On magnetic dipole form factors in deformed nuclei

Properties of magnetic dipole form factors for deformed nuclei are discussed in terms of the angular momentum projected Hartree-Fock-Bogoljubov approximation and the neutron-proton interacting boson model. It is pointed out that there exists a relation between the M1 form factor for the excitation of the orbital K^π=1⁺ band, the M1 form factor for the ground-state band, and the collective M1 form factor in odd-A nuclei.     

A study of the (τ, α) reaction on 50Cr

The ⁵⁰Cr(τ, α)⁴⁹Cr reaction has been studied at E_τ = 16.0 MeV using the Tandem Van de Graaff accelerator and the multichannel magnetic spectrograph of the Nuclear Physics Laboratory, Oxford. Twenty-nine levels up to an excitation of ≈ 6.8 MeV have been observed, including a few analogues. The angular distributions have been analyzed in terms of the DWBA theory of direct reaction. The J^π limits and spectroscopic factors are obtained for various levels.     

Pion production in two-body pd collisions

The reactions d(p, π⁺)t and d(p, π^o)³ He are analyzed in terms of the pp → π⁺d sub-process. The exclusion principle induces an additional exchange contribution involving the πd scattering amplitude. Acceptable deuteron and tritron (³H) wave functions which reproduce the charge form factors yield results consistent with experimental angular distributions at 470, 590, 754 and 1192 proton lab. energies. The forward peak is not sensitive to details of the wave functions. Both the direct and exchange form factors develop a zero which is imposed by the dip in the ³He charge form factor. The associated interference pattern governs the backward cross section.     

Pionic contribution to the muon magnetic moment

A procedure is developed to derive an optimal lower bounds for the pionic contribution to the muon magnetic moment from analyticity of the pion form factor F(t), its normalization F(0)=1 and from experimental information from both the processes e^?p → e^?π⁺n and e⁺e^? → π⁺π^?. It represents essentially the solution of a certain kind of optimization problem in Hilbert space. Numerical results are presented and compared to the recent data for the muon magnetic moment; we find a_μ(π⁺π^?) ? 42 × 10^?9.     

Measurement of the slope of the π0-electromagnetic form factor

Using a magnetic spectrometer, we have studied 30 000 π⁰ → e⁺e^?γ events coming from K_π2⁺ decays in flight. We find a positive value for the slope of the neutral-pion electromagnetic form factor: a = +0.10 ± 0.03 (or a = +0.05 ± 0.03 without radiative corrections). This value is higher than the predictions of vector meson models.     

Pion-nucleon scattering: The P11 channel

A simple model is presented for the πN scattering in the P₁₁ channel from the threshold to the Roper resonance N(1470). The model starts with the πBB′ coupling of the Yukawa type where B (and B') stands for N, R or Δ. A unitarized scattering amplitude is constructed from the K-matrix which is obtained perturbatively. With appropriate coupling constants and form factors for the πBB′ interactions, which conform to the quark model, the P₁₁ scattering can be well reproduced. It is emphasized that the process πN → ππΔ → πN, which has been ignored hitherto, plays a crucial role in the energy region considered.     

Solitons in the one-dimensional antiferromagnet TMMC

It is shown that magnetic solitons are expected to occur when a magnetic field is applied to a planar antiferromagnetic chain. Neutron inelastic scattering measurements have been performed at low energy on the one dimensional antiferromagnetic compound TMMC. A new fluctuation is observed, around q = π and ω = 0 which is well interpreted in terms of magnetic solitons.     

Elastic backward scattering of negative pions on protons at 25 and 38 GeV/c

The backward elastic scattering reaction π^?p → pπ^? at momenta 25 and 38 GeV/c have been measured using a magnetic spectrometer with hybrid chambers. The experimental data on the dependence of the cross section dσ/du on the momentum transfer u as well as the energy dependence dσ/du at u = 0 are given.     

Charged-pion photoproduction measurement on deuterium in the Δ(1236) region using a quasi-monochromatic photon beam

Charged-pion photoproduction spectra on hydrogen and deuterium have been measured using an in-flight positron annihilation photon beam. Pions were detected in magnetic spectrometers. The experiment consisted of π^± angular distributions at 300 MeV, and fixed-angle excitation curves at 20° (π^±) and 55° (π^±) in the photon energy range 300–460 MeV. Experimental data are compared to a calculation by Laget which includes final-state nucleon-nucleon interaction and Pauli correlations. The overall agreement is satisfactory; however, the model slightly overestimates the nucleon-nucleon rescattering contribution.     

Electroexcitation of magnetic dipole and other modes in46Ti and48Ti

With high-resolution inelastic electron scattering measurements on⁴⁶Ti and⁴⁸Ti the excitation mechanism of the transition into low lying J^π=1⁺ states is investigated. The experimental evidence of considerable contribution of the orbital part of theM1 operator to the total transition strength is given by a model dependent analysis of form factors. The possibility of physical relationship to low lying J^π=1⁺ states in the rare earth nuclei is discussed in various models. MoreoverE2 form factors and good candidates forM3 form factors are presented.     

