General multipole expansion of polarization observables in deuteron electrodisintegration

Formal expressions are derived for the multipole expansion of the structure functions of a general polarization observable of exclusive electrodisintegration of the deuteron using a longitudinally polarized beam and/or an oriented target. This allows one to exhibit explicitly the angular dependence of the structure functions by expanding them in terms of the small rotation matrices d ^j _m'm(θ), whose coefficients are given in terms of the electromagnetic multipole matrix elements. Furthermore, explicit expressions for the coefficients of the angular distributions of the differential cross-section including multipoles up to L _max = 3 are listed in tabular form. Received: 19 November 2002 / Accepted: 7 May 2002     

Analyzing powers Ayy , Axx , Axz and Ay in the dd → 3Hen reaction at 270 MeV

The data on the tensor A_yy, A_xx, A_xz and vector A_y analyzing powers in the dd → ^3Hen obtained at T _d = 270 MeV in the angular range 0^° - 110^° in the c.m. are presented. The observed negative sign of the tensor analyzing powers A_yy, A_xx and A_xz at small angles clearly demonstrate the sensitivity to the ratio of the D - and S -wave component of the ³He wave function. However, the one-nucleon exchange calculations by using the standard ³He wave functions have failed to reproduce the strong variation of the tensor analyzing powers as a function of the angle in the c.m.     

Beam normal spin asymmetries: Theory

The beam normal spin asymmetry in elastic electron-nucleon scattering is discussed. This beam normal spin asymmetry depends on the imaginary part of two-photon exchange processes between electron and nucleon, and measures the non-forward structure functions of the nucleon. After briefly reviewing the theoretical formalism, we discuss calculations in the threshold region, in the resonance region, as well as in the diffractive region, corresponding with high energy and forward angles.     

Nucleon electromagnetic form factors and polarization observables in space-like and time-like regions

We perform a global analysis of the experimental data of the electromagnetic nucleon form factors, in space-like and time-like regions. We give the expressions of the observables in annihilation processes, such as p + ¯↦ℓ⁺ + ℓ^-, ℓ = e or μ, in terms of form factors. We discuss some of the phenomenological models proposed in the literature for the space-like region, and consider their analytical continuation to the time-like region. After determining the parameters through a fit on the available data, we give predictions for the observables which will be experimentally accessible with large statistics, polarized annihilation reactions     

Precision measurement of vector and tensor analyzing powers in elastic deuteron-proton scattering

High-precision vector and tensor analyzing powers of elastic deuteron-proton ( d + p) scattering have been measured at intermediate energies to investigate effects of three-nucleon forces. Angular distributions in the range of 70^°-120^° in the center-of mass frame for incident-deuteron energies E _d ^lab = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the ^12C (d, α)^10B(2⁺) reaction at 0^°. Results of the measurements are compared with state-of-the-art three-nucleon calculations. The present modeling of nucleon-nucleon forces and its extension to the three-nucleon system is not sufficient to describe the high-precision data consistently and requires, therefore, further investigation.     

Ab initio calculation of the 4He(e, e'd )d reaction

The two-body knock-out reaction ⁴He(e, e'd )d is calculated at various momentum transfers. The full four-nucleon dynamics is taken into account microscopically both in the initial and the final states. As NN interaction the central MT-I/III potential is used. The calculation shows a strong reduction of the coincidence cross-section due to the final-state interaction. Nonetheless, the theoretical results exhibit a considerable overestimation of the experimental cross-section at lower momentum transfer. Comparisons with other, less complete, calculations suggest that consideration of a more realistic ground state might not be sufficient for a good agreement with experiment, rather a more realistic final-state interaction could play an essential role.     

Measurement of the cross-section asymmetry of deuteron photodisintegration process by linearly polarized photons in the energy range E γ = 0.8–1.6 GeV

The first measurements of the cross-section asymmetry for the deuteron photodisintegration process at a cm angle of 90° up to 1.6 GeV were performed at Yerevan Electron Synchrotron. These results are in reasonable agreement with previous measurements at lower energy. Our data show agreement with the asymptotic meson exchange model predictions in the energy range 0.8-1.6 GeV. Received: 3 April 2000 / Accepted: 25 May 2000     

Phenomenology of the deuteron electromagnetic form factors

A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm⁻¹. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data. Received: 28 January 2000 / Revised version: 25 February 2000     

Asymptotic behavior of nucleon electromagnetic form factors in time-like region

We study the asymptotic behavior of the ratio of Pauli and Dirac electromagnetic nucleon form factors, F₂/F₁, in time-like region, for different parametrizations built for the space-like region. We investigate how fast the ratio F₂/F₁ approaches the asymptotic limits according to the Phragmèn-Lindel?f theorem. We show that the QCD-inspired logarithmic behavior of this ratio results in very far asymptotics, experimentally unachievable. This is also confirmed by the normal component of the nucleon polarization, P_y, in e⁺ + e^-↦N + ˉ (in collisions of unpolarized leptons), which is a very interesting observable, with respect to this theorem. Finally we observe that the 1/Q parametrization of F₂/F₁ contradicts this theorem.     

