Search Results (39 total)

Measurements are reported for the np-elastic analyzing power from 30° to 128° c.m., at 485 and 788 MeV, with a typical precision of 0.005 and absolute accuracy of 2%. Results strengthen the isospin-0 phase-shift analysis, and clarify the absolute normalization of the polarized neutron beam and the isospin-0 inelasticity. © 1996 The American Physical Society.

pp-elastic differential cross sections are reported at 492 MeV from 40° to 90°, and at 576, 642, 728, and 793 MeV from 75° to 90° c.m., with an absolute accuracy of less than 1%. These data, obtained with polyethylene targets, agree with recent measurements at the same energies obtained with a liquid-hydrogen target. © 1996 The American Physical Society.

Absolute pp-elastic-differential cross sections were measured at incident energies 492, 576, 642, 728, and 793 MeV from about 30° to 90° c.m. The total uncertainty was determined to be less than 1%, made possible by particle counting for beam normalization and extensive cross-checks of systematic effects. These new data are consistent with previous data above 600 MeV but have uncertainties about a factor of 10 smaller. Near 500 MeV these data are consistent with 90° data from TRIUMF, but differ significantly from similar data from PSI; the cause of this discrepancy is discussed.

We have measured the analyzing power A_NO and the spin transfer K_NN for np-elastic scattering from about 60° to 170° c.m. at 485, 635, and 788 MeV. The new data clarify previous discrepancies and complete the first-order determination of nucleon-nucleon elastic scattering at these energies.

We have measured the spin-transfer parameters K_LL, K_SL, K_LS, and K_SS at 635 MeV from 50° to 178° c.m. and at 485 MeV from 74° to 176° c.m. These new data have a significant impact on the phase-shift analyses. There are now sufficient data near these energies to overdetermine the elastic nucleon-nucleon amplitudes.

An energy-dependent analysis and set of energy-independent analyses are presented for the nucleon-nucleon elastic-scattering data below 1.6 GeV. The database from which the energy-dependent and 25 pp(18 np) single-energy solutions are obtained consists of 11 880 pp and 7572 np data. A resonancelike structure is found to occur in the ¹D₂, ³F₃, and ³P₂-³F₂ partial waves; this behavior is associated with poles in the complex energy plane. The pole positions and residues are obtained through analytic continuation of the "production" piece of the T matrix obtained in the energy-dependent solution.

Measurements of the spin-transfer parameter K_LL for ²H(p,n)2p at 0° to calibrate the neutron-beam polarization clarify a normalization discrepancy affecting np data at LAMPF. The new data are in good agreement with theoretical predictions.

23 p-d elastic scattering spin observables, most of them in linear combinations of two observables, were measured at 794 MeV over a range of four-momentum transfer t from -0.257 to -0.630 (GeV/c)². By changing the beam polarization between S, N, and L type and by alternating the target vector polarization between negative and positive, six independent combinations of beam and target polarization were obtained. The target was dynamically polarized deuterated ammonia. An average target polarization of 30% was achieved. Transverse polarization components of the scattered protons (S and N type) were measured directly by using a polarimeter. The longitudinal polarization component (L type) was measured after precessing it to N type. Typical uncertainties for two-spin coefficients were 0.02 and for three-spin coefficients 0.1–0.2. The data are compared with the theoretical predictions calculated by fitting the previously available data to a relativistic multiple-scattering model with derivative couplings. Although relativistic impulse approximation calculations do not predict the data well, they are also included in the comparisons.

We have measured the spin-transfer parameters K_LL, K_SL, K_LS, and K_SS at 788 MeV from 47° to 177° c.m., and also uncovered a 10–16 % normalization discrepancy which affects all previous np elastic spin data from LAMPF. Results disagree significantly from previous phase-shift predictions. With the inclusion of these new data the NN phase shifts and amplitudes (isospin 0 and 1) become well determined for the first time near 800 MeV.

