Polarization effects in inelastic deuteron scattering in the region of baryon-resonance excitation

Within the impulse approximation, polarization effects in inelastic deuteron scattering on nuclei are investigated in the region around the resonance of mass about 2190 MeV/c ². It is shown that the spin-dependent part of the NN → NN*(2190) amplitude plays a significant role at high momentum transfers. Predictions are obtained for some polarization observables and cross sections for various deuteron-spin-flip processes.     

Deuteron electrodisintegration at high energy and momentum transfer

Inelastic electron-deuteron scattering has been calculated at backward angles for energy transfers up to 50 MeV and momentum transfers up to 60 fm^?2. Exchange currents from the pion, vector mesons and mixed ?πγ and ωπγ were taken into account. The effect of the meson-nucleon form factor is studied, and various approximations of the mesonic currents are discussed. Baryon resonance configurations in the wave function have been used to calculate the Δ-resonance currents. We show that the effect from meson-nucleon form factors, the ?πγ, ωπγ and Δ currents cancels almost exactly against the vector meson contribution at low momentum transfer. Thus the pure pionic current defines a reasonable choice. In the high momentum region this approximation breaks down.     

Nuclear-charge polarization at scission in the 12 MeV proton-induced fission of <Superscript>232</Superscript>Th

The most probable charges of secondary fragments, produced after neutron evaporation from primary fragments, have been evaluated using fractional cumulative and mass yields in the 12MeV proton-induced fission of ²³²Th . The nuclear-charge polarization of primary fragments at scission has been obtained by correcting the most probable charge of secondary fragments for neutron evaporation. The fragment mass dependence of the nuclear-charge polarization at scission shows good agreement with that for thermal neutron-induced fission of ²³⁵U , indicating that the nuclear-charge polarization is nearly insensitive to mass and excitation energy of the fissioning nucleus for asymmetric fission in the actinide region.     

Alpha particle scattering in the rigid projectile approximation

We study elastic α-particle scattering offp,α-particle and¹²C targets at 17.9 GeV/c incident momentum in the rigid projectile approximation of the Glauber model. Differential and total cross-sections are computed and compared with the data. Reasonable agreement with the observed differential cross-sections is found for small momentum transfers but short-range dynamical correlations in the target will probably have to be taken into account to get better agreement at larger momentum transfers, particularly in the case of α-¹²C scattering.     

Electromagnetic and Axial Form Factors of Octet and Decuplet Baryons

We report from a study of the elastic electromagnetic and axial form factors of all lowest baryon states with flavors up, down, and strange along relativistic constituent-quark models. We consider the baryons as relativistic bound states of three constituent quarks and solve the eigenvalue problem of the invariant mass operator. The corresponding eigenstates are employed to calculate manifestly covariant form factors within the point form of Poincaré-invariant quantum mechanics. The electromagnetic and axial current operators are constructed along the spectator model in point-form relativistic dynamics. We have thus obtained covariant predictions for the electroweak form factors, for momentum transfers up to Q ² ~ 4 GeV², as well as the electric radii, magnetic moments, and axial charges. The theoretical results in general agree very well with existing phenomenological data. In cases, where no experimental information is yet available, the results are well compatible with data from lattice quantum chromodynamics.     

Measurement of the polarization of positive muons produced in high-energy antineutrino interactions

The question whether scalar-type interactions contribute to weak interactions at large momentum transfer has been investigated by a measurement of the longitudinal polarization of positive muons produced in charged-current interactions of high-energy antineutrinos with iron. At an average momentum transfer <Q ²>=4 GeV² the muon spin is found to be oriented forward with respect to the muon momentum vector, with an average polarization of 1.10±0.24, consistent with positive helicity. A limit on scalar contributions of σ_{s, p}/σ_tot <7% at the 95% confidence level can be deduced. A search for violation of time reversal invariance which could manifest itself by a polarization component perpendicular to the muon production plane gave a limit of σ_tv/σ_tot <16% (95% c.l.). It is concluded that the weak leptonic charged current retains its dominant vector and axial vector structure at large momentum transfers.     

On the use of realistic wave functions in the coherent pion photoproduction on 3He nuclei

We analyze the influence of the nuclear wave functions generated from a set of different realistic soft-core two-body potentials on the coherent charged pion photoproduction on ³He nuclei at threshold and for small momentum transfers. This process is calculated in the framework of the impulse approximation including the Fermi motion. At threshold and below the resonance, our results reproduce fairly well the experimental data. At the first γN resonance region, the agreement with experiments varies with the momentum transfer.     

Spin observables for 208Pb(→p, →p) elastic scattering at 290 MeV

A newly constructed focal-plane polarimeter for the medium resolution spectrometer at TRIUMF has been used to measure polarizations and polarization transfer coefficients for protons elastically scattered from ²⁰⁸Pb at 290 MeV. These results combined with existing cross section data at 300 MeV completely determine the elastic scattering amplitudes for momentum transfers q<2.6 fm⁻¹. The data are in quantitative agreement with Dirac calculations which take the effects of Pauli blocking into account, but disagree at small momentum transfer with density-dependent Schrödinger calculations.     

