Recoil Polarization Research Articles

A polarized pure [Hvec][Dvec] target for nuclear physics experiments with real photons

Abstract The microscopic structure of baryon resonances provides a good test for models of the strong interaction. In fact, quark models are quite successful in describing the static properties like spins, parities, masses and magnetic moments. However, dynamical properties, as for example the photon coupling strengths corresponding to transitions from the ground states (proton and neutron) to the excited states (baryon resonances), are much more difficult to handle and provide an excellent test of the wave functions that quark models produce. For real photons, the coupling strength can be expressed by the total helicity amplitudes A1/2 and A3/2. It can be shown (1) that the complete determination of these amplitudes requires polarized photons, polarized targets and even a measurement of the recoil polarization. Therefore, modern real photon facilities should aim at having at least photons with both circular or linear polarizations and polarized targets (proton and neutron), with high and well-controlled ...

Neutrino mass effect on the nuclear muon capture

Multipole expansion of the partial transition amplitude in the nuclear muon capture with massive lefthanded Dirac neutrino has been derived. The multipole amplitudes for the partial nuclear transitions are given as the explicit functions of the neutrino mass parameter. As an example, the capture rate, the recoil asymmetry and the neutrino polarization are investigated in terms of these multipole amplitudes. The transversal neutrino polarization provides a connection between theT-violation and the neutrino mass: ifT-odd component in the neutrino polarization is observed, then neutrino must be a massive particle. It turns out that in the capture rate and recoil polarization, the effects due to very small neutrino mass can be proportional to the square ratio of the neutrino mass to its momentum, while the neutrino transversal polarization is proportional to this ratio only. Under the recent limits on the muon neutrino mass, the observable effects inthe partial transition may be below the order of ≃10−3.

Magnetic moment of the short-lived β-emitter 23Mg

The magnetic moment of 23 Mg (I π= 3 2 +, T 1 2 =11.3 s ) has been determined to be |μ( 23 Mg)| = 0.5364±0.0003 μ N by means of a β-NMR detection with recoil polarization obtained through a nuclear reaction. The deduced spin expectation values are in agreement with the systematic behavior of the mirror doublets in the sd shell.

Wigner-Thomas spin precession in polarized coincidence electronuclear scattering.

The role of the Wigner-Thomas precession in nucleon recoil polarization measurements in coincidence electron scattering processes is examined. The necessary formalism is developed within the framework of the Jacob-Wick method, and then applied to two processes: the pseudoscalar electroproduction off a nucleon and the deuteron two-body electrodisintegration.

Magnetic moment of23Mg

The magnetic moment of the23Mg (Iπ=3/2+, T1/2=11.3 s), has been determined as |μ(23Mg)|=0.5364±0.003 µN by use of β-NMR detection with the recoil polarization obtained through a low energy nuclear reaction.

Quark models and polarized electroproduction of the Roper resonance

We calculate the recoil polarization observables for neutral pion electroproduction on the proton. In particular, for theN(938)→N*(1440) transition, we study these observables for several quark models of the resonant amplitudes. We find that the polarization response functions, unlike the unpolarized cross section, have encouragingly large sensitivity to the presence of the Roper. Furthermore, these observables can clearly reveal the presence of a longitudinal coupling.

Nucleon recoil polarization in electromagnetic quasi-free knockout including two-body currents

Polarization observables are considered for the outgoing nucleon knocked out in quasi-free electron scattering. The theoretical framework is based on the one-photon exchange approximation and the electromagnetic current of the target nucleus is built with one- and two-body contributions coming from meson-exchange currents and isobar configurations in intermediate nuclear states. Specific calculations are presented for both proton and neutron knockout, taking an 16O target nucleus as an example to set the scale for possible experiments. The sensitivity to final-state interactions, mesonic effects and isobaric configurations is discussed.

