171 research outputs found
Determination of the cross section of the proton, pion and neutron inelastic interaction with lead and carbon nuclei at 0.5 - 5.0 TeV energies (PION experiment)
Experimental results on the cross section of the single pion, proton and neutron inelastic interaction with carbon and lead nuclei in the 0.5 to 5.0 TeV energy interval obtained on the PION installation (Mount Aragats, Armenia, 3250 m) are presented. For this purpose the (N pi)/(N p) and inelastic (p Fe)/(pi Fe) ratios measured directly on the installation as well as the calculated inelastic (p A)/(pi A) dependence on the target nucleus atomic numbers were used
Demkov-Kunike model for cold atom association: weak interaction regime
We study the nonlinear mean-field dynamics of molecule formation at coherent
photo- and magneto-association of an atomic Bose-Einstein condensate for the
case when the external field configuration is defined by the quasi-linear level
crossing Demkov-Kunike model, characterized by a bell-shaped pulse and finite
variation of the detuning. We present a general approach to construct an
approximation describing the temporal dynamics of the molecule formation in the
weak interaction regime and apply the developed method to the nonlinear
Demkov-Kunike problem. The presented approximation, written as a scaled
solution to the linear problem associated to the nonlinear one we treat,
contains fitting parameters which are determined through a variational
procedure. Assuming that the parameters involved in the solution of the linear
problem are not modified, we suggest an analytical expression for the scaling
parameter.Comment: 6 pages, 4 figure
Measurement of the Beam Asymmetry in the Forward Direction for pi0 Photoproduction
Photoproduction of neutral pions has been studied with the CBELSA/TAPS
detector for photon energies between 0.92 and 1.68~GeV at the electron
accelerator ELSA. The beam asymmetry~ has been extracted for of the ~meson and for . The new beam asymmetry data improve the world database for
photon energies above 1.5~GeV and, by covering the very forward region, extend
previously published data for the same reaction by our collaboration. The
angular dependence of shows overall good agreement with the SAID
parameterization.Comment: 11 pages, 10 figures, published in Phys. Rev. C, included LEPS data
and MAID 2007 predictions for comparison with our dat
Photoproduction of Neutral Pions off Protons
Photoproduction of neutral pions has been studied with the CBELSA/TAPS
detector in the reaction for photon energies between 0.85
and 2.50 GeV. The mesons are observed in their dominant neutral decay
mode: . For the first time, the differential cross
sections cover the very forward region, . A
partial-wave analysis of these data within the Bonn-Gatchina framework observes
the high-mass resonances (2190), (2080), and (2070).Comment: 12 pages, 9 figures, minor modifications to PWA sectio
Photoproduction of meson pairs: First measurement of the polarization observable I^s
The polarization observable I^s, a feature exclusive to the acoplanar
kinematics of multi-meson final states produced via linearly polarized photons,
has been measured for the first time. Results for the reaction g p -> p pi0 eta
are presented for incoming photon energies between 970 MeV and 1650 MeV along
with the beam asymmetry I^c. The comparably large asymmetries demonstrate a
high sensitivity of I^s to the dynamics of the reaction. Fits using
Bonn-Gatchina partial wave analysis demonstrate that the new polarization
observables carry significant information on the contributing partial waves.Comment: 11 pages, 6 figures, v2 to appear in Phys. Lett.
Quasi-free photoproduction of eta-mesons of the neutron
Quasi-free photoproduction of eta-mesons off nucleons bound in the deuteron
has been measured with the CBELSA/TAPS detector for incident photon energies up
to 2.5 GeV at the Bonn ELSA accelerator. The eta-mesons have been detected in
coincidence with recoil protons and recoil neutrons, which allows a detailed
comparison of the quasi-free n(gamma,eta)n and p(gamma,eta)p reactions. The
excitation function for eta-production off the neutron shows a pronounced
bump-like structure at W=1.68 GeV (E_g ~ 1 GeV), which is absent for the
proton.Comment: accepted for publication in Phys. Rev. Let
High statistics study of the reaction
The photoproduction of 2 mesons off protons was studied with the
Crystal Barrel/TAPS experiment at the electron accelerator ELSA in Bonn. The
energy of photons produced in a radiator was tagged in the energy range from
600\,MeV to 2.5\,GeV. Differential and total cross sections and
Dalitz plots are presented. Part of the data was taken with a diamond radiator
producing linearly polarized photons, and beam asymmetries were derived.
Properties of nucleon and resonances contributing to the
final state were determined within the BnGa partial wave analysis. The data
presented here allow us to determine branching ratios of nucleon and
resonances for their decays into via several intermediate states.
Most prominent are decays proceeding via , ,
, , but also , , and
contribute to the reaction.Comment: 28 pages, 17 figures, 7 table
Variational ansatz for the nonlinear Landau-Zener problem for cold atom association
We present a rigorous analysis of the Landau-Zener linear-in-time term
crossing problem for quadratic-nonlinear systems relevant to the coherent
association of ultracold atoms in degenerate quantum gases. Our treatment is
based on an exact third-order nonlinear differential equation for the molecular
state probability. Applying a variational two-term ansatz, we construct a
simple approximation that accurately describes the whole-time dynamics of
coupled atom-molecular system for any set of involved parameters. Ensuring an
absolute error less than for the final transition probability, the resultant
solution improves by several orders of magnitude the accuracy of the previous
approximations by A. Ishkhanyan et al. developed separately for the weak
coupling [J. Phys. A 38, 3505 (2005)] and strong interaction [J. Phys. A 39,
14887 (2006)] limits. In addition, the constructed approximation covers the
whole moderate-coupling regime, providing for this intermediate regime the same
accuracy as for the two mentioned limits. The obtained results reveal the
remarkable observation that for the strong-coupling limit the resonance
crossing is mostly governed by the nonlinearity, while the coherent
atom-molecular oscillations arising soon after the resonance has been crossed
are basically of linear nature. This observation is supposed to be of a general
character due to the basic attributes of the resonance crossing processes in
the nonlinear quantum systems of the discussed type of involved quadratic
nonlinearity
Photoproduction of {\omega} Mesons off the Proton
The differential cross sections and unpolarized spin-density matrix elements
for the reaction were measured using the CBELSA/TAPS
experiment for initial photon energies ranging from the reaction threshold to
2.5 GeV. These observables were measured from the radiative decay of the
meson, . The cross sections cover the full
angular range and show the full extent of the -channel forward rise. The
overall shape of the angular distributions in the differential cross sections
and unpolarized spin-density matrix elements are in fair agreement with
previous data. In addition, for the first time, a beam of linearly-polarized
tagged photons in the energy range from 1150 MeV to 1650 MeV was used to
extract polarized spin-density matrix elements.
These data were included in the Bonn-Gatchina partial wave analysis (PWA).
The dominant contribution to photoproduction near threshold was found
to be the partial wave, which is primarily due to the sub-threshold
resonance. At higher energies, pomeron-exchange was found to
dominate whereas -exchange remained small. These -channel contributions
as well as further contributions from nucleon resonances were necessary to
describe the entire dataset: the , , and partial waves
were also found to contribute significantly.Comment: 8 pages, 5 figures, accepted for publication in Physics Letters
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