First Measurements of the Double-Polarization Observables F , P , and H in ω Photoproduction off Transversely Polarized Protons in the N* Resonance Region (original) (raw)

Physical Review C, 2001

The role of the nucleon resonances (N * ) in ω photoproduction is investigated by using the resonance parameters predicted by Roberts [Phys. Rev. D 46, 2864 (1992); 49, 4570 (1994)]. In contrast with the previous investigations based on the SU(6) × O(3) limit of the constituent quark model, the employed N * → γN and N * → ωN amplitudes include the configuration mixing effects due to the residual quark-quark interactions. The contributions from the nucleon resonances are found to be significant relative to the non-resonant amplitudes in changing the differential cross sections at large scattering angles and various spin observables. In particular, we suggest that a crucial test of our predictions can be made by measuring the parity asymmetry and beam-target double asymmetry at forward scattering angles. The dominant contributions are found to be from N 3 2 + (1910), a missing resonance, and N 3 2 − (1960) which is identified as the D 13 (2080) of the Particle

Photoproduction of π0 Mesons off Neutrons in the Nucleon Resonance Region

Physical Review Letters, 2014

Precise angular distributions have been measured for the first time for the photoproduction of π 0 -mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-stateinteraction effects has been estimated by a comparison of the reaction cross section for quasi-free protons bound in the deuteron to the results for free protons and then applied as a correction to the quasi-free neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 GeV and 1.4 GeV. The results are compared to the predictions from reaction models and partial-wave analyses based on data from other isospin channels. The model predictions show large discrepancies among each other and the present data will provide much tighter constraints. This is demonstrated by the results of a new analysis in the framework of the Bonn-Gatchina coupled-channel analysis which included the present data.

Photoproduction of π0 mesons off protons and neutrons in the second and third nucleon resonance regions

Physical Review C, 2018

Background: Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Purpose: Study experimentally single π 0 photoproduction off quasi-free nucleons from the deuteron. Investigate nuclear effects by a comparison of the results for free protons and quasi-free protons. Use the quasi-free neutron data (corrected for nuclear effects) to test the predictions of reaction models and partial wave analysis (PWA) for γn → nπ 0 derived from the analysis of the other isospin channels. Methods: High statistics angular distributions and total cross sections for the photoproduction of π 0 mesons off the deuteron with coincident detection of recoil nucleons have been measured for the first time. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45 GeV and 1.4 GeV, using an almost 4π electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Results: Significant effects from final state interactions (FSI) were observed for participant protons in comparison to free proton targets (between 30% and almost 40%). The data in coincidence with recoil neutrons were corrected for such effects under the assumption that they are identical for participant protons and neutrons. Reaction model predictions and PWA for γn → nπ 0 , based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. Conclusions: The results demonstrate clearly the importance of a mesurement of the fully neutral final state for the isospin decmposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood.

Evidence for Nucleon-Resonance Excitation in ω-Meson Photoproduction

Physical Review Letters, 2006

The photoproduction of the ! 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.

Meson photoproduction on the nucleon with polarized photons

European Physical Journal A, 2007

Meson photoproduction with polarized photons has proved to be a powerful tool to identify contributions of baryon resonances that are not evident in the differential cross-sections. It provides information that are complementary to those extracted using pion-nucleon scattering data. Extensive results have been produced in the past on beam asymmetries by the Graal collaboration for η and π 0 on the proton. New results are now available for the same reactions on the quasi-free neutron and for the K+ photoproduction on the proton. Contributions from hitherto undetected baryon resonances may be important to understand the results.

Evidence for nucleon-resonance excitation in omega-meson photoproduction

Physical review letters, 2006

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.

New Measurement of Σ Beam Asymmetry for η Meson Photoproduction on the Proton

Physical Review Letters, 1998

We present new S beam asymmetry data for h meson photoproduction on the proton, using a novel tagged, laser backscattered, linearly polarized photon beam up to 1.1 GeV. The data show large, positive asymmetries, at all incident photon energies. In addition to the S 11 ͑1535͒ and D 13 ͑1520͒ resonances necessary to reproduce the cross sections, P 13 ͑1720͒ and D 15 ͑1675͒ "four stars" resonances contribute to the S observable, but cannot reproduce the strong forward asymmetries measured at energies higher than 900 MeV. [S0031-9007(98)06957-9] PACS numbers: 13.60. Le, 13.88. + e, 14.40.Aq The underlying substructure of the nucleon gives rise to a rich spectrum of excited states, many of which have been associated with the baryon resonances seen in pN scattering [1] and p photoproduction. These baryon resonances and their associated gNN ‫ء‬ electromagnetic couplings form bench marks for models of hadron structure. Quark models have been quite successful in accounting for the masses of most observed resonances, although in some cases the electromagnetic couplings have presented more of a challenge [2].

Nucleon resonances in Ï photoproduction

Physical Review C, 2001

First Measurements of the Double-Polarization Observables F , P , and H in ω Photoproduction off Transversely Polarized Protons in the N* Resonance Region (original) (raw)

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