Polarization Transfer Coefficients Research Articles

Measurement of the polarization-transfer coefficientKyy'of the fusion reactionH2(d→,p→)H3at Ed=58keV

We measured the polarization-transfer coefficient ${K}_{y}^{{y}^{'}}$ of the fusion reaction $^{2}\mathrm{H}$($\stackrel{\ensuremath{\rightarrow}}{d},\stackrel{\ensuremath{\rightarrow}}{p}$ )$^{3}\mathrm{H}$ at E${}_{d}=58$ keV at the laboratory reaction angle $\ensuremath{\theta}={45}^{\ifmmode^\circ\else\textdegree\fi{}}$. The result is compared with theoretical predictions based on Faddeev-Yakubovsky equations, calculated with and without inclusion of the Coulomb interaction, and a prediction based on a T-matrix parametrization of all available data of this reaction at energies below 500 keV.

Reaction mechanism for natural parity (p,p') transitions inB10

We report angular distribution measurements of the cross section, analyzing power, induced polarization, and all polarization transfer coefficients for the natural parity transitions in $^{10}\mathrm{B}$($\stackrel{\ensuremath{\rightarrow}}{p},{\stackrel{\ensuremath{\rightarrow}}{p}}^{'}){}^{10}$B at 197 MeV. All of the transitions closely follow the pattern for spin-1/2 scattering from spin-0, namely $A=P,{D}_{{\mathit{SS}}^{'}}={D}_{{\mathit{LL}}^{'}}$, and ${D}_{{\mathit{SL}}^{'}}=\ensuremath{-}{D}_{{\mathit{LS}}^{'}}$. Small deviations from ${D}_{{\mathit{NN}}^{'}}=1$ reflect spin-flip contributions to these transitions. Distorted wave impulse approximation calculations were generally successful, supporting the use of an empirical effective nucleon-nucleon interaction, the inclusion of channel-coupling in the ground state and the ${3}^{+}\ensuremath{\leftrightarrow}{4}^{+}$ transition, and the procedure of increasing the $L=2$ strength of shell-model particle-hole matrix elements to match the collective contribution to these transitions.

Polarization transfer measurement forH1(d⃗,p⃗)H2elastic scattering at135MeV∕nucleonand three-nucleon force effects

The deuteron to proton polarization transfer coefficients for the $d$--$p$ elastic scattering were precisely measured with an incoming deuteron energy of 135 MeV/u at the RIKEN Accelerator Research Facility. The data are compared to theoretical predictions based on exact solutions of three-nucleon Faddeev equations with high--precision nucleon--nucleon forces combined with different three-nucleon forces (3NFs), representing the current, most popular models: the $2\pi$-exchange Tucson-Melbourne model, a modification thereof closer to chiral symmetry TM'(99), and the Urbana IX 3NF. Theory predicts large 3NF effects, especially in the angular range around the cross section minimum, but the present data only partially concurs, predominantly for $K_{xx}^{y'}-K_{yy}^{y'}$ ($K_{xx}^{y'}$, $K_{yy}^{y'}$). For the induced polarization, $P^{y'}$, the TM$'$(99) and Urbana IX 3NFs reproduce the data, but the Tucson-Melbourne 3NF fails to describe the data. For the polarization transfer coefficients, $K_{y}^{y'}$ and $K_{xz}^{y'}$, the predicted 3NF ffects are in drastic conflict to the data. These facts clearly reveal the defects of the 3NF models currently used.

Medium modification of the proton form factor

I argue that the double ratio of proton-recoil polarization-transfer coefficients, P'_x and P'_z, of the quasielastic 4He(e,e'p)3H reaction with respect to the elastic 1H(e,e'p) reaction is sensitive to possible medium modifications of the proton form factor in 4He. Recent measurements at both Mainz and Jefferson Lab of this double ratio at four-momentum transfers squared between between 0.4 GeV2 and 2.6 GeV2 are discussed. I show that the data challenge state-of-the-art conventional meson-nucleon calculations, as these are unable to describe the results. The data hint at the need to include medium modifications of the proton form factor, as predicted by a quark-meson-coupling model, in the calculations. A recently approved follow-up experiment at a Q2 of 0.8 GeV2 and 1.3 GeV2 with unprecedented precision will provide one of the most stringent tests of the applicability of various calculations.

