Complete experiment in eN-elastic scattering, in presence of two-photon exchange

Using a general parametrization of the spin structure of the matrix element for elastic eN-scattering, in terms of three independent complex amplitudes, we found the expressions for all polarization observables, in electron–proton elastic scattering. This allows to suggest possible methods to measure the nucleon electromagnetic form factors, in presence of two-photon exchange. We show that the measurements of the differential cross section for electron and positron nucleon elastic scattering, in the same kinematical conditions, allows to extract the nucleon electromagnetic form factors. The same is correct for the polarization method, with the measurement of the P_x,z components of the final nucleon polarization (for the scattering of longitudinally polarized electrons and positrons). An alternative way, in absence of positron beam, is to measure a definite set of T-odd polarization observables, which includes three different experiments or only T-even observables, with five independent experiments. In both cases, the ratio G_E(Q²)/G_M(Q²) is related to quantities of the order of and requires different polarization experiments with very high accuracy.     

动量空间中能质子-12C弹性散射截面和自旋量的研究

在KMT理论框架下，应用微观的动量空间一级光学势，包括了库仑修正，自旋关联，NN振幅反对称，离壳效应，核子反冲和结合能转换，Lorentz不变的角变换.在整个中能区域系统地计算了质子-¹²C弹性散射微分截面和自旋观测量，并与实验数据及Glauber理论框架下或已有的其他理论计算结果做了比较，其结果显示，在200—1000MeV，该理论与实验结论符合程度较好.     

Vacuum polarization effects in elastic scattering of protons by nuclei

Sensitivity of spin observables in elastic proton scattering by nuclei to the vacuum polarization correction δϱ_VAC is explored. The Dirac optical potential is calculated from a complete set of Lorentz invariant amplitudes, Dirac-Hartree densities and the existing estimate of δϱ_VAC based on quantum hadrodynamics.     

Radiative corrections to deep inelastic electron-deuteron scattering: The case of tensor-polarized deuteron

Model-independent radiative corrections to deep inelastic scattering of an unpolarized electron beam off the tensor-polarized deuteron target are considered. The contribution to the radiative corrections due to the hard photon emission from the elastic electron-deuteron scattering (the so-called elastic radiative tail) is also investigated. The calculation is based on the covariant parametrization of the deuteron quadrupole polarization tensor. Radiative corrections to the polarization observables are estimated numerically for the kinematical conditions of the current experiment at HERA.     

Radiative corrections to polarization observables in elastic electron-deuteron scattering in hadronic variables

Model-independent QED radiative corrections to polarization observables in the elastic scattering of unpolarized and longitudinally polarized electron beam by a deuteron target are calculated. Two experimental setups are considered: the deuteron target is arbitrarily polarized, or the vector and/or tensor polarization of the recoil deuteron is measured. The calculations are based on taking all essential Feynman diagrams into account and using the covariant parametrization of the deuteron polarization state. The radiative corrections are calculated for the hadronic variables using invariant integration of the leptonic tensor. Numerical estimates of the radiative corrections to the polarization observables are made for various values of the kinematical vari-ables.     

Models for high-energy inclusive processes and screening in deuterium

The screening correction to the high energy (p_lab > 10 GeV/c) elastic hadron-deuteron scattering amplitude is discussed. It is found that the correction cannot completely be calculated using as input only the data for cross sections of inclusive reactions on free nucleons. Nevertheless measurements of high energy screening corrections provide sensitive tests for models of inclusive processes. In particular elastic screening does not dominate over the inelastic screening if, as indicated by recent fits, the triple pomeron coupling does not vanish for three mass-zero pomerons. If this is the case, the theory of high energy elastic scattering on heavier nuclei would have to be reconsidered. The discussion is illustrated by a numerical calculation for elastic πd scattering in the 10GeV–2000 GeV energy range.     

Spin dependence of the parity non-conserving neutron-nucleus interaction

We show that the spin dependence of the parity violating amplitudes can provide a clue to the precise origin of the large parity non-conserving effects observed in neutron scattering on nuclei. The polarization asymmetries for longitudinal and transverse polarization of the incoming neutrons allow the separation of these spin amplitudes. In the mechanism of parity admixing of the virtually excited compound nucleus states, the spin dependence of the weak amplitudes is determined by the spin dependence of the strong interaction amplitudes for the elastic channel of the decay of the p-wave resonance     

Nucleon–nucleon scattering observables in large-Nc QCD

Nucleon–nucleon scattering observables are considered in the context of the large N_c limit of QCD for initial states with moderately high momenta (pN_c). The scattering is studied in the framework of the time-dependent mean-field approximation. We focus on the dependence of those observables on the spin and isospin of the initial state which may be computed using time-dependent mean-field theory. We show that, up to corrections, all such observables must be invariant under simultaneous spin and isospin flips (i.e., rotations through π/2 in both spin and isospin) acting on either particle. All observables of this class obtained from spin unpolarized measurements must be isospin independent up to 1/N_c corrections. Moreover, it can be shown that the leading correction is of relative order 1/N_c² rather than 1/N_c.     

