DWIA Calculations Research Articles

Structures and production cross sections of p-shell Lambda-hypernuclei calculated with multi-configuration shell model

The high-resolution data of the 10B (e, e′K +) Be experiment done at the Jefferson National Laboratory reported a new bump, which cannot be explained by the DWIA calculation by employing the conventional shell-model wave functions. To describe the new bump, we have extended the model space by introducing a new configuration with 1ħω excitation for both nuclear and hyperon states. We show that the DWIA calculation by using the extended shell-model wave functions successfully explains the new bump for the first time, and that the p-state Λ in the lower molecular orbit plays an important role in the appearance of the new bump.

Quasi-free neutron and proton knockout reactions from light nuclei in a wide neutron-to-proton asymmetry range

The quasi-free scattering reactions 11C(p,2p) and 10,11,12C(p,pn) have been studied in inverse kinematics at beam energies of 300–400 MeV/u at the R3B-LAND setup. The outgoing proton-proton and proton-neutron pairs were detected in coincidence with the reaction fragments in kinematically complete measurements. The efficiency to detect these pairs has been obtained from GEANT4 simulations which were tested using the 12C(p,2p) and 12C(p,pn) reactions. Experimental cross sections and momentum distributions have been obtained and compared to DWIA calculations based on eikonal theory. The new results reported here are combined with previously published cross sections for quasi-free scattering from oxygen and nitrogen isotopes and together they enable a systematic study of the reduction of single-particle strength compared to predictions of the shell model over a wide neutron-to-proton asymmetry range. The combined reduction factors show a weak or no dependence on isospin asymmetry, in contrast to the strong dependency reported in nucleon-removal reactions induced by nuclear targets at lower energies. However, the reduction factors for (p,2p) are found to be 'significantly smaller than for (p,pn) reactions for all investigated nuclei.

Theoretical study of structure and production of [formula omitted] as a gateway to sd-shell hypernuclei

Energy level structures of the typical light sd-shell hypernucleus FΛ19, together with 18F, have been studied in detail with the multi-configuration shell model. Both positive-parity and negative-parity nuclear core excitations are fully taken into account by removing the spurious center-of-mass excitation effects. Corresponding to the J-PARC proposal of the 19F (K−,π−γ) FΛ19 experiment, the production cross sections have been estimated extensively, including the angular distributions. Starting with the elementary amplitudes for the K−n→Λπ− process, the microscopic DWIA calculations at high energy kaon momenta up to 1.8 GeV/c have been carried out for the first time. The calculated wave functions are also used to estimate the electromagnetic transition probabilities for both 18F and FΛ19. The detailed γ-decay schemes are presented and discussed.

Λhypernuclear production in (Kstop−,π) reactions reexamined

DWIA calculations of Lambda-hypernuclear production rates in stopped K- reactions on several p-shell targets used recently in experiments by the FINUDA Collaboration are reported. Chirally motivated K- + N -> pion + Lambda in-medium transition amplitudes are employed and the sensitivity of the calculated rates to the initial K- atomic wavefunctions and final pion distorted waves is studied. The calculated rates are compared with measured rates, wherever available, confirming earlier observations that (i) the calculated rates are generally lower than the measured rates, and (ii) the deeper the K- nuclear potential, the worse is the discrepancy. The A dependence of the calculated 1s Lambda hypernuclear production rates is discussed for the first time, providing a useful tool in resolving the issue of depth of the K- nuclear potential near threshold.

Elastic and inelastic scattering ofπ+andπ−onC12at 995 MeV/c

${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ elastic and inelastic scattering to the ${2}_{1}^{+}$(4.44 MeV) state on $^{12}\mathrm{C}$ at 995 MeV/$c$ were measured over an angular range for elastic-scattering from ${5.4}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${28.2}^{\ifmmode^\circ\else\textdegree\fi{}}$ and for inelastic scattering from ${15.2}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${22.8}^{\ifmmode^\circ\else\textdegree\fi{}}$. Both of the elastic-scattering data sets were well reproduced by first-order factorized momentum-space optical potential calculations with free \ensuremath{\pi}-$N$ elementary amplitudes and three different ground state densities, which were deduced from the charge density and microscopic model calculations, the cluster model and the shell model. We also extracted ${\ensuremath{\sigma}}_{\mathrm{tot}},{\ensuremath{\sigma}}_{\mathrm{el}}$, and ${\ensuremath{\sigma}}_{R}$ phenomenologically and compared them with a Fermi averaging model. The inelastic cross sections of ${\ensuremath{\pi}}^{+}$-$^{12}\mathrm{C}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$-$^{12}\mathrm{C}$ were compared with the DWIA calculations, one using the transition density(${0}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$) deduced by the cluster model and the other using the transition density deduced by the shell model.

