Hard Photodisintegration of 3He

Large angle photodisintegration of two nucleons from the 3He nucleus is studied within the framework of the hard rescattering model (HRM). In the HRM the incoming photon is absorbed by one nucleon's valence quark that then undergoes a hard rescattering reaction with a valence quark from the second nucleon producing two nucleons emerging at large transverse momentum . Parameter free cross sections for pp and pn break up channels are calculated through the input of experimental cross sections on pp and pn elastic scattering. The calculated cross section for pp breakup and its predicted energy dependency are in good agreement with recent experimental data. Predictions on spectator momentum distributions and helicity transfer are also presented.Comment: 7 pages, 4 figure

Teaching geography for a sustainable world: a case study of a secondary school in Spain

Geography has a major responsibility in delivering education for sustainable development (ESD), especially because the geographical concepts of place and space are key dimensions for the analysis and pursuit of sustainability. This paper presents the results of a research that investigated how the teaching of geography in secondary education in Catalonia (Spain) contributes to ESD. For the development of this research it was explored what is involved in understanding and resolving issues about sustainable development and how geography teachers might best conceptualize and teach in this new domain. As a result of this theoretical reflection it has been defined a proposal or model for reorienting the geography curriculum from the basis of the ESD paradigm, which is based and structured in four groups of criteria and recommendations as follows: recommendations for defining competences and learning objectives; criteria for selecting geographical contents and themes; criteria for selecting geographical areas and for the use of scale; and finally, recommendations for choosing the most suitable teaching and learning approach

Light-front representation of chiral dynamics in peripheral transverse densities

The nucleon's electromagnetic form factors are expressed in terms of the transverse densities of charge and magnetization at fixed light-front time. At peripheral transverse distances $b = O(M_\pi^{-1})$ the densities are governed by chiral dynamics and can be calculated model-independently using chiral effective field theory (EFT). We represent the leading-order chiral EFT results for the peripheral transverse densities as overlap integrals of chiral light-front wave functions, describing the transition of the initial nucleon to soft pion-nucleon intermediate states and back. The new representation (a) explains the parametric order of the peripheral transverse densities; (b) establishes an inequality between the spin-independent and -dependent densities; (c) exposes the role of pion orbital angular momentum in chiral dynamics; (d) reveals a large left-right asymmetry of the current in a transversely polarized nucleon and suggests a simple interpretation. The light-front representation enables a first-quantized, quantum-mechanical view of chiral dynamics that is fully relativistic and exactly equivalent to the second-quantized, field-theoretical formulation. It relates the charge and magnetization densities measured in low-energy elastic scattering to the generalized parton distributions probed in peripheral high-energy scattering processes. The method can be applied to nucleon form factors of other operators, e.g. the energy-momentum tensor.Comment: 28 pages, 9 figure

Chiral dynamics and peripheral transverse densities

In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at transverse distances b = O(M_pi^{-1}) and compute them in a parametrically controlled manner. A dispersion relation connects the large-distance behavior of the transverse charge and magnetization densities to the spectral functions of the Dirac and Pauli form factors near the two-pion threshold at timelike t = 4 M_pi^2. Using relativistic chiral effective field theory in the leading-order approximation, we (a) derive the asymptotic behavior (Yukawa tail) of the isovector transverse densities in the "chiral" region b = O(M_pi^{-1}) and the "molecular" region b = O(M_N^2/M_pi^3); (b) perform the heavy-baryon expansion; (c) explain the relative magnitude of the peripheral charge and magnetization densities in a simple mechanical picture; (d) include Delta intermediate states and study the densities in the large-N_c limit of QCD; (e) quantify the spatial region where the chiral components are numerically dominant; (f) calculate the chiral divergences of the b^2-weighted moments of the transverse densities (charge and magnetic radii) and determine their spatial support. Our approach provides a concise formulation of the spatial structure of the nucleon's chiral component and offers new insights into basic properties of the chiral expansion. It relates the information extracted from low-t elastic form factors to the generalized parton distributions probed in peripheral high-energy scattering processes.Comment: 52 pages, 13 figure

Multi-wavelength, all-solid-state, continuous wave mode locked picosecond Raman laser

We demonstrate the operation of a cascaded continuous wave (CW) mode-locked Raman oscillator. The output pulses were compressed from 28 ps at 532 nm down to 6.5 ps at 559 nm (first Stokes) and 5.5 ps at 589 nm (second Stokes). The maximum output was 2.5 W at 559 nm and 1.4 W at 589 nm with slope efficiencies up to 52%. This technique allows simple and efficient generation of short-pulse radiation to the cascaded Stokes wavelengths, extending the mode-locked operation of Raman lasers to a wider range of visible wavelengths between 500 - 650 nm based on standard inexpensive picosecond Nd:YAG oscillators