Noneikonal effects in spin-dependent proton-nucleus interactions

Simple expressions are derived for the non-eikonal corrections to the Glauber diffraction approximation for the proton-nucleus scattering amplitudes, with the spin dependence of the proton-nucleon amplitudes taken into account. As an example, we study the numerical importance of these corrections for elastic p ⁵⁸Ni scattering at 800 MeV.     

Coulomb-hadronic interference with polarized protons at intermediate energies

The theory of Coulomb-hadronic interference for particles with spin is discussed. At intermediate energies it is favourable to introduce Bethe phases for each of the amplitudes. For proton-proton scattering the values of the Bethe phases as well as the magnitudes of other correction terms are estimated on the basis of amplitudes reconstructed from current phase shifts. Suitable parameterizations for observables are proposed.     

Pion-Exchange Effects in Elastic Backward Proton-Deuteron Scattering

 The elastic backward proton-deuteron scattering is analyzed within a covariant approach based on the deuteron vertex function obtained by the Bethe-Salpeter equation with realistic meson-exchange interaction. Contributions of the one-nucleon and one-pion exchange mechanisms to the cross section and polarization observables are investigated in explicit form. Results of numerical calculations for the cross section, tensor analyzing power and spin transfers are presented. The one-pion exchange contribution is essential for describing the spin-averaged cross section, while in polarization observables it is found to have a small effect. Received December 22, 1998; revised November 8, 1999; accepted November 10, 1999     

Two-photon physics

A brief discussion is given on the status of two-photon exchange contributions to elastic electron-nucleon scattering. The apparent discrepancy in the extraction of elastic nucleon form factors between unpolarized Rosenbluth and polarization transfer experiments is discussed, as well as the understanding of this puzzle in terms of two-photon exchange corrections. It is also discussed how the imaginary part of the two-photon exchange amplitude can be accessed from the beam normal spin asymmetry in elastic electron-nucleon scattering. Correspondence: M. Vanderhaeghen, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA     

Radiative corrections to polarization observables in elastic electron-deuteron scattering in leptonic variables

The model-independent QED radiative corrections to polarization observables in elastic scattering of unpolarized and longitudinally polarized electron beams by a deuteron target are calculated in leptonic variables. The experimental setup when the deuteron target is arbitrarily polarized is considered and the procedure for applying the derived results to the vector or tensor polarization of the recoil deuteron is discussed. The calculation is based on taking all essential Feynman diagrams into account, which results in the form of the Drell-Yan representation for the cross section, and the use of the covariant parameterization of the deuteron polarization state. Numerical estimates of the radiative corrections are given in the case where event selection allows undetected particles (photons and electron-positron pairs) and the restriction on the lost invariant mass is used.     

Investigating neutron polarizabilities through Compton scattering on 3He

We examine manifestations of neutron electromagnetic polarizabilities in coherent Compton scattering from the helium-3 nucleus. We calculate gamma3He elastic scattering observables using chiral perturbation theory to next-to-leading order [O(e2Q)]. We find that the unpolarized differential cross section can be used to measure neutron electric and magnetic polarizabilities, while two double-polarization observables are sensitive to different linear combinations of the four neutron spin polarizabilities.     

Study of spin effects in neutron-proton interactions at intermediate energies at PSI

An intensive program of n-p measurement of spin observables in elastic and pion production reactions has been performed at the Paul Scherrer Institute taking advantage of the high intensity polarized neutron beam. In the elastic reaction 16 different spin observables have been measured for kinetic energies from 210 to 590 MeV with the centre of mass angular range from 60 to 180 degrees. This will allow to perform direct reconstruction in the model independent way of the isospin I=0 scattering amplitudes in elastic NN interaction. Three body final state process \(\vec np - pp\pi ^ - \) with polarized neutrons in exclusive experiment has been investigated.     

Spin observables in the NN→NΔ transition

The 16 independent amplitudes making up the NN → NΔ scattering matrix are written in forms suitable for calculating observables, particularly, spin observables. Some of these observables are calculated, using amplitudes of the unitary Aaron-Amado-Young three-body model with iterated pion-exchange forces and displayed as functions of the production angle, the incident energy and the invariant mass of Δ. Comparisons with simpler models are also given.     

Spin observables in the NN → NΔ transition

The 16 independent amplitudes making up the NN → NΔ scattering matrix are written in forms suitable for calculating observables, particularly, spin observables. Some of these observables are calculated, using amplitudes of the unitary Aaron-Amado-Young three-body model with iterated pion-exchange forces and displayed as functions of the production angle, the incident energy and the invariant mass of Δ Comparisons with simpler models are also given.     

Complete Experiment for - and - Backward Elastic Scattering

. The problem of a complete experiment in backward elastic scattering of particles with spins of 1 and is considered. For the first time all possible effects induced by polarization of one or two initial and one final particles are touched upon. The minimal set of measurements allowing to reconstruct all of four amplitudes describing this process is proposed. Some observables are expected to be sensitive to hitherto largely unexplored deuteron properties, such as a possible P-wave component. The technique developed is a good tool to calculate easily impulse-approximation predictions for any observables. Accelerator facilities suitable for fulfilling the complete experiment are listed. Received May 30, 1997; accepted in final form October 8, 1997