The photoproduction of the omega meson has been studied at GRAAL from threshold up to a photon energy of 1.5 GeV. The differential cross sections and beam asymmetries have been measured precisely at ...all angles. The total cross section is also obtained. Systematic enhancements of the differential cross section at large angles and nonzero beam asymmetries at intermediate angles provide clear evidence for s- and u-channel resonant processes. The data are compared to the results of hadron and quark models.
Neutral pion photoproduction has been measured from 550 to 1500 MeV with the GRAAL facility, located at the ESRF in Grenoble. Differential cross-section and beam asymmetry have been measured over a ...wide angular range. These high-precision data improve significantly the database for the beam asymmetry in the second and third resonance regions covering for the first time the energy domain 1100-1500 MeV. New partial-wave analyses including these data are presented for which the beam asymmetry brings crucial constraints.
The electron–ion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the International Facility for Antiproton and Ion Research (FAIR) in ...Darmstadt, Germany. It offers an unique opportunity to use electrons as probe in investigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented.
Photonuclear methods used earlier in experiments at electron accelerators have been adapted for femtosecond pulsed lasers. In particular, the problem of measuring wide electron spectra under ...conditions of a high counting rate and, hence, a high probability of pulse pileup has been solved. To provide long-term stability of electron beams from plasma, a magnetic spectrometer combined with a magnetic-induction sensor has been developed. This spectrometer is capable of measuring the electron-beam characteristics in each ultrashort laser pulse. The results of the experiments carried out with the femtosecond laser system at the International Laser Center of the Moscow State University are presented.
The double polarization (beam-recoil) observables Ox and Oz have been measured for the reaction γp → K+Λ from threshold production to E ∼ 1500MeV. The data were obtained with the linearly polarized ...beam of the GRAAL facility. Values for the target asymmetry T could also be extracted despite the use of an unpolarized target. Analyses of our results by two isobar models tend to confirm the necessity to include new or poorly known resonances in the 1900MeV mass region.
Beam asymmetries and hyperon recoil polarizations for the reactions $\gamma p \to K^{+}\Lambda$ and $\gamma p \to K^{+}\Sigma^{0}$ have been measured from the threshold production to 1500 MeV with ...the GRAAL facility located at the ESRF in Grenoble. These results complement the database for the beam asymmetry, covering for the first time the production threshold region. Recent theoretical analyses are presented for which the beam asymmetry data bring interesting new information and allow to better determine some resonance parameters. Most importantly, these results strengthen the need of a new D$_{13}$ state around 1900 MeV.
The $ \Sigma$ beam asymmetry in the photoproduction of neutral pions from quasi-free nucleons in a deuteron target was measured for the first time between 0.60 and 1.50GeV, with the GRAAL polarized ...and tagged photon beam. The asymmetry values from the quasi-free proton were found equal to the ones extracted from a pure proton target. The asymmetries from quasi-free proton and quasi-free neutron were found equal up to 0.82GeV and substantially different at higher energies. The results are compared with recent partial-wave analyses.
K+Λ(1405) photoproduction has been studied at the BGOOD experiment via the all neutral decay, Λ(1405)→Σ0π0. The unique BGOOD experimental setup allows both the cross section and Λ(1405) invariant ...mass distribution (line shape) to be measured over a broad K+ polar angle range, extending to extreme forward K+ angles unattainable at previous experiments.
Evidence is provided for the role of a triangle singularity driven by the N⁎(2030) resonance, which appears to contribute significantly to K+Λ(1405) photoproduction. This is observed in the integrated cross section which was determined with unprecedented energy resolution and supported by the angular distributions. The measured line shape is also in agreement with the previous results of CLAS and ANKE, and is consistent with two poles derived in χPT based models.
New data on the fragmentation of carbon nuclei by photons with energies from 800 to 1500 MeV, obtained in the collaboration GRAAL, are presented. These data include the yields of heavier fragments ...than nucleons. Comparison of new results with literature data, obtained with real and virtual photons in reactions with electrons and relativistic ions (Coulomb dissociation) is done using a general approach in frame of the Weizsäcker–Williams model. Possible reasons for the observed differences between them are discussed.
PDF
