Measurement of the proton polarization in deuteron photodisintegration at photon energies between 350 and 700 MeV

The proton polarization in the γd → pn reaction has been measured at a c.m. angle of 90° and photon energies between 350 and 700 MeV, using a carbon polarimeter. The magnitude of the polarization shows a sharp energy dependence with a peak of about ?80% at around 500–550 MeV. This feature cannot be explained by conventional models and seems to indicate a new mechanism in the dibaryon system.     

Differential cross sections of proton Compton scattering in the energy range between 450 and 950 MeV

The differential cross sections of the proton Compton scattering around the second resonance have been measured at a c.m. angle of 90° for incident photon energies between 450 MeV and 950 MeV in steps of 50 MeV, and at an angle of 60° for energies between 600 MeV and 800 MeV. The results show that the peak of the 2nd resonance agrees with that of the pion photoproduction process. We also calculated the proton Compton scattering based on unitarity and fixed-t dispersion relations. The calculation describes well the data of the cross section and the recoil proton polarization.     

Measurement of the angular distribution of the polarization of the recoil proton from the photoproduction of neutral pions on hydrogen at a photon energy of 360 MeV. II

The angular distribution of the polarization of the recoil protons from the reactionγ+p→π ⁰+p has been measured at a photon energy of 360 MeV and at pion CM angles of 58°, 75°, 96° and 105°. The polarization of the protons has been determined by the left to right ratio in scattering on a helium gas target. The trajectory of each scattered proton has been measured by a system of spark chambers.     

Measurement of the polarization of the recoil proton from the photoproduction of neutral pions on hydrogen in the region of the first resonance. I

The polarization of the recoil proton from the reactionγ+p→π ⁰+p has been measured using liquid helium as polarization analyser. The photon energy has been varied between 250 and 360 MeV, the pion angle (CM) between 58° and 100°.     

The polarization of protons from the^{12} C\left( {d,\vec p_0 } \right)^{13} C reaction at low deuteron energies

The polarization of protons produced in the \(^{12} C\left( {d,\vec p_0 } \right)^{13} C\) reaction has been measured at 45° lab for deuteron energies between 0·25 and 1·15 MeV. Besides, the angular distribution of proton polarization at 0·975 MeV has also been measured. The result was analysed in terms of associated Legendre polynomials expansion.     

Angular dependence of the polarization of the recoil proton from the reaction γp→π0 p in the region of the second resonance

The polarization of the recoil proton from the reactionγp→π ⁰ p has been measured for photon energies between 600 and 1,200 MeV and pion c.m. angles between 90° and 150°.     

Differential cross sections of proton compton scattering at photon laboratory energies between 700 and 1000 MeV

Differential cross sections of proton Compton scattering have been measured at the Bonn 2.5 GeV synchrotron. 78 data points are presented as angular distributions at photon lab energies of 700, 750, 800, 850, 900, and 950MeV. The c.m. scattering angle ranges from 40°–130°, corresponding to a variation of the four momentum transfer squared betweent=?0.10 tot=?0.96 GeV² at 700 and 950 MeV, respectively. Two additional differential cross sections have been measured at 1000MeV, 35.6° and 47.4°. The angular distributions show forward peaks whose extrapolations to 0° are consistent with calculated forward cross sections taken from literature. The small angle data (|t| ?0.2 GeV²) together with the calculated cross sections at 0° are also consistent with the assumption of a slope parameterB of 5 GeV^?2. For the first time a rerise of the angular distributions towards backward angles has been observed. It becomes less steep with increasing energy. The most interesting feature of the angular distributions is a sharp structure which appears betweent=?0.55 GeV² at 700MeV andt=?0.72 GeV² at 950 MeV. Such a rapid varation of the differential cross section witht has never been ovserved in elastic hadron-hadron scattering or photoproduction processes. It indicates the existence of a dynamical mechanism which could be a peculiarity of Compton scattering.     

