47,941 research outputs found
Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
The main background above 3\,MeV for in-beam nuclear astrophysics studies
with -ray detectors is caused by cosmic-ray induced secondaries. The
two commonly used suppression methods, active and passive shielding, against
this kind of background were formerly considered only as alternatives in
nuclear astrophysics experiments. In this work the study of the effects of
active shielding against cosmic-ray induced events at a medium deep location is
performed. Background spectra were recorded with two actively shielded HPGe
detectors. The experiment was located at 148\,m below the surface of the Earth
in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data
with the same detectors at the Earth's surface, and at depths of 45\,m and
1400\,m, respectively.Comment: Minor errors corrected; final versio
Information on the structure of the a1 from tau decay
The decay is analysed using different methods to
account for the resonance structure, which is usually ascribed to the a1. One
scenario is based on the recently developed techniques to generate axial-vector
resonances dynamically, whereas in a second calculation the a1 is introduced as
an explicit resonance. We investigate the influence of different assumptions on
the result. In the molecule scenario the spectral function is described
surprisingly well by adjusting only one free parameter. This result can be
systematically improved by adding higher order corrections to the iterated
Weinberg-Tomozawa interaction. Treating the a1 as an explicit resonance on the
other hand leads to peculiar properties
From real materials to model Hamiltonians with density matrix downfolding
Due to advances in computer hardware and new algorithms, it is now possible
to perform highly accurate many-body simulations of realistic materials with
all their intrinsic complications. The success of these simulations leaves us
with a conundrum: how do we extract useful physical models and insight from
these simulations? In this article, we present a formal theory of
downfolding--extracting an effective Hamiltonian from first-principles
calculations. The theory maps the downfolding problem into fitting information
derived from wave functions sampled from a low-energy subspace of the full
Hilbert space. Since this fitting process most commonly uses reduced density
matrices, we term it density matrix downfolding (DMD).Comment: 24 pages, 12 figures; Huihuo Zheng and Hitesh J. Changlani
contributed equally to this wor
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