Polarisation parameters in positive pion photoproduction

Measurements have been made of the polarisation parameters Σ, T and P for the process γp → π⁺n in the photon energy range 520–2250 MeV at c.m. angles between 30° and 120°. These data were obtained in a double polarisation experiment, using the polarised photon beam from the Daresbury electron synchrotron incident on a polarised proton target. The data are compared with predictions from current theoretical analyses.     

Differential cross sections of neutral pion photoproduction from hydrogen in the energy region from 390 MeV to 975 MeV

The differential cross sections of the reaction γp→π⁰p have been measured at photon energies between 390 MeV and 975 MeV with an energy step of 20 or 25 MeV. The angular region covers 11 angles between 15° and 130° in the c.m.s. A combination of a magnetic spectrometer and photon detector was used for the measurement in the angular region from 50° to 130°. At forward angles of 15°, 35° and 50°, π⁰ mesons were detected using a π⁰ detector consisting of a pair of photon detectors. The data obtained with two different detection systems overlap at the angle of 50° and coincide with each other within the experimental error. The results are compared with those of phenomenological partial-wave analyses.     

Positive pion production from polarized protons by linearly polarized photons in the energy range 280–420 MeV

The method is described of measuring the polarization observables Σ, P and T for the reaction γp → nπ⁺ in a double polarization experiment (polarized target + polarized beam). The measured angular distribution of these observables are presented for the photon energy range 280–420 MeV at c.m. pion emission angles between 30° and 150°. The obtained experimental data are included in the energy-independent multipole analysis of the reactions γp → Nπ.     

Measurement of polarized target asymmetry on γn→π−p around the second resonance region

The polarized target asymmetry for γn→π^?p was measured over the second resonance region from 0.55 to 0.9 GeV at pion c.m. angles between 60° and 120°. A double-arm spectrometer was used with a deuterated butanol target to detect both the pion and the proton, thus considerably improving the data quality. Including the new data in the amplitude analysis, the radiative decay widths of three resonances were determined more accurately than before. The results are compared with various quark models.     

Forward photoproduction of neutral pions on protons in the third resonance region

Four angular distributions of the differential cross section of the reaction γ + p → π⁰ + p have been measured at the Bonn 2.5 GeV Synchrotron at pion c.m. angles between 3° and 63° in the photon energy range from 0.9 GeV to 1.2 GeV. The π⁰ mesons were detected by their two decay photons. The data are compared with data of other laboratories and predictions of two recent partial-wave analyses.     

Measurement and MIA analysis of the neutron differential cross section and polarization in the α-D break-up at 33 MeV c.m.

Differential cross sections at 0° and 20° and polarizations at 20° have been measured for the ²H(α, n) αp reaction at E_α = 100 MeV and the ⁴He(d, n) αp reaction at E_d = 50 MeV. Data have been analyzed by the Modified Impulse Approximation (MIA). Satisfactory agreement was obtained but some discrepancy remained in the analysis of polarization data.     

Exchange-component analysis of neutral pseudoscalar meson photoproduction

π⁰ and η photoproduction data in the region of 4 GeV are decomposed into t-channel exchange components of definite isospin and parity. The latter are discussed in terms of Regge exchange models and compared to vector-meson dominance related processes. The isospin-one natural parity-exchange component is smooth and structureless. The dominant unatural parity exchange in π⁰ photoproduction has isospin zero. As in π^± photoproduction the ratio of natural to unnatural parity exchange is found to be larger than the vector-dominance expectation. Complementary information from a recent spin decomposition of γp → π⁰p gives further insight into the SU (3) properties of the exchanges. We predict unmeasured quantities and stress, in particular, the importance of studying γn → π⁰n with polarised photons.     

