6,794 research outputs found
First Results from the HDMS experiment in the Final Setup
The Heidelberg Dark Matter Search (HDMS) is an experiment designed for the
search for WIMP dark matter. It is using a special configuration of Ge
detectors, to efficiently reduce the background in the low-energy region below
100 keV. After one year of running the HDMS detector prototype in the Gran
Sasso Underground Laboratory, the inner crystal of the detector has been
replaced with a HPGe crystal of enriched Ge. The final setup started
data taking in Gran Sasso in August 2000. The performance and the first results
of the measurement with the final setup are discussed.Comment: 8 pages, revtex, 7 figures, Home Page of Heidelberg Non-Accelerator
Particle Physics Group: http://www.mpi-hd.mpg.de/non_acc
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
First experimental evidence for quantum echoes in scattering systems
A self-pulsing effect termed quantum echoes has been observed in experiments
with an open superconducting and a normal conducting microwave billiard whose
geometry provides soft chaos, i.e. a mixed phase space portrait with a large
stable island. For such systems a periodic response to an incoming pulse has
been predicted. Its period has been associated to the degree of development of
a horseshoe describing the topology of the classical dynamics. The experiments
confirm this picture and reveal the topological information.Comment: RevTex 4.0, 5 eps-figure
Encircling an Exceptional Point
We calculate analytically the geometric phases that the eigenvectors of a
parametric dissipative two-state system described by a complex symmetric
Hamiltonian pick up when an exceptional point (EP) is encircled. An EP is a
parameter setting where the two eigenvalues and the corresponding eigenvectors
of the Hamiltonian coalesce. We show that it can be encircled on a path along
which the eigenvectors remain approximately real and discuss a microwave cavity
experiment, where such an encircling of an EP was realized. Since the
wavefunctions remain approximately real, they could be reconstructed from the
nodal lines of the recorded spatial intensity distributions of the electric
fields inside the resonator. We measured the geometric phases that occur when
an EP is encircled four times and thus confirmed that for our system an EP is a
branch point of fourth order.Comment: RevTex 4.0, four eps-figures (low resolution
Anterior insula coordinates hierarchical processing of tactile mismatch responses
The body underlies our sense of self, emotion, and agency. Signals arising from the skin convey warmth, social touch, and the physical characteristics of external stimuli. Surprising or unexpected tactile sensations can herald events of motivational salience, including imminent threats (e.g., an insect bite) and hedonic rewards (e.g., a caressing touch). Awareness of such events is thought to depend upon the hierarchical integration of body-related mismatch responses by the anterior insula. To investigate this possibility, we measured brain activity using functional magnetic resonance imaging, while healthy participants performed a roving tactile oddball task. Mass-univariate analysis demonstrated robust activations in limbic, somatosensory, and prefrontal cortical areas previously implicated in tactile deviancy, body awareness, and cognitive control. Dynamic Causal Modelling revealed that unexpected stimuli increased the strength of forward connections along a caudal to rostral hierarchy-projecting from thalamic and somatosensory regions towards insula, cingulate and prefrontal cortices. Within this ascending flow of sensory information, the AIC was the only region to show increased backwards connectivity to the somatosensory cortex, augmenting a reciprocal exchange of neuronal signals. Further, participants who rated stimulus changes as easier to detect showed stronger modulation of descending PFC to AIC connections by deviance. These results suggest that the AIC coordinates hierarchical processing of tactile prediction error. They are interpreted in support of an embodied predictive coding model where AIC mediated body awareness is involved in anchoring a global neuronal workspace
Rabi Oscillations at Exceptional Points in Microwave Billiards
We experimentally investigated the decay behavior with time t of resonances
near and at exceptional points, where two complex eigenvalues and also the
associated eigenfunctions coalesce. The measurements were performed with a
dissipative microwave billiard, whose shape depends on two parameters. The
t^2-dependence predicted at the exceptional point on the basis of a two-state
matrix model could be verified. Outside the exceptional point the predicted
Rabi oscillations, also called quantum echoes in this context, were detected.
To our knowledge this is the first time that quantum echoes related to
exceptional points were observed experimentally.Comment: 10 pages, 3 figure
Non-existence of stationary two-black-hole configurations
We resume former discussions of the question, whether the spin-spin repulsion
and the gravitational attraction of two aligned black holes can balance each
other. To answer the question we formulate a boundary value problem for two
separate (Killing-) horizons and apply the inverse (scattering) method to solve
it. Making use of results of Manko, Ruiz and Sanabria-G\'omez and a novel black
hole criterion, we prove the non-existence of the equilibrium situation in
question.Comment: 15 pages, 3 figures; Contribution to Juergen Ehlers Memorial Issue
(GeRG journal
Experimental Test of a Trace Formula for a Chaotic Three Dimensional Microwave Cavity
We have measured resonance spectra in a superconducting microwave cavity with
the shape of a three-dimensional generalized Bunimovich stadium billiard and
analyzed their spectral fluctuation properties. The experimental length
spectrum exhibits contributions from periodic orbits of non-generic modes and
from unstable periodic orbit of the underlying classical system. It is well
reproduced by our theoretical calculations based on the trace formula derived
by Balian and Duplantier for chaotic electromagnetic cavities.Comment: 4 pages, 5 figures (reduced quality
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