Relativistically invariant analysis of -isobar production in deuteron electrodisintegration: : General analysis of polarization effects

The differential cross-section and the polarization observables for Δ-isobar production in the deuteron electrodisintegration process, e^-+d→e^-+Δ+N, are calculated in a general formalism based on structure functions. The obtained expressions have a general nature, hold for one-photon-exchange, assuming P-invariance of the electromagnetic interaction and the conservation of the hadron electromagnetic current. The dependence of the differential cross-section of the e^-+d→e^-+Δ+N reaction on the vector and tensor polarizations of the deuteron target with unpolarized and longitudinally polarized electrons is considered. The general dependence of the asymmetries on two of five kinematic variables, the azimuthal angle φ and (linear polarization of the virtual photon) is calculated. A similar analysis is performed for the polarization of the nucleon produced in γ^*d→ΔN reaction provided the electron beam is unpolarized or longitudinally polarized. Polarization effects, which are due to the strong ΔN-interaction in the final state are calculated. The photoproduction of the Δ-isobar on the deuteron target has been considered in detail, as a particular case. The differential cross-section and various polarization observables have been derived in terms of the reaction amplitudes. The polarization observables due to the linear and circular polarizations of the photon, when the deuteron target is arbitrarily polarized have been derived in terms of the reaction amplitudes. The polarization of the final nucleon is also considered.     

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     

General survey of polarization observables in deuteron electrodisintegration

Polarization observables in inclusive and exclusive electrodisintegration of the deuteron using a polarized beam and an oriented target are systematically surveyed using the standard nonrelativistic framework of nuclear theory but with leading-order relativistic contributions included. The structure functions and the asymmetries corresponding to the various nucleon polarization components are studied in a variety of kinematic regions with respect to their sensitivity to realistic NN-potential models, to subnuclear degrees of freedom in terms of meson exchange currents, isobar configurations and to relativistic effects in different kinematical regions, serving as a benchmark for a test of present standard nuclear theory with effective degrees of freedom.     

General formulae for polarization observables in deuteron electrodisintegration and linear relations

Formal expressions are derived for all possible polarization observables in deuteron electrodisintegration with longitudinally polarized incoming electrons, oriented deuteron targets and polarization analysis of outgoing nucleons. They are given in terms of general structure functions which can be determined experimentally. These structure functions are Hermitean forms of theT-matrix elements which, in principle, allow the determination of allT-matrix elements up to an arbitrary common phase. Since the set of structure functions is overcomplete, linear relations among various structure functions exist which are derived explicitly.Supported by the Deutsche Forschungsgemeinschaft (SFB 201)     

Correlation and polarization characteristics of the nuclear quasi-free (p,dπ<Superscript>+</Superscript>) reaction

An extended set of observables of the nuclear quasi-free (p, dπ⁺) reaction including the triple differential cross-section for coincidence measurements, its analyzing power in case of polarized proton beams and, also, the parameters of the polarization of the excited recoil nucleus and the produced deuteron are considered in the framework of the distorted-wave impulse approximation using the reaction ¹⁶O(p, dπ⁺)¹⁵N at a proton energy of 650 MeV as an example. The calculations show a high sensitivity of the differential cross-section and, especially, of the polarization transfer characteristics of the reaction to the spin-multipole decomposition of the amplitude of the basic two-body pp → dπ⁺ process.     

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     

QED corrections to {\vec A}({\vec e},e'B)X and A({\vec e},e'{\vec B})X reactions: The case of tensor polarization

The model-independent leading radiative corrections to polarization observables in semi-inclusive longitudinally polarized electron-nucleus scattering with the registration of a produced hadron and scattered electron in coincidence were calculated using the Drell-Yan representation in electrodynamics. The cases of a tensor-polarized target or a produced hadron with tensor polarization were considered. The exclusive process of the electrodisintegration of a polarized deuteron was also studied.     

Exclusive deuteron electrodisintegration and off-shell effects

In the framework of a covariant formalism relying on a relativistic deuteron wave function (RDWF) with one nucleon on the mass shell one deals with an exclusive deuteron electrodisintegration process in the impulse approximation. The influence of the off-shell effect of the RDWF on possible analytic and dynamic cross-section factorizations is investigated. Contributions of direct and interference electrodisintegration amplitudes have been calculated taking into account the off-shell behavior of the electromagnetic nucleon vertex. Corresponding results are compared with data on three kinematics of the SaclayD(e, é p)n experiments. It is shown that off-shell effects both of the RDWF and electromagnetic nucleon vertex must be considered properly in order to get reliable information on the high-momentum component of the RDWF.     