Polarization of recoil protons from the reaction γp → π0p in the proton energy range 450–800 MeV

Measurement of secondary-proton polarization from the reaction γp → π⁰p have been performed in the proton energy range 500–800 MeV at c.m. pion emission angles 100°, 120°, 140°. The experiment was carried out using an optical spark chamber telescope at the output of the magnetic spectrometer. The obtained experimental data are included in a Walker-type analysis in order to verify the parameters of the resonances P₁₁(1470), D₁₃(1570) and S₁₁(1535). Proton polarization in the reaction γp → π⁰p was measured for a photon energy of 450 MeV at a c.m. pion emission angle of 105° using photons linearly polarized at 45° to the reaction plane. A liquid hydrogen target in the field of a superconducting magnet was used for the separation of the P_x′ and P_z′ components of the secondary-proton polarization vector.Data are obtained for three components (P_x′, P_y, P_z′) of the proton polarization. The obtained results are compared with predictions of different multipole analyses of photoproduction.     

Systematics of (p,p′) and (p, α) spectra from 14 MeV proton bombardment of medium-A targets

Differential cross sections have been measured between 30° and 150° for the (p, p′) and (p, α) reactions induced by 14 MeV protons in the following targets: ³⁵Mn, ³⁶Fe, ⁵⁸Ni, ⁵⁹Co, ⁶²Ni, ⁶³Cu and ⁶⁴Zn. The results have been compared with the spin-dependent statistical theory and good agreement was obtained for the (p, α) reactions with a level density parameter a = (0.138±0.008)A MeV^?1. This value is substantially lower than that obtained in a spin-independent analysis of the same data. The agreement of the (p, p′) spectra with theory is poor and it is found that a 15–40% contribution from precompound emission is required. The emission of low-energy protons from the (p, np) reaction was observed in all cases and comparison of the cross sections with these of the corresponding (p, n) reactions yields information on the competition between γ-ray and proton emission.     

Fluctuations in inelastic proton scattering from58Ni in the energy range 17.1 to 20.6 MeV

Excitation functions of proton elastic and inelastic scattering on⁵⁸Ni have been measured for proton energies in the range 17.1 to 20.6 MeV, at laboratory angles of 90°, 120° and 155°. All show cross section fluctuations. Excitation functions are presented for the elastic and for five inelastic groups in the energy range 18.1 to 18.59 MeV. These were analyzed by the Fourier analysis method, and the average level width found to be about 13 keV. The observation of strong fluctuations in the higher inelastic yields has implications for several microscopic analyses reported in the literature of⁵⁸Ni(p, p′) data obtained at 17.7 MeV incident proton energy.     

DSA lifetime measurements in21Ne at high recoil velocity

States in²¹Ne up to 5 MeV excitation energy have been populated using the inverted reaction²H(²⁰Ne,pγ). The Doppler shift attenuation (DSA) analysis of thepγ coincidence spectra taken in a Ge(Li) detector at 45° and 135° and an annular silicon surface barrier detector near 0° yielded the lifetimes of 8 states in²¹Ne. Due to the large recoil ofπ _i/c～ 4% three new lifetimes were determined for the short lived levels at 2.80, 4.68 and 4.73 MeV, namely 10±4 fs, 16±4 fs and 10±4 fs, respectively. The results are compared with rotational and shell model calculations.     

Statistical analysis of the (d,p) and (d,d) reactions on 40Ca

Excitation functions of the ⁴⁰Ca(d, p)⁴¹Ca and ⁴⁰Ca(d, d)⁴⁰Ca reactions have been measured at 45°, 90°, 135° and 170° from E_d = 4.50 to 5.43 MeV in 10 keV steps. Angular distributions of these reactions have been taken at E_d = 4.70, 5.00 and 5.30 MeV from 25° to 170° in 5° steps. Transitions were observed to the excited states for the range 0.0 ≦ E_x ≦ 3.74 MeV in ⁴¹Ca. Rapid fluctuations in the excitation functions and strong variations of the angular distributions with the incident energy were observed, suggesting that the contribution from compound nucleus processes is very large. Various quantities extracted from the experimental data were compared to the predictions of the statistical theories combined with the DWBA theory for the calculation of the direct reaction amplitudes. The results of the present analysis are consistent with the predictions of the standard statistical theories based on the neglect of the channel-channel correlation.     

