Nuclear effects in the structure functions

By using a relativistic framework and accurate nuclear spectral function the structure functions F_2A andF _3A of deep inelastic charged lepton and neutrino scattering are calculated in nuclei and results are presented.     

Nuclear effects on the structure functions

We calculate the branching ratio for the semihadronic decay τ→ηππν, a test fo the Wess-Zumino term for chiral anomalies.     

Nuclear dependence of structure functions in coordinate space

The momentum distributions of partons in bound nucleons are known to depend significantly on the size of the nucleus. The Fourier transform of the momentum (x _Bj) distribution measures the overlap between Fock components of the nucleon wave function which differ by a displacement of one parton along the light cone. The magnitude of the overlap thus determines the average range of mobility of the parton in the nucleon. By comparing the Fourier transforms of structure functions for several nuclei we study the dependence of quark mobility on nuclear size. We find a surprisingly small nuclear dependence (< 2% for He, C and Ca) for displacements t = z ? 2.5 fm, after which a nuclear suppression due to shadowing sets in. The nuclear effects observed in momentum space for x _Bj ? 0.4 can be understood as a reflection of only the large distance shadowing in coordinate space.     

Nuclear effects on the extraction of neutron structure functions

Nuclear effects due to the presence of spin-1 isosinglet 6-quark clusters in the deuteron on the extraction of both spin-independent and spin-dependent neutron structure functions are investigated. The x-dependences of the 6-quark cluster structure functions are estimated by using a perturbative QCD (pQCD) dimensional counting rules. Within this framework, the ratio of the deuteron structure function to the free nucleon structure function can be well described. We find that the nuclear effect on the extracted spin-dependent neutron structure function is very different from that on the spin-independent neutron structure function. The effect enhances the Bjorken sum by about 10%, whereas it decreases the Gottfried sum by about 7%. The formalism for calculating nuclear effects is further used to evaluate the spin-dependent structure function of the He nucleus and a good self-consistent check is obtained. Received: 1 December 2000 / Revised version: 15 February 2001 / Published online: 25 April 2001     

Quark antisymmetrization and deep-inelastic scattering II. Nuclear structure functions

We consider the effects of quark antisymmetrization for nuclear structure functions. Antisymmetrizing the naive folding of nuclear wave functions in terms of nucleons and the nucleon wave function in terms of quarks, introduces additional contributions. Using the calculated results on quark three-momentum distributions, we calculate the effects on the deep-inelastic structure functions for s- and p-wave nuclei. The effects of quark antisymmetrization turn out to be small.     

The structure ofT=1 levels inA=14 nuclei

States in¹⁴C, populated via the¹¹B(α, p) reaction at 14 MeV bombarding energy, were investigated with the Doppler Shift Attenuation Method (DSAM). The analysis ofpγ coincidence spectra taken in a Ge(Li) detector at 0? and 120? with the particle detector near 0? with respect to the beam direction yielded the following lifetimes and lifetime limits for the states at 6.09, 6.59, 7.01 and 7.34 MeV, respectively, <20 fs, <1,200 fs, <7 fs and 160±60 fs. Shell model calculations using the MSDI and an empirical interaction fitted to nuclear states in 1p and 2s 1d shell nuclei, are shown to account very well for the experimental levels andγ-transition rates of 5 different multipolarities. The structure of the (J ^*,T)=(2⁺, 1) levels is discussed in the light of the experimentally observed T_z-dependence of the 2⁺, 1→0⁺, 1E2 matrix elements.     

Nuclear structure in the vicinity of the N = Z line in the A = 90-100 region

Neutron-deficient nuclei in the mass region A≈ 90-100 exhibit a large variety of phenomena. In this region the heaviest N = Z nuclei are identified and enhanced neutron-proton correlations are expected when protons and neutrons occupy identical orbitals. A variety of nuclear shapes are predicted and observed for A? 91, including superdeformed shapes. The nucleus ¹⁰⁰Sn is the heaviest N = Z doubly magic nucleus believed to be bound. Knowledge of the shell structure around ¹⁰⁰Sn is of utmost importance for understanding the nuclear shell model. New results on both the N = Z nucleus ⁸⁸Ru, superdeformed structures in A≈ 90 nuclei as well as the first result on the level structure in ¹⁰³Sn, and an extended level structure in ¹⁰²In are presented. The limitations of using stable beams and targets and the possibilities with new radioactive beams are briefly outlined. Received: 1 May 2001 / Accepted: 4 December 2001     

Nuclear structure studies of the neutron deficientN=50 nucleus96Pd

The neutron deficient nucleus⁹⁶Pd, four proton holes below the doubly magic¹⁰⁰Sn, has been studied in the reaction⁶⁴Zn (³⁶Ar, 2p 2n). Innγ andγγ coincidences levels up to 7 MeV excitation energy were established, and a new neutron core-excited isomer with T_1/2=35(4)ns and g=0.83 (5) was identified. A detailed shell model study yields excellent agreement for states within the π(p_1/2,g_9/2) configuration space but fails to reproduce the isomerism andg-factor for the core-excited state.     

