Weak interactions in polarized semi-inclusive DIS

We calculate, within the pQCD parton model at leading orders, the expression of the polarization P of spin 1/2 hadrons (typically baryons), produced in polarized semi-inclusive DIS in all possible cases in which weak interactions are involved. We discuss how to gather new information on fragmentation and distribution functions and give numerical estimates in the cases for which data are or will soon be available. Received: 7 June 2001 / Published online: 10 August 2001     

Pionic effects in inelastic electron-nucleus scattering

We calculate the structure functions for deep inelastic electron scattering on baryons in a two-dimensional model which incorporates pionic degrees of freedom explicitly. We analyze the behavior of these structure functions in the Bjorken limit and conclude that scaling and Regge behavior are satisfied. A trivial extension as a parton model can be achieved by just introducing the structure functions for the pion. We next generalize our calculation to nuclear matter and study the behavior of such a system under electron scattering. Scaling but not Regge behavior appears in the Bjorken limit. The diverse behavior in these two situations is carefully analyzed. Most of the results obtained in this paper are qualitatively independent of the dimensions of the model and therefore will hold in its four-dimensional generalization.     

Quark exchange in quasi-elastic electron-nucleus scattering

In this paper the consequences of the Pauli principle applied at the quark level are investigated for nuclear structure functions in electron-nucleus scattering in the quasi-elastic scattering region. The effect of quark exchange contributions is studied for both inclusive and exclusive electron-nucleus scattering and is shown to give rise to nonnegligible corrections to the impulse approximation picture. Examples are given for light nuclei using gaussian wave functions.     

Forbidden transitions in anisotropic electron-nucleus interactions

Forbidden transitions in electron-nucleus systems are treated by perturbation theory for an arbitrary shape of the spin-spin interaction tensor.     

Analysis of parity-violating asymmetries in elastic electron-nucleus scattering

Parity violating asymmetries in elastic electron scattering on nuclei with arbitrary spin and isospin are considered in detail, extending our previous work on this matter [1]. Examples are given for the target nuclei¹²C,⁴⁰Ca,²⁰⁸Pb,³H,³He,⁴¹Ca,²⁰⁹Bi. Several ways of extracting information on the structure of weak neutral current couplings are presented. Besides, as a further possibility to check the validity of the standard gauge model [2] at intermediate energies, the chances to distinguish among different classes of gauge models are discussed.     

Structural considerations for elastic magnetic electron-nucleus scattering

To explain the form factors obtained by magnetic electron scattering on ¹⁷O it is clear that core polarization has to be taken into account. We discuss how this can be done by means of the Hartree-Fock theory. We note that projection from an intrinsic state of definite K gives an incorrect answer for weakly deformed systems such as ¹⁷O and we present an alternative procedure for extracting the moments. Using a purely velocity dependent Skyrme interaction (only t₀ and t₁ are non-zero) a Hartree-Fock calculation is carried out for the seventeen-nucleon system. The calculation leads to a suppression of the M3 form factor. It is emphasized that the suppression arises from the fact that not only is the ¹⁶O core deformed, but that spin-up particles have a different deformation than spin-down particles. This arises from the spin dependence of the interaction and from the Pauli principle. A peculiar feature with the interaction that is used is that the M5 form factor gets enhanced. This is attributed to the repulsive velocity dependent term in the interaction. The origin of the velocity dependence is discussed. The effect of the velocity dependence on the magnetic moment operator is also considered.     

A-dependence of high-energy inelastic electron-nucleus scattering

Cross sections for inclusive inelastic electron scattering from H, D, Be, Al, Cu and Au have been measured at 6° for incident energies up to 19.5 GeV. Within the stated errors, the cross sections were found to be directly proportional to the sum of the constituent nucleon cross sections.     

Inelastic electron-nucleus interactions at 5 GeV detected by ARGUS

Beam-gas events taken with the ARGUS detector at thee ⁺ e ^?-storage ring DORIS-II have been used to study interactions ofe ^± at 5 GeV with light nuclei mainly¹⁶O. The selection ofe ^{± 16}O events is discussed. The spectra of secondary protons and charged pions are found to be similar to those of hA interactions in accordance with the nuclear scaling. Measurements of like-particle (p p andπ π) correlations at small relative momenta were used to determine the radius of particle emission region ine ^{± 16}O interactions. This radius proved to be equal within errors to the radius of particle emission region in hC interactions. No any narrow diproton resonance has been observed in the mass region from 1.9 to 2.2 GeV.     

