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Photons originating from coherent bremsstrahlung have been measured over a large dynamic range for the reaction of 200 MeV alpha particles with protons. At low photon energies the bremsstrahlung spectrum exhibits the classical behavior with an approximate 1/E-gamma shape. At higher photon energies there is a pronounced contribution from capture into the unbound ground state and first excited state of Li-5. These results allow one, for the first time, to test theoretical models for a consistent description of bremsstrahlung and radiative capture in a complex system. Calculations predict both features qualitatively but fail to account for their relative importance.

The proton-proton bremsstrahlung process, including both coplanar and non-coplanar kinematics, has been measured with polarized protons of 190 MeV. High-precision cross sections and analyzing powers have been obtained. Cross sections as a function of non-coplanarity angle are presented and show large variations of dynamical origin. Non-coplanar analyzing powers have been measured for the first time and are compared to theoretical predictions. (C) 2000 Elsevier Science B.V. All rights reserved.

An exclusive proton-proton bremsstrahlung measurement has been performed with polarized protons of 190 MeV. Absolute cross sections and analyzing powers have been measured with unprecedented accuracy in a large part of the phase space. The data are compared with state-of-the-art theoretical calculations including higher-order off-shell effects, like the Delta isobar and meson-exchange currents. Surprisingly, the calculations are unable xo describe the data in detail.

We report on a measurement of subthreshold eta and pi(0) mesons in the reaction Ar + Ca at 180A MeV. We find that the ratio of the eta to pi(0) meson-production cross section is more than a factor of 20 smaller than the one expected from threshold-energy scalings of meson production. In addition, the multiplicity of high m(t) pi(0) increases faster with the centrality of the reaction than the multiplicity of the bulk of pi(0) mesons. This behavior is explained by the rescattering of pi mesons in nuclear matter at the origin of most energetic particles.

Two high-accuracy measurements of cross sections and analyzing powers for the proton-proton bremsstrahlung reaction have been performed at 190 MeV beam energy. These measurements provide not only the most accurate exclusive cross-section and analyzing-power data to date, but also a wide phase-space coverage. Thus, an accurate test of nucleon-nucleon interaction models is made feasible. The experimental setup and the analysis procedure are discussed in detail. Microscopic calculations and calculations based on the soft-photon theorem show deficiencies in explaining the bulk of the data.

Data on proton-neutron bremsstrahlung have been obtained from a measurement of the quasifree breakup channel in proton-deuteron bremsstrahlung. This high-precision measurement, with an incident proton energy of 190 MeV, is fully exclusive; i.e., the protons, the neutron, and the photon have been detected. The quasifree differential cross sections obtained are compared with microscopic calculations and calculations based on soft-photon models. There are sizable differences between the models and also between the models and the data obtained for this simple process.

For the first time a high-precision proton-deuteron bremsstrahlung experiment has been performed in which all the different exit channels have been distinguished separately. High-precision cross sections and analyzing powers in one of the outgoing channels, namely, the coherent bremsstrahlung with a proton and a deuteron in the final state, are presented at 190 MeV incoming proton beam energy and are compared to calculations based on the low-energy theorem. The results of the calculations vary considerably calling for a fully microscopic calculation. However, using a recipe including the initial- and final-state interactions, the predictions come close to the data.

We report on a measurement of hard photons (Eg>30 MeV) in the reaction Ar+Ca at 180A MeV at an energy in which photons from the decay of pi0 mesons are dominating. Simultaneous measurement with the TAPS spectrometer of the photon spectrum and photon-photon coincidences used for the identification of pi0 enabled the subtraction of pi0 contribution. The resulting photon spectrum exhibits an exponential shape with an inverse slope of E0=(53+-0.03(stat)-5+8(syst)) MeV. The photon multiplicity, equal to (1.21+-0.03(stat)+0.3-0.2(syst))10E0-2, is roughly one order of magnitude larger than the value extrapolated from existing systematics. This enhancement of the hard photon production is attributed to a strong increase in the contribution of secondary np collisions to the total photon yield. We conclude that, on average, the number of np collisions which contribute to the hard photon production is 7 times larger than the number of first chance np collisions in the reaction Ar+Ca at 180A MeV., 15 pages, 4 figures, references added

