Electromagnetic Productions of KLambda and KSigma on the Nucleons

We briefly review the progress and problems in the electromagnetic production of KLambda on the nucleon. The problem of the data discrepancy in this channel as well as the corresponding physics consequence are highlighted. We also discuss the effect of the new beam-recoil polarization data Cx and Cz on our analysis. For this purpose we use the isobar model Kaon-Maid and a recent multipoles model that can describe recent experimental data. We also present a new multipoles model for the KSigma channels to complete our analysis.Comment: 8 pages, 6 figures, invited talk at 6th International Conference on Perspectives in Hadronic Physics, Trieste, Italy, 12-16 May 200

Relativistic Quark-Model Results for Baryon Ground and Resonant States

Latest results from a study of baryon ground and resonant states within relativistic constituent quark models are reported. After recalling some typical spectral properties, the description of ground states, especially with regard to the nucleon and hyperon electromagnetic structures, is addressed. In the following, recent covariant predictions for pion, eta, and kaon partial decay widths of light and strange baryon resonances below 2 GeV are summarized. These results exhibit a characteristic pattern that is distinct from nonrelativistic or relativized decay studies performed so far. Together with a detailed analysis of the spin, flavor, and spatial structures of the wave functions, it supports a new and extended classification scheme of baryon ground and resonant states into SU(3) flavor multiplets

On the effects of the final state interaction in the electro-disintegration of the deuteron at intermediate and high energies

The role of the final state interactions (FSI) in the inclusive quasi-elastic disintegration of the deuteron is investigated treating the two-nucleon final state within the exact continuum solutions of the non-relativistic Schroedinger equation, as well as within the Glauber multiple scattering approach. It is shown that for values of the Bjorken scaling variable $x_{Bj}\simeq 1$ both approaches provide similar results, unless the case $x_{Bj}\gtrsim 1$, where they appreciably disagree. It is demonstrated that present experimental data, which are mostly limited to a region of four-momentum transfer ($Q^2 \lesssim 4 (GeV/c)^2$) where the Center-of-Mass energy of the final state is below the pion threshold production, can be satisfactorily reproduced by the approach based on the exact solution of the Schroedinger equation and not by the Glauber approach. It is also pointed out that the latter, unlike the former, does not satisfy the inelastic Coulomb sum rule, the violation being of the order of about 20%.Comment: 16 LaTeX pages, 10 eps-figures, 1 tabl

Ground-state correlations and final state interactions in the process 3He(e,e'pp)n

The two-proton emission process $^3He(e,e'pp)n$ is theoretically investigated using realistic three-nucleon wave functions and taking the final state interaction into account by an approach which can be used when the value of the three-nucleon invariant mass is either below or above the pion emission threshold. Various kinematical conditions which enhance or minimize the effects of the final state interaction are thoroughly analyzed.Comment: 26 pages, 12 eps-figures. Introduction and abstract updated, few references added and Apendix A remove

Realistic Model of the Nucleon Spectral Function in Few- and Many- Nucleon Systems

By analysing the high momentum features of the nucleon momentum distribution in light and complex nuclei, it is argued that the basic two-nucleon configurations generating the structure of the nucleon Spectral Function at high values of the nucleon momentum and removal energy, can be properly described by a factorised ansatz for the nuclear wave function, which leads to a nucleon Spectral Function in the form of a convolution integral involving the momentum distributions describing the relative and center-of-mass motion of a correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions of $^3He$ and infinite nuclear matter resulting from the convolution formula and from many-body calculations are compared, and a very good agreement in a wide range of values of nucleon momentum and removal energy is found. Applications of the model to the analysis of inclusive and exclusive processes are presented, illustrating those features of the cross section which are sensitive to that part of the Spectral Function which is governed by short-range and tensor nucleon-nucleon correlations.Comment: 40 pages Latex , 16 ps figures available from the above e-mail address or from [email protected]

Measles resurges in Italy: preliminary data from September 2007 to May 2008.

Following an incidence rate of 1/100,000 inhabitants in 2006 [1], Italy has been facing an upsurge of measles cases since September 2007, with outbreaks being reported in various regions. In Italy, measles vaccination is currently offered free of charge as combined measles-mumps-rubella (MMR) vaccine. The current national vaccination schedule recommends two doses of MMR vaccine, given respectively at 11-12 months and 5-6 years of age. Although childhood vaccination coverage has increased in recent years, reaching the national average of 88% in 2006 (source: Ministry of Health), with some regional variability (Figure 1), it is still below the target of 95% set by the National Measles Elimination Plan (MEP) launched in 2003 [2], and outbreaks continue to occur

Morphological evidence for enhanced kisspeptin and neurokinin B signaling in the infundibular nucleus of the aging man.