Magnetic electron-nucleus scattering using the Nilsson model: 13C

We try to explain the results of magnetic electron-nucleus scattering in the Op shell, specifically elastic scattering from the $\text{J =}\text{1}\text{2}{}^{\mathrm{?}}$ ground state of ¹³C, by using factorized wave functions with intrinsic states given by single Slater determinants, as given by the Nilsson model. We introduce a term proportional to σ_z in the Nilsson hamiltonian. This violates time reversal invariance in the intrinsic state, but not, of course, over all. With the presence of this term one obtains contributions to the expectation value of a magnetic operator not only from the odd nucléon but also from the core.     

Approximate scattering solutions of the dirac equation for electron-nucleus processes in light nuclei

Scattering solutions of the second-order Dirac equation for the case of the Coulomb potential and which are correct to first order in the coupling constantZe ²/hc are investigated and found to describe pure Coulomb scattering equally well as the Sommerfeld-Maue wave functions. Errors introduced by the use of these solutions are studied in a numerical calculation of cross sections for nuclear electric-quadrupole excitation by high-energy electrons. The use of these wave functions is suggested for simplified calculations of lowest-order Coulomb corrections to Born approximation results for various electron-nucleus processes.     

Asymmetry in polarized e-d inelastic scattering

The parity violating asymmetry is calculated for polarized electron-deuteron inelastic scattering in the closure approximation for the outgoing nucleons. The results are applicable in the intermediate-energy region of the incident electron where asymmetries are found to be in the range accessible to the present experiments.     

Neutrino scattering on polarized deuterons

The possible presence of anI=0 axial vector piece in the hadronic neutral current may be detected by looking for an asymmetry in the emission of the recoil deuterons in elastic scattering of neutrinos or antineutrinos on polarized deuterons. It is estimated that this asymmetry could be about 40% with the incident neutrinos in the energy range of tens of MeV.     

Search for a new gauge boson in electron-nucleus fixed-target scattering by the APEX experiment

We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.     

Quasi-free scattering of polarized protons

Cross section and analyzing power, energy-sharing spectra have been measured for the ¹⁶O($\text{p}$, 2p) reaction at an incident energy of 200 MeV for twenty-four different pairs of angles of the detected final-state protons. This general survey is intended to test the validity of the distorted wave impulse approximation (DWIA), particularly with respect to the predicted j-dependent analyzing power caused by the distorting optical potentials and nuclear spin-orbit coupling. Although the data in general confirm this j-dependence, agreement in detail between DWIA calculations and the analyzing power data becomes worse as the momentum of the recoiling nucleus increases. Predictably, the cross-section calculations show more sensitivity to the optical-model parameters than do the analyzing powers. Within the present limits imposed by scanty elastic scattering data, there seems to remain a choice between predicted ($\text{p}$, 2p) cross sections which either are unreasonably large or which have the incorrect energy-sharing shapes. More comprehensive elastic scattering and total reaction cross section data are clearly needed.     

Jet production in polarized proton proton scattering

We propose a model of polarized partonic densities based on Regge behaviour, quark counting rules,U(1) _A Goldberger-Treiman relation and positivity constraints. The resulting polarized proton structure function is found to be in agreement with EMC and SLAC data. From this input we compute double helicity asymmetries for 1 and 2 jet inclusive production in polarized proton proton scattering at high energies. We obtain asymmetries of 10–20% at energies \(\sqrt s = 50 - 500\) GeV.     

Tagged-photon events in polarized deep inelastic scattering

Deep inelastic scattering events of a longitudinally polarized electron by a polarized proton with a tagged collinear photon radiated from the initial-state electron are considered. The corresponding cross section is derived in the Born approximation. The model-independent radiative corrections to the Born cross section are also calculated. The obtained result is applied to the elastic scattering.