescope area of order m for TeV neutrinos, a
threshold near 50 GeV and a pointing accuracy of 2.5 degrees per muon
track, the AMANDA detector represents the first of a new generation of high
energy neutrino telescopes, reaching a scale envisaged over 25 years ago. We
describe early results on the calibration of natural deep ice as a particle
detector as well as on AMANDA's performance as a neutrino telescope.Comment: 12 pages, Latex2.09, uses espcrc2.sty and epsf.sty, 13 postscript
files included. Talk presented at the 18th International Conference on
Neutrino Physics and Astrophysics (Neutrino 98), Takayama, Japan, June 199
Electroweak Precision Observables within a Fourth Generation Model with General Flavour Structure
We calculate the contributions to electroweak precision observables (EWPOs)
due to a fourth generation of fermions with the most general (quark-)flavour
structure (but assuming Dirac neutrinos and a trivial flavour structure in the
lepton sector). The new-physics contributions to the EWPOs are calculated at
one-loop order using automated tools (FeynArts/FormCalc). No further
approximations are made in our calculation. We discuss the size of non-oblique
contributions arising from Z--quark--anti-quark vertex corrections and the
dependence of the EWPOs on all CKM mixing angles involving the fourth
generation. We find that the electroweak precision observables are sensitive to
two of the fourth-generation mixing angles and that the corresponding
constraints on these angles are competitive with those obtained from flavour
physics. For non-trivial 4x4 flavour structures, the non-oblique contributions
lead to relative corrections of several permille and should be included in a
global fit
Comparison of large-angle production of charged pions with incident protons on cylindrical long and short targets
The HARP collaboration has presented measurements of the double-differential
pi+/pi- production cross-section in the range of momentum 100 MeV/c <= p 800
MeV/c and angle 0.35 rad <= theta <= 2.15 rad with proton beams hitting thin
nuclear targets. In many applications the extrapolation to long targets is
necessary. In this paper the analysis of data taken with long (one interaction
length) solid cylindrical targets made of carbon, tantalum and lead is
presented. The data were taken with the large acceptance HARP detector in the
T9 beam line of the CERN PS. The secondary pions were produced by beams of
protons with momenta 5 GeV/c, 8 GeV/c and 12 GeV/c. The tracking and
identification of the produced particles were performed using a small-radius
cylindrical time projection chamber (TPC) placed inside a solenoidal magnet.
Incident protons were identified by an elaborate system of beam detectors.
Results are obtained for the double-differential yields per target nucleon d2
sigma / dp dtheta. The measurements are compared with predictions of the MARS
and GEANT4 Monte Carlo simulations.Comment: 43 pages, 20 figure
The History of Astrophysics in Antarctica
We examine the historical development of astrophysical science in Antarctica
from the early 20th century until today. We find three temporally overlapping
eras, each having a rather distinct beginning. These are the astrogeological
era of meteorite discovery, the high energy era of particle detectors, and the
photon astronomy era of microwave, sub--mm and infrared telescopes, sidelined
by a few niche experiments at optical wavelengths. The favourable atmospheric
and geophysical conditions are briefly examined, followed by an account of the
major experiments and a summary of their results.Comment: 29 pages, 10 figures, 1 table Submitted to PASA in April 200
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