<Superscript>53</Superscript>Cr NMR study of CuCrO<Subscript>2</Subscript> multiferroic

The magnetically ordered phase of the CuCrO₂ single crystal has been studied by the nuclear magnetic resonance (NMR) method on ⁵³Cr nuclei in the absence of an external magnetic field. The ⁵³Cr NMR spectrum is observed in the frequency range ν_res = 61–66 MHz. The shape of the spectrum depends on the delay tdel between pulses in the pulse sequence τ_π/2–t _del–τ_π–t _del–echo. The spin–spin and spin–lattice relaxation times have been measured. Components of the electric field gradient, hyperfine fields, and the magnetic moment on chromium atoms have been estimated.     

Formfaktor des π-Mesons und Struktur der Nukleonen

Recent measurements of electron-proton scattering at Stanford have shown that the electric and magnetic form factors are not equal. Therefore, the isotopic vector parts of the form factorsG _e ^v andG _m ^v are recalculated with unsubtracted dispersion relations in the 2π-approximation. For the isotopic scalar parts we useG _e ^s (s)≈G _e ^v (s) andG _m ^s (s)≈ 0 which is known to be valid for moderate energy-momentum transfers. We obtain a simple closed expression for the electromagnetic form factor of the pionF _π in terms of the scattering lengtha ₁ and the effective ranger ₁ of the π-π-scattering in the stateL=T=1.a ₁ is roughly known from pion production by pions. With this value and a suitabler ₁,F _π has a resonance in the region of time-like energy-momentum transfer; and the pion rms-radius becomes\(\overline {v_\pi ^2 } = (0.82 \times 10^{ - 13} cm)^2 \). The calculated anomalous magnetic moment, the electric and the magnetic rms-radii of the proton are then within 10% of the experimental values, the electric charge within 30%. Moreover, the proton form factors are different from each other and up to an energy-momentum transfer of\(s = \frac{{ - q^2 }}{{m_\pi ^2 }} = 23\) within the experimental error of the new measurements. The deviations for higher values of the energy-momentum transfer may be explained in terms of the isotopic scalar parts of the form factors. In this case the electric form factor of the neutron will be different from zero in that region and the magnetic form factor of proton and neutron will no longer be equal. For comparison with other experiments we also calculate the π⁺?π^? cross section with neglect of other states thanL=T=1. Under this assumption the π?π cross section has a resonance for low energy-momentum transfer.     

Photoproduction of negative pions on a polarized neutron target in the resonance region

At the Bonn 2.5 GeV electron synchrotron the first measurements of the target asymmetry for the reaction γ + n ↑ → π^? + p have been performed. The negative pions were detected in a magnetic spectrometer at a constant pion c.m. angle of 40° and photon energies between 0.45 GeV and 2.0 GeV. Deuterated butanol was used as target material. The polarization of the deuterons was about 16%. The results show a significant difference from the previously measured π⁺ asymmetry.     

Observation of the decay τ → πv

The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τ→πv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction.     

Photoproduction of charged pions on deuterium in the first resonance region

Photoproduction of π⁺ and π^? on deuterium has been measured in the photon energy range from 240 to 400 MeV and for pion c.m. angles between 15° and 180°. The pions were analysed in angle and momentum by a magnetic spectrometer. From the measured π^?/π⁺ ratio, corrected for Coulomb interactions in the final state, differential cross sections of the reaction γ+n→π^?+p were calculated. Together with the π⁺ photoproduction our data show no isotensor contribution. Comparison of our data with the recent experiments done on the inverse reaction shows no evidence of a violation of time reversal invariance. With the measured π⁺ photoproduction on deuterium, a test of the spectator model has been made. Using the closure-approximation of Chew and Lewis our data agree within a range of ±10%.     

Character of frustration on magnetic correlation in doped Hubbard model

The magnetic correlation in the Hubbard model on a two-dimensional anisotropic triangular lattice is studied by using the determinant quantum Monte Carlo method. Around half filling, it is found that the increasing frustration t^′/t could change the wave vector of maximum spin correlation along(π,π) → (π, 5π/6) → (5π/6, 5π/6) → (2π/3, 2π/3),indicating the frustration’s remarkable effect on the magnetism. In the studied filling region ?n? = 1.0 ? 1.3, the doping behaves like some kinds of frustration, which destroys the (π,π) AFM correlation quickly and push the magnetic order to a wide range of the (2π/3, 2π/3)120^° order when the t^′/t is large enough. Our non-perturbative calculations reveal a rich magnetic phase diagram over both the frustration and electron doping.     

Core-polarization effects on the magnetic transitions in the 208Pb region

We show that there is a reduction of the magnetic transition strength at high momentum transfer due to core polarization. This accounts substantially for the observed reduction of 50% of the J^π=12^? and 14^? transitions in ²⁰⁸Pb. The core polarization does not affect the shape of the high J form factors in the vicinity of their main peaks. However, a significant q-dependent effect is predicted for the ground state M1 moment of ²⁰⁷Pb.     

Investigation of impurity diffusion in dilute alloys by nuclear magnetic resonance

The diffusion of Al in a Cu: 3.8 at % Al alloy has been investigated by observing the rotating-frame nuclear magnetic relaxation time T_1π of ²⁷Al as a function of temperature. It is shown that relaxation measurements of the solute atoms in a dilute alloy provide the correlation time of the diffusive motion of these atoms, if quadrupolar interactions form the main contribution to the relaxation time. From the correlation times the Al-diffusion coefficient in the alloy has been determined.     

Veneziano model for the ρ contribution to the nucleon form factors

The Igi-Veneziano model forπN scattering, combined with the experimental pion form factor is used to study theρ contribution to the isovector electromagnetic nucleon form factors.