Dynamics of polarization buildup by spin filtering

There has been much recent research into polarizing an antiproton beam, instigated by the recent proposal from the PAX (Polarized Antiproton eXperiment) project at GSI Darmstadt. It plans to polarize an antiproton beam by repeated interaction with a polarized internal target in a storage ring. The method of polarization by spin filtering requires many of the beam particles to remain within the ring after scattering off the polarized internal target via electromagnetic and hadronic interactions. We present and solve sets of differential equations which describe the buildup of polarization by spin filtering in many different scenarios of interest to projects planning to produce high-intensity polarized beams. These scenarios are: 1) spin filtering of a fully stored beam; 2) spin filtering while the beam is being accumulated, i.e. unpolarized particles are continuously being fed into the beam; 3) the particle input rate is equal to the rate at which particles are being lost due to scattering beyond the ring acceptance angle, the beam intensity remaining constant; 4) increasing the initial polarization of a stored beam by spin filtering; 5) the input of particles into the beam is stopped after a certain amount of time, but spin filtering continues. The rate of depolarization of a stored polarized beam on passing through an electron cooler is also shown to be negligible.     

Selectivity of the nucleon-induced deuteron breakup and relativistic effects

Theoretical predictions for the nucleon-induced deuteron breakup process based on solutions of the three-nucleon Faddeev equation including such relativistic features as the relativistic kinematics and boost effects are presented. Large changes of the breakup cross section in some complete configurations are found at higher energies. The predicted relativistic effects, which are mostly of dynamical origin, seem to be supported by existing data.     

Measurement of GEp/GMp via polarization transfer at Q2 = 0.4 GeV /c2

The polarization transfer from longitudinally polarized electrons to protons in the elastic scattering p( e, e' p) has been measured around Q² = 0.4 (GeV/c)² with the three-spectrometer facility at the Mainz microtron MAMI. From this polarization transfer the ratio G _Ep/(G _Mp/μ_p) has been determined. The ratio is found to be slightly less than unity in agreement with recent results from other laboratories and from the Rosenbluth separation of cross-sections measured with unpolarized electrons. Received: 26 July 2001 / Accepted: 25 September 2001     

Polarization observables in elastic electron deuteron scattering including parity- and time-reversal-violating contributions

The general formalism for polarization observables in elastic electron deuteron scattering is extended to incorporate parity- and time-reversal-violating contributions. Parity-violating effects arise from the interference of γ and Z exchange as well as from the hadronic sector via a small parity-violating component in the deuteron. In addition we have allowed for time-reversal-invariance-violating contributions in the hadronic sector. Formal expressions for the additional structure functions are derived, and their decomposition into the various multipole contributions are given explicitly. Received: 19 December 2000 / Accepted: 14 February 2001     

Nucleon elastic form factors

The nucleon form factors are still the subject of active investigation even after an experimental effort spanning 50 years. This is because they are of critical importance to our understanding of the electromagnetic properties of nuclei and provide a unique testing ground for QCD motivated models of nucleon structure. Progress in polarized beams, polarized targets and recoil polarimetry have allowed an important and precise set of data to be collected over the last decade. I will review the experimental status of elastic electron scattering from the nucleon along with an outlook for future progress.     

Incoherent pion photoproduction on the deuteron including polarization effects

Incoherent pion photoproduction on the deuteron including polarization effects is studied in the energy region from π-threshold up to the Δ(1232)-resonance with inclusion of all leading πNN effects. For the elementary pion photoproduction operator, a realistic effective Lagrangian approach is used which displays chiral symmetry, gauge invariance, and crossing symmetry, as well as a consistent treatment of the spin-3/2 interaction. The interactions in the final two-body subsystems are taken in separable form. Effects of final state interaction are investigated and their role in unpolarized and polarization observables are found to be significant. The extracted cross sections and spin asymmetries are compared with available experimental data and predictions of other works, and a satisfactory agreement is obtained. In addition, the sensitivity of results to the elementary N(γ, π)N operator is investigated. Considerable dependence of the d(γ, π)NN results on the elementary amplitude is found. This indicates that it can serve as a filter for different elementary operators.     

Final-state interaction in semi-inclusive DIS off nuclei

The Final-State Interaction (FSI) in Deep-Inelastic Scattering (DIS) of leptons off a nucleus A, due to the propagation of the struck nucleon debris and its hadronization in the nuclear environment is considered. The effective cross-section of such a partonic system with the nucleons of the medium and its time dependence are estimated, for different values of the Bjorken scaling variable, on the basis of a model which takes into account both the production of hadrons due to the breaking of the color string, which is formed after a quark is knocked out off a bound nucleon, as well as the production of hadrons originating from gluon radiation. It is shown that the interaction, the evolution and the hadronization of the partonic system in the nuclear environment can be thoroughly investigated by a new type of semi-inclusive process, denoted A(e, e'(A - 1))X, in which the scattered lepton is detected in coincidence with a heavy nuclear fragment, namely a nucleus (A - 1) in low energy and momentum states. As a matter of fact, if the FSI is disregarded, the momentum distribution of (A - 1) is directly related to the momentum distribution of the nucleon before γ^* absorption, i.e. the same quantity which appears in the conventional A(e, e'N)X process, where N denotes a nucleon. The rescattering of the struck nucleon debris with the medium damps and distorts the momentum distributions of (A - 1) in a way which is very sensitive to the details of the effective cross-section of the debris with the nucleons of the medium. The total cross-section of the process A(e, e'(A - 1))X on ⁴He, ¹⁶O, and ⁴⁰Ca, related to the probability that after a target nucleon experiences a DIS process, the recoiling (A - 1) nucleus remains intact in spite of the strong FSI, is evaluated, and the distorted momentum distribution of the recoiling (A - 1) system is obtained. It is shown that both quantities are very sensitive to the details of the early stage of hadronization of the nucleon debris in the nuclear medium. Received: 28 June 2002 / Accepted: 15 January 2003 / Published online: 5 May 2003