84 research outputs found
K^- ^3He and K^+K^- interactions in the pd -> ^3He K^+K^- reaction
We investigate the K^- ^3He and K^+ K^- interactions in the reaction pd ->
^3He K^+ K^- near threshold and compare our model calculations with data from
the MOMO experiment at COSY-Juelich. A large attractive effective K^- p
amplitude would give a significant K^- ^3He final-state interaction effect
which is not supported by the experimental data. We also estimate upper limits
for the a_0(980) and f_0(980) contributions to the produced K^+ K^- pairs.Comment: 5 pages, 2 figures, accepted for publication in PR
The elastic electron-deuteron scattering beyond one-photon exchange
We discuss the elastic ed scattering beyond Born approximation. It is shown
that the reaction amplitude contains six generalized form factors, but only
three linearly independent combinations of them (we call them generalized
charge, quadrupole and magnetic form factors) contribute to the reaction cross
section in the second order perturbation theory. We examine two-photon exchange
and find that it includes two types of diagrams, when two virtual photons
interact with the same nucleon and when the photons interact with different
nucleons. Estimations based on nonrelativistic calculations with the deuteron
wave function for realistic NN potential show that the main contribution to the
generalized charge, quadrupole and magnetic form factors comes from diagrams of
the first type.Comment: v2, published version in PR
Search for evidence of two photon contribution in elastic electron proton data
We reanalyze the most recent data on elastic electron proton scattering. We
look for a deviation from linearity of the Rosenbluth fit to the differential
cross section, which would be the signature of the presence of two photon
exchange. The two photon contribution is parametrized by a one parameter
formula, based on symmetry arguments. The present data do not show evidence for
such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more
explicit explanation
Cross section and polarization observables for the reaction
A model independent formalism for the electron positron annihilation reaction
has been derived. The differential and total cross
sections and the elements of the spin--density matrix of the -meson were
calculated in terms of the electromagnetic form factors of the corresponding
current. Simple models of form factors have been fitted
to the available cross section data and they allow to give numerical
predictions for the different observables.Comment: 19 pages, 6 figures Added formulas for axial meson decay in 3 pions
Modified version to appear in PR
Polarization effects in the reaction and determination of the meson form factors in the time--like region
The electron positron annihilation reaction into four pion production has
been studied, through the channel . The
differential (and total) cross sections and various polarization observables
for this reaction have been calculated in terms of the electromagnetic form
factors of the corresponding current. The elements of the
spin--density matrix of the meson were also calculated. Numerical
estimations have been done, with the help of phenomenological form factors
obtained in the space--like region of the momentum transfer squared and
analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev
Analysis of polarization observables and radiative effects for the reaction
The expressions for the differential cross section and of the polarization
observables for the reaction are given in terms
of the nucleon electromagnetic form factors in the laboratory system. Radiative
corrections due to the emission of virtual and real soft photons from the
leptons are also calculated. Unlike the center-of- mass system case, they
depend on the scattering angle. Polarization effects are derived in the case
when the antiproton beam, the target and the electron in the final state are
polarized. Numerical estimations have been done for all observables for the
PANDA experimental conditions using models for the nucleon electromagnetic form
factors in the time-like region. The radiative corrections to the differential
cross section are calculated as function of the beam energy and of the electron
angle.Comment: 18 pages, 8 figure
Potassium Ions are More Effective than Sodium Ions in Salt Induced Peptide Formation
Prebiotic peptide formation under aqueous conditions in the presence of metal ions is one of the plausible triggers of the emergence of life. The salt-induced peptide formation reaction has been suggested as being prebiotically relevant and was examined for the formation of peptides in NaCl solutions. In previous work we have argued that the first protocell could have emerged in KCl solution. Using HPLC-MS/MS analysis, we found that K(+) is more than an order of magnitude more effective in the L-glutamic acid oligomerization with 1,1'-carbonyldiimidazole in aqueous solutions than the same concentration of Na(+), which is consistent with the diffusion theory calculations. We anticipate that prebiotic peptides could have formed with K(+) as the driving force, not Na(+), as commonly believed
Polarization effects in and determination of time like deuteron form factors
Polarization effects in the reaction have been
investigated for the case of longitudinally polarized electron beam and
arbitrary polarization of the produced deuteron, with the aim of a
determination of the time-like complex deuteron electromagnetic form factors.
General expressions of polarization observables are derived and numerical
estimations have been carried out by means of various models of deuteron
electromagnetic form factors, for kinematical conditions near threshold.Comment: 19 pages, 3 figure
Radiative corrections to polarization observables in elastic electron-deuteron scattering in leptonic variables
The model--independent QED radiative corrections to polarization observables
in elastic scattering of unpolarized and longitudinally--polarized electron
beam by the deuteron target have been calculated in leptonic variables. The
experimental setup when the deuteron target is arbitrarily polarized is
considered and the procedure for applying derived results to the vector or
tensor polarization of the recoil deuteron is discussed. The basis of the
calculations consists of the account for all essential Feynman diagrams which
results in the form of the Drell-Yan representation for the cross-section and
use of the covariant parametrization of the deuteron polarization state. The
numerical estimates of the radiative corrections are given for the case when
event selection allows the undetected particles (photons and electron-positron
pairs) and the restriction on the lost invariant mass is used.Comment: 43 pages,3 figures. To be published in ZhTEF. revised 14.02.2012.
arXiv admin note: text overlap with arXiv:nucl-ex/0002003 by other author
The K^- \alpha scattering length and the reaction dd \to \alpha K^+ K^-
We present predictions for the the K^- \alpha scattering length obtained
within the framework of the multiple scattering approach. Evaluating the pole
position of the K^- \alpha scattering amplitude within the zero range
approximation, we find a loosely bound K^- \alpha state with a binding energy
of E_R = -2 ... -7 MeV and a width \Gamma_R = 11 ... 18 MeV. We propose to
measure the K^- \alpha scattering length through the final state interaction
between the \alpha and K^- meson produced in the reaction dd \to \alpha K^+
K^-. It is found that the K^-\alpha invariant mass distribution from this
reaction at energies near the threshold provides a new tool to determine the
s-wave K^- \alpha scattering length.Comment: 6 pages, 3 PS figure
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