Neutral current effects in the parity violating nuclear force

The measurements of the ΔI = 1 part of the parity violating nuclear force when combined with information on neutral current couplings from neutrino scattering and pion production experiments allow an estimate of the isoscalar admixture in the neutral current if it has a vector axial-vector structure has been shown.     

Neutral current effects in muonic atoms: E1-E2 interferences

We study the parity-violating neutral current effects in muonic atoms which might result from an interference between E1 and E2 amplitudes in 3D → 1S transitions. We conclude that polarization asymmetries may be measurable in heavy atoms (Z ~ 70) exhibiting large nuclear deformations.     

Meson exchange current effects in the electroexcitation of magnetic states in closed shell nuclei

A microscopic approach to evaluate the contributions of one-pion exchange currents to the inelastic (e,e') scattering form factor of closed shell nuclei is developed. Both seagull and pionic parts of the two-body term are treated on the same footing and their final expressions are simple, clear and physically transparent. Application to the magnetic stretched states 4^?(18.98 MeV) of ¹⁶O and 14^?(6.74 MeV) of ²⁰⁸Pb is done. Agreement with the available experimental data is discussed. It is found that the effect of the meson exchange currents is a smooth but non-negligible enhancement ?15% at the first scattering maximum) at small momentum transfers and an increase by a factor bigger than 1.5 in the region of the second maximum.     

Many-body effects in nuclei

A correction to nuclear structure calculations due to the finite lifetime of the excited states of a nucleus entails many-body effects of different nature. The analytical structure, as well as the results of numerical calculations, are given and discussed.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Neutral current parity violation and gauge flavours

In a large class of gauge theories the trace of the weak neutral axial charge operator over any complete irreducible gauge multiplet is shown to vanish. This implies a relation involving deep inelastic neutrino-induced neutral current parity-violating cross sections which can be used to test the correctness of the Weinberg-Salam gauge multiplet structure of quarks.     

Neutral current cross-sections for neutrinos on protons

Defining the ratiosr _p =σ(vp →vx)/σ(vp →μ ⁻ x) and we obtain the bounds 0.28 ⩽r _p ⩽ 0.61 and using only the parton model and the data of CDHS group with iron target. We also give the complete set of parton-model relations which would allow the determination of all the neutral-current coupling constants from inclusive cross sections alone.     

Six-quark cluster effects in nuclei

Based upon the experiments on the electric form factor for the deuteron, we use the valon model to determine the valon distribution functions in a six-quark cluster and calculate the ratio of the structure functions of the nucleon bound in a light or intermediate heavy nucleus to the ones bound in the deuteron.     

Alpha-clustering effects in heavy nuclei

The study of cluster structures in light nuclei is extending to the heavy nuclei in these years. As for the stable N = Z nuclei, from the lighter ⁸Be, ¹²C nuclei to the heavier ²⁰Ne and even the ⁴⁰Ca and ⁴⁴Ti medium nuclei, the α cluster structures have been well studied and confirmed. In heavy nuclei, due to the dominated mean field, the existence of α cluster structure is not clear as light nuclei but some clues were found for indicating the core+α cluster structure in some nuclei, in particular, the ²⁰⁸Pb+α structure in ²¹²Po. We review some recent progress about the theoretical and experimental explorations of the α-clustering effects in heavy nuclei. We also discuss the possible α cluster structure of heavy nuclei from the view of α decay.     

Neutral strange particle production in antineutrino-neon charged current interactions

Neutral strange particle production in \(\bar v\) Ne charged current interactions is studied using the bubble chamber BEBC, exposed to the CERN SPS antineutrino wide band beam. From a sample of 1191 neutral strange particles, the inclusive production rates are determined to be (15.7±0.8)% forK ⁰ mesons, (8.2±0.5)% for Λ, (0.4±0.2)% for \(\bar \Lambda \) and (0.6±0.3)% for Σ⁰ hyperons. The inclusive production properties ofK ⁰ mesons and Λ hyperons are investigated. The Λ hyperons are found to be polarized in the production plane.     