The absolute p-d elastic-scattering differential cross sections were measured at 641.3 and 792.7 MeV beam energies over a range of c.m. angles from ∼35° to ∼115° and ∼35° to ∼140°, respectively. The longitudinally polarized (L-type) proton beam produced by the Lamb-shift ion source at LAMPF was used. The beam intensity was measured to high accuracy (∼0.1%) by a scintillator-beam particle-counting system designed and developed prior to the experiment. Typical uncertainties in the absolute cross sections were about 2–3% total, somewhat larger at back angles. The present results were compared with the existing measurements and the controversy about the previous data at 800 MeV was resolved. The present data can be fit with a relativistic multiple-scattering theory which uses off-mass-shell extrapolations of the nucleon-nucleon amplitudes suggested by the structure of derivative meson-nucleon couplings. Relativistic-impulse-approximation calculations do not fit these data at either energy.

We have measured 14 spin observables for pp elastic scattering at 730 MeV and extracted the isospin-one amplitudes directly from the data. These new data complete the 730-MeV data set to the same standard as the 580-, 650-, and 800-MeV data.

Inclusive quasielastic p→+²H analyzing-power and spin-rotation depolarization (D_ij) data are reported for the nucleon-nucleon center-of-momentum angular ranges 46.9°–118.0° and 58.3°–110.0° at 647 and 800 MeV, respectively. Exclusive quasielastic p→p and p→n analyzing-power data and exclusive p→p D_ij data are also presented. A simple isospin weighting model successfully describes the inclusive data and is used to estimate the free p→n D_ij values. The new data are compared with those of previous experiments and with predictions of phase-shift analyses. The deduced p→n D_ij values extend the angular range of previous 800 MeV data and provide entirely new information at 647 MeV.

Spin correlation parameters A_LL, A_SL,A_NL, A_NO, A_SO, A_LO, andA_OL have been measured for pp→npπ⁺ at 492, 576, 643, 729, and 796 MeV over a large part of phase space, using a longitudinally polarized target and a polarized beam. Results rule out broad dibaryons in this mass range in NN ³P₂ and ³F₃; in ¹D₂ some phase variation is observed, resembling that expected of a strong inelastic threshold.

As part of an experimental study of the nucleon-nucleon interaction at medium energy, the free neutron-proton analyzing power A_n(θ_n^*,T_n) has been measured at nine incident neutron energies in the range 375≤T_n≤775 MeV and for neutron c.m. angles in the range 57°≤θ_n^*≤159°. Unpolarized neutrons with a broad continuum of energies, produced by interaction of an 800 MeV proton beam with a beryllium target, were scattered from a polarized proton target. At each angle, for the whole energy region, the scattered neutron and conjugate recoil proton were detected in coincidence. A previously unseen minimum is observed in the energy dependence of A_n(θ^*∼100°) near 625 MeV.

Spin-correlation parameters A_LL, A_SL, A_NL, A_N0, A_S0, A_L0, and A_0L have been measured for the reaction pp→npπ⁺ at 492, 576, 643, 729, and 796 MeV. An isobar analysis determines magnitudes and phases of partial waves up to NN ³F₃. For the amplitude NN(¹D₂)→NΔ(⁵S₂), the phase shows a strong threshold enhancement in the NΔ channel, dropping from 44.4°±4.4° at 492 MeV to 11.9°±1.9° at 796 MeV. Other phases show little activity. Broad dibaryons are conclusively ruled out in ¹D₂, ³F₃, and ³P₂ in this energy range.

The Wolfenstein polarization observables D_NN, D_SΩ, and D_LΩ, where Ω denotes a mixture of S and L polarization components, and the induced polarization P have been measured for the reaction pp→pπ⁺n at 800 MeV, at geometries corresponding to Δ⁺⁺ production from ∼10° to 80° in the center of mass. Comparisons are made to results from the model of Dubach, Kloet, and Silbar.