Angular dependence of the polarization of the recoil proton from the reaction γp→π0 p in the region of the third resonance

The polarization of the recoil proton from the reactionγp→π ⁰ p has been measured for photon energies between 900–1,350 MeV and pion c.m. angles between 70° and 150°. There are significant deviations from recent analysis.     

Polarization of preequilibrium proton emission in the 93Nb + 14N reaction

Spin polarization of protons emitted at 20° and 40° in the ⁹³Nb + ¹⁴N reaction at 95 MeV has been measured by the double scattering method using a polarimeter particularly designed for protons having a continuous energy distribution.The result shows that the polarization is small for low-energy protons, but increases smoothly with the increase of proton energy, reaching around + 20 % at about 20 MeV in the center-of-mass system. Energy and angular distributions of protons measured in the same reaction indicate coexistence of equilibrium and preequilibrium components in the proton emission of interest, the fraction of the preequilibrium component increasing with the increasing proton energy. If we assume that protons emitted in equilibrium are completely unpolarized, and that the value of polarization (P) for the preequilibrium component is independent of proton energy, the present result is consistent with $\text{P ? + 22 \%}$ for the emission at 20° and $\text{P ? + 38 \%}$ for the emission at 40°.The result is discussed in terms of the hot-spot model for precompound decay.     

Cross-section asymmetry in the photodisintegration of the deuteron by polarized photons

The asymmetry of cross sections for the photodisintegration of the deuteron has been measured in the linearly polarized photon energy range 80–600 MeV at c.m. proton emission angles 75°–150°. The obtained data are not found to be in agreement with theoretical predictions.     

Compton scattering from deuterium and the polarizabilities of the neutron

A new program of Compton scattering on deuterium is under way at the tagged-photon facility at MAX-Lab in Lund, Sweden. We will measure differential cross sections between 60° and 150° over the photon energy range 60–115?MeV in 5?MeV steps, with the ultimate goal of obtaining new precision information on the electric and magnetic polarizabilities of the neutron.     

Large angle cross section and analyzing power for proton-4he elastic scattering between 185 and 500 MeV

The differential cross section for the elastic scattering of protons from ⁴He has been measured for ten proton energies between 185 and 500 MeV in the angular range 144° to 168° in the lab system. The analyzing power has also been measured for seven energies in the same angular range. The differential cross section does not show the marked backward peaking that has been observed at both lower and higher energies. The possible structure in the 180° excitation function suggested for energies around 240 MeV is not observed. The analyzing power is large and negative, and shows strong dependence on both energy and angle.     

Photoproduction of neutral pions on hydrogen at photon energies between 200 and 440 MeV

At the Bonn 500 MeV electron synchrotron the differential cross section of the reaction γ+p → π⁰+p has been measured detecting the recoil proton by a magnetic spectrometer. Angular distributions between pion c.m. angles of 50 ° and 160 ° were taken at photon energies between 220 and 420 MeV.     

Two-body photodisintegration of 3He and 4He in the Δ(1236) region

Differential cross sections for the reactions ³He(γ, p)d and ⁴He(γ, p)t were measured at proton c.m. angles of 60° and 90° for photon energies ranging from 150–450 MeV with an average resolution of 8 MeV. Bremsstrahlung was used as the photon source; deuterons/tritons were analyzed in a magnetic spectrometer whereas coincident protons were detected in a plastic scintillator telescope. The experimental method includes a calibration by means of ¹H(γ, π⁰)p differential cross section measurement at 90° c.m. in the same photon energy range. The ³He and ⁴He two-body photodisintegration differential cross sections show a monotonically decreasing variation with photon energy. In addition, partial data on the differential cross section of the reaction ⁴He(γ, n)τ at 90° and 120° neutron c.m. angle are given.     