Polarization transfer in the 4He(e-->,e'p-->)3H reaction up to Q2=2.6 (GeV/c)2.

We have measured the proton recoil polarization in the 4He(e-->,e(')p-->)4H reaction at Q(2)=0.5, 1.0, 1.6, and 2.6 (GeV/c)(2). The measured ratio of polarization transfer coefficients differs from a fully relativistic calculation, favoring the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model. In addition, the measured induced polarizations agree reasonably well with the fully relativistic calculation indicating that the treatment of final-state interactions is under control.

Polarization transfer measurement for d-p scattering and three nucleon force effects

Precise measurements of the deuteron to proton polarization transfer coefficients for the d-p elastic scattering has been made at 135 MeV/u at RIKEN Accelerator Research Facility. The obtained results are compared with the Faddeev calculations based on modern nucleon-nucleon forces together with Tucson-Melbourne, Tucson-Melbourne' and Urbana-Argonne type of three nucleon forces.

Measurement and microscopic analysis of the11B(p→,p→)reaction atEp=150MeV.II. Depolarization in elastic scattering from odd-Anuclei

The polarization-transfer coefficient ${D}_{{\mathrm{nn}}^{\ensuremath{'}}}$ in the elastic scattering of 150-MeV protons from ${}^{11}\mathrm{B}$ has been measured in the angular range $5\ifmmode^\circ\else\textdegree\fi{}<{\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}<31\ifmmode^\circ\else\textdegree\fi{}.$ Significant deviations of ${D}_{{\mathrm{nn}}^{\ensuremath{'}}}$ from unity are observed starting around a center-of-mass scattering angle of $23\ifmmode^\circ\else\textdegree\fi{}.$ The observed angular variation of ${D}_{{\mathrm{nn}}^{\ensuremath{'}}}$ is analyzed using phenomenological and microscopically generated optical-model potentials to describe the monopole attributes of elastic scattering and to generate the distorted waves used in a distorted-wave approximation evaluation of nonzero multipole contributions to the elastic scattering process. The same approach is used to analyze datasets of ${D}_{{\mathrm{nn}}^{\ensuremath{'}}}$ in elastic scattering from ${}^{13}\mathrm{C}$ and off ${}^{15}\mathrm{N},$ which are available in the literature. The agreement of the fully microscopic analysis with the data is comparable or, in the case of ${}^{11}\mathrm{B},$ slightly better than what is achieved with conventional phenomenological optical-model calculations.

THREE-BODY EFFECTS IN $\vec{p}d$ ELASTIC SCATTERING AT 250 MEV

The angular distributions of the cross section, the proton analyzing power and all of proton polarization transfer coefficients of [Formula: see text] elastic scattering were measured at 250 MeV. The present data are compared with theoretical predictions based on exact solutions of the three-nucleon Faddeev equations and modern realistic nucleon-nucleon potentials combined with three-nucleon forces. These results call for a better understanding of the spin structure of the three-nucleon force and very likely for a full relativistic treatment of the three-nucleon continuum.

POLARIZATION TRANSFER MEASUREMENT FOR d-p ELASTIC SCATTERING: TO SEARCH FOR THREE NUCLEON FORCE EFFECTS

Precise measurements of the deuteron to proton polarization transfer coefficients for the d-p elastic scattering have been made at 135 MeV/u at RIKEN Accelerator Research Facility. The obtained results are compared with the Faddeev calculations based on modern nucleon-nucleon forces together with Tucson-Melbourne Tucson-Melbourne' and Urbana–Argonne type of three nucleon forces.