The spin-rotation parameters D_NN, D_SS, D_LS, D_SL, and D_LL; induced polarization P; and vector analyzing power A at 496 and 647 MeV and D_SL and D_LL at 800 MeV for p-d elastic scattering have been measured using a polarized proton beam. This work represents the first measurement of the final state L component parameters D_SL and D_LL for p-d elastic scattering. Comparison with the noneikonal multiple scattering theory reveals large discrepancies between the data and current theory at 800 and 650 MeV but fairly good agreement is seen at 500 MeV. The data also provide for a test of time-reversal invariance.

We have measured the spin parameters D_SS, D_LS, D_SL, D_LL (K_SS, K_LS, K_SL, K_LL), and P from 18° to 134° c.m. for pp→pp at 597, 647, 699, 750, and 800 MeV. (We also include four D_NN points that cross-check previous data.) The pp elastic phase shifts are now overdetermined near 597, 647, and 800 MeV and well determined near 699 and 750 MeV. The data are in satisfactory agreement with preexisting phase shift analyses and show no new energy dependence.

Kinematically complete data (analyzing powers and polarized cross sections) for the reaction p→+p→p+π⁺+n at 800 MeV have been accumulated at twelve angle pairs with polarized beam and unpolarized target. Analyzing powers as large as 0.6 are observed in the regions of phase space where the Δ⁺⁺ resonant state can be produced. The four-momentum transfer to the proton-pion Δ⁺⁺ resonance varied between 0.09 (GeV/c)² to 0.81 (GeV/c)². Current theories are not capable of reproducing these results in detail.

NUCLEAR REACTIONS p→(p, n)π⁺p, measured d³σ / dp₁dΩ₁dΩ₂ and analyzing power.

Measurements have been made of the spin depolarization parameters D_NN, D_SS, and D_LS (27°<~θ_c.m.<~90°) and the spin transfer parameters K_NN, K_SS, and K_LS (56°<~θ_c.m.<~90°) for pp→pp at 647 MeV. Typical uncertainties are about 0.03 compared with about 0.1 for previous data. Previous data are reviewed. The present data are in agreement with corrected previous data, and are in agreement with Arndt's phase-shift solutions.

NUCLEAR REACTIONS ¹H(p, p,)¹H, E=647 MeV, measured D_NN, D_SS, D_LS, K_NN, K_SS, K_LS, θ=27° to 90° c.m.

The analyzing power of polarized 50 MeV neutrons on deuterons has been measured for center-of-mass angles between 90° and 150°. The data, combined with forward angle measurements, are compared with recent p→+d analyzing power measurements at 49.3 MeV and also with a three-body calculation at 46.3 MeV.

NUCLEAR REACTIONS ²H(n→,n)²H, E=50.0 MeV; measured A_y(θ) from 89.7° to 149.8°, about every 5° c.m.

The spin correlation parameter A_nn and the analyzing power A have been measured at 643 MeV from 35 to 90° c.m., with statistical uncertainties of ±0.01 to ±0.02 and normalization uncertainty of ±2%. The data are in fair agreement with phase shift predictions and with the trend of most previous data near this energy.

NUCLEAR REACTIONS ¹H(p,p)¹H, E=643 MeV; measured A_nn(θ), A(θ); θ=35 to 90° c.m.

The spin depolarization parameters D_NN, D_SS, D_LS, and the spin transfer parameters K_NN, K_SS, K_LS have been measured for pp→pp at 800 MeV. Angular range is 21 to 90° c.m. for the D parameters, and 46 to 90° c.m. for the K parameters. Typical uncertainties are about ±0.025. These data, when combined with previous data make possible a complete isovector phase shift and amplitude analysis at 800 MeV.

NUCLEAR REACTIONS ¹H(p,p)¹H, E=800 MeV, measured D_NN, D_SS, D_LS, K_NN, K_SS, K_LS, θ=21 to 90° c.m.

The analyzing power A and spin-transfer parameters K_NN, K_SS, K_SL, and K_LL have been measured in the np charge-exchange (np→pn) region at 790 MeV. These data provide new and unique information on the spin dependence of the np interaction in the charge-exchange region. Models which explain the charge-exchange peak in the np elastic differential cross section as being due to interference between one-pion exchange and a slowly varying background are in basic agreement with the data.