Limitations of the distorted-wave impulse approximation in describing the energy dependence of theB10(n,p)Be10(g.s.) reaction

We report differential cross section measurements for the stretched transition from the $^{10}\mathrm{B}$ ground state (${J}^{\ensuremath{\pi}}={3}^{+}$) to the $^{10}\mathrm{Be}$ ground state (${J}^{\ensuremath{\pi}}={0}^{+}$) in the $^{10}\mathrm{B}$($n,p$)$^{10}\mathrm{Be}$ (g.s.) reaction. These data were obtained over the energy range from 70 to 240 MeV, covering momentum transfer values from 0.6 to 2.5 fm${}^{\ensuremath{-}1}$. In this momentum transfer range, the isovector tensor effective interaction dominates the transition. Cross sections are compared to zero- and finite-range distorted wave impulse approximation calculations using modern free and density-dependent effective interactions and a transition density consistent with ($e,{e}^{'}$) data. Good agreement is observed at energies above 120 MeV, but below this energy the cross sections are larger than the calculated values by more than 40%. The implications for DWIA calculations are discussed.

Measurement of single and double spin-flip probabilities in inelastic deuteron scattering on 12C at 270 MeV

The deuteron single and double spin-flip probabilities, S1 and S2, have been measured for the 12C(pol{d},pol{d}') reaction at Ed = 270 MeV for an excitation energy range between 4 and 24 MeV and a scattering angular range between Theta_lab = 2.5 and 7.5 deg. The extracted S1 exhibits characteristic values depending on the structure of the excited state. The S2 is close to zero over the measured excitation energy range. The SFP angular distribution data for the 2+ (4.44 MeV) and 1+ (12.71 MeV) states are well described by the microscopic DWIA calculations.

Spectroscopy of light Λ hypernuclei

We recently measured high-statistics and high-resolution spectra of p-shell Λ hypernuclei produced by the ( π +, K +) reaction. In this article, cross sections and their angular distributions of Λ 12C and Λ 16O are reported. The obtained cross sections are well reproduced by DWIA calculations.

Two-Step Contribution to Intermediate Energy (p, p') and (p, n) Reactions

We calculate the two-step contribution to (p,p') and (p,n) reactions at intermediate energy. We describe the motion of the incident nucleon with plane wave and compare the contribution from the two-step processes with that from the one-step processes. To describe the two-step processes, we extende the response functions into the nondiagonal ones with respect to the momentum transfer q. We performed a numerical calculation for the cross sections of the $^{12}$C, $^{40}$Ca(p,p') scatterings and the spin longitudinal and the spin transverse cross sections of the $^{12}$C,$^{40}$Ca(p,n) reactions at 346 MeV and 494 MeV. We found that the two-step contribution is appreciable in comparison with the one-step processes in higher energy transfer region for the spin longitudinal and the spin transverse (p,n) reactions. We also found that the two-step processes give larger contribution to the spin transverse (p,n) reaction than to the spin longitudinal reaction. This finding is very encouraging to interpret the discrepancy between the DWIA calculation and the experimental results of the spin longitudinal and the spin transverse cross sections.

Measurement of the 6Li(e,e′p) reaction cross sections at low momentum transfer

The triple differential cross sections for the 6Li(e,e′p) reaction have been measured in the excitation energy range from 27 to 46 MeV in a search for evidence of the giant dipole resonance (GDR) in 6Li. The cross sections have no distinct structures in this energy region, and decrease smoothly with the energy transfer. Angular distributions are different from those expected with the GDR. Protons are emitted strongly in the momentum-transfer direction. The data are well reproduced by a DWIA calculation assuming a direct proton knockout process.

