Proton polarization observables for the elastic and inelastic scattering of 500 MeV protons from Ca and Pb

Measurements for the elastic and inelastic scattering of 500 MeV protons from ⁴⁰Ca and ²⁰⁸Pb at small momentum transfers are reported. The induced proton polarization P and the spin rotation parameter Q were measured for the elastic scattering. The spin rotation parameters D_SS′, D_SL′, D_LL′, d_LS′ and the induced polarization P were measured for transitions to the 3⁻(3.37 MeV) and 5⁻(4.48 MeV) states in ⁴⁰Ca and the 3⁻(2.61 MeV) state in ²⁰⁸Pb. Comparisons of the data with the theoretical calculations were carried out in the framework of nonrelativistic and relativistic approaches. We extracted the spin-up and spin-down channels for the elastic scattering cross sections and found that predictions of the relativistic and nonrelativistic approaches agree well with the spin-up channel data and differ considerably in the spin-down channel.     

Microscopic, many-body approach to inelastic pion-nucleus scattering

We develop a microscopic, Fermi liquid approach to (π, π′;) scattering to low-lying final states. Application to excitation of a neutron particle-hole state in infinite nuclear matter shows that the ratio of π⁻ to π⁺ cross sections is sensitive to Fermi liquid parameters.     

Hadron-nucleus bound states

A new type of nuclear spectroscopy to study hadron-nucleus bound states is described. The first successful experiment was to search for deeply bound π⁻ states in heavy nuclei using the ²⁰⁸Pb(d,³He) reaction at GSI, in which a narrow peak arising from the 2p π⁻ orbital coupled with the neutron-hole states was observed at 135 MeV excitation energy. An improved experiment has just been carried out to separately identify the 1s and 2p π⁻ states. These experiments provide important information on the local potential strength, from which the effective mass of π⁻ is deduced to be 20 MeV. This method will be extended to search for η and ω bound states as well as for K⁻ bound states. The advantage of the bound-state spectroscopy versus invariant mass spectroscopy is emphasized.     

βγ(CP) correlation measurements and anti-analogue structure in the decay of Ca

β-γ(CP) correlation measurements have been carried out on the sequence in the decay of the ground state of ⁴⁹Ca to the (presumed) anti-analogue state at 3.105 MeV excitation in ⁴⁹Sc. An asymmetry parameter of A = −0.132 ± 0.017 was obtained, making any spin-parity assignment other than very unlikely for the 3.105 MeV state. The deduced Fermi matrix element for the decay is |M_{v| = |1.4 ± 9.7| × 10⁻³}, which leads to an isospin impurity ( ) corresponding to the mixing of the analogue state (at 11.6 MeV) and the 3.105 MeV state of ||² 1.6 × 10⁻⁵. This leads in turn to an effective Coulomb matrix element of |H_c| = |3.9 ± 27.4| keV, a low value compared to the value of 100 keV obtained from a theoretical estimate based on simple shell-model wave functions for the single-particle states involved.     

Electro-pion production on O to bou nd states of the residual nuclei

Differential cross sections for the reactions 16O(γ, π−π+−)16F16F to the sum of the four lowest lying states in 16F and 16N have been measured as a function of angle for pions with a kinetic energy of 30 MeV. The extracted ratios R = σ(γ, π−)/σ(γ, π+), the first ones to discrete final states as a function of angle, are in fair agreement with results obtained for the nucleon. For positive pions the energy dependence of the cross section has been measured at the angles of 45° and 90°. Distorted wave impulse approximation calculations fail to describe the energy dependence.     

The (p, t) and (p, τ) reactions on O at 39.8 MeV

Differential cross sections have been measured at forward angles for (p, t) and (p, τ) transitions from ¹⁷O to the ⁻ ground states and lowest-energy ⁻ states in the ¹⁵O and ¹⁵N mirror nuclei. The data are compared with DWBA calculations using simple single-particle and single-hole wave functions. When the (p, t) and (p, τ) transitions are considered separately, the calculated and experimental ratios of the ⁻ integrated cross sections to the ⁻ integrated cross sections agree to within 30 %; however, the ratios of (p, τ) cross sections to the mirror state (p, t) cross sections are calculated to be about twice as large as actually measured. This experimentally observed reduction of the (p, τ) cross section relative to the (p, t) cross section can possibly be attributed to interference between the S = 0 and S = 1 components of the (p, τ) transitions.     

