Time reversal violation in the nuclear interaction and p-3He scattering

Using T-violating boson-exchange interactions T-violating effects in low energy p-³ He scattering are calculated. The results are below 10^?3 even for full strong (not millistrong) T-violation in the nucleon-nucleon system. It is argued, that the smallness of the effects is not a particularity of the p-³He system but a general property of low energy processes.     

Analyzing Power of 3He(n, n)3He Between 1.60 and 5.54 MeV

We report the measurements of the analyzing power A _y (θ) of n-³He elastic scattering with unprecedented accuracy and angular coverage at five incident neutron energies between 1.60 and 5.54 MeV. To this end, we employed the polarization-transfer reactions ³H(p, n)³He and ²H(d, n)³He at 0° for neutron generation and a recently developed high-pressure ³He gas scintillator as an active target, enabling neutron-time-of-flight and ³He recoil-energy determinations. We obtained simultaneously the neutron polarization with a ⁴He-based polarimeter, capitalizing on the well-known n-⁴He A _y (θ). Our n-³He A _y (θ) data are compared to rigorous four-nucleon calculations using high-precision nucleon–nucleon potential models. The agreement between data and calculations is fair at the lower energies and becomes less satisfactory with increasing neutron energy. However, in comparison to the pure isotriplet p-³He system in the same energy region, the agreement between measured and calculated A _y is much better for the mixed (isotriplet and isosinglet) n-³He system, indicating large and somewhat counterintuitive isospin effects. We note that the incorporation of a Δ-mediated three-nucleon force in calculations of n-³He scattering was found to affect A _y (θ) negligibly, suggesting the need for the reconsideration of fundamental interactions in resolving the four-nucleon analyzing power puzzle first established about a decade ago in p-³He scattering.     

Analyzing power measurements for p-3He elastic scattering from 1.75 to 4.50 MeV

Analyzing powers for p-³He elastic scattering have been measured at 12 energies between 1.75 and 4.50 MeV for θ_c.m. = 40° to 150°. A comparison of our results with earlier data of Drigo et al. shows substantial differences at all energies. The R-matrix fits to our data that were included in the global search calculations of Hale and Dodder are shown. These calculations established the ordering of the lowest-lying T = 1 levels of ⁴He as J^π = 2^?, 1^? (triplet), 0^?, and 1^? (singlet), which is the WMI (MHI) ordering.     

Winkelverteilung und Wirkungsquerschnitt der Reaktion6Li(p, α)3He im Energiebereich von 50 bis 190 keV

In the angular distribution 1+A ¹ cos ?+A₂cos²? of the³He particles (cm. system)A ₁ decreases from +0.152±0.018 at 188 keV to ?0.017±0.023 at 62 keV. The slope of the A₁-curve is not approaching zero in this energy range, thereby showing the participation of terms of opposite parity even at very low energies. The total reaction cross section deviates from ans-wave Gamow-plot above appr. 130 keV, being 10 mb at 130 keV. The experimental results are discussed in connection with suggested level diagrams of the compound nucleus⁷Be.     

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 ¹S₀ 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.     

3H(p,n)3He reaction with polarized protons from threshold to 2.9 MeV

A polarized beam was used to measure angular distributions of the analyzing power of the ³H($\text{p}$, n)³He reaction at 9 energies from 1.30 to 2.90 MeV. The data were measured typically to an accuracy of 0.02 with a target 25 keV thick at 2 MeV bombarding energy. The analyzing power can be fitted with associated Legendre polynomials. The coefficient of P₁¹ is small, near zero at the upper and lower energies and negative in between; the coefficient of P₂¹ is much larger and positive, rising to a maximum at 2.2 MeV. Comparison of the analyzing power A with earlier data for the neutron polarization P induced with unpolarized protons shows the coefficients of P₁¹ to be equal and those of P₂¹ to have a similar energy dependence but with larger values for A than for P. Theoretical treatment elsewhere of the inequality of P and A infers that transitions between ³P₂ and ³F₂ are responsible. Polarization contour maps are given.     

Angular dependences of the tensor analyzing powers in the dd → 3Hen reaction at intermediate energies

The tensor analyzing powers A _yy, A _xx, and A _xx in the dd → ³Hen reaction at intermediate energies are considered in the framework of the one-nucleon-exchange approximation. Their strong sensitivity to the ³He and deuteron spin structure at short distances is shown.     

