435 research outputs found
Particle detection experiment for Applications Technology Satellite 1 /ATS-1/ Final report
Applications technology satellite particle detection experiment for measuring energy spectra of earth magnetic fiel
Особливості змісту права громадян на екологічну безпеку
В статье сделан анализ содержания права граждан на экологическую безопасность, определяется момент, с которого право на экологическую безопасность считается нарушенным
Examination of the production of an isotensor dibaryon in the pp → ppπ+π− reaction
Exclusive measurements of the quasi-free reaction have been performed by means of collisions at = 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region GeV ( = 2.35 - 2.46 GeV), which includes the regions of and resonance excitations. Calculations describing these excitations by -channel meson exchange are at variance with experimental differential cross sections and underpredict substantially the measured total cross section. An isotensor dibaryon resonance with produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong and more recently calculated by Gal and Garcilazo
Combinatorial nuclear level density by a Monte Carlo method
We present a new combinatorial method for the calculation of the nuclear
level density. It is based on a Monte Carlo technique, in order to avoid a
direct counting procedure which is generally impracticable for high-A nuclei.
The Monte Carlo simulation, making use of the Metropolis sampling scheme,
allows a computationally fast estimate of the level density for many fermion
systems in large shell model spaces. We emphasize the advantages of this Monte
Carlo approach, particularly concerning the prediction of the spin and parity
distributions of the excited states, and compare our results with those derived
from a traditional combinatorial or a statistical method. Such a Monte Carlo
technique seems very promising to determine accurate level densities in a large
energy range for nuclear reaction calculations.Comment: 30 pages, LaTex, 7 figures (6 Postscript figures included). Fig. 6
upon request to the autho
Beam-helicity asymmetries for single-hadron production in semi-inclusive deep-inelastic scattering from unpolarized hydrogen and deuterium targets
A measurement of beam-helicity asymmetries for single-hadron production in
deep-inelastic scattering is presented. Data from the scattering of 27.6 GeV
electrons and positrons off gaseous hydrogen and deuterium targets were
collected by the HERMES experiment. The asymmetries are presented separately as
a function of the Bjorken scaling variable, the hadron transverse momentum, and
the fractional energy for charged pions and kaons as well as for protons and
anti-protons. These asymmetries are also presented as a function of the three
aforementioned kinematic variables simultaneously
Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility
The search for 4He-eta bound states was performed with the WASA-at-COSY
facility via the measurement of the excitation function for the dd->3He n pi0
and dd->3He p pi- processes. The beam momentum was varied continuously between
2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He
eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined
based on the dd->3He n reaction and quasi-free proton-proton scattering via
dd->pp n_spectator n_spectator reactions. The excitation functions determined
independently for the measured reactions do not reveal a structure which could
be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the
total cross sections for the bound state production and decay in
dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes
were determined taking into account the isospin relation between both the
channels considered. The results of the analysis depend on the assumptions of
the N* momentum distribution in the anticipated mesic-4He. Assuming as in the
previous works, that this is identical with the distribution of nucleons bound
with 20 MeV in 4He, we determined that (for the mesic bound state width in the
range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about
3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on
the recent theoretical findings of the N*(1535) momentum distribution in the
N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector
acceptance decreases and hence the corresponding upper limits are 5 nb and 10
nb for npi0 and ppi- channels respectively.Comment: This article will be submitted to JHE
Measurement of the Reaction in Search for the Recently Observed Resonance Structure in and systems
Exclusive measurements of the quasi-free reaction have
been performed by means of collisions at = 1.2 GeV using the WASA
detector setup at COSY. Total and differential cross sections have been
obtained covering the energy region = (2.35 - 2.46) GeV, which
includes the region of the ABC effect and its associated resonance structure.
No ABC effect, {\it i.e.} low-mass enhancement is found in the
-invariant mass spectrum -- in agreement with the constraint from
Bose statistics that the isovector pion pair can not be in relative s-wave. At
the upper end of the covered energy region -channel processes for Roper,
and excitations provide a reasonable description
of the data, but at low energies the measured cross sections are much larger
than predicted by such processes. Adding a resonance amplitude for the
resonance at =~2.37 GeV with =~70 MeV and observed
recently in and reactions leads to an
agreement with the data also at low energies
Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy
We present new data for angular distributions and on the cross section ratio
of the p + d -> 3He + eta reaction at excess energies of Q = 48.8 MeV and Q =
59.8 MeV. The data have been obtained at the WASA-at-COSY experiment
(Forschungszentrum J\"ulich) using a proton beam and a deuterium pellet target.
While the shape of obtained angular distributions show only a slow variation
with the energy, the new results indicate a distinct and unexpected total cross
section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the
variation of the production mechanism within this energy interval.Comment: 9 pages, 9 figure
Neutron-Proton Scattering in the Context of the (2380) Resonance
New data on quasifree polarized neutron-proton scattering, in the region of
the recently observed resonance structure, have been obtained by
exclusive and kinematically complete high-statistics measurements with WASA at
COSY. This paper details the determination of the beam polarization, checks of
the quasifree character of the scattering process, on all obtained
angular distributions and on the new partial-wave analysis, which includes the
new data producing a resonance pole in the - coupled partial
waves at () MeV -- in accordance with the dibaryon
resonance hypothesis. The effect of the new partial-wave solution on the
description of total and differential cross section data as well as specific
combinations of spin-correlation and spin-transfer observables available from
COSY-ANKE measurements at = 2.27 GeV is discussed
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