Neutron-proton Final-state Interaction Research Articles

Measurement of the Vector and Tensor Asymmetries at Large Missing Momentum in Quasielastic (e[over →],e^{'}p) Electron Scattering from Deuterium.

We report the measurement of the beam-vector and tensor asymmetries A_{ed}^{V} and A_{d}^{T} in quasielastic (e[over →],e^{'}p) electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500 MeV/c. Data were collected simultaneously over a momentum transfer range 0.1<Q^{2}<0.5 (GeV/c)^{2} with the Bates Large Acceptance Spectrometer Toroid using an internal deuterium gas target polarized sequentially in both vector and tensor states. The data are compared with calculations. The beam-vector asymmetry A_{ed}^{V} is found to be directly sensitive to the D-wave component of the deuteron and has a zero crossing at a missing momentum of about 320 MeV/c, as predicted. The tensor asymmetry A_{d}^{T} at large missing momentum is found to be dominated by the influence of the tensor force in the neutron-proton final-state interaction. The new data provide a strong constraint on theoretical models.

Model-independent analysis of the neutron–proton final-state interaction region in the pp→pnπ+ reaction

Experimental data on the pp -> pn pi^+ reaction measured in an exclusive two-arm experiment at 800 MeV show a narrow peak arising from the strong proton-neutron final-state interaction. It was claimed, within the framework of a certain model, that this peak contained up to a 25% spin-singlet final state contribution. By comparing the data with those of pp -> d pi^+ in a largely model-independent way, it is here demonstrated that at all the angles measured the whole of the peak could be explained as being due to spin-triplet final states, with the spin-singlet being at most a few percent. Good qualitative agreement with the measured proton analysing power is also found within this approach.

New investigation of the neutron-neutron and neutron-proton final-state interaction in then-dbreakup reaction

The neutron-neutron final-state interaction (FSI) has been investigated in the ${}^{2}\mathrm{H}(n,np)n$ reaction at 25.3 and 16.6 MeV, detecting neutrons and protons in coincidence in a geometry which should enable a practically model-independent determination of the ${}^{1}{S}_{0}$ neutron-neutron scattering length ${a}_{\mathrm{nn}}.$ The analysis was performed by means of detailed Monte Carlo simulations based on rigorous three-body calculations with realistic nucleon-nucleon potentials. At 25.3 MeV, the value of ${a}_{\mathrm{nn}}$ deduced from the absolute cross section in the FSI peak is $\ensuremath{-}16.3\ifmmode\pm\else\textpm\fi{}0.4\mathrm{fm}$ while the relative cross section, normalized in the region of neutron-proton quasifree scattering, gives $\ensuremath{-}16.1\ifmmode\pm\else\textpm\fi{}0.4\mathrm{fm}.$ The relative data obtained at 16.6 MeV yielded ${a}_{\mathrm{nn}}=\ensuremath{-}16.2\ifmmode\pm\else\textpm\fi{}0.3\mathrm{fm}.$ In addition, the ${}^{1}{S}_{0}$ neutron-proton scattering length was measured at 25.2 MeV in the same configuration for comparison. While our results for ${a}_{\mathrm{nn}}$ are incompatible with those of a similar investigation performed recently at 13 MeV where the two neutrons were detected, both results for ${a}_{\mathrm{np}}$ are in good agreement with the accurately known value from free n-p scattering.

N Delta interaction in pi d breakup.

The effects of the residual nucleon-delta interaction proposed by Ferreira et al. to eliminate the discrepancies between theory and experiment in \ensuremath{\pi}d elastic scattering are studied for the breakup reaction at 228 and 294 MeV. It is found that in first order the residual interaction lowers the cross section particularly in the region of the neutron-proton final-state interaction. However, the effects of higher-order corrections generated by the N\ensuremath{\Delta} interaction are found to be non-negligible, which implies that the parameters extracted by Ferreira et al. probably must be modified.

3He-induced d* production

A measurement of the absolute differential cross sections for the reaction 3He(d,3He p)n at Ed=23.083 MeV was performed. The particular kinematical configuration allowed for the neutron-proton final-state interaction at zero relative energy. A narrow peak, corresponding to singlet deuteron production, has been found. The d* formation cross section has been extracted by integrating the experimental cross sections and turns out to be about two orders of magnitude smaller than the corresponding elastic cross section.

Final-state interactions in the high-energy proton-deuteron break-up reaction: D-state effects

A separable potential with tensor plus central terms is introduced to describe the low-energy neutron-proton final-state interaction in the break-up reaction pd to ppn. The inclusion of the D-wave terms improves significantly the agreement with data at 1 GeV on the cross section and asymmetry at high spectator momenta. The spectator momentum distribution for fixed momentum transfer also provides a strong signal of the importance of the final-state interaction which is confirmed experimentally.

