Compton scattering from 4He in the Δ(1232) resonance region

Selke, O.; Hünger, A.; Kraus, Alfred A.; Schumacher, M.; Wichmann, R.; Ahrens, J.; Arends, H. J.; Beck, R.; Peise, J.; Schneider, M.; Wissmann, F.

doi:10.1016/0370-2693(95)01580-9

Cited by 9 publications

(9 citation statements)

References 11 publications

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“…At energies above the ∆ peak the results of different implementations [46,109] of the ∆-hole model are different. A nice agreement with the experimental small-angle data [44] was found in Ref. [46], in which the ∆ contribution was calculated with the parameters borrowed from [108,253].…”

Section: The Extended Schematic Modelsupporting

confidence: 82%

“…The occurance of this discrepancy was very surprising because θ LAB = 40 • is close enough to the forward direction so that any theory which reproduces the photoabsorption cross section and has a correct low-energy limit should also reproduce the Compton scattering differential cross section. It is interesting to note that the same observation was made in first interpretations of Compton differential cross sections measured for 4 He at the same angle θ LAB = 40 • [44,109] This observation seemed to suggest that some omission should be in the ∆-hole approach as formulated in Refs. [107,108].…”

Section: Compton Scattering Bysupporting

confidence: 57%

“…The results of the recent Mainz experiments [44,46] for the differential cross section are shown in Fig. 6.1 together with theoretical predictions to be discussed below.…”

Section: Compton Scattering By 4 He In the ∆ Rangementioning

confidence: 88%

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Compton scattering by nuclei

et al. 2000

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The concept of Compton scattering by even-even nuclei from giant-resonance to nucleon-resonance energies and the status of experimental and theoretical researches in this field are outlined. The description of Compton scattering by nuclei starts from different complementary approaches, namely from second-order S-matrix and from dispersion theories. Making use of these, it is possible to incorporate into the predicted nuclear scattering amplitudes all the information available from other channels, viz. photon-nucleon and photon-meson channels, and to efficiently make use of models of the nucleon, the nucleus and the nucleon-nucleon interaction. The total photoabsorption cross section constrains the nuclear scattering amplitude in the forward direction. The specific information obtained from Compton scattering therefore stems from the angular dependence of the nuclear scattering amplitude, providing detailed insight into the dynamics of the nuclear and nucleon degrees of freedom and into the interplay between them. Nuclear Compton scattering in the giant-resonance energy-region provides information on the dynamical properties of the in-medium mass of the nucleon. Most prominently, the electromagnetic polarizabilities of the nucleon in the nuclear medium can be extracted from nuclear Compton scattering data obtained in the quasideuteron energy-region. In our description of this latter process special emphasis is laid upon the exploration of many-body and two-body effects entering into the nuclear dynamics. Recent results are presented for two-body effects due to the mesonic seagull amplitude and due to the excitation of nucleon internal degrees of freedom accompanied by meson exchanges. Due to these studies the inmedium electromagnetic polarizabilities are by now well understood, whereas the understanding of nuclear Compton scattering in the ∆-resonance range is only at the beginning. Furthermore, phenomenological methods how to include retardation effects in the scattering amplitude are discussed and compared with model predictions.

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Section: The Extended Schematic Modelsupporting

confidence: 82%

Section: Compton Scattering Bysupporting

confidence: 57%

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Compton scattering by nuclei

et al. 2000

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“…In this way the increase of the degree of linear polarization with decreasing u coll was investigated. Though improvements on the degree of linear polarization of coherent bremsstrahlung as a consequence of collimation have been discussed already for a long time [6], experiments have been carried out only to find collimation effects on the photon intensity [7-10], whereas the degree of linear polarization of collimated coherent bremsstrahlung has never been measured.The tagged photon facility at MAMI is especially suited for experiments of this type because the divergence if the electron beam is small (#0.1 mrad) and the electron energy is comparatively low (E 0 855 MeV) so that collimation effects can be seen at technically feasible collimation angles.The experimental arrangement was the same as described previously [11]. It consisted of the Mainz 48 cm diam 3 64 cm modular NaI(Tl) detector [12] positioned at a scattering angle of u lab 37 ± .…”

mentioning

confidence: 99%

“…The experimental arrangement was the same as described previously [11]. It consisted of the Mainz 48 cm diam 3 64 cm modular NaI(Tl) detector [12] positioned at a scattering angle of u lab 37 ± .…”

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confidence: 99%

Beam Asymmetry of Coherentπ° Photoproduction on4Hein theΔ(1232) Range M

et al. 1997

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Using coherent bremsstrahlung at MAMI (Mainz), the beam asymmetry of the differential cross sections for coherent p ± photoproduction on 4 He has been measured in the energy interval from 200 to 500 MeV at an angle of u lab 37 ± . The coherent (g, p ± ) reaction is used as a precise linear polarimeter for the first time. Agreement with predictions has been obtained on a *3% level of precision. [S0031-9007 (97)04489-X] PACS numbers: 25.20.Lj, 24.70. + s, 29.27.Hj Linearly polarized photons from backscattered laserlight or coherent bremsstrahlung [1] are indispensable tools of intermediate-energy nuclear and hadron physics.In parallel to their applications there is a need to investigate these processes in order to achieve the highest possible precision in predicting the degrees of linear polarization. In this connection the beam asymmetry of coherent p ± photoproduction on 4 He is of special interest because this quantity fulfills all the conditions required for a precise polarimeter. Both the nucleus and the p ± meson have no spins, so that p ± mesons are exclusively emitted as p waves through M1 excitation of the D resonance, a channel which is already strongly favored for the free nucleon. As a consequence, the degree of linear polarization of the photon beam is completely transferred to the azimuthal asymmetry of the p ± mesons. In the cm system the differential cross section is given bywhere e denotes the polarization vector, k the direction of the photon, and q the direction of the pion. The form factor F͑ D͒ is related to the density of nucleon centers. C͑v͒ is a polarization independent normalization factor.The present experiment has been carried out using the Glasgow tagged-photon facility [2] at MAMI (Mainz) [3]. A 100 mm diamond crystal has been used to produce coherent bremsstrahlung [4,5]. The beam was collimated using different opening angles u coll . In this way the increase of the degree of linear polarization with decreasing u coll was investigated. Though improvements on the degree of linear polarization of coherent bremsstrahlung as a consequence of collimation have been discussed already for a long time [6], experiments have been carried out only to find collimation effects on the photon intensity [7-10], whereas the degree of linear polarization of collimated coherent bremsstrahlung has never been measured.The tagged photon facility at MAMI is especially suited for experiments of this type because the divergence if the electron beam is small (#0.1 mrad) and the electron energy is comparatively low (E 0 855 MeV) so that collimation effects can be seen at technically feasible collimation angles.The experimental arrangement was the same as described previously [11]. It consisted of the Mainz 48 cm diam 3 64 cm modular NaI(Tl) detector [12] positioned at a scattering angle of u lab 37 ± . This angle is close to the maximum of the angular dependent differential cross section for coherent p ± photoproduction. In order to suppress the cosmic-ray background the NaI(Tl) detector is surrounded by a modul...

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