Time reversal test in the nuclear muon capture

Possible effects of breaking CP-symmetry are looked for in the muon capture by a linearly polarized target nucleus. With this aim the recoil polarization in the partial transitions\(0\xrightarrow{{\mu ^ - }}I,1/2\xrightarrow{{\mu ^ - }}J\) and\(1\xrightarrow{{\mu ^ - }}I\) is investigated in a nuclear model independent way. It is shown that the hyperfine structure of the muonic atom significantly influences theT-odd correlations in the recoil polarization formula, and the expectation for theT- odd signal in case of the linearly polarized target is higher by one order of magnitude. We obtain the complete set of theT-odd observables which could enter the polarization formula. As an example, within the impulse approximation for the weak interaction hamiltonian, we analyse the nonstandard, CP-breaking extension of the Fermi theory using complex Fujii-Primakoff form factorGV eiφ.

Recoil polarization observables in coincident pion electroproduction

We present an analysis of the recoil polarization observables in neutral pion electroproduction on the proton. In particular, for the N → Δ transition, we investigate the sensitivity of these observables to models of the resonant and non-resonant amplitudes. We find that the resonant quadrupole amplitudes have a large effect on the polarization response functions in the reaction plane while the Born terms significantly influence the polarization normal to this plane. At large four-momentum transfer, the higher nucleon resonances are found to interfere strongly with the Δ amplitudes.

Recoil-proton polarization in pi p elastic scattering at 547 and 625 MeV/c.

The polarization of the recoil proton in ${\ensuremath{\pi}}^{+}$p and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$p elastic scattering using a liquid-hydrogen target has been measured for backward angles at 547 and 625 MeV/c. The scattered pion and recoil proton were detected in coincidence using the large-acceptance spectrometer to detect and analyze the momentum of the pions and the JANUS polarimeter to identify and measure the polarization of the protons. Results from this experiment agree with other measurements of the recoil polarization, with analyzing-power data previously taken by this group, and with predictions of partial-wave analyses.

Radiative pion capture and pion photoproduction in a chiral bag model.

Radiative pion capture on nucleons is studied in a chiral bag model at pion laboratory momenta in the range q/sub L/approx.300--500 MeV. We calculate dsigma/d..cap omega.. and L-R asymmetry. Through detailed balance and time reversal invariance we also calculate dsigma/d..cap omega.. and P(theta) (nucleon recoil polarization) for pion photoproduction at equivalent photon laboratory momenta. A detailed comparison is made with the data.

Neutrino neutral current reactions in 12C

The differential and total cross sections for the nuclear reaction ν μ + 12 C (g.s) → 12C ∗ (1 +; T = 1, 15.1 MeV) + ν μ are investigated for values of 50 ≤ E ν μ ≤ 300 MeV. An effective Hamiltonian for the above nuclear reaction is constructed from the neutrino-quark neutral current weak interaction, by first constructing the neutrino-nucleon neutral current interaction and then using the impulse approximation along with the non-relativistic reduction procedure. The Weinberg-Salam model is the basis of the calculations. Detailed expressions for the differential cross sections are derived including the nucleon momentum-dependent terms. The numerical results are obtained using the general 1 p-shell wavefunctions of Cohen and Kurath. The sensitivity of the total cross sections to the nuclear models and to the Weinberg angle is studied. The corresponding anti-neutrino reaction is also investigated. The ratio R = (σ T ν μ − σ T ν μ ) (σ T ν μ + σ T ν μ ) is found to be independent of the nuclear wavefunctions but very sensitive to the Weinberg angle. Thus this observable can be used to determine the free parameter θ w in a nuclear reaction, thereby complementing the studies involving free nucleons. The recoil polarization of the final nucleus 12C ∗(1 +; T = 1, 15.1 MeV) is also studied and its importance is pointed out.

Recoil polarization of [formula omitted] in neutrino neutral current interactions

We report the results of the average recoil polarization of 12 C ∗ (1 +; T=1; 15.1 MeV) excited in neutrino neutral current interactions in 12C. Cohen-Kurath wave functions are used to obtain the numerical values of the recoil polarization. It is found to be insensitive to the choice of the nuclear wave functions.