The neutron-proton final-state interaction in proton-induced deuteron break-up at 8.5 MeV

Two-dimensional coincidence spectra of the two protons from the reaction 2H(p, 2p)n at 8.5 MeV were measured at 14 angular settings corresponding to zero relative energy of the n-p subsystem. The spectra and the FSI differential cross sections were compared with results of calculations by means of the Ebenhöh-Bruinsma-Stuivenberg code (EBS code) solving the Faddeev equations for rank-one separable s-wave N-N potentials with the correct isospin dependence.

Competition between neutron-proton rescattering and deuteron break-up in (d, np) reactions

Existing final-state interaction (FSI) theories predict observable rescattering effects in low-energy nuclear reactions with three or more particles in the final state. Obvious yields which could be attributed to this effect have only been reported in (d, np) reactions. However,n-p rescattering might be confused with the neutron-proton FSI following deuteron break-up since both contribute strongest at low relative neutron-proton energies. We have re-examined the (d, np) reactions on12C and40Ca in a kinematically complete experiment making special effort to try to distinguish between rescattering and then-p FSI. Data have been taken within and outside the reaction plane at different bombarding energies. Attempts to simultaneously fit the detailed shapes of the proton spectra and the azimuthal angularn-p correlations with theoretical predictions in a consistent way were unsuccessful forboth reaction mechanisms. Improvements in the fits at particular energy and angle combinations were always at the expense of the agreement at other angles or energies. Therefore it must be concluded from our analysis that on the basis of calculations available at present the contributions fromn-p rescattering and deuteron break-up cannot be distinguished in a conclusive manner in the (d, np) experiments performed to date.

A study of the neutron-proton final state interaction in proton-induced deuteron breakup

Proton-proton and proton-neutron coincidences corresponding to a near-zero relative energy neutron-proton system being emitted at fixed angles in the c.m. were measured in the reaction 2H(p, pn)p. Excitation functions were taken in the proton bombarding energy range 8–12 MeV in 0.5 MeV increments for each of five fixed c.m. angles: 50°, 60°, 70°, 75° and 80°. The cross-section values obtained from both proton-proton and neutron-proton coincidence spectra agreed quite well over the entire range of bombarding energies and detection angles. The cross sections have been presented as excitation functions and angular distributions. All five excitation functions decreased monotonically over the bombarding energy range 8–12 MeV.

Quasi-free scattering and final state interactions in the reaction 2H(p,2p)n at 585 MeV

The reaction 2H(p,pp)n has been observed in a kinematically complete experiment at 585 MeV. A neutron-proton final state interaction was observed for an angle pair of 41°-61°. The spectral shape agrees reasonably well with the simple final state interaction theory. Quasi-free scattering was observed in the momentum spectrum for symmetric angles of 41°-41°. The spectator neutron momentum ranged from 0 to 425 MeV/ c. The simple impulse approximation using the Hulthén wave function describes the data very well out to 240 MeV/ c, at which point a sudden departure is observed.

Neutron-proton final state interaction in the 3H( 3He, pα)n reaction at low bombarding energies

The 3H( 3He, pα)n reaction has been studied in a kinematically complete experiment at 3He bombarding energies between 0.31 and 2.80 MeV in order to detect a possible resonant energy dependence of the spin singlet ( T = 1) neutron-proton final state interaction (FSI). The data in the region of low n-p relative energies have been analyzed in terms of the Watson-Migdal formalism. Only a slight relative increase of the 1S 0 n-p FSI is observed with increasing bombarding energy. This result is not easily related to the strong isospin violations found in the two-body reaction 3H( 3He, d) 4He at similar 3He energies.

A new analysis of angular distributions attributed to the neutron-proton final state interaction in the reaction pd → ppn

Recently measured angular distributions attributed to the neutron-proton final state interaction at zero relative energy in the reaction pd → ppn are analyzed with an exact threebody theory using spin-dependent separable potentials for relative S-states of two nucleons. The relation between the Watson factorization ansatz and the exact theory is demonstrated for the case of the angular distribution measured with an incident beam of 52 MeV deuterons.

Neutron-proton final state interaction in p-d breakup at Ep = 585 MeV

The first observation of the neutron-proton final-state interaction above E p = 200 MeV is reported. The cross section is larger than expected from lower-energy data and pole graph considerations.

The 2H(p, pn)p reaction at 9.0 MeV

The 2H(p, pn) reaction has been studied at a bombarding energy of 9.0 MeV and several coincidence detection angles using the Rice University tandem Van de Graaff accelerator and computer-analyzer system. The energies of the detected, coincident particles were determined using a solid-state surface barrier detector for the proton and time-of-flight measurement on the neutron. The contributions of the neutron-proton final state interaction and neutron-proton quasi-free scattering have been observed. The final state interaction contribution has been reproduced using Phillips, Griffy and Biedenharn theory. The shape of quasi-free scattering contribution spectrum is in reasonable agreement with simple impulse approximation prediction. The absolute value of cross section is smaller than predicted by spectator model calculations.