Elastic and inelastic scattering of K + from 6Li and 12C

Cross sections for inelastic scattering of 635 and 715 MeV/ c K + from 12C are compared with DWIA calculations in order to check for possible density-dependent effects on K +-nucleon cross sections within nuclei. New fits to 715 MeV/ c K + scattering spectra from 6Li give elastic and inelastic cross sections and permit an evaluation of the density dependence of these effects. The same DWIA methods are also used to estimate quadrupole non-central contributions to elastic K + scattering from the 1 + ground state of 6Li, and these are found to be very small.

Formation of deeply bound1spionic states in the206Pb(d,3He)reaction

Recently, deeply bound pionic states were found experimentally in (d,$^3$He) reactions on $^{208}$Pb. The observed spectrum showed an excellent agreement with the DWIA calculation and the dominant peak was attributed to the pionic 2p state contribution. We studied theoretically $^{206}$Pb(d,$^3$He) reactions within the same model, and found that it is very likely to observe the pionic 1s state as an isolated peak in the $^{206}$Pb(d,$^3$He) reaction with feasible energy resolution and statistics.

12C(p,n)12N reaction at 135 MeV.

We report observations from the (p,n) reaction on $^{12}\mathrm{C}$ at 135 MeV. The experiment was performed with the beam-swinger neutron time-of-flight system at the Indiana University Cyclotron Facility. Neutrons were detected in large-volume plastic scintillation detectors located in three detector stations at 0\ifmmode^\circ\else\textdegree\fi{}, 24\ifmmode^\circ\else\textdegree\fi{}, and 45\ifmmode^\circ\else\textdegree\fi{} with respect to the undeflected beam line; the flight paths were 91 m, 91 m, and 74 m, respectively. Overall time resolutions of about 825 ps provided energy resolutions of about 350 keV in the first two stations and about 425 keV in the third station. The angular distributions for states with excitation energies up to 10 MeV are presented and comparisons are made with DWIA calculations that use one-body density matrices from 0\ensuremath{\Elzxh}\ensuremath{\omega} and 1\ensuremath{\Elzxh}\ensuremath{\omega} shell-model calculations. New information is deduced on the excitation energies, widths, and spin-parity assignments for several energy levels of $^{12}\mathrm{N}$. \textcopyright{} 1996 The American Physical Society.

Excitation of the 2.65 MeV state in the 20Ne(p,n)20Na reaction at 135 MeV.

The {sup 20}Ne({ital p},{ital n}){sup 20}Na reaction at 135 MeV was studied experimentally using the beam-swinger neutron time-of-flight facility at the Indiana University Cyclotron Facility. Backgrounds {similar_to}10{times} lower than an earlier experiment were obtained using the ``stripper loop`` storage ring to achieve {similar_to}2 {mu}s between beam bursts. We were able to see a weakly excited state at 2.65 MeV in {sup 20}Na with a {Delta}{ital l}=2 angular distribution. The angular distribution is consistent with a DWIA calculation assuming a 3{sup +} final state. The characteristics of this state are important to know for considerations of possible breakout in the hot CNO cycle in supernovae explosions.

Spin-flip strength in the continuum and effective tensor interactions via polarization transfer DNN(0 degrees) for (p

The first measurements of {ital D}{sub {ital NN}}(0{degree}) for ({ital {rvec p}},{ital {rvec n}}) reactions at 295 MeV yield large negative values up to 50 MeV excitation for the {sup 6}Li,{sup 11}B,{sup 12}C, {sup 13}C({ital {rvec p}},{ital {rvec n}}) reactions, suggesting much stronger spin-flip strength than observed at lower bombarding energies. DWIA calculations using the Franey and Love (FL) 270 MeV interaction reproduce differential cross sections and {ital D}{sub {ital NN}}(0{degree}) values, while the FL 325 MeV interaction yield {ital D}{sub {ital NN}}(0{degree}) values less negative than the experimental values, suggesting that its exchange tensor part is too strong at large momentum transfer ({ital Q}{congruent}3.4 fm{sup {minus}1}).

DWIA calculations for deuteron inelastic scattering at intermediate energies

We have developed a DWIA method to calculate ( d, d′ ) inelastic scattering at intermediate energies. Comparison is made to existing data for 12C( d, d′) at 400 MeV for dσ dΩ , A y , A yy , P y , K y y and the spin-flip probability. All observables are correctly reproduced.