Exclusive charge exchange reaction pD↦n(pp) within the Bethe-Salpeter formalism

The exclusive charge exchange reaction pD↦n(pp) at intermediate and high energies is studied within the Bethe-Salpeter formalism. The final-state interaction in the detected pp pair at nearly zero excitation energy is described by the ¹ S ₀ component of the Bethe-Salpeter amplitude. Results of numerical calculations of polarization observables and differential cross-section persuade that, as in the non-relativistic case, this reaction i) can be utilized as a “relativistic deuteron polarimeter” and ii) delivers further information about the elementary nucleon-nucleon charge exchange amplitude. Received: 26 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003     

Polarization phenomena in NN ↔ Dπ reactions

On the basis of a relativistic approach, NN ? Dπ reactions are analyzed in detail. The coherent sum of one-nucleon-exchange and pion-rescattering diagrams is calculated. It is shown that polarization observables are highly sensitive to off-mass-shell effects within the deuteron and that some of these observables can change sign upon taking these effects into account. The effect of the deuteron P wave is also investigated. The results obtained by calculating a full set of observables are compared with experimental data on the reaction pp → Dπ ⁺.     

Relativistic theory of inverse beta-decay of polarized neutron in strong magnetic field

The relativistic theory of the inverse beta-decay of polarized neutron,ν _e +n → > p +e ^-, in strong magnetic field is developed. For the proton wave function we use the exact solution of the Dirac equation in the magnetic filed that enables us to account exactly for effects of the proton momentum quantization in the magnetic field and also for the proton recoil motion. The effect of nucleons anomalous magnetic moments in strong magnetic fields is also discussed. We examine the cross-section for different energies and directions of propagation of the initial neutrino accounting for neutron polarization. It is shown that in the super-strong magnetic field the totally polarized neutron matter is transparent for neutrinos propagating antiparallel to the direction of polarization. The developed relativistic approach can be used for calculations of cross-sections of the other URCA processes in strong magnetic fields.     

Longitudinal polarization transfer in the D(d,n)3He reaction at 0°

We have measured the longitudinal neutron polarization in the $\text{D(}\text{d}\text{,}\text{n}\text{)}{}^3\text{He}$ reaction, at θ=0°, for an incident longitudinally polarized deuteron beam. A deuteron energy range of 3.3–14.9 MeV was covered. The polarization transfer from the deuteron to the neutron is found to be large, and the reaction is potentially useful as a source of polarized neutrons.     

Propagation regimes of intense circularly polarized laser beam in magnetoactive plasma

This paper presents an analytical and numerical investigation of an intense circularly polarized wave propagating along the static magnetic field parallel to oscillating magnetic field in magnetoactive plasma. In the relativistic regime such a magnetic field is created by pulse itself. The authors have studied different regimes of propagation with relativistic electron mass effect for magnetized plasma. An appropriate expression for dielectric tensor in relativistic magnetoactive plasma has been evaluated under paraxial theory. Two modes of propagation as extraordinary and ordinary exist; because of the relativistic effect, ultra-strong magnetic fields are generated which significantly influence the propagation of laser beam in plasma. The nature of propagation is characterized through the critical-divider curves in the normalized beam width with power plane For given values of normalized density (ω_p/ω) and magnetic field (ω_c/ω) the regions are namely steady divergence (SD), oscillatory divergence (OD) and self-focusing (SF). Numerical computations are performed for typical parameters of relativistic laser-plasma interaction: magnetic field B = 10-100 MG; intensity I = 10¹⁶ to 10²⁰ W/cm²; laser frequency ω = 1.1 × 10¹⁵ s⁻¹; cyclotron frequency ω_c = 1.7 × 10¹³ s⁻¹; electron density n_e = 2.18 × 10²⁰ cm⁻³. From the calculations, we confirm that a circularly polarized wave can propagate in different regimes for both the modes, and explicitly indicating enhancement in wave propagation, beam focusing/self-guiding and penetration of E-mode in presence of magnetic field.     