The investigation of short-range 3He, 3H and deuteron spin structure via the measurement of the angular distributions of the analyzing power in the \vec dd \to {}^3Hen and \vec dd \to Hp reactions at 140, 200 and 270 MeV

The results on the vector A _y and tensor A _yy , A _xx and A _xz analyzing powers of the $\vec dd \to {}^3Hen$ and $\vec dd \to {}^3Hp$ reactions obtained at intermediate energies at RARF(RIKEN, Japan) are presented. The high precision experimental data are compared with the theoretical calculation within the one nucleon exchange model by using standard ³He, ³H and deuteron wave functions. The data demonstrate the sensitivity to the short-range ³He, ³H and deuteron spin structure.     

R-matrix formulation and phase shifts for n-He and p-He scattering for energies up to 20 MeV

An R-matrix formulation for a single level with a background approximation has been used to analyse n-⁴He and p-⁴He elastic scattering data below the inelastic thresholds near 22 MeV. For every partial wave a single level and a distant pole contribution constant with energy has been employed. Simple relations between neutron and proton scattering parameters have been sought to possibly derive more dependable values for neutron phase shifts and analysing powers at energies where little experimental information exists. The R-matrix parameters corresponding to ⁵He and ⁵Li ground and 1st excited states, phase shifts up to 20 MeV and neutron analysing powers up to 15 MeV are given in tabular form and are compared to results of earlier analyses. Differences in n-⁴He phase shifts are discussed and shown to be due to a scarcity of accurate neutron scattering data above 11 MeV. Some typical fits to n-⁴He scattering data are shown.     

Search for Ay = 1 and Ayy = 1 points in the 6Li(d, α)4He reaction

A search for vector analysing power A_y = 1 and tensor analysing power A_yy = 1 values of the ⁶Li(d, α)⁴He reaction in the energy region between 5.0 and 6.5 MeV as well as between 8.0 and 10.0 MeV was performed experimentally. Two A_yy maxima which are compatible with unity were found. No A_y = 1 point could be detected. The precise energies and angles for the maxima were determined by interpolation of the experimental data.     

Effect of Three Nucleon Forces in p − 3He Scattering

The effect of the inclusion of different models of three nucleon (3N) forces in p ? ³He elastic scattering at low energies is studied. Two models have been considered: one derived from effective field theory at next-to-next-to-leading order and one derived from a more phenomenological point of view—the so-called Illinois model. The four nucleon scattering observables are calculated using the Kohn variational principle and the hyperspherical harmonic technique and the results are compared with available experimental data. We have found that with the inclusion of both 3N force models the agreement with the experimental data is improved, in particular for the proton vector analyzing power A _y .     

Proton-3He elastic scattering: A phase-shift analysis by a separable potential model

All the available experimental data (cross sections, projectile and target polarizations, polarization transfer coefficients) on p-³He elastic scattering up to ~10 MeV are analyzed on a unified basis in the framework of a separable potential model. This allows a phase-shift analysis which is model dependent, but is averaged over a wide energy interval (757 experimental points are reproduced by 27 model parameters). The calculations confirm some indications, already present in the literature, of a weak S-D tensor mixing, and strong singlet-triplet mixing in the P-states. Our conclusions are that probably the leading non-central effect is given by the coupling s₁ · l between the incident proton spin s₁ and the orbital angular momentum of relative motion. Finally, the phase shifts and observables are recalculated using the p-³He potential parameters, but switching off the Coulomb interaction. The results are compared with the (few) n-³H experimental cross sections of the literature, and the agreement is good, as expected on the basis of the charge-symmetry law.     

Phenomenological optical model for p-4He elastic scattering

The results of a Dirac equation optical model analysis of p-⁴He elastic scattering data are reported. The optical potential obtained at 1029 MeV reproduces the systematics of p-⁴He data over the energy range from 560 to 1730 MeV.     

