37 research outputs found
Experimental Review of Baryons in the Nuclear Medium
Inclusive studies of nuclear photoabsorption have provided clear evidence of
medium modifications but the results have not yet been explained in a model
independent way. A deeper understanding of the situation is anticipated from a
detailed experimental study of meson photoproduction from nuclei in exclusive
reactions. Recent results on meson production in photonuclear experiments
indicate a large difference between quasifree meson production from the nuclear
surface and non-quasifree components.Comment: Proceedings Baryons200
Subthreshold phi-meson production in heavy-ion collisions
Within a transport code of BUU type the production of phi-mesons in the
reactions Ni+Ni at 1.93 AGeV and Ru+Ru at 1.69 AGeV is studied. New elementary
reaction channels rho+N(Delta) to phi+N and pi+N(1520) to phi+N are included.
In spite of a substantial increase of the \phi multiplicities by these channels
the results stay below the tentative numbers extracted from experimental data.Comment: 17 pages(LaTeX), two new figures adde
Double pion photoproduction on nucleon and deuteron
Photoproduction of two pions on nucleon and deuteron is studied for photon
energies from threshold up to GeV. For the elementary operator
an effective Lagrangean approach is used with resonance and Born contributions.
The model parameters are fixed by resonance decay widths and multipole analyses
of single pion photoproduction. A satisfactory description of total cross
sections of two-pion production on the proton for various charge channels is
achieved, except for production for which a significant
underestimation is found near threshold. The operator then serves for the
evaluation of this reaction on the deuteron in the impulse approximation. In
addition, rescattering in the final state is taken into account, but and rescatterings are neglected. Results are presented for total
cross sections and target asymmetries.Comment: 28 pages revtex including 12 ps-figure
NN coupling and two-pion photoproduction on the nucleon
Effects of non-resonant photoproductions arising from two different
couplings are investigated in the reaction. We find that
the pseudoscalar (PS) coupling is generally preferable to the
pseudovector (PV) coupling and particularly the total cross sections
are successfully described by the model with the PS coupling. In order
to see the difference between the two couplings, we also show the results of
invariant mass spectra and helicity-dependent cross sections in various isospin
channels calculated with the PS and PV couplings.Comment: 35 pages, 11 figures, minor changes and version to be published in
Phys.Rev.
Surface and volume effects in the photoabsorption of nuclei
Recent experimental results for meson photoproduction from nuclei obtained
with TAPS at MAMI are analyzed in view of the suppression of the second nucleon
resonance region in total photoabsorption. The cross sections can be split into
a component from the low density surface region of nuclei and a component which
scales more like the nuclear volume. The energy dependence of the surface
component is similar to the deuteron cross section, it shows a clear signal for
the second resonance peak assigned to the excitation of the P11(1440),
D13(1520), and S11(1535). The volume component behaves differently, it is
lacking the second resonance peak and shows an enhancement at intermediate
photon energies.Comment: accepted for publication in Eur. J. Phys.
Hadrons in Nuclei: Experiments and Perspectives
The question of the origin of hadron masses is one major issue in the
understanding of the strong interaction. The challenge is addressed by
searching for indications of in-medium modifications of hadron properties and
studying hadrons in nuclei. The quest driving in-medium studies is to
understand the origin of hadron masses in the context of spontaneous chiral
symmetry breaking.
The experimental status of the modification of hadron properties in the
nuclear medium is discussed including experiments using hadron, heavy-ion, and
photon beams. Particular emphasis is put on the production of light mesons from
nuclei.
A number of experimental programs is underway to provide a detailed
comparison of properties of free hadrons and hadrons embedded in nuclei. The
existing experimental efforts are discussed and possibilities are introduced
for the new WASA-at-COSY facility, initially focussed on investigations of
symmetries and symmetry breaking, to contribute to the field.Comment: To appear in the proceedings of 23rd International Nuclear Physics
Conference (INPC 2007), Tokyo, Japan, 3-8 Jun 200
In-medium modifications of the interaction in photon-induced reactions
Differential cross sections of the reactions
and have been measured for several
nuclei (H,C, and Pb) at an incident-photon energy of
=400-460 MeV at the tagged-photon facility at MAMI-B using the TAPS
spectrometer. A significant nuclear-mass dependence of the
invariant-mass distribution is found in the channel. This
dependence is not observed in the channel and is
consistent with an in-medium modification of the interaction in the
==0 channel. The data are compared to -induced measurements and to
calculations within a chiral-unitary approach
Photoproduction of mesons from nuclei - In-medium properties of hadrons
Recent experimental results for the in-medium properties of hadrons obtained
with photoproduction of mesons from nuclei are discussed. The experiments were
done with the TAPS detector at the tagged photon beam of the MAMI accelerator
in Mainz. Measured were the final states , , , and
for C, Ca, Nb, and Pb up to the
second resonance region. The results were used for an investigation of the
in-medium properties of the P(1232), the P(1440), the
D(1520), and the S(1535) resonances. It was found that the cross
sections can be spilt into a component which originates from the low density
surface region of the nuclei and a component which scales like the nuclear
volume. The energy dependence of the surface component is strikingly similar to
the deuteron, it shows a clear signal for the second resonance peak. The volume
component is lacking this peak and shows an enhancement at intermediate
energies. Furthermore the measurement of coherent -photoproduction and
the final state from He is discussed in the context of the search
for -mesic nuclei.Comment: Proceedings of International School of Nuclear Physics, 26th Course,
Lepton Scattering and the Structure of Hadrons and Nuclei, Erice-Sicily,
Italy 16. - 24. September 2004, to be published in Prog. Part. Nucl. Phy