Are There Diquarks in the Nucleon?

This work is devoted to the study of diquark correlations inside the nucleon. We analyze some matrix elements which encode information about the non-perturbative forces, in different color anti-triplet diquark channels. We suggest a lattice calculation to check the quark-diquark picture and clarify the role of instanton-mediated interactions. We study in detail the physical properties of the 0+ diquark, using the Random Instanton Liquid Model. We find that instanton forces are sufficiently strong to form a diquark bound-state, with a mass of ~500 MeV, which is compatible with earlier estimates. We also compute its electro-magnetic form factor and find that the diquark is a broad object, with a size comparable with that of the proton.Comment: Final version, accepted for publication on Phys. Rev.

Approximate treatment of electron Coulomb distortion in quasielastic (e,e') reactions

In this paper we address the adequacy of various approximate methods of including Coulomb distortion effects in (e,e') reactions by comparing to an exact treatment using Dirac-Coulomb distorted waves. In particular, we examine approximate methods and analyses of (e,e') reactions developed by Traini et al. using a high energy approximation of the distorted waves and phase shifts due to Lenz and Rosenfelder. This approximation has been used in the separation of longitudinal and transverse structure functions in a number of (e,e') experiments including the newly published 208Pb(e,e') data from Saclay. We find that the assumptions used by Traini and others are not valid for typical (e,e') experiments on medium and heavy nuclei, and hence the extracted structure functions based on this formalism are not reliable. We describe an improved approximation which is also based on the high energy approximation of Lenz and Rosenfelder and the analyses of Knoll and compare our results to the Saclay data. At each step of our analyses we compare our approximate results to the exact distorted wave results and can therefore quantify the errors made by our approximations. We find that for light nuclei, we can get an excellent treatment of Coulomb distortion effects on (e,e') reactions just by using a good approximation to the distorted waves, but for medium and heavy nuclei simple additional ad hoc factors need to be included. We describe an explicit procedure for using our approximate analyses to extract so-called longitudinal and transverse structure functions from (e,e') reactions in the quasielastic region.Comment: 30 pages, 8 figures, 16 reference

Characterisation of the secondary-neutron production in particle therapy treatments with the MONDO tracking detector

Particle Therapy (PT) is a non-invasive technique that exploits charged light ions for the irradiation of tumours that cannot be effectively treated with surgery or conventional radiotherapy. While the largest dose fraction is released to the tumour volume by the primary beam, a non-negligible amount of additional dose is due to the beam fragmentation that occurs along the path towards the target volume. In particular, the produced neutrons are particularly dangerous as they can release their energy far away from the treated area, increasing the risk of developing a radiogenic secondary malignant neoplasm after undergoing a treatment. A precise measurement of the neutron flux, energy spectrum and angular distributions is eagerly needed in order to improve the treatment planning system software, so as to predict the normal tissue toxicity in the target region and the risk of late complications in the whole body. The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project is dedicated to the characterisation of the secondary ultra-fast neutrons ([20-400] MeV energy range) produced in PT. The neutron tracking system exploits the reconstruction of the recoil protons produced in two consecutive (n, p) elastic scattering interactions to measure simultaneously the neutron incoming direction and energy. The tracker active media is a matrix of thin squared scintillating fibers arranged in orthogonally oriented layers that are read out by a sensor (SBAM) based on SPAD (Single-Photon Avalanche Diode) detectors developed in collaboration with the Fondazione Bruno Kessler (FBK)

Three-dimensional architecture and mechanical properties of bovine bone mixed with autologous platelet liquid, blood, or physiological water: An in vitro study

In recent years, several techniques and material options have been investigated and developed for bone defect repair and regeneration. The progress in studies of composite graft materials and autologous platelet-derived growth factors for bone regeneration in dentistry and their biological and biomechanical properties has improved clinical strategies and results. The aim of this study was to evaluate the three-dimensional architecture and mechanical properties of three different combinations of composite bovine graft, adding autologous platelet liquid (APL), blood, or physiological water. One experimental group for each combination of biomaterials was created. In particular, in Group I, the bovine graft was mixed with APL; in Group II, it was mixed with blood, and in Group III, the biomaterial graft was combined with physiological water. Then, the composite biomaterials were evaluated by scanning electron microscopy (SEM), and a compression-loading test was conducted. The evaluation showed a statistical significance (p < 0.01) of the elastic regime of deformation resistance, in which the combination of APL with bone graft resulted in an 875% increase in the mechanical resistance. The protocol of APL mixed with bovine bone graft produced a composite sticky graft block that was capable of increasing the mechanical properties in order to improve its clinical use in the treatment of the maxillary bone defects

Nonperturbative versus perturbative effects in generalized parton distributions

Generalized parton distributions (GPDs) are studied at the hadronic (nonperturbative) scale within different assumptions based on a relativistic constituent quark model. In particular, by means of a meson-cloud model we investigate the role of nonperturbative antiquark degrees of freedom and the valence quark contribution. A QCD evolution of the obtained GPDs is used to add perturbative effects and to investigate the GPDs' sensitivity to the nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 17 pages, 10 figures; submitted to Phys. Rev.

Double Parton Distributions in Light-Front Constituent Quark Models

Double parton distribution functions (dPDF), accessible in high energy proton-proton and proton-nucleus collisions, encode information on how partons inside a proton are correlated among each other and could represent a tool to explore the 3D proton structure. In recent papers, double parton correlations have been studied in the valence quark region, by means of constituent quark models. This framework allows to understand clearly the dynamical origin of the correlations and to establish which, among the features of the results, are model independent. Recent relevant results, obtained in a relativistic light-front scheme, able to overcome some drawbacks of previous calculations, such as the poor support, will be presented. Peculiar transverse momentum correlations, generated by the correct treatment of the boosts, are obtained. The role of spin correlations will be also shown. In this covariant approach, the symmetries of the dPDFs are unambiguously reproduced. The study of the QCD evolution of the model results has been performed in the valence sector, showing that, in some cases, the effect of evolution does not cancel that of correlations

Orbital Angular Momentum Parton Distributions in Light-Front Dynamics

We study the quark angular momentum distribution in the nucleon within a light-front covariant quark model. Special emphasis is put into the orbital angular momentum: a quantity which is very sensitive to the relativistic treatment of the spin in a light-front dynamical approach. Discrepancies with the predictions of the low-energy traditional quark models where relativistic spin effects are neglected, are visible also after perturbative evolution to higher momentum scales. Orbital angular momentum distributions and their contribution to the spin sum rule are calculated for different phenomenological mass operators and compared with the results of the MIT bag model.Comment: 14 pages; latex; 3 ps figure