Nucleon parton distributions in a light-front quark model

Continuing with our analysis of parton distributions in the nucleon, we extend our light-front quark model in order to obtain both the helicity independent and helicity dependent parton distributions, analytically matching the results of global fits at the initial scale $\mu \sim 1$ GeV, and which also contain the correct Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution. We also calculate the transverse parton, Wigner and Husimi distributions from a unified point of view, using our light-front wave functions and expressing them in terms of the parton distributions $q_v(x)$ and $\delta q_v(x)$. Our results are very relevant for the current and future program of the COMPASS experiment at SPS (CERN)

Possible hadronic molecule structure of the Y(3940) and Y(4140)

In the present article we report on evidence for hadronic molecule structures in the charmonium sector. In particular we discuss the Y(3940) and the recently observed Y(4140) as heavy hadron molecule states with quantum numbers $J^{PC} = 0^{++}$ or $2^{++}$. The Y(3940) state is considered to be a superposition of $D^{\ast +}D^{\ast -}$ and $D^{\ast 0} \overline{D^{\ast 0}}$, while the Y(4140) is a bound state of $D_s^{\ast +}$ and $D_s^{\ast -}$ mesons. We give predictions for both the strong Y(3940) to J/psi omega, Y(4140) to J/psi phi and radiative Y(3940)/Y(4140) to gamma gamma decay widths in a phenomenological Lagrangian approach. The results for the strong hidden charm decay modes clearly support the molecular interpretation of the Y(3940) and Y(4140), while our estimates for the radiative decays provide a sensitive test for the underlying meson structure of the two Y mesons discussed here. The alternative assignment of $J^{PC} = 2^{++}$ is also tested, giving similar results for the strong decay widths.Comment: 5 pages, 2 figures. To appear in the Proceedings of XIII International Conference on Hadron Spectroscopy, November 29 - December 4, 2009, Florida State Universit

Nucleon Properties in the Perturbative Chiral Quark Model

We apply the perturbative chiral quark model (PCQM) to analyse low-energy nucleon properties: electromagnetic form factors, meson-nucleon sigma-terms and pion-nucleon scattering. Baryons are described as bound states of valence quarks surrounded by a cloud of Goldstone bosons (pi, K, eta) as required by chiral symmetry. The model is based on the following guide lines: chiral symmetry constraints, fulfilment of low-energy theorems and proper treatment of sea-quarks, that is meson cloud contributions. Analytic expressions for nucleon observables are obtained in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling constant, strong pion-nucleon form factor) and of only one model parameter (radius of the nucleonic three-quark core). Our results are in good agreement with experimental data and results of other theoretical approaches.Comment: 8 pages. Invited talk given at Workshop on the Physics of Excited Nucleons "NSTAR2001", Mainz, Germany, March 7-10, 200

Determination of a Definition of Solar Grade Silicon

A definition of solar grade silicon was determined by investigating the singular and the combined effect of the impurities usually found in metallurgical grade silicon on solar cell device performance. The impurity matrix was defined by Jet Propulsion Laboratory Technical Direction Memorandum. The initial work was focussed on standardizing the solar cell process and test procedure, growing baseline crystals, growing crystals contaminated with carbon, iron, nickel, zirconium, aluminum and vanadium, solar blank preparation, and material characterization

Nucleon resonances in AdS/QCD

We describe the electroproduction of the N(1440) Roper resonance in soft-wall AdS/QCD. The Roper resonance is identified as the first radially excited state of the nucleon, where higher-Fock states in addition to the three-quark component are included. The main conclusion is that the leading 3q component plays the dominant role in the description of electroproduction properties of this resonance: form factors, helicity amplitudes and charge densities. The obtained results are in good agreement with the recent results of the CLAS Collaboration at JLab.Comment: 20 pages. arXiv admin note: text overlap with arXiv:1204.661