Top quark polarization in polarized e+e− annihilation near threshold

Top quark polarization in e⁺e^{t -} annihilation into tt? is calculated for linearly polarized beams. The Green function formalism is applied to this reaction near threshold. The Lippmann—Schwinger equations for the S-wave and P-wave Green functions are solved numerically for the QCD chromostatic potential given by the two-loop formula for large momentum transfer and Richardson’s ansatz for intermediate and small momenta. S- P— wave interference contributes to all components of the top quark polarization vector. Rescattering of the decay products is considered. The mean values 〈nl〉 of the charged lepton four-momentum projections on appropriately chosen directions n in semileptonic top decays are proposed as experimentally observable quantities sensitive to top quark polarization. The results for 〈nl〉 are obtained including S- P— wave interference and rescattering of the decay products. It is demonstrated that for the longitudinally polarized electron beam a highly polarized sample of top quarks can be produced.     

Effects of new neutral currents at linear electron-positron colliders

Effects that are induced by contact four-fermion interactions in the processes e ⁺ e ^? → μ ⁺ μ ^?, $\bar bb$ , and $\bar cc$ at $\sqrt s = 0.5$ TeV linear electron-positron colliders are investigated for the case of longitudinally polarized initial beams. This analysis employs new integrated observables constructed from the polarized cross sections for the scattering of final fermions into the forward (σ _F) and the backward (σ _B) hemisphere in such a way that they single out the helicity cross sections for the processes in question. This property of the observables makes it possible to perform, in the most general form, a model-independent analysis of contact four-fermion interactions and to set constraints on their parameters. It is also shown that the sensitivity of new polarization observables to contact interactions is noticeably higher than the corresponding sensitivity of canonical observables like σ, A _FB, A _LR, and A _LR,FB.     

Probing scalar particle and unparticle couplings in e^{+}e^{-}\to t\bar{t} with transversely polarized beams

In searching for indications of new-physics scalar particle and unparticle couplings in $e^{+}e^{-}\to t\bar{t}$ , we consider the role of transversely polarized initial beams at e ⁺ e ^? colliders. By using a general relativistic spin density matrix formalism for describing the particles spin states, we find analytical expressions for the differential cross section of the process with t or $\bar{t}$ polarization measured, including the anomalous coupling contributions. Thanks to the transversely polarized initial beams these contributions are first order anomalous coupling corrections to the Standard Model (SM) contributions. We present and analyze the main features of the SM and anomalous coupling contributions. We show how differences between SM and anomalous coupling contributions provide means to search for anomalous coupling manifestations at future e ⁺ e ^? linear colliders.     

On complete sets of polarization observables

A new criterion is developed which provides a check as to whether a chosen set of polarization observables is complete with respect to the determination of all independent T-matrix elements of a reaction of the type a + b → c + d + … As an illustrative example, this criterion is applied to the longitudinal observables of deuteron electrodisintegration.     

Polarization in hyperon photo- and electro-production<Superscript>⋆</Superscript>

Multiple polarization observables must be measured to access the amplitude structure of pseudoscalar meson photoproduction off the proton. The hyperon-producing reactions are especially attractive to study, since the weak decays allow straightforward measurement of the induced and recoil polarization observables. In this paper we emphasize γ + p → K ⁺ + Λ , discussing recent measurements of C_x, C_z, and P for this reaction. An empirical constraint on the helicity amplitudes is obtained. A simplified model involving spin-flip and spin-non-flip amplitudes is presented. Finally, a semi-classical model of how the polarization may arise is presented.     

Observation of nonstationary effects in saturation spectroscopy

We have studied the nonstationary effects in saturated absorption spectroscopy of the ⁸⁷Rb D₂ line. Varying the size of the σ⁺ polarized pump laser beam, we observed saturated absorption spectra for the σ^± polarized probe beam. For equal polarizations of the pump and probe beams, we found that the resonance signal for the F_g = 1 → F_e = 2 line, and the crossover lines between F_g = 1 → F_e = 2 and F_g = 1 → F_e = 1 (and 0) lines increased to a greater extent than the others. This observation can be understood from the calculated time evolution of the populations of the ground-state sublevels by means of a rate equation model. We also compared experimental data for other conditions with the calculated results. We found good agreement between the calculated results and the data.