Bremsstrahlung emitted in the α + p reaction at 50 MeV/nucleon was studied using a 200 MeV α -particle beam and a liquid hydrogen target. Double-differential photon cross sections were measured over a wide range of angles and energies. Coherent bremsstrahlung was found to be strong for all photon energies. The cross section is enhanced at the highest photon energies and is characteristic of direct capture to the unbound 5 Li ground and first excited state. With direct capture as a limiting case of coherent bremsstrahlung a consistent reaction picture can be obtained.

Virtual bremsstrahlung yields measured in \(\vec p + p \to p + p + {e^ + } + {e^ - }\) and \(\vec p + d \to {}^3{\text{He}} + {e^ + } + {e^ - }\) are presented. The experiments were performed with a 190 MeV polarized proton beam obtained from the cyclotron AGOR at KVI in Groningen. Differential cross sections, response functions and analyzing po- wers were obtained for both reactions in exclusive measurements in which all outgoing particles were measured in a coincidence setup between SALAD and TAPS. The data are compared with gauge-invariant calculations using a NN T-matrix fitted to elastic phase-shifts. For pp→ppe + e - a reasonable agreement is found for all measured virtual-photon invariant masses, M γ >15 MeV/c2 up to 80 MeV/c2. For the pd→3He e + e - angular distributions, the calculations un- derestimate the data for θCM >100° similar to what is found in the real-photon capture reaction.

A series of bremsstrahlung measurements have been performed at KVI with the 190 MeV polarized proton beam of the new superconducting cyclotron, AGOR. The aim of these measurements is to investigate the dynamics of interactions involving intermediate off-shell nucleons. Nucleon-nucleon bremsstrahlung is the most fundamental process used for such studies as it involves the strong interaction between two nucleons and the well-known electromagnetic interaction. The present experiment provides the most accurate data on the proton-proton system. In addition the first exclusive proton-proton virtual-bremsstrahlung data ever is presented. The accuracy of the real bremsstrahlung data is high enough to investigate higher-order effects such as the virtual Δ-isobar and meson-exchange currents. None of the microscopic calculations is able to describe the data both in magnitude and in shape. The virtual-bremsstrahlung data are integrated over the detector acceptance. This same integration is done for two different soft-photon calculations for comparison.

Exclusive differential cross sections of virtual bremsstrahlung in proton-proton scattering below the pion-production threshold have been measured and their leptonic-angle dependence was exploited to determine all six nucleon-nucleon electromagnetic response functions in the timelike region. The data are compared to a low-energy calculation and a fully relativistic microscopic model. Over the entire phase space the low-energy calculation gives a better description of the cross sections than does the microscopic model. At large virtual-photon masses both models are unable to account for the observed strength of the interference response functions.

Exclusive differential cross sections of virtual bremsstrahlung ih proton-proton scattering below the pion-production threshold have been measured for the first time. The total cross section integrated over photon invariant masses of 15 to 80 MeV/c(2) and integrated over the acceptance of the detector is 3.2 +/- 0.1 +/- 0.5 pb. The data are compared to a low-energy calculation and a fully relativistic microscopic model, which predict a virtual bremsstrahlung cross section of 3.4 and 5.9 pb, respectively. Over the entire experimentally covered phase space, the low-energy calculation gives a better description of the data than the microscopic model. [S0031-9007(99)08793-1].

A series of bremsstrahlung measurements have been performed at KVI with the 190 MeV polarized proton beam of the new superconducting cyclotron AGOR. The aim of these measurements is to investigate the dynamics of interactions involving intermediate off-shell nucleons. Nucleon-nucleon bremsstrahlung is the most fundamental process used for such studies as it involves the strong interaction between two nucleons and the well-known electromagnetic interaction. The present experiment provides the most accurate experiment to date on the proton-proton system. The accuracy is high enough to investigate higher order effects such as the virtual Δ-isobar and meson exchange currents. Surprisingly, none of the microscopic calculations is able to describe the data both in magnitude and in shape.