Die Energieabhängigkeit des Polarisationsgrades der Neutronen aus der Reaktion3H(d,n)4He unter 70° (Lab.) für Deuteronenenergien unterhalb 2 MeV

The polarization of neutrons from thed-t reaction was measured at seven deuteron energies between 0.3 and 1.83 MeV at 70° (lab.). In a time-of-flight experiment with a high pressure helium gas scintillator as a scatterer the left and right scattered neutrons were detected in two plastic scintillators. The phase shifts fromHoop andBarschall were used to deduce neutron polarizations from scattering asymmetries. The neutron polarizations are atE _d=0.3, 0.6, 0.95, 1.26, 1.4, 1.56, 1.83 MeV respectively ?0.5±1.3, ?3.9±1.6, ?4.2±1.1, ?6.8±1.7, ?11.7±1.4, ?13.1 ±1.4, ?13.5±1.2%. These results indicate that at deuteron energies as low as 0.3 MeV thed-t reaction has to be described bys-wave deuterons.     

Measurement of the two-body photodisintegration of3He in theΔ(1236) resonance region

The³He(γ, p)d reaction has been measured in the photon energy region between 200 MeV and 450 MeV at proton c.m. angles between 20° and 150°. Protons and deuterons were detected in coincidence with two time-of-flight spectrometers consisting of scintillation counters; both particles were identified and their energies and angles were measured. The angular distributions show a strong forward peak. The differential cross sections fall off with increasing photon energy without showing a significant influence of theΔ resonance.     

Winkelverteilung der Polarisation der Neutronen aus der Reaktion14C(d,n 0)15N bei Deuteronenenergien zwischen 1,3 und 1,9 MeV

Polarization distributions of ground state neutrons emitted from the¹⁴C(d,n ₀)¹⁵N reaction were investigated over the angular range from 15 ° (lab) to 150 ° (lab) at bombarding energies of 1.28, 1.55 and 1.88 MeV. Scattering of neutrons from helium served as polarization analyzer. The experimental results show a large variation with energy of the polarization ranging betweenP(Θ_lab=130 °)=?21% andP(Θ_lab=130 °)=+50% at 1.28 and 1.88 MeV respectively.     

Measurement of the proton polarization in the 3He(d,p)4He Rection between 2.0 and 6.0 MeV

Angular distributions of the polarization of ³He(d, p)⁴He protons have been measured for unpolarized deuterons with laboratory energies of 1.99, 2.81, 3.94 and 6.00 MeV. The polarizations were determined from the left-right asymmetry of elastic scattering through 60° in ⁴He gas using a vaned polarimeter whose analyzing power was computed by trajectory tracing from the known p-α polarizations. A contour diagram of proton polarization for deuteron energies of 1 to 12 MeV is presented. A Legendre polynomial expansion of four or five terms has been fitted to the products p(θ)σ(θ). The coefficients of the expansions of these and other measurements show resonance-like behaviour at ⁵Li excitations of 20.0 and 20.9 MeV. The vector-polarized beam and polarized-target analyzing powers are compared with the proton polarization. The proton polarizations are in good agreement with the ³H(d, n)⁴He neutron polarizations when compared at the same entrance-channel energy but disagree when compared at equal exit-channel energies or compound-nucleus excitations.     

Study of three-nucleon mechanisms in the photodisintegration of 3He

The cross section of the ³He(γ,pp)n reaction has been measured for the first time over a wide photon energy and proton angular range (200 MeV ≤ E_γ ≤ 800 MeV; 20° ≤ ϑ_p^lab ≤ 160°) using the large acceptance detector DAPHNE at the tagged photon facility of the MAMI microtron in Mainz. The wide kinematical coverage of the measurement has allowed a detailed analysis of three-nucleon absorption mechanisms. A model developed by Laget explains the main characteristics of the data in the Δ resonance region.     

Forward photodisintegration of the deuteron at 10.74 MeV photon energy

The absolute differential cross section for the photodisintegration of the deuteron at 0° for the outgoing proton has been measured at 10.74 MeV lab photon energy using a bremsstrahlung beam, a deuterated target, a magnet system, and a surface barrier detector. The absolute cross section is (4.7±0.85) b/sr and was determined with an angular resolution of 1.25°. The result, pertaining to a 4.6 MeV wide photon energy interval, favours a minimum in the differential cross section around 10 MeV photon energy.Supported in part by the Deutsche Forschungsgemeinschaft (SFB 201)