Peptidergic neurons synthesizing kisspeptin (KP) and neurokinin B (NKB) in the hypothalamic infundibular nucleus have been implicated in negative sex steroid feedback to GnRH neurons. In laboratory rodents, testosterone decreases KP and NKB expression in this region. In the present study, we addressed the hypothesis that the weakening of this inhibitory testosterone feedback in elderly men coincides with enhanced KP and NKB signaling in the infundibular nucleus. This central hypothesis was tested in a series of immunohistochemical studies on hypothalamic sections of male human individuals that were divided into arbitrary "young" (21-49 yr, n = 11) and "aged" (50-67 yr, n = 9) groups. Quantitative immunohistochemical experiments established that the regional densities of NKB-immunoreactive (IR) perikarya and fibers, and the incidence of afferent contacts they formed onto GnRH neurons, exceeded several times those of the KP-IR elements. Robust aging-dependent enhancements were identified in the regional densities of KP-IR perikarya and fibers and the incidence of afferent contacts they established onto GnRH neurons. The abundance of NKB-IR perikarya, fibers, and axonal appositions to GnRH neurons also increased with age, albeit to lower extents. In dual-immunofluorescent studies, the incidence of KP-IR NKB perikarya increased from 36% in young to 68% in aged men. Collectively, these immunohistochemical data suggest an aging-related robust enhancement in central KP signaling and a moderate enhancement in central NKB signaling. These changes are compatible with a reduced testosterone negative feedback to KP and NKB neurons. The heavier KP and NKB inputs to GnRH neurons in aged, compared with young, men may play a role in the enhanced central stimulation of the reproductive axis. It requires clarification to what extent the enhanced KP and NKB signaling upstream from GnRH neurons is an adaptive response to hypogonadism or, alternatively, a consequence of a decline in the androgen sensitivity of KP and NKB neurons

Relativistic Structure of the Deuteron: 1.Electro-disintegration and y-scaling

Realistic solutions of the spinor-spinor Bethe-Salpeter equation for the deuteron with realistic interaction kernel including the exchange of pi, sigma, omega, rho, eta and delta mesons, are used to systematically investigate relativistic effects in inclusive quasi-elastic electron-deuteron scattering within the relativistic impulse approximation. Relativistic y-scaling is considered by generalising the non relativistic scaling function to the relativistic case, and it is shown that y-scaling does occur in the usual relativistic scaling variable resulting from the energy conservation in the instant form of dynamics. The present approach of y-scaling is fully covariant, with the deuteron being described by eight components, viz. the 3S_1^{++}, 3S_1^{--}, 3D_1^{++}, 3D_1^{--}, 3P_1^{+-}, 3P_1^{-+}, 1P_1^{+-}, 1P_1^{-+} waves. It is demonstrated that if the negative relative energy states 1P_1, 3P_1 are disregarded, the concept of covariant momentum distributions N(p_0,p), with p_0=M_D/2-\sqrt{p^2+m^2}, can be introduced, and that calculations of lectro-disintegration cross section in terms of these distributions agree within few percents with the exact calculations which include the 1P_1, 3P_1 states, provided the nucleon three momentum |p|\<= 1 GeV/c; in this momentum range, the asymptotic relativistic scaling function is shown to coincide with the longitudinal covariant momentum distribution.Comment: 32 LaTeX pages, 18 eps-figures. Final version to appear in Phys. Rev.

Structure functions for the three nucleon system

The spectral functions and light-cone momentum distributions of protons and neutrons in 3He and 3H are given in terms of the three-nucleon wave function for realistic nucleon-nucleon interactions. To reduce computational complexity, separable expansions are employed for the nucleon-nucleon potentials. The results for the light-cone momentum distributions suggest that they are not very sensitive to the details of the two-body interaction, as long as it has reasonable short-range repulsion. The unpolarised and polarised structure functions are examined for both 3He and 3H in order to test the usefulness of 3He as a neutron target. It is found that the measurement of the spin structure function of polarised 3H would provide a very clear test of the predicted change in the polarised parton distributions of a bound proton.Comment: 30 pages, REVTeX, 11 figure

Finite formation time effects in quasi-elastic (e,e′)(e,e') scattering on nuclear targets

The problem of the final state interaction in quasi-elastic $(e,e')$ scattering at large $Q^2$, is investigated by exploiting the idea that the ejected nucleon needs a finite amount of time to assume its asymptotic form. It is shown that when the dependence of the scattering amplitude of the ejected nucleon on its virtuality is taken into account, the final state interaction is decreased. The developed approach is simpler to implement than the one based on the color transparency description of the damping of the final state interaction, and is essentially equivalent to the latter in the case of the single rescattering term. The $(e,e')$ process on the deuteron is numerically investigated and it is shown that, at $x=1$, appreciable finite formation time effects at $Q^2$ of the order of 10 (GeV/c)$^2$ are expected.Comment: 23 pages, 3 figure