Double-differential cross sections and kerma coefficients for light-charged particles produced by 96 MeV neutrons on carbon

Double-differential cross sections of inclusive light-ion (p, d, t, ³He and α) production in carbon induced by 96 MeV neutrons have been measured at eight laboratory angles from 20° to 160° in steps of 20°. Experimental techniques, as well as procedures for data taking and data reduction, are presented. Deduced energy-differential and production cross sections are herewith reported. Experimental cross sections are compared with theoretical reaction model calculations and experimental data in the literature. The measured production cross sections for protons, deuterons, tritons, ³He, and α particles support the trends suggested by data at lower energies. Deduced partial kerma coefficients for carbon are also shown.     

Forward photoproduction of neutral pions on polarized protons in the third resonance region

Angular distributions of the target symmetry for the reaction γ + p → π⁰ + p have been measured at the Bonn 2.5 GeV Electron Synchrotron at pion c.m. angles between 13° and 63° and photon energies of 1.0 and 1.1 GeV. The π⁰ mesons were detected by their two decay photons with total absorption lead-glass ?erenkov counters. Butanol was used as target material in a continuous flow ³He cryostat operating at 0.5 K and 25 kG. The π⁰ counting rate from free protons in the butanol target was derived from the measurements of the differential cross section on hydrogen. The data are compared with data of other laboratories and the results of two recent partial-wave analyses.     

Measurement of polarized target asymmetry in γp → π+n below 1.02 GeV

The polarized target asymmetry for the process γp → π⁺n has been measured for incident photon energies below 1.02 GeV over a range of c.m. angles from 40° to 160°. π⁺ mesons from a polarized butanol target were detected by a magnetic spectrometer. The results are compared with predictions given by existing analyses. A tentative interpretation of the data is performed, and a larger contribution of S-wave resonances is suggested. The photocouplings of dominant resonances were hardly changed by the inclusion of new data and they seem to be almost uniquely determined.     

Study of the (p,pn) reaction in light nuclei

The (p, pn) reaction on ²H, ⁶Li, ⁷Li, ⁹Be has been studied at 47 MeV bombarding energy. Excitation energy spectra and energy sharing spectra are presented. Fragmentary information on ¹⁰B, ¹¹B and ¹²C was also obtained. Sequential decay contributions to the ⁶Li(p, pn)⁵Li¹ reaction suggest an admixture of parentage $\text{(α)π(}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)π(}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)}$ for the (3^?), 23 MeV excited state of ⁶Be. A possible 15.5 MeV excited state in ⁶Be is reported. An extensive study of the ⁹Be (p, pn)⁸Be reaction for 45 MeV protons was made. Results for θ_p = θ_n = 25°, 30°, 35°, 40°, 45°, 55°, 65°; θ_n = 40°, θ_p = 25°, 30°, 35°, 40°, 45°, 55°, 65°; θ_p/θ_n = 40°/45°, 38.5° are reported and compared to DWIA calculations. Agreement is good when the lower momentum components of the wave function are sampled, and deteriorates as higher momenta are required. Results are in agreement with the Cohen and Kurath spectroscopic factors for ⁹Be.     

Differential cross sections for the photoproduction of eta mesons from protons near 2 GeV

Differential cross sections for the process γp → pη have been measuredd at c.m. angles of 28°, 35° and 42° at incident energies between 2 GeV and 2.8 GeV. Data from an earlier experiment below 2 GeV have been re-analysed and corrected. The whole set of data is compared with the form (s?M²)² dσ/dt, which fits data at higher energies. There is good agreement above 2 GeV, particularly at the largest angle, but strong departures below.     

A measurement of polarization in π−p→ K°Λ° at 5 GeV/c

We have measured the Λ° polarization in π^?p→ K°Λ° at 5 GeV/c, using a data sample of 3709 events. The polarization is positive for small t, passes through zero near t = ?0.3 (GeV/c)², and becomes large and negative at larger t, consistent with a value of ?1.0 for t between ?0.7 and ?1.6(GeV/c)².     

Impact parameter description of the charge exchange process π+ p → π° (π+ p)

The “Reggeometry” model — universal impact parameter profile and Reggen behaviour — is applied to recent data on π⁺ p → π° (π⁺ p) at different energies and (π⁺p) missing masses, including Δ production. We are able, in particular, to explain the filling of the dips and the variation of the slope with respect to the missing mass.