Spectroscopy of C

The ¹⁴C(t, p)¹⁶C reaction locates five new states in ¹⁶C, at excitation energies of 3120 ± 15, 3983 ± 10, 4136 ± 10 and 6109 ± 15 keV, in addition to the g.s. and 1.76 MeV states. The 3.02 and 3.98 MeV states appear to be the second 0⁺ and 2⁺ 2p-2h states, respectively. The 4.14 MeV state has J^π = 4⁺ and the 6.11 MeV state has J^π = 2⁺, 3⁻, or 4⁺.     

Intermediate energy proton scattering and nuclear transition densities in nickel isotopes

Using the high-resolution spectrometer SPES-I, the angular distribution of 1.047 GeV protons scattered from ⁵⁸Ni, ⁶⁰Ni, ⁶²Ni, ⁶⁴Ni have been measured in the angular range 4–18°, up to 4.8 MeV excitation energy. The data are analyzed within the framework of Glauber multiple scattering theory using a spin-dependent NN scattering amplitude. The parameters of the neutron density distributions have been determined by a χ² analysis of elastic scattering. The inelastic data corresponding to the first 2⁺ and 3⁻ states are analyzed with the collective model and an attempt has been made to extract information about the corresponding neutron transition densities.     

Pionic excitation of giant resonances in Y

Inelastic scattering of π⁺ and π⁻ exhibits strongly excited giant resonance structures. Besides the giant quadrupole resonance centered around 14 MeV, structures are observed at 16.8 MeV which can be fitted with a mixing of L=0 and L=1, and around 25 MeV (E_x = 110A^−1/3).     

Elastic and inelastic scattering of neutrons from Fe and Cu : (II). Scattering and nuclear structure effects from coupled channels calculations

The differential cross sections for neutron scattering from ^{54, 56}Fe and ^{63, 65}Cu at energies between 8 and 14 MeV, which were reported in a companion paper, have been analyzed in the framework of the coupled channels formalism. Neutron potential deformations were extracted and compared with corresponding deformations deduced from the reanalysis of proton scattering measurements and Coulomb excitation results. The size of the Coulomb correction term in the absorptive proton potential is discussed. Matter root-mean-square radii are estimated from our potential and compared with results from -particle folding model calculations.     

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θcms = 75° and θcms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M1+3/2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M1+3/2-photoproduction amplitude at the resonance energy of 320 MeV is: |M1+3/2| = (39.6 ± 0.4) × 10−3 mπ+−1.     

The elastic scattering of protons by deuterium

Proton-deuteron elastic scattering was investigated with a gas target. Excitation curves were taken at 45.28°, 90.26°, and 118.92° c.m. for lab proton energies from 4.5 to 11.5 MeV. Angular distribution were taken at 4.45, 5.45, 6.50, 7.46, 8.47, 9.47, 10.47 and 11.47 MeV from 30° to 140° c.m. Differential cross sections were measured with an absolute error of less than ±3%. The scattering data were compared with predictions derived from the scattering amplitudes of Aaron, Amado and Yam ¹⁰). No evidence for the existence of ³He excited states was found in this energy range.     

DWBA and CCBA analysis of selected transitions in the C(d,τ) B reaction at Ed = 80 MeV

Angular distribution of the reaction ¹²C(d,τ) ¹¹B leading to the 3/2⁻ ground state and the 4.44 MeV excited (5/2⁻ state ¹¹B have measured at E_d = 80 MeV up to about 70° and 40°, respectively. The inclusion of second-order processes in the framework of CCBA calculations gives a good reproduction of the 3/2⁻ as well as of the DWBA forbidden 3/2⁻ angular distribution. The strong dependence of the cross section on the sign of the deformation supports a positive β₂ value for ¹¹B.     

