Quasi-free Proton Research Articles

Medium effects on spin observables of proton knockout reactions.

Medium modifications of the properties of bound nucleons and mesons are investigated by means of intermediate energy quasifree proton knockout reactions with polarized incident protons, by comparison of quantities which are insensitive against wave distortions. The sensitivity of the spin observables of the quasifree proton-proton cross section to modifications of the nucleon and meson properties is studied using the Bonn one-boson exchange model of the nucleon-nucleon interaction. A method proposed to extract the pp analyzing power in medium from the (p, 2p) asymmetries indicates a reduction of this quantity compared to its free space value. This reduction is linked to modifications of masses and coupling constants of the nucleons and mesons in the nucleus. The implications of these modifications for another spin observable to be measured in the future are discussed.

Total cross sections, elastic scattering observables and direct reconstruction of scattering matrix in np Interactions between 0.8 and 1.1 GeV at SATURNE II

Neutron-proton total cross section differences with the beam and target polarizations orientated either transversally or longitudinally with respect to the beam direction, as well as 11 spin dependent elastic scattering observables measured at SATURNE II as a function of energy and angle are presented. A major part of results was measured using the quasimonoenergetic polarized neutron beam and/or the polarized proton target. A small part of data was obtained using a polarized deuteron beam considered as a beam of quasifree neutrons and protons. The present paper represents a review of measured observables. Several sets of present data are compared with results obtained in other laboratories below 0.8 GeV. Imaginary parts of spin dependent forward amplitudes for np scattering and for the isospin stateI=0 were determined. First direct reconstruction of the np scattering matrix at 0.84 GeV is shown.

Physics results from the AmPS electron scattering facility

The programme in intermediate energy hadronic physics at NIKHEF (Amsterdam) with the Amsterdam Pulse Stretcher and Storage Ring (AmPS) is now in full operation. With the ring operating in stretcher mode a beam with a current of ≥ 10 μA and with a (50 – 70) % duty factor has been used to probe high momentum components in 208Pb with the quasi-free proton knockout reaction. Ongoing coincidence experiments of type ( e, e′ p) and ( e, e′2 p) with broadband proton detectors of 500 msr solid angle are presented. We discuss an experiment with the beam in storage mode interacting with a tensor-polarized deuterium target, a storage cell fed by an atomic beam source.

A dependence of transparency in high pt quasi-free proton scattering

The measured A dependence of the high momentum transfer quasi-elastic scattering cross section in nuclei is shown to be consistent with normal “Glauber model” expectations. The transparency, T, which is the probability that there is no initial or final state scattering accompanying the high momentum (p, 2p) interaction, shows no evidence for the enhancement expected were there are appreciable effects due to “color screening”.

Polarization observables and asymmetry in electromagnetic quasi-free proton knockout

Polarization observables and helicity asymmetry of the coincidence cross section for the electromagnetic knockout of polarized protons from unpolarized targets are investigated in the quasi-elastic region. Specific calculations, based on the theoretical framework of the one-photon exchange approximation, are shown for a 16O target nucleus as an example to study the sensitivity to final state interactions, mesonic effects and isobaric configurations. Peculiar properties of the helicity asymmetry are analyzed and discussed.

4He( pi, pi 'p)3H reaction: Quasifree and resonance scattering.

Exclusive $^{4}\mathrm{He}$(${\mathrm{\ensuremath{\pi}}}^{\ifmmode\pm\else\textpm\fi{}}$,${\mathrm{\ensuremath{\pi}}}^{\ifmmode\pm\else\textpm\fi{}}$'p${)}^{3}$H spectra in the excitation energy range between 21.5 and 44 MeV in $^{4}\mathrm{He}$ were measured at ${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}$=180 MeV at several pion and proton angles. The cross section ratio ${\mathit{R}}_{\mathrm{\ensuremath{\pi}}\mathit{p}}$=\ensuremath{\sigma}(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{+}$'p)/\ensuremath{\sigma}(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$'p) was found to be between 1 and 2 near 22 MeV which is in the region of the ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${2}^{\mathrm{\ensuremath{-}}}$, T=0 state. Between 25 and 40 MeV in the continuum, which comprises the giant dipole resonance and broad ${2}^{\mathrm{\ensuremath{-}}}$ and ${2}^{+}$ states, ${\mathit{R}}_{\mathrm{\ensuremath{\pi}}\mathit{p}}$ ranges from 0.22 to 45 in sharp contrast to the predicted values of \ensuremath{\approxeq}1 from a model assuming the entire yield is due to the sequential decay of a state of good isospin, and 6 to 9 from a distorted-wave impulse approximation calculation assuming quasifree proton knockout.

Quasifree proton knockout reaction in the distorted wave impulse approximation.

We investigate the applicability of the distorted wave impulse approximation on the factorization assumption for the (p,2p) reaction in the lower incident energy. We calculate contour maps of analyzing powers and cross sections for the $^{12}$C(p\ensuremath{\rightarrow},2p) reaction at an incident energy ${E}_{p}$=84 MeV using distorted wave impulse approximation including the spin-orbit interaction for the distorted waves. The proton-proton t matrix elements are calculated with the effective nucleon-nucleon interaction by Love-Franey taking account of the off-shell effect. Our calculations agree well with both experimental analyzing power and cross section data on the whole region of the contour maps.