Hadronic vacuum polarization effects in Bhabha and Moller scattering

Effects of hadronic vacuum polarization in the reactions e⁺e^? → e⁺e^? and e^±e^± → e^±e^± are discussed. The cross sections with spin polarization are given. Measurements of these effects could directly determine in the hadronic vacuum polarization at spacelike momentum transfers and could improve tests of quantum electrodynamics.     

Charge radii and polarization effects in the oxygen region

When using reasonable monopole polarization charges, it is possible to fit the systematics of charge radii in the oxygen region, if core-excited components are taken into account.     

Momentum transfer dependence behaviors of ionization and dissociation of oxygen

The decay pathways of the structured ionization region of oxygen at different momentum transfers,i.e.,0,0.23 a.u.(atomic unit),and 0.91 a.u.,are studied by measuring the ion and the scattered electron coincidently.It is found that the dipole-forbidden superexcited states of(2σu)-1(c4Σu-)npσu 3Σg-← X3Σg-decay into different channels according to the principal quantum number n.The broad ridge above 35 eV,which may be due to inner-valence excited states of(2σg)-1nλ or multiply excited states,is observed both at small and large momentum transfers,and its decay channel of O++ O is dominant.     

The 116Sn(d,t)115Sn reaction at 23 MeV

The levels of ¹¹⁵Sn up to 4 MeV excitation energy have been studied with 15–18 keV energy resolution, and many previously unreported levels have been observed. Angular momentum transfers and spectroscopic factors have been determined for most of the levels up to 3 MeV. The main features of the observed fragmentation of the strength are rather well reproduced by means of a weak coupling calculation.     

Form factors for exotic baryons of isospin <Emphasis Type="Italic">I</Emphasis> = 5/2

Electric form factors for exotic baryons are calculated within the relativistic quark model in the region of low and intermediate momentum transfers, Q ² ≤ 1 GeV². The charge radii of E ⁺⁺⁺ baryons are determined.     

Static and dynamic quadrupole moments of high-spin isomers in the Pb-region

Quadrupole moments of high-spin isomers in the Pb-region are studied by using core polarization charges induced by the coupling of single-particle states to giant resonances. We found that the core polarization charges are enough to reproduce the observed quadrupole moments of the isotones with neutron number N=126 quantitatively without any intrinsic deformation. The mass number dependence of the quadrupole moments in the Rn-isotopes is also discussed by taking into account the configuration mixing involving the neutron excited first 2⁺ state.     

On the nuclear longitudinal charge response in the quasi-elastic peak region

We calculate in a semiclassical RPA approach the nuclear charge response of ¹²C, ⁴⁰Ca, and ⁵⁶Fe in the quasi-elastic peak region for moderate momentum transfers (q = 1.0–2.0 fm⁻¹). Using the Gogny force and taking full account of antisymmetrization effects we find with no free parameters good agreement with the (e, é) data for ¹²C. However for ⁴⁰Ca and ⁵⁶Fe the missing charge problem persists. Arguments that this may be due to strong influence of 2p-2h states in the isovector channel are advanced.     

Delta-isobar configurations in 12C and 16O nuclei

The differential yield of the reaction ¹⁶O(γ, π ⁺ p) at the maximum photon energy of 450 MeV was measured in the region of high momentum transfers to the residual nuclear system. The experimental results obtained for the ¹⁶O nucleus and the cross section measured earlier for the reaction ¹²C(γ, π ⁺ p) were analyzed on the basis of a model that takes into account the admixture of isobar states in the nuclear wave function. The probabilities for the delta-isobar configurations in the ground states of the carbon and oxygen nuclei per nucleon were estimated empirically at 0.012 ± 0.003 ± 0.002 and 0.019 ± 0.003 ± 0.003, respectively.     

Role of two-nucleon mechanisms in pion photoproduction on nuclei in the region of high momentum transfers

The role of two-nucleon mechanisms in pion photoproduction on nuclei was studied in the region of high momentum transfers to the residual nucleus. The process in which the photoproduction of negative pions on a ¹²C nucleus is accompanied by proton emission was considered by way of example. The results of the calculations were compared with available experimental data.     

Spin effects and factorization in the Drell-Yan process

We discuss the idea that the nontrivial vacuum structure in QCD may induce transverse momentum and spin correlations of the initial state partons in Drell-Yan type reactions, i.e. in hadron-hadron collisions with production of a vector bosonV=γ ^*,Z,W ^±. Transverse momentum correlations are found to have practically no effect on observable quantities, but spin correlations have drastic consequences for the polarization density matrices of theV-bosons. We therefore propose measurements of theV polarization as a good test for the basic factorization hypothesis which, so far, has been assumed to be valid in numerous applications of the naive and QCD-improved parton model. We compare our ansatz for a spin correlation violating factorization with data from the NA 10 collaboration onγ ^* production inπ ^? N scattering. We find that the data give an indication of spin correlations of the partons in the initial state to be present.     

Longitudinal sum rule for inelastic electron scattering and nucleon-nucleon correlations

We have considered the influence of short-range dynamical and statistical correlations on the inelastic scattering of electrons from light nuclei. The correlation effects are discussed on the example of the longitudinal sum rule for the ¹⁶O and ¹²C nuclei. A remarkable increase in the sum rule, caused by the short-range correlations at medium momentum transfers (100–200 MeV), is pointed out.