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تسجيل مستخدم جديدPhotoproduction of eta mesons off protons for photon energies from 0.75 GeV to 3 GeV
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Total and differential cross sections for the reaction p(gamma, eta)p have been measured for photon energies in the range from 750 MeV to 3 GeV. The low-energy data are dominated by the S11 wave which has two poles in the energy region below 2 GeV. Eleven nucleon resonances are observed in their decay into p eta. At medium energies we find evidence for a new resonance N(2070)D15 with (mass, width) = (2068+-22, 295+-40) MeV. At photon energies above 1.5 GeV, a strong peak in forward direction develops, signalling the exchange of vector mesons in the t channel.
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section as well as the angular and momentum distributions of $eta$-mesons are in quantitative agreement with the Quantum Molecular Dynamics (QMD) model calculations in which the $eta$-meson emission processes other than the $S_{11}$(1535) resonance are also incorporated as proposed in the $eta$-MAID model. It is shown that the excitation of the $D_{15}$(1675) resonance might play an important role for $E_{gamma}>900$ MeV.
Photoproduction of $eta$ mesons off $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{nat}$Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined s
etup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S$_{11}$(1535) nucleon resonance and the study of the absorption properties of nuclear matter for $eta$ mesons. Careful consideration was given to contributions from $etapi$ final states and secondary production mechanisms of $eta$-mesons e.g. from inelastic $pi N$ reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross section $sigma_{Neta}$ for $eta$ mesons is constant over a wide range of the $eta$ momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU-model show no unexplained in-medium modifications of the S$_{11}$(1535).
Total and differential cross sections for $eta$ and $eta ^prime$ photoproduction off the proton have been determined with the CBELSA/TAPS detector for photon energies between 0.85 and 2.55 GeV. The $eta$ mesons are detected in their two neutral decay
modes, $etatogammagamma$ and $etato 3pi^0to 6gamma$, and for the first time, cover the full angular range in $rm cos theta_{cm}$ of the $eta$ meson. These new $eta$ photoproduction data are consistent with the earlier CB-ELSA results. The $eta ^prime$ mesons are observed in their neutral decay to $pi^0pi^0etato 6gamma$ and also extend the coverage in angular range.
Single pi0 photoproduction has been studied with the CB-ELSA experiment at Bonn using tagged photon energies between 0.3 and 3.0 GeV. The experimental setup covers a very large solid angle of about 98% of 4 pi. Differential cross sections (d sigma)/(
d Omega) have been measured. Complicated structures in the angular distributions indicate a variety of different resonances being produced in the s channel intermediate state gamma p --> N* (Delta*) --> p pi0. A combined analysis including the data presented in this letter along with other data sets reveals contributions from known resonances and evidence for a new resonance N(2070)D15.
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