Cross-Section Fluctuations in Chaotic Scattering

For the theoretical prediction of cross-section fluctuations in chaotic scattering, the cross-section autocorrelation function is needed. That function is not known analytically. Using experimental data and numerical simulations, we show that an analytical approximation to the cross-section autocorrelation function can be obtained with the help of expressions first derived by Davis and Boose. Given the values of the average S-matrix elements and the mean level density of the scattering system, one can then reliably predict cross-section fluctuations

Status of Evidence for Neutrinoless Double Beta Decay

The present experimental status in the search for neutrinoless double beta decay is reviewed, with emphasis on the first indication for neutrinoless double beta decay found in the Heidelberg-Moscow experiment, giving first evidence for lepton number violation and a Majorana nature of the neutrinos. Future perspectives of the field are briefly outlined.Comment: 37 pages, latex, 23 figures, Published in Found. Phys. 32 (2002) 1181-1223 and Presented at Fourth Heidelberg International Conference on Dark Matter in Astro- and Particle Physics, DARK2002, Cape Town, South Africa, 4 - 9 February, 2002, eds. H.V. Klapdor-Kleingrothaus and R. Viollier, Springer-Verlag Heidelberg, (2002) 367-403 see Home Page of Heidelberg Non-Accelerator Particle Physics Group: http://www.mpi-hd.mpg.de/non_acc/buecher.html#DARK200

Search for neutrinoless double beta decay with enriched 76Ge in Gran Sasso 1990-2003

The results of the HEIDELBERG-MOSCOW experiment which searches with 11 kg of enriched 76Ge for double beta decay in the GRAN Sasso underground laboratory are presented for the full running period August 1990 - May 2003. The duty cycle of the experiment was ~80%, the collected statistics is 71.7 kg y. The background achieved in the energy region of the Q value for double beta decay is 0.11 events/ kg y keV. The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events. The confidence level for the neutrinoless signal has been improved to 4.2 sigma.Comment: 19 pages, latex, 9 figures, 2 table

Nonperiodic echoes from mushroom billiard hats

Mushroom billiards have the remarkable property to show one or more clear cut integrable islands in one or several chaotic seas, without any fractal boundaries. The islands correspond to orbits confined to the hats of the mushrooms, which they share with the chaotic orbits. It is thus interesting to ask how long a chaotic orbit will remain in the hat before returning to the stem. This question is equivalent to the inquiry about delay times for scattering from the hat of the mushroom into an opening where the stem should be. For fixed angular momentum we find that no more than three different delay times are possible. This induces striking nonperiodic structures in the delay times that may be of importance for mesoscopic devices and should be accessible to microwave experiments.Comment: Submitted to Phys. Rev. E without the appendi

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 $^{73}$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

Scattering Experiments with Microwave Billiards at an Exceptional Point under Broken Time Reversal Invariance

Scattering experiments with microwave cavities were performed and the effects of broken time-reversal invariance (TRI), induced by means of a magnetized ferrite placed inside the cavity, on an isolated doublet of nearly degenerate resonances were investigated. All elements of the effective Hamiltonian of this two-level system were extracted. As a function of two experimental parameters, the doublet and also the associated eigenvectors could be tuned to coalesce at a so-called exceptional point (EP). The behavior of the eigenvalues and eigenvectors when encircling the EP in parameter space was studied, including the geometric amplitude that builds up in the case of broken TRI. A one-dimensional subspace of parameters was found where the differences of the eigenvalues are either real or purely imaginary. There, the Hamiltonians were found PT-invariant under the combined operation of parity (P) and time reversal (T) in a generalized sense. The EP is the point of transition between both regions. There a spontaneous breaking of PT occurs