High-momentum components in the 1 p orbitals of 16O

We have investigated that part of the proton momentum distribution of 16O that is linked through the (e, e′p) reaction to low-lying discrete states in 15N. The MAMI facility with its new generation of 100%-duty-cycle electron accelerator has allowed to cover in this experiment the previously not accessible momentum range of 265 < p m < 700 MeV/c. The reduced cross sections are compared to DWIA calculations in which the proton in its initial state is assumed to be bound in the mean field of a Woods-Saxon well. At low momenta, our results at T p = 93 MeV are in excellent agreement with a measurement performed at NIKHEF. At high momenta the rise above the mean-field prediction is modest.

Measurements of quasi-elastic scattering and DNN(0°) with ( p, n) reactions

The quasi-elastic scattering (QES) process has been studied for the ( p, n) reaction at 300 and 400 MeV. Energy spectra for targets ranging from 2H to nat Pb have been obtained for a wide range of scattering angles corresponding to momentum transfers q = 1.0 – 2.4 fm −1. Energy shift of the QES peak from that of 2H to higher excitation energy is observed for all targets studied, with a gradual increase with target mass reaching almost a constant value of ∼26 MeV beyond 12C. The mass dependence oo the effective neutron number ( N eff ) for the ( p, n) QFS process is well represented by N eff = 0.85 N 0.5 over a wide mass range from 2H to nat Pb except for 6Li, 7Li and 9Be which deviate significantly. The analyzing powers of the QES peak region for the 12C and 40Ca targets are compared to those of the 2H( p, n) reaction at 300 and 400 MeV and found to be almost identical for q ≤ 1.5 fm −1. Transverse polarization transfer coefficients at 0 degree D NN (0°) have been measured for the 1p shell nuclei at 300 MeV. Large negative D NN (0°) values are observed for the continuum region up to an excitation energy of 50 MeV irrespective of targets. The D NN (0°) values observed for the GT transitions are around −0.28 which indicates the contribution from the tensor interactions. The DWIA calculations well reproduce the observed D NN (0°) values.

Recent results on the isoscalar spin response in 40Ca and 12C

A signature S d y of isoscalar spin-transfer strength has been tested in the inelastic scattering of 400 MeV deuterons from 12C. It was applied to search for ΔS=1 ΔT=0 strength in 40Ca and 12C. In 40Ca, spin excitations were found in the 9 MeV region and over a broad range in the continuum with a cluster of strength around 15 MeV. In 12C, ΔS=1 ΔT=0 levels were observed at 12.7 MeV (well known T=0 1 + level), 18.3 MeV (2 − T=0 level) and 20.4 MeV. Resonances were found at 20 MeV and at 30 MeV. Beyond 35 MeV the ΔS=1 ΔT=0 response is similar to the one observed in 40Ca. Microscopic DWIA calculations agree nicely with the 12C data.

Spin polarization effects in the 3He(d, 3He p)n and the 3He(d, t p)p reactions at Ed = 17 MeV

Triple-differential cross sections and vector analyzing powers were measured for the 3He(d, 3He p)n and the 3He(d, t p)p reactions at E d = 17 MeV. Data are presented for four pairs of coplanar detection angles for the 3He/triton and proton where quasi-free scattering (QFS) or quasi-free reaction (QFR) processes are expected to be dominant, and for five sets of angles where the kinematics favor the nucleon-nucleon final-state interaction (NN FSI). Tensor-analyzing-power measurements, T 20 and T 22, are also presented for two sets of angles. For the angle pairs where the QFS/QFR mechanism is important, the data are compared with the predictions of PWIA and DWIA calculations. While both calculations are only partly successful in describing the shapes of the quasi-free peaks, the DWIA better predicts their magnitudes. The vector analyzing powers (VAP) in the quasi-free region are at best only qualitatively reproduced by both calculations for the QFS, while for the QFR there is quantitative agreement between both calculations and the data only in the energy region near the center of the QFR maximum. Data obtained for the angle pairs where the NN FSI is present are compared to the predictions of a simple two-step model. The reaction is assumed to proceed by pickup of a nucleon from the 3He by the deuteron, followed by breakup of the recoil dinucleon system. These calculations describe the shapes and magnitudes of the NN FSI peaks reasonably well. The VAP predictions are for the most part also consistent with the two-step assumption. In all of the data, strong contributions are present from nucleon-trion FSI corresponding to the 0 − and 2 − resonances in 4He at E x = 21.1 and 22.1 MeV, respectively.