5,018 research outputs found
Leading twist contribution to color singlet decays
In this paper the leading twist contribution to
decays in the color singlet approximation is considered. It is shown, that the
predictions for \Br(\chi_0\to\omega\omega) is in a good agreement with the
experimental data, while \Br(\chi_{c2}\to\omega\omega) differs from the
experiment significantly.Comment: 4 pages, RevTeX; minor changes, some refrences adde
Non-sequential double ionization below laser-intensity threshold: Anticorrelation of electrons without excitation of parent ion
Two-electron correlated spectra of non-sequential double ionization below
laser-intensity threshold are known to exhibit back-to-back scattering of the
electrons, viz., the anticorrelation of the electrons. Currently, the widely
accepted interpretation of the anticorrelation is recollision-induced
excitation of the ion plus subsequent field ionization of the second electron.
We argue that another mechanism, namely simultaneous electron emission, when
the time of return of the rescattered electron is equal to the time of
liberation of the bounded electron (the ion has no time for excitation), can
also explain the anticorrelation of the electrons in the deep below
laser-intensity threshold regime. Our conclusion is based on the results of the
numerical solution of the time-dependent Schr\"{o}dinger equation for a model
system of two one-dimensional electrons as well as an adiabatic analytic model
that allows for a closed-form solution.Comment: 6 pages and 3 figure
GEM operation in helium and neon at low temperatures
We study the performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne
and Ne+H2 at temperatures in the range of 2.6-293 K. In He, at temperatures
between 62 and 293 K, the triple-GEM structures often operate at rather high
gains, exceeding 1000. There is an indication that this high gain is achieved
by Penning effect in the gas impurities released by outgassing. At lower
temperatures the gain-voltage characteristics are significantly modified
probably due to the freeze-out of impurities. In particular, the double-GEM and
single-GEM structures can operate down to 2.6 K at gains reaching only several
tens at a gas density of about 0.5 g/l; at higher densities the maximum gain
drops further. In Ne, the maximum gain also drops at cryogenic temperatures.
The gain drop in Ne at low temperatures can be reestablished in Penning
mixtures of Ne+H2: very high gains, exceeding 10000, have been obtained in
these mixtures at 50-60 K, at a density of 9.2 g/l corresponding to that of
saturated Ne vapor near 27 K. The results obtained are relevant in the fields
of two-phase He and Ne detectors for solar neutrino detection and electron
avalanching at low temperatures.Comment: 13 pages, 14 figures. Accepted for publishing in Nucl. Instr. and
Meth.
Conceptual inconsistencies in finite-dimensional quantum and classical mechanics
Utilizing operational dynamic modeling [Phys. Rev. Lett. 109, 190403 (2012);
arXiv:1105.4014], we demonstrate that any finite-dimensional representation of
quantum and classical dynamics violates the Ehrenfest theorems. Other
peculiarities are also revealed, including the nonexistence of the free
particle and ambiguity in defining potential forces. Non-Hermitian mechanics is
shown to have the same problems. This work compromises a popular belief that
finite-dimensional mechanics is a straightforward discretization of the
corresponding infinite-dimensional formulation.Comment: 5 pages, 2 figure
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