The induced pseudoscalar coupling and the neutrino helicity from [formula omitted

Recent measurements by Roesch et al. of recoil polarizations in 12 C(μ,ν μ) 12 B (g.s.) are analysed when the sign of the helicity h ν of the emitted neutrino is allowed to change. Although the analysis of observables in terms of a ratio of two amplitudes remains the same, the dynamical information on couplings contained in this ratio is different. We conclude, from the experimental results, that the nuclear pseudoscalar coupling is ƒ p =−1.02 if h ν =−1, whereas ƒ p =+2.79 if h ν =+1.

Measurement of the capture rates to the excited states in 12C(μ −, δ) 12B ∗ and a novel technique to deduce the alignment of 12B ∗(1 −)

The capture rates to 12B ∗ states were measured yielding Γ(1 −) = 380(100) s −1, Γ(2 −) = 120(80) s − and Γ(2 +)= 270(100) s −, in disagreement with published values. A novel technique for measuring the alignment of the 1 − state, using combined Doppler shape analysis and angular correlation techniques, is described; it yields A(1 −) = 0.6(0.7). Improved correction factors for the ground state recoil polarizations P av and P L are deduced.

Recoil nuclei polarization in the partial [formula omitted] transitions

The average linear recoil polarization of recoil nuclei in the reaction μ − + 12 C(g.s.) → ν μ + 12 B(I π) is investigated, and the results have been compared to the issue of the Louvain-Saclay- ETH experiment. The generalized Helm model has been used for the nuclear part of the problem, and its reliability is compared with the findings of the recent papers. The compatibility of the results with the recent experimental data has been confirmed within the model used, and qualitative explanation of the differences between the μ -capture rates from the Helm model and the experiment is proposed.

Semileptonic weak and electromagnetic interactions in nuclei: Recoil polarization in muon capture

An analysis of the polarization of the recoiling nucleus following the capture of polarized muons by nuclei is performed. New general expressions for abitrary nuclear spin are obtained in terms of the same reduced matrix elements which govern inelastic electron scattering and β -decay. As an application we consider the A = 12 system and study uncertainties in the nuclear structure by using different sets of one-body density matrices. With the canonical values of the weak form factors (i.e. absence of second-class currents) we achieve a fairly good agreement with the experimental data including the inelastic form factor at high momentum transfers and the recently measured average 12B polarization. Implications Of the new corrected value of the average polarization on weak form factors and nuclear structure are discussed.

Qualitative measurement of the longitudinal recoil polarization in the reaction [formula omitted

For the reaction 12 C(μ −, ν) 12 B(g.s.) , we have performed the muonic analogue of the Goldhaber-Grodzins-Sunyar experiment in e-capture, i.e. measured the sign and magnitude of the longitudinal polarization of the 12B recoil. The result, P L = −0.83(21) implies a neutrino polarization h ν = 0.89(23) (left-handed).

A note on the induced pseudo-scalar coupling constant in μ − + 12C(g.s)→ 12B(1 +,g.s+ ν μ

The sum of the induce pseudo-scalar g P and the second-class induced tensor g T couplings in muon capture is found to be ( g P + g T) g A= (13.3 + 1.8) by comparing with recent data on the recoil polarization of 12B(1 +) in the μ − + 12C→ 12B+ ν μ process, even aaking into account the corrections due to the gamma decay of the excited states of 12B to 12B(1 +;g.s.). With the canonical value for g P and in the absence of meson exchange effects, our results indicate a large positive value for g T which is in strong contradiction with the conclusion of the Louvain-Saclay—ETH experiment.

Induced tensor and pseudotensor form factors in the reactionμ− + C12→B12 + νμ

Using the experimental data on the capture rate and the recoil polarization in the reaction ${\ensuremath{\mu}}^{\ensuremath{-}} + ^{12}\mathrm{C}\ensuremath{\rightarrow}^{12}\mathrm{B} + {\ensuremath{\nu}}^{\ensuremath{\mu}}$ the weak-magnetism form factor is deduced independently of a specific value of the pseudoscalar form factor ${g}_{P}({q}^{2})$. It is found to be in good agreement with the conserved-vector-current hypothesis. Then we look at the range of compatibility of the induced form factors for the given experimental data.