Kyy′(0°)for3He(d,p)4Henear theJπ=32+resonance

The polarization transfer coefficient ${K}_{y}^{{y}^{\ensuremath{'}}}(0\ifmmode^\circ\else\textdegree\fi{})$ has been measured for the ${}^{3}\mathrm{He}{(d,p)}^{4}\mathrm{He}$ reaction at energies of 520, 890, and 1490 keV. The measured values are $\ensuremath{\approx}\ensuremath{-}2/3,$ consistent with expectations based on the presence of a broad ${J}^{\ensuremath{\pi}}={\frac{3}{2}}^{+}$ resonance at ${E}_{d}=430\mathrm{keV}.$ A comparison with data taken at somewhat higher energies reveals a large change in this observable as the reaction becomes dominated by direct neutron transfer.

Cross section and complete set of proton spin observables inp→delastic scattering at 250 MeV

The angular distributions of the cross section, the proton analyzing power, and all proton polarization transfer coefficients of $\stackrel{\ensuremath{\rightarrow}}{p}d$ elastic scattering were measured at 250 MeV. The range of center-of-mass angles was $10\ifmmode^\circ\else\textdegree\fi{}--165\ifmmode^\circ\else\textdegree\fi{}$ for the cross section and the analyzing power, and about $10\ifmmode^\circ\else\textdegree\fi{}--95\ifmmode^\circ\else\textdegree\fi{}$ for the polarization transfer coefficients. These are the first measurements of a complete set of proton polarization observables for $\stackrel{\ensuremath{\rightarrow}}{p}d$ elastic scattering at intermediate energies. The present data are compared with theoretical predictions based on exact solutions of the three-nucleon Faddeev equations and modern realistic nucleon-nucleon potentials combined with three-nucleon forces (3NF), namely, the Tucson-Melbourne (TM) $2\ensuremath{\pi}$-exchange model, a modification thereof ${(\mathrm{T}\mathrm{M}}^{\ensuremath{'}}$) closer to chiral symmetry, and the Urbana IX model. Large effects of the three-nucleon forces are predicted. The inclusion of the three-nucleon forces gives a good description of the cross section at angles below the minimum. However, appreciable discrepancies between the data and predictions remain at backward angles. For the spin observables the predictions of the TM 3NF model deviate strongly from the other two 3NF models, which are close together, except for ${K}_{y}^{{y}^{\ensuremath{'}}}.$ In the case of the analyzing power all 3NF models fail to describe the data at the upper half of the angular range. In the restricted measured angular range the polarization transfer coefficients are fairly well described by the ${\mathrm{TM}}^{\ensuremath{'}}$ and Urbana IX 3NF models, whereas the TM 3NF model mostly fails. The transfer coefficient ${K}_{y}^{{y}^{\ensuremath{'}}}$ is best described by the Urbana IX but the theoretical description is still insufficient to reproduce the experimental data. These results call for a better understanding of the spin structure of the three-nucleon force and very likely for a full relativistic treatment of the three-nucleon continuum.

Polarization transfer measurements for the13C(p→,n→)13Nreaction at 197 MeV and empirical isovector spin-longitudinal response for the(1/2)g.s.−→(1/2)1+transition

We present differential cross sections and complete sets of polarization-transfer coefficients, ${D}_{\mathrm{ij}},$ obtained in the ${}^{13}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{p},\stackrel{\ensuremath{\rightarrow}}{n}{)}^{13}\mathrm{N}$ reaction studied at 197 MeV incident proton energy and laboratory angles between $0\ifmmode^\circ\else\textdegree\fi{}$ and $33\ifmmode^\circ\else\textdegree\fi{}.$ These complete sets of polarization observables are used to obtain spin-longitudinal and spin-transverse components for transitions to the ground state, to the first, and to the unresolved second and third excited states in ${}^{13}\mathrm{N}$ at 2.36 MeV and $(3.50+3.55) \mathrm{MeV},$ respectively. The results are used to obtain the two $\ensuremath{\Delta}{J}^{\ensuremath{\pi}}$ contributions for the ground and first excited state transitions and are compared with corresponding distorted-wave impulse approximation (DWIA) calculations. In particular, empirical angular distribution values for the unique spin-longitudinal $\ensuremath{\Delta}{J=0}^{\ensuremath{-}}$ transition to the first excited state in ${}^{13}\mathrm{N}$ are obtained and compared with DWIA calculations.