High energy pion photoproduction amplitudes from fixed-t dispersion relations and duality

Contributions to the high energy imaginary parts of the charged and neutral pion photoproduction amplitudes from degenerate ? and A₂ exchanges and ω and B exchanges are parametrized similarly to the dual absorptive model. These contributions together with the imaginary parts of the amplitudes found at low energies from partial-wave analyses are then used to evaluate the high energy real parts of the photoproduction amplitudes from fixed-t dispersion relations. A fit is made to data on pion photoproduction at 3.4 and 16 GeV incident photon energies, for momentum transfers up to ?1(GeV/c)². It is shown that much of the data is reproduced both qualitatively and quantitatively by our model. The high energy imaginary parts of the photoproduction amplitudes given by the fit are shown to be in accord with their average low energy behaviour.     

Energy dependence of the optical model parameters for 3He ions scattered from 40Ca and 58Ni

The differential cross sections for the elastic scattering of ³He ions on targets of ⁴⁰Ca and ⁵⁸Ni have been measured at incident energies of 27.7, 51.4, 73.2 and 83.5 MeV. The results of optical model analyses showed that only one unique potential (J_R ≈ 330 MeV · fm³) with a surface absorptive term can provide acceptable fits to the large angle elastic scattering cross sections at 83.5 MeV. The particular geometrical set found at 83.5 MeV could not, however, give an adequate fit to the data with energy less than 40 MeV. Subsequent analyses indicated that a break in the energy dependence of the real potential is observed for the low energy data. Explicit energy dependent terms were obtained by fitting all the data simultaneously. These phenomenological potentials were also compared with the folded nucleon-nucleus potential. The influence of the α-particle channels on the elastic scattering of ³He ions at 83.5 MeV was also examined.     

Mean field for the p+90Zr system in the energy range −60 MeV<E<+65 MeV and single-particle features of proton states in 90Zr from a dispersive optical-model analysis

Data on the scattering of protons with energies 5 MeV<E<65 MeV by ⁹⁰Zr nuclei and data on the energies of proton particle and hole levels in the A+1 and A?1 systems with A=90 are analyzed within the dispersive optical model. The parameters of the mean proton field for ⁹⁰Zr are determined in the energy range ?60 MeV<E<+65 MeV. The predicted single-particle features of the levels (root-mean-square radii of orbits, occupation numbers, spread widths, spectroscopic factors, and spectral functions) comply well with experimental data obtained in (d, ³He), (³He, d), (n, d), and (d, n) reactions for levels near the Fermi surface and in (e, e′p) and (p, 2p) reactions for deep levels.     

Comparison of analyzing power and polarization in the reaction 3H(p,n)3He: (II). New polarization results below 4 MeV

The polarization P^y for the ³H(p, n)³He reaction was measured for energies between 2 and 4 MeV. Special care was given to minimizing the effects of background and to interpreting the experimental spectra. The new values for P^y are significantly higher than previous values, and comparison to the available data for the analyzing power A_y for the same reaction now shows that in this energy range P^y and A_y are equal within experimental uncertainties. This equality negates earlier conclusions that sizeable differences existed between these observables. In particular, our new results demonstrate that in this reaction the effects of charge symmetry breaking on differences between these observables must be small.     

Preliminary results of the study of the d(d,n)3He reaction in the astrophysical energy range with the use of a Hall plasma accelerator

The possibility of using a plasma accelerator based on a pulsed Hall ion source to study the characteristics of pd, dd, d³He, ³He, and⁴He reactions in the astrophysical energy range (2–12 keV) has been considered. The preliminary experimental data on measurement of the astrophysical S factor for the dd reaction (dd → ³He + n (2.5 MeV)) at average deuteron collision energies E _col = 4.5 and 4.95 keV and the deuteron beam energy spread FWHM = 18% are reported. The found value of the S factor is in agreement with the results of the experiments carried out by us previously using linear plasma in the inverse Z-pinch configuration.     

Energy loss of deuterons in 3He gas: a threshold effect

The energy loss of deuterons in ³He gas was measured at E _d = 15 to 100 keV using the ³He pressure dependence of the ³He(d,p)⁴He cross-section at a given incident energy. At the highest energies, the observed energy loss is in good agreement with a standard compilation. However, with decreasing energy the experimental values drop steadily below the theoretical values and near E _d = 18 keV they drop sharply (within 1 keV) reaching the domain of nuclear stopping power. This threshold behavior is due to the minimum 1s → 2s electron excitation of the He target atoms, i.e. it is a quantum effect. Some consequences are discussed.