E. Hernández

Theoretical study of the NN → NNππ reaction

We have developed a model for the N N --> N N pi pi reaction and evaluated cross sections for the different charged channels. The low energy part of those channels where the pions can be in an isospin zero state is dominated by N* excitation, driven by an isoscalar source recently found experimentally, followed by the decay N* --> N (pi pi, T=0, s-wave). At higher energies, and in channels where the pions are not in T=0, Delta excitation mechanisms become relevant. A rough agreement with the experimental data is obtained in most channels. Repercussions of the present findings for the ABC effect and the p p --> p p pi0 reaction close to threshold are also suggested.

Single π production in neutrino-nucleus scattering

We study

CONSTITUENT QUARK MODEL DESCRIPTION OF CHARMONIUM PHENOMENOLOGY

1\ensuremath{\pi}

Partial conservation of the axial current and axial exchange currents in the nucleon

production in both charged and neutral current neutrino-nucleus scattering for neutrino energies below 2 GeV. We use a theoretical model for one pion production at the nucleon level that we correct for medium effects. The results are incorporated into a cascade program that apart from production also includes the pion final state interaction inside the nucleus. Besides, in some specific channels coherent

B decays into radially excited charmed mesons

\ensuremath{\pi}

NonleptonicB→D(*)DsJ(*)decays and the nature of the orbitally excited charmed-strange mesons

production is also possible and we evaluate its contribution as well. Our results for total and differential cross sections are compared with recent data from the MiniBooNE Collaboration. The model provides an overall acceptable description of the data, better for neutral-current than for charged-current channels, although the theory is systematically below the data. Differential cross sections, folded with the full neutrino flux, show that most of the missing pions lie in the forward direction and at high energies.

A heavy quark symmetry approach to baryons

We review how quark models are able to describe the phenomenology of the charm meson sector. The spectroscopy and decays of charmonium and open charm mesons are described in a particular quark model and compared with the data and the results of other existing models in the literature. A quite reasonable global description of the heavy meson spectra is reached. A new assignment of the ψ(4415) resonance as a 3D state leaving aside the 4S state to the X(4360) is tested through the analysis of the resonance structure in e+e- exclusive reactions around the ψ(4415) energy region. We make tentative assignments of some of the XYZ mesons. To elucidate the structure of the 1+cs states, i.e., Ds1(2460) and Ds1(2536), we study the strong decay properties of the Ds1(2536) meson. We also perform a calculation of the branching fractions for the semileptonic decays of B and Bs mesons into final states containing orbitally excited charmed and charmed-strange mesons, which have become a very important source of information about the structure of heavy mesons. Analysis of the nonleptonic B-meson decays into D(*)DsJ are also included.

Theoretical study of the N N ---> N N pi pi reaction

Abstract We discuss the axial form factors of the nucleon within the context of the nonrelativistic chiral quark model. Partial conservation of the axial current (PCAC) imposed at the quark operator level enforces an axial coupling for the constituent quarks which is smaller than unity. This leads to an axial coupling constant of the nucleon g A in good agreement with experiment. PCAC also requires the inclusion of axial exchange currents. Their effects on the axial form factors are analyzed. We find only small exchange current contributions to g A , which is dominated by the one-body axial current. On the other hand, axial exchange currents give sizeable contributions to the axial radius of the nucleon r A 2 , and to the non-pole part of the induced pseudoscalar form factor g P . For the latter, the confinement exchange current is the dominant term.

Heavy Quark Spin Symmetry and Heavy Baryons: Electroweak Decays

All the details on the constituent quark model we usehave been described in Ref. [8] and we will only sketchhere its main features. The model is based on the as-sumption that the constituent quark mass of the lightquarks is due to the spontaneous chiral symmetry break-ing of the QCD Lagrangian. To restore the original sym-metry an interaction term, due to Goldstone-Boson ex-changes, appears between light quarks. This interactionis added to the perturbative One-GluonExchange(OGE)and the non-perturbative confining interactions. In theheavy quark sector, chiral symmetry is explicitly brokenand Goldstone-boson exchanges do not appear. There-fore, the corresponding potential for the system stemsfrom the nonrelativistic reduction of the OGE interactionand the confinement component. Explicit formulae andmodel parameters used herein can be find in Refs. [9, 13].Concerning the new discovered mesons, D(2550) andD

Neutrino induced coherent pion production

The Belle Collaboration has recently reported a study of the decays