Irreducible pionic effects in nucleon-deuteron scattering below 20 MeV

The consequences of a recently introduced irreducible pionic effect in low-energy nucleon-deuteron scattering are analyzed. Differential cross-sections, nucleon (vector) and deuteron (vector and tensor) analyzing powers, and four different polarization transfer coefficients are considered. This 3NF-like effect is generated by the pion exchange diagram in presence of a two-nucleon correlation and is partially cancelled by meson retardation contributions. Indications are provided that such type of effects are capable to selectively increase the vector (nucleon and deuteron) analyzing powers, while in the considered energy range they are almost negligible on the differential cross-sections. These indications, observed with different realistic nucleon-nucleon interactions, provide additional evidences that such 3NF-like effects have indeed the potential for solving the puzzle of the vector analyzing powers. Smaller but non-negligible effects are observed for the other spin observables. In some cases, we find that the modifications introduced by such pionic effects on these spin observables (other than the vector analyzing powers) are significant and interesting and could be observed by experiments.

Spin Transfer Measurements in $(\vec{p},\vec{n})$ Reactions

The measurement of complete sets of spin transfer coefficients in nuclear transitions, induced via charge-exchange (\((\vec p, \vec n)\)) reactions at intermediate energies, is a unique form of separating the spin-dependent and spin-independent contributions to the differential cross section. The two components of the spin-dependent contribution, the spin-longitudinal and spin-transverse components may equally be separated. This is extremely important in cases where the target nuclei has a non-integer ground state spin. In this study and as an example of the above, we present differential cross section and complete set of polarization transfer coefficients obtained in the (\(^{13} C(\vec p, \vec n)\)) 13N reaction studied at angles between 0° and 33° and at 197 MeV incident proton energy. Polarization transfer coefficients are used to obtain the fraction of the Gamow-Teller (GT) component in the mirror ground state transition, which is a combination of the spin-independent Fermi (F) and spin-dependent GT components. Data are also presented for the transition to the first excited state in 13N at 2.34 MeV. This is a (1/2)− → (1/2)+ transition and the cross section is an incoherent admixture of ΔJ π = 1− and ΔJ π = 0− components. The complete set of polarization transfer coefficients are used to obtain differential cross section data for both components. The empirical results are compared with Distorted Wave Impulse Approximation calculations, DWIA.

DeuteronPwave in elastic backward proton-deuteron scattering

The elastic backward proton-deuteron scattering is analyzed within a fully covariant approach based on the invariant expansion of the reaction amplitude. The method of calculation of any observables for any reaction mechanism is developed. The cross section and spin observables, like tensor analyzing power and polarization transfer coefficient etc., are investigated in explicit form within framework of the impulse approximation using different kinds of the relativistic deuteron wave function (DWF) with P-wave components. Our results of numerical calculation for complete set of polarization observables are compared with the experimental data and other calculations performed within both the non-relativistic and relativistic approaches. An experimental verification of the reaction mechanism is suggested by constructing some combinations of different observables.

