1,288 research outputs found
Form Factors and Strong Couplings of Heavy Baryons from QCD Light-Cone Sum Rules
We derive QCD light-cone sum rules for the hadronic matrix elements of the
heavy baryon transitions to nucleon. In the correlation functions the
and -baryons are interpolated by three-quark
currents and the nucleon distribution amplitudes are used. To eliminate the
contributions of negative parity heavy baryons, we combine the sum rules
obtained from different kinematical structures. The results are then less
sensitive to the choice of the interpolating current. We predict the
form factor and calculate the widths of the and decays. Furthermore, we consider double
dispersion relations for the same correlation functions and derive the
light-cone sum rules for the and strong
couplings. Their predicted values can be used in the models of charm production
in collisions.Comment: 45 pages, 3 figure
Semileptonic charm decays D \to \pi l \nu_{\l} and from QCD Light-Cone Sum Rules
We present a new calculation of the and form factors from
QCD light-cone sum rules. The scheme for the -quark mass is
used and the input parameters are updated. The results are , and
. Combining the calculated form
factors with the latest CLEO data, we obtain and
where the first and second errors are of experimental origin and the third
error is due to the estimated uncertainties of our calculation. We also
evaluate the form factors and and predict the slope
parameters at . Furthermore, calculating the form factors from the sum
rules at , we fit them to various parameterizations. After analytic
continuation, the shape of the form factors in the whole
semileptonic region is reproduced, in a good agreement with experiment.Comment: 34 pages, 5 figure
First measurement of the helicity asymmetry for in the resonance region
The first measurement of the helicity dependence of the photoproduction cross
section of single neutral pions off protons is reported for photon energies
from 600 to 2300\,MeV, covering nearly the full solid angle. The data are
compared to predictions from the SAID, MAID, and BnGa partial wave analyses.
Strikingly large differences between data and predictions are observed which
are traced to differences in the helicity amplitudes of well known and
established resonances. Precise values for the helicity amplitudes of several
resonances are reported
Experimental constraints on the -nucleus real potential
In a search for mesic states, the production of -mesons in
coincidence with forward going protons has been studied in photon induced
reactions on C for incident photon energies of 1250 - 3100 MeV. The
pairs from decays of bound or quasi-free -mesons have
been measured with the CBELSA/TAPS detector system in coincidence with protons
registered in the MiniTAPS forward array. Structures in the total energy
distribution of the pairs, which would indicate the population
and decay of bound B states, are not observed. The
cross section of 0.3 nb/MeV/sr observed in the bound state energy regime
between -100 and 0 MeV may be accounted for by yield leaking into the bound
state regime because of the large in-medium width of the -meson. A
comparison of the measured total energy distribution with calculations suggests
the real part of the B potential to be small and only
weakly attractive with 35(stat) 20(syst) MeV
in contrast to some theoretical predictions of attractive potentials with a
depth of 100 - 150 MeV.Comment: 13 pages, 8 figure
How much charm can PANDA produce?
We consider the production of charmed baryons and mesons in the
proton-antiproton binary reactions at the energies of the future ANDA
experiment. To describe these processes in terms of hadronic interaction
models, one needs strong couplings of the initial nucleons with the
intermediate and final charmed hadrons. Similar couplings enter the models of
binary reactions with strange hadrons. For both charmed and strange hadrons we
employ the strong couplings and their ratios calculated from QCD light-cone sum
rules. In this method finite masses of and quarks are taken into
account. Employing the Kaidalov's quark-gluon string model with Regge poles and
adjusting the normalization of the amplitudes in this model to the calculated
strong couplings, we estimate the production cross section of charmed hadrons.
For it can reach several tens of at
, whereas the cross sections of and pair
production are predicted to be smaller.Comment: 22 pages, 6 figures, matches published versio
The polarization observables T, P, and H and their impact on multipoles
Data on the polarization observables T, P, and H for the reaction are reported. Compared to earlier data from other experiments, our
data are more precise and extend the covered range in energy and angle
substantially. The results were extracted from azimuthal asymmetries measured
using a transversely polarized target and linearly polarized photons. The data
were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS
detector. Within the Bonn-Gatchina partial wave analysis, the new polarization
data lead to a significant narrowing of the error band for the multipoles for
neutral-pion photoproduction
Final State Interaction Effects in pol 3He(pol e,e'p)
Asymmetries in quasi-elastic pol 3He(pol e,e'p) have been measured at a
momentum transfer of 0.67 (GeV/c)^2 and are compared to a calculation which
takes into account relativistic kinematics in the final state and a
relativistic one-body current operator. With an exact solution of the Faddeev
equation for the 3He-ground state and an approximate treatment of final state
interactions in the continuum good agreement is found with the experimental
data.Comment: 11 pages, 6 figures, submitted to Phys. Lett. B, revised version,
sensitivity study to relativity and NN-potential adde
Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E
Photoproduction of mesons from neutrons} \abstract{Results from
measurements of the photoproduction of mesons from quasifree protons and
neutrons are summarized. The experiments were performed with the CBELSA/TAPS
detector at the electron accelerator ELSA in Bonn using the
decay. A liquid deuterium target was used for the
measurement of total cross sections and angular distributions. The results
confirm earlier measurements from Bonn and the MAMI facility in Mainz about the
existence of a narrow structure in the excitation function of . The current angular distributions show a forward-backward
asymmetry, which was previously not seen, but was predicted by model
calculations including an additional narrow state. Furthermore, data
obtained with a longitudinally polarized, deuterated butanol target and a
circularly polarized photon beam were analyzed to determine the double
polarization observable . Both data sets together were also used to extract
the helicity dependent cross sections and . The
narrow structure in the excitation function of
appears associated with the helicity-1/2 component of the reaction
The N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions
New data on the polarization observables T, P, and H for the reaction are reported. The results are extracted from azimuthal
asymmetries when a transversely polarized butanol target and a linearly
polarized photon beam are used. The data were taken at the Bonn electron
stretcher accelerator ELSA using the CBELSA/TAPS detector. These and earlier
data are used to perform a truncated energy-independent partial wave analysis
in sliced-energy bins. This energy-independent analysis is compared to the
results from energy-dependent partial wave analyses
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