A relativistic quark-diquark model for the nucleon

We developed a constituent quark-diquark model for the nucleon and its resonances using a harmonic oscillator potential for the interaction. The effects due to relativistic kinetic energy correction are studied. Finally, charge form factor of the model is calculated and compared with experimental data.      

Weak radiative decays of hyperons within theSU(6) broken quark-diquark model

In view of persisting discrepancy between experimental and theoretical results, specially in the weak radiative decays of∑ ⁺ andΞ ⁰, we analyse these decays within the framework of the QCD inspired quark-diquark model. On introducing a slightSU(6) breaking we obtainα(∑ ⁺→p+γ)≈?0.9 which is in excellent agreement with experimental value. Other decays are also improved in this scheme.     

Baryon magnetic moments in a dynamical quark-diquark model

The magnetic moments of baryons are calculated in a dynamical quark-diquark model using current-quark masses as input. Except for theΞ ^? moment, results are in fairly good agreement with experiment.     

Veneziano model for nucleon nucleon and nucleon antinucleon scattering. I

The thermal conductivity has been measured on two niobium samples of different purity (ratio of mean free path to coherence length 220 and 10, respectively), in the mixed state, with heat current parallel (k _∥) and normal (k _⊥) to the magnetic field. The experimental results are compared with theories; the range of validity is discussed. Maki's relation (k-k _n) ～ (H _c2 -H)^1/2 could be verified only for the purer sample in the field range (H _c2 -H)?140 Oe. The relationsk _∥/k ₁>1 forT?T _c andk _∥/k ₁<1 forT?T _c were found to be valid for the whole range of fields in the mixed state.     

Nucleon properties in the covariant quark-diquark model

In the covariant quark-diquark model the effective Bethe-Salpeter (BS) equations for the nucleon and the Δ are solved including scalar and axial vector diquark correlations. Their quark substructure is effectively taken into account in both, the interaction kernel of the BS equations and the currents employed to calculate nucleon observables. Electromagnetic current conservation is maintained. The electric form factors of proton and neutron match the data. Their magnetic moments improve considerably by including axial vector diquarks and photon induced scalar-axial vector transitions. The isoscalar magnetic moment can be reproduced, the isovector contribution is about 15% too small. The ratio μG _E/G _M and the axial and strong couplings g _A, g _NN, provide an upper bound on the relative importance of axial vector diquarks confirming that scalar diquarks nevertheless describe the dominant 2-quark correlations inside nucleons. Received: 3 July 2000 / Accepted: 15 August 2000     

Search for nucleon decays induced by GUT magnetic monopoles with the MACRO experiment

The interaction of a Grand Unification Magnetic Monopole with a nucleon can lead to a barion-number violating process in which the nucleon decays into a lepton and one or more mesons (catalysis of nucleon decay). In this paper we report an experimental study of the effects of a catalysis process in the MACRO detector. Using a dedicated analysis we obtain new magnetic monopole (MM) flux upper limits at the level of for , based on the search for catalysis events in the MACRO data. We also analyze the dependence of the MM flux limit on the catalysis cross section. Received: 2 August 2002 / Published online: 25 October 2002     

Pionic decays of Λ-hypernuclei and nucleon occupation probabilities

It is argued that pionic decays of Λ hypernuclei can be probe to see real occupation probabilities of nucleon hole orbits. Pionic decay rates are evaluated by taking into account correlation probability effects and are found to show a saturation property in heavy hypernuclei, which is necessary to be compatible with experimental indications.     

Quark model for kaon nucleon scattering

Kaon nucleon elastic scattering is studied using chiral SU(3) quark model including antiquarks. Parameters of the present model are essentially based on nucleon–nucleon and nucleon–hyperon interactions. The mass of the scalar meson σ is taken as 635 MeV. Using this model, the phase shifts of the S and P partial waves of the kaon nucleon elastic scattering are investigated for isospins 0 and 1. The results of numerical calculations of different partial waves are in good agreement with experimental data.     

更精确地研究核子

位于美国弗吉尼亚洲的ThomasJefferson国家加速器实验室的一群国际科学家们 ,共同对质子内夸克自旋是如何取向的问题进行研究 .粗略地说 ,夸克自旋可以看成是一个微小的磁棒 ,指向某一确定的方向并具有一定的强度 .有关夸克自旋的信息可提供这些基本粒子在核子 (如中子与质子 )     

Measurements of decays into and

Based on a sample of 5.8×10⁷ J/ψ events taken with the BESII detector, the branching fractions of J/ψ→2(π⁺π⁻)η and J/ψ→3(π⁺π⁻)η are measured for the first time to be (2.26±0.08±0.27)×10⁻³ and (7.24±0.96±1.11)×10⁻⁴, respectively.     

Statistical model for the structure functions of the nucleon

The deep-inelastic structure functions of the nucleon are calculated in a statistical model considering the nucleon to be composed of a gas of quarks and gluons. Several differences with the standard parton-model approach are pointed out. To zeroth order in perturbative QCD, the model is worked out completely. A fit to the large-x part of the structure functions requires a temperature of about 40–50 MeV for the quarks and gluons and a chemical potential around 200 MeV.     

Charmonium cross-sections and the QGP

In this contribution we summarize experimental information and theoretical results for the dissociation cross-sections of charmonium by light hadrons, which are of great importance for the identification of a quark-gluon plasma (QGP). Recent theoretical predictions for these cross-sections differ by orders of magnitude over the physically relevant energy range. The methods discussed here include a color-dipole model, meson exchange models, a quark interchange model, and QCD sum rules.Received: 30 September 2002, Published online: 22 October 2003PACS: 25.75.-q Relativistic heavy-ion collisions - 25.75.Dw Particle and resonance production