Hypernuclei with sigma particles

The production of Σ particles in the (K⁻, π⁻) on ⁹Be at 720 MeV/c has been studied at the CERN proton synchrotron (PS). The missing-mass spectrum shows structures in the Σ region, which have been interpreted as belonging to hypernuclei with sigma particles. An upper limit of 8 MeV for the width of these states has been estimated.     

Hadronic production by ee collisions at the energy 990 MeV with the Orsay storage ring

Data were taken at the energy 2E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e⁺e⁻ annilations. Assuming a π⁺π⁻π⁰π⁰ production by the quasi two-body process e⁺e⁻ → → ωπ⁰ we give the correspondi ng cross section σ(e⁺e⁻ → π⁺π⁻π⁰π⁰) = (1.1 ± 0.5) 10⁻³² cm². Since no events with 3 and 4 charged pions have been observed σ(e⁺e⁻ → π⁺π⁻π⁰π⁻) 1.5 × 10⁻³³ cm².     

The elastic and inelastic scattering of intermediate energy protons on deuterium at small momentum transfer

The differential cross sections for the elastic and inelastic scattering of protons on deuterium have been measured for scattering angles less than 14° at 198.5, 297.6 and 456.6 MeV. These quantities were determined relative to dσ / dΩ for pp elastic scattering with a precision of typically 2%. The range of excitation energies for the (p, p') reaction was chosen to emphasize the region near the np threshold dominated by the final-state interaction in the ¹S₀ channel. Particular attention was given to the dependence on excitation energy of the spectra at 198.5 MeV to examine the sensitivity to the ¹S₀ scattering length, a_np In this paper all data are compared with a new, detailed formulation of a simple model of the reaction mechanism based on the impulse approximation. The experimental results differ from the predictions by typically 10% and the differential cross sections exhibit a sensitivity to the intermediate-energy nucleon-nucleon amplitudes. If the impulse approximation is used to estimate a_np from the data at 198.5 MeV a value of − 24.7 ± 0.4 fm is obtained.     

On the static quadrupole moments of the 21 states in Te and Te

The reorientation effect in Coulomb excitation was used to measure the static quadrupole moments of the first 2⁺ states in ¹²⁶Te and ¹²⁸Te. The particle-γ coincidence technique using a large NaI(Tl) crystal was employed to measure relative excitation probabilities at backward and forward projectile scattering angles. The Winther-de Boer multiple Coulomb excitation program was used to analyze the data. The influence of the deorientation effect was also determined. For positive interference via the second 2⁺ state the extracted quadrupole moments of the first 2⁺ states are; −0.20±0.09 b and -0.24±0.08 b for ¹²⁶Te and ¹²⁸Te respectively. The quadrupole moments of the first 2⁺ states of^{122,124,126,128,130}Te determined by different techniques are in excellent agreement with one another. The values are compared with recent theoretical calculations.     

Pion-transfer (n, d) and (d, He) reactions leading to deeply bound pionic atoms

Theoretical studies are given on the (n, d) and (d, ³He) reactions leading to deeply bound pionic atoms in heavy nuclei of configuration [(nl)_π·j_n⁻¹]J. The cross sections for various pionic and neutron-hole configurations in the case of a ²⁰⁸Pb target are calculated at incident energies 300–1000 MeV/u by using the effective number approach and the eikonal approximation for distortion. The effective number with a pion in the 1s or 2p state and a neutron hole in the orbit peaks around the same incident energy (T_n = 600 MeV) as the elementary cross section n+n→d+π⁻, where the momentum transfer matches the angular-momentum transfer of L = 5–7. The DWIA cross section for (n,d) producing a pion in the 1s or 2p orbit at T_n = 600 MeV is found to be around 42 or 75 μb/sr, respectively. At T_n = 350 MeV, where the momentum transfer is small, quasi-substitutional states of configurations and are preferentially populated with (n, d) cross sections of 95 and 190 μb/sr, respectively. The (d, ³He) cross sections are estimated to be an order of magnitude smaller than the (n, d) cross sections. Thus, the (n, d) and (d, ³He) reactions are found to be suited for the production of deeply bound pionic atoms.