Nuclear structure of the heavyN=82 isotones:144Sm and146Gd

For single-closed shell nuclei with a large number of extra-protons, outside theZ=50,N=82 double-closed shell nucleus, a standard shell-model calculation yields dimensions of the Hamiltonian matrices beyond the scope of present computer technology. A quasi-particle (QP) calculation however, is able to describe the most important proton-excitations in a much restricted configuration space. Extended BCS+TDA calculations are performed on the single-closed shell¹⁴⁴Sm and¹⁴⁶Gd nuclei with a Gaussian force as effective two-body interaction. The influence of the nonconservation of the exact number of extra-protons in the BCS-approach is studied by performing a projection onto the states with an exact number of extra-protons (BCS+P). The first excited 2⁺, 4⁺ and 6⁺ states in¹⁴⁶Gd are described mainly by the (1g7/2) ₀ ⁸ (2d5/2) ₀ ⁴ \((1h11/2)_{J^\pi }^2 \) configuration.     

Nuclear structure effects in the mass region aroundA=100, derived from experimentalQ β -values

The endpoint energies ofβ-transitions in 15 neuron-rich nuclei with mass numbers 101≦A≦106 have been measured with a plastic scintillator telescope in coincidence with a large Ge(Li)-detector at the on-line mass separator LOHENGRIN. From theQ _β -values obtained in these experiments, nuclear structure effects in this region of the nuclear chart are deduced. Finally, nuclear masses derived from theseQ _β -values are compared with the predictions of different theoretical mass calculations.     

Nuclear structure functions and heavy flavour leptoproduction off the nucleus at small x in perturbative QCD

Nuclear structure functions and cross-sections for heavy flavour production in lepton–nucleus collisions are investigated in the low x region accessible now or in the near future. The scattering on a heavy nucleus is described by the sum of fan diagrams of BFKL pomerons, which is exact in the high-colour limit. The initial condition for the evolution at x=0.01 is taken from a saturation model, which reproduces the experimental data on the proton. The dependence of the structure functions is well described by a power factor , with reaching values as low as 1/2 at extremely low x. The total cross-sections for heavy flavour production reach values of the order of mb, and the corresponding transverse momentum distributions are sizable up to transverse momenta larger than the initial large scale . Received: 10 July 2001 / Revised version: 23 September 2001 / Published online: 5 November 2001     

Nuclear core in hypernuclear structure

Hypernuclear structure models are briefly reviewed. Phenomena related to hypernuclear polarization are displayed. A discussion is given of nuclear and hypernuclear neutron orbitals extraction. Preliminary results on ^– angular distributions for the reaction⁶Li(K ^–, ^–) ⁶ Li are presented.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.The collaboration of Dr. M. Sotona and Dr. L. Majling in the speedy preparation of the AD results and discussions with them and with Prof. B. Povh are greatly acknowledged.     

Nuclear structure in ideal space

The boson method, previously developed for quasiparticles, is used to transcribe the shell model Hamiltonian directly from the particle space to the boson space preserving both the particle number and the Pauli principle. The method is tested with a calculation of the spectrum of ⁵⁹Ni.     

Masses in structure functions

We derive an approximate formula for the quark mass in ξ-formalism. Using the QCD-based form of structure function, we analyse the SLAC-MIT data to estimate the experimentally allowed ranges of quark mass. The possible variation of our results with QCD cut-off parameter, gluon distribution, hard intrinsic charm component of the proton wavefunction and the higher twist effects are also discussed.     

Nuclear equilibrium shapes nearA=100

Nuclear equilibrium shapes in the regionA=100 are studied in the context of the cranked shell model. Many nuclides with large equilibrium ground state deformations are found. Equilibrium deformations atI=20 are typically found to be substantially reduced.     

1/N calculation of structure functions

We calculate the quark and pion structure functions in CP^n?1 models with quarks using 1/N expansions. We find that the quark structure function, in the lowest order in 1/N, is just the free parton result with a modified coupling constant. The pion structure function resembles the phenomelogically successful fit but contains correction terms which modulate the function.     

Nuclear properties of Z=114 isotopes and shell structure of ~(298)114

The two-neutron separation energies(S_(2n)) and α-decay energies(Q_α) of the Z=114 isotopes are calculated by the deformed Skyrme-Hartree-Fock-Bogoliubov(SHFB) approach with the SLy5,T22,T32 and T43 interactions.It is found that the tensor force effect on the bulk properties is weak and the shell closure at N=184 is seen evidently with these interactions by analyzing the S_(2n) and Q_α evolutions with neutron number N.Meanwhile,the single-particle energy spectra of ~(298)114 are studied using the spherical SHFB approach with these interactions to furthermore examine the shell structure of the magic nucleus ~(298)114.It is shown that the shell structure is almost not changed by the inclusion of the tensor force in the Skyrme interactions.Finally,by examining the energy splitting of the three pairs of pseudospin partners for the protons and neutrons of ~(298)114,it is concluded that the pseudospin symmetry of the neutron states is preserved better than that of the proton states and not all of the pseudospin symmetries of the proton and neutron states are influenced by the tensor force.