Moinester et al. respond.

The amplitude pion minus capture by diprotons cannot be determined by studying quasi-free proton reactions. (AIP)

Effect of the nuclear medium on the proton investigated with the 12C(e,e'p)11B reaction.

A longitudinal-transverse separation has been carried out for the coincident quasifree proton knockout reaction on $^{12}\mathrm{C}$ in the range of three-momentum transfer 0.27-0.46 GeV/c. The deduced ratio of longitudinal and transverse response functions indicates a significant effect of the nuclear medium on the coupling of the virtual photon with the proton. The observed modification of this coupling implies a breakdown of the impulse approximation.

A proton and neutron beam polarimeter at SATURNE II

A beam polarimeter using CH 2 and carbon targets has been used to measure proton and neutron beam polarization in the energy range 0.4–2.8 GeV in one of the beam lines at the SATURNE II accelerator. The analyzing power for np-scattering is calibrated against the known analyzing power for pp-scattering by using the polarized deuteron beam to measure simultaneously the asymmetries for scattering of quasifree protons and neutrons in the deuterons. A low level of systematic errors is achieved by pulse to pulse polarization reversal at the ion source of the accelerator, and by measuring left and right scattering simultaneously. The detailed operation procedure and the beam polarizations measured during all experiments from 1981 to 1984 are presented.

Analysing power of reaction p↑C ⇒p′X from 0.52 to 2.8 GeV

The emission of charged particles in proton-carbon interactions results from several different reactions: elastic or inelastic coherent scattering off the nucleus and elastic or inelastic scattering on quasi-free protons or neutrons. The polarized-beam asymmetry for the reaction p↑C ⇒- p′X involving all of these channels was measured at several laboratory angles between 11.6° and 73° at 20 energies from 0.52 to 2.8 GeV.

Quasi-free collisions of 400 MeV protons in deuterium and carbon

Abstract The first results from a program to compare quasi-free proton and neutron knockout from nuclei are presented. The binding energy of the s and p neutron hole states in 12 C have been obtained. Relative cross sections for proton and neutron knockout from 2 H and 12 C were determined for two very different kinematical conditions. The ratio, R of σ(p, pn) to σ(p, 2p) is in agreement with estimates based on the impulse approximation for 2 H but there is a deviation for 12 C. These observations suggest that refinements will have to be made to the theoretical ideas used to analyze quasi-free knockout reactions.

Quasi-Free Proton Scattering at 1 GeV: The Effect of Multiple Scattering

The so-called quasi-elastic multiple scattering at 1 GeV is related to the initial-state interaction. We investigate how the quasi-elastic multiple scattering effect has an influence on quasifree proton scattering amplitudes. Numerical calculation for C/sup 12/(p,2p)B/sup 11/ at 1GeV is performed. We deal with the singly knocked-out process of one nucleon in the target nucleus, one quasi-elastic collision which the incident proton makes with the individual nucleons before the knocked-out process, two quasi-elastic collisions and three quasi-elastic collisions. The numerical results taking account of the multiple scattering reproduce the experimental data well. The difference from the DWIA calculation is discussed.

Quasifree Proton-Proton and Proton-Deuteron Scattering onHe3

Quasifree proton scattering from $^{3}\mathrm{He}$ is examined on the basis of available data. Cross sections are given in the pole-dominance approximation for either two protons or a proton and deuteron detected in coincidence. The cross sections are evaluated for a constant $^{3}\mathrm{He}$ vertex and a separable-potential model of the $^{3}\mathrm{He}$ vertex amplitude. Both two- and three-body breakup of $^{3}\mathrm{He}$ are considered, with final-state rescattering included between the spectator nucleons in three-body breakup. It is shown that the asymptotic form of the coordinate-space $^{3}\mathrm{He}$ wave function governs the shape of these low-momentum-transfer cross sections and that final-state rescattering between the spectator pair in $^{3}\mathrm{He}(p,2p)\mathrm{pn}$ mainly affects the magnitude of this cross section.

Non-coplanar quasi-free scattering

It is postulated that the angular correlation distributions of the coplanar and non-coplanar quasi-free proton scattering are controlled by the momentum distribution of the nuclear protons for medium weight nuclei. This assumption differs from that of Jacob and Maris, who suggested that the angular distribution would show a diffraction pattern. The incoming and outgoing protons are represented by waves distorted in a square well potential. It is shown that the two angular correlation distributions are very similar for the same magnitude of momentum transfer. It is also shown that if the distorting potential is real, the angular correlation distributions do not depend on the nuclear protons which have non-zero magnetic quantum number.

Quasi-Free Proton-Proton Scattering from Ca40at 180 Mev

Experimental results of quasi-free proton scattering on Ca/sup 40/ at 180 Mev were compared with theoretical results calculated by means of the single particle picture for Ca/sup 40/. A solution obtained from the harmonic oscillator potential with Thomas type spin-orbit coupling for the initial wave function of the protons to be knocked out in the final state and the plane waves for the incoming and outgoing protons is used. It is assumed that the (p,2p) reaction takes place in the surface region. Angular distributions were presented for the 5/sub 1/2/, d/sub 3/2, and d/sub 5/2/proton groups.