Nuclear anapole moment and axial neutral current in nuclei

Nuclear anapole moments and axial neutral currents are calculated for a set of nuclei. The accuracy of the leading approximation is studied in detail. The core polarization renormalizing both the anapole moment and the axial current is treated in the random-phase approximation with effective forces. Parameters of parity-violating nuclear forces are discussed. The experimental value of the anapole moment of the ¹³³Cs nucleus as extracted from data with allowance for axial-current renormalization is found to be κ=0.39±0.06.     

Neutral current and the nuclear scattering of reactor antineutrinos

Expressions are derived for evaluating the integrated inelastic cross section, $\text{}\text{?}\text{gs}{}_{\mathrm{v}}$, for the nuclear scattering of reactor antineutrinos in terms of experimentally determined B(Ml) values and Gamow-Teller matrix elements. These expressions are used to compute $\text{}\text{?}\text{gs}{}_{\mathrm{v}}$ for many nuclear transitions.     

Relativistic expressions for current electric moments of nuclei

Relativistic expressions for the operators of current electric moments caused by electromagnetic spin-orbit interaction are obtained. Formulas for the matrix elements of the current electric moments of nuclei are derived. The contributions of the current electric moments to the quadrupole moment of the deuteron and to its root-mean-square radius are calculated with allowance for relativistic effects.     

Neutral strange particle exclusive production in charged current high-energy antineutrino interactions

The cross section of the quasi-elastic reactions \(\bar v_\mu p \to \mu ^ + \Lambda (\Sigma ^0 )\) in the energy range 5–100 GeV is determined from Fermilab 15′ bubble chamber antineutrino data. TheQ ² analysis of quasi-elastic Λ events yieldsM _A=1.0±0.3 GeV/c² for the axial mass value. With zero µΛ K ⁰ events observed, the 90% confidence level upper limit \(\sigma (\bar v_\mu p \to \mu ^ + \Lambda {\rm K}^0 )< 2.0 \cdot 10^{ - 40} cm^2 \) is obtained. At the same time, we found that the cross section of reaction \(\bar v_\mu p \to \mu ^ + \Lambda {\rm K}^0 + m\pi ^0 \) is equal to \(\left( {3.9\begin{array}{*{20}c} { + 1.6} \\ { - 1.3} \\ \end{array} } \right) \cdot 10^{ - 40} cm^2 \) .     

Neutral current in the heavy top quark limit and the renormalization of the singlet axial current

We use a simple renormalization group argument to demonstrate that the large top mass limit of the axial neutral current in QCD is unambiguously determined by the renormalization of the singlet axial current which suggests a natural scheme independent normalization condition for the latter. By calculating the anomalous dimension of the singlet axial current at three-loop level in the scheme we derive the result for the top quark decoupling from the axial neutral current valid up to (and including) the terms of order _s ² .Work supported by DFG Grant Nr. Ku 502/3-1     

EMC and polarized EMC effects in nuclei

We determine nuclear structure functions and quark distributions for ⁷Li, ¹¹B, ¹⁵N and ²⁷Al. For the nucleon bound state we solve the covariant quark–diquark equations in a confining Nambu–Jona-Lasinio model, which yields excellent results for the free nucleon structure functions. The nucleus is described using a relativistic shell model, including mean scalar and vector fields that couple to the quarks in the nucleon. The nuclear structure functions are then obtained as a convolution of the structure function of the bound nucleon with the light-cone nucleon distributions. We find that we are readily able to reproduce the EMC effect in finite nuclei and confirm earlier nuclear matter studies that found a large polarized EMC effect.     

Exchange current corrections for partial capture rates of muons in nuclei

A calculation is made of exchange current corrections for partial capture rates of muons in¹²C,¹⁶O,³²S and⁴⁰Ca nuclei. One-pion exchange is taken into account. Adler-Dothan's results are used to obtain the weak pion production amplitude. The nuclear states are described in the Tamm-Dancoff approximation. It is found that the corrections are very erratic and state dependent. A large effect is found for the 0⁺→0^? transitions due to the size of the time part of the axial exchange current.