Polarization transfer coefficientKyy′in the2H(d,p)3Hreaction atθ=0°at very low energies

The polarization transfer coefficient ${K}_{y}^{{y}^{\ensuremath{'}}}$ has been measured for the ${}^{2}\mathrm{H}{(d,p)}^{3}\mathrm{H}$ reaction at a scattering angle of 0\ifmmode^\circ\else\textdegree\fi{} at very low energies (\ensuremath{\leqslant}90 keV). The polarization of the emitted protons from the reaction was measured with a proton polarimeter using $p\ensuremath{-}{}^{28}\mathrm{Si}$ elastic scattering. A value of $0.09\ifmmode\pm\else\textpm\fi{}0.10$ was obtained for ${K}_{y}^{{y}^{\ensuremath{'}}}.$ This value was compared with the value for ${K}_{y}^{{y}^{\ensuremath{'}}}$ that we have calculated from the transition amplitudes determined by Lema\^{\i}tre and Schieck for the ${}^{2}\mathrm{H}{(d,p)}^{3}\mathrm{H}$ reaction [Ann. Physik 2, 503 (1993)].

General formalism in collinear regime for pseudoscalar meson production in NN collisions

The spin structure of the matrix element for the pseudoscalar meson production processes in nucleon-nucleon collisions is established in the collinear kinematical regime in terms of 3 independent scalar amplitudes. This result is valid for any reaction mechanism and for any energy of the colliding and the produced particles. The complete experiment for the full reconstruction of all 3 complex amplitudes must contain two different classes of polarization experiments. The polarization transfer coefficients can be used to determine the moduli of all 3 amplitudes, whereas the spin correlation coefficients for \(\) + \(\) collisions are sensitive to the relative phases of different amplitudes.

Polarization phenomena in the reactionp+α→p+π0+α

We present a general analysis of polarization phenomena for three-body processes (in noncoplanar kinematics), in terms of a P- and T-odd acoplanarity parameter. The spin structure of the matrix element and the polarization phenomena contain new contributions, with respect to binary processes, which can be conveniently expressed as functions of this parameter. We apply this formalism to the reaction $p+\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\alpha}}p+{\ensuremath{\pi}}^{0}+\ensuremath{\alpha},$ in view of characterizing the different mechanisms involved and studying the excitation of the Roper resonance. We find that the polarization transfer coefficient ${D}_{\mathrm{nn}},$ where $\stackrel{\ensuremath{\rightarrow}}{n}$ is normal to the proton scattering plane, is especially sensitive to the spin of the exchanged particle.

Zero degree polarization transfer measurements for the13C(p→,n→)13Nreaction at 197 MeV and empirical Gamow-Teller strength distribution

In this paper, we present differential cross sections and complete sets of polarization transfer coefficients, ${D}_{\mathrm{ij}},$ obtained in the ${}^{13}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{p},\stackrel{\ensuremath{\rightarrow}}{n}{)}^{13}\mathrm{N}$ reaction studied at zero degree and at 197 MeV incident proton energy. The complete set of polarization observables is used to obtain the Fermi and Gamow-Teller (GT) cross section contributions in the ground state transition, which are then used to deduce GT transition strengths. The sum of the GT strength up to 20 MeV of excitation is compared with shell model calculations. In the region between 20 to 46 MeV of excitation, the differential cross section has been separated in spin and nonspin components.

A proton polarimeter for 3He(d,p) 4He polarization transfer studies

A compact polarimeter has been constructed and calibrated to measure the polarization of 13–16 MeV protons, such as those emitted from the 3He(d,p) 4He reaction near the E d=430 keV resonance. The polarimeter uses p- 4He elastic scattering as an analyzer. It consists of a 4He gas cell pressurized to 2.76 MPa and a left–right pair of CsI detectors collimated at 65° to maximize the figure of merit for the device. The effective analyzing power and efficiency of the polarimeter have been measured as a function of energy using a collimated polarized proton beam. These measured values are in good agreement with a Monte Carlo computer simulation that forms the basis for the calibration curve for the device. Preliminary results from the 3He(d,p) 4He reaction with polarized deuterons confirm that the proton polarimeter can be used to determine polarization transfer coefficients near the low-energy resonance.