1,720,987 research outputs found
Generalized Parton Distributions of Light Nuclei
No full textThe measurement of nuclear generalized parton distributions (GPDs) in hard exclusive processes, such as deeply virtual Compton Scattering (DVCS), will be one of the main achievements of a new generation of experiments at high luminosity. Let us mention those under way at the Jefferson Laboratory (JLab) with the 12 GeV electron beam and, above all, those planned at the future Electron Ion Collider. The CLAS collaboration at JLab has recently demonstrated the possibility to disentangle the the coherent and incoherent channels of nuclear DVCS, a first step towards the measurement of GPDs of nuclei and of bound nucleons, respectively, opening new exciting perspectives in the field. In this scenario, accurate calculations, ultimately realistic, become mandatory. Light nuclei, for which realistic studies are affordable and conventional nuclear effects can be safely estimated, so that possible exotic effects can be exposed, play an important role. The status of the calculation of GPDs for light nuclei will be summarized, in particular for 3He and 4He, and some updates will be presented. The prospects for the next years, related to the new series of measurements at future facilities, will be addressed
Poincaré Covariant Light-Front Spectral Function and Transverse Momentum Distributions
No full textIn valence approximation the fermion correlator is simply related to the light-front spectral function. Then the leading twist time-reversal even transverse momentum distributions can be explicitly obtained from the light-front wave function of the system and the twist-three distributions are linear combinations of the transverse distributions at leading twist
Incoherent deeply virtual Compton scattering off He 4
No full textVery recently, for the first time, the two channels of nuclear deeply virtual Compton scattering, the coherent and incoherent ones, have been separated by the CLAS collaboration at the Jefferson Laboratory, using a He4 target. The incoherent channel, which can provide a tomographic view of the bound proton and shed light on its elusive parton structure, is thoroughly analyzed here in the impulse approximation. A convolution formula for the relevant nuclear cross sections in terms of those for the bound proton is derived. Novel scattering amplitudes for a bound moving nucleon have been obtained and used. A state-of-the-art nuclear spectral function, based on the Argonne-18 potential, exact in the two-body part, with the recoiling system in its ground state, and modelled in the remaining contribution, with the recoiling system in an excited state, has been used. Different parametrizations of the generalized parton distributions of the struck proton have been tested. A good overall agreement with the data for the beam spin asymmetry is obtained. It is found that the conventional nuclear effects predicted by the present approach are relevant in deeply virtual Compton scattering and in the competing Bethe-Heitler mechanism, but they cancel each other to a large extent in their ratio, to which the measured asymmetry is proportional. Besides, the calculated ratio of the beam spin asymmetry of the bound proton to that of the free one does not describe that estimated by the experimental collaboration. This points to possible interesting effects beyond the impulse approximation analysis presented here. It is therefore clearly demonstrated that the comparison of the results of a conventional realistic approach, as the one presented here, with future precise data, has the potential to expose quark and gluon effects in nuclei. Interesting perspectives for the next measurements at high luminosity facilities, such as JLab at 12 GeV and the future Electron Ion Collider, are addressed
QUARK TRANSVERSE MOMENTUM DISTRIBUTIONS INSIDE A NUCLEON: A LIGHT-FRONT HAMILTONIAN DYNAMICS STUDY
No full textThrough an impulse approximation analysis of single spin Sivers and Collins asymmetries in the Bjorken limit, the possibility to extract the quark transverse-momentum distributions in the neutron from semi-inclu- sive deep inelastic electron scattering off polarized 3He is illustrated. The analysis is generalized to finite momentum transfers in a light-front Poincaré covariant framework, defining the light-front spin-dependent spectral func- tion of a J = 1/2 system. The definition of the light-front spin-dependent spectral function for constituent quarks in the nucleon allows us to show that, within the light-front dynamics, only three of the six leading twist T-even transverse-momentum distributions are independent
Parton Correlations in Double Parton Scattering
No full textDouble parton scattering events are directly sensitive to the correlations between two partons inside a proton and can answer fundamental questions on the connections between the proton constituents. In this chapter, the different types of possible correlations, our present knowledge of them, and the processes where they are likely to be important, are introduced and explained. The increasing integrated luminosity at the LHC and the refinements of the theory of double parton scattering, lead to interesting prospects for measuring, or severely constraining, two-parton correlations in the near future.</p
Distorted spin-dependent spectral function of an A=3 nucleus and semi-inclusive deep inelastic scattering processes
Full text linkThe distorted spin-dependent spectral function of a nucleon inside an A = 3 nucleus is introduced as a
novel tool for investigating the polarized electron scattering off polarized 3He in the semi-inclusive DIS regime
(SiDIS), going beyond the standard plane-wave impulse approximation. This distribution function is applied 3⃗ ′2
to the study of the spectator SiDIS, He(e⃗,e H)X, to properly take into account the final-state interaction
between the hadronizing quark and the detected deuteron, with the final goal of a more reliable extraction of the
polarized parton distribution g1(x) inside a bound proton. Our analysis allows one to single out two well-defined
kinematical regions where the experimental asymmetries could yield very interesting information: the region
where the final-state effects can be minimized, and therefore the direct access to the parton distributions in the
proton is feasible, and the one where the final-state interaction dominates, and the spectator SiDIS reactions can
elucidate the mechanism of the quark hadronization itself. The perspectives of extending our approach (i) to
the mirror nucleus, 3H, for achieving a less model-dependent flavor decomposition and (ii) to the asymmetries 3⃗′
measured in the standard SiDIS reactions, e⃗ + He → e + h + X, with h a detected fast hadron, with the aim of extracting the neutron transversity, are discussed
Transversity studies with a polarized 3He target
Full text linkA realistic study of the SiDIS process He(e, e π)X in the Bjorken
limit is briefly reviewed, showing that the nuclear effects, present in the extraction of the neutron information, are largely under theoretical control, within an Impulse- Approximation approach. In view of the forthcoming experimental data, we shortly present a novel Poincar ́e covariant description of the nuclear target, implementing a Light-Front analysis at finite Q2, within the Bakamijan-Thomas construction of the Poincar ́e generators. Furthermore, as a by-product of the introduction of a Light- Front spin-dependent spectral function for a J = 1/2 system, we straightforwardly extend our analysis to the quark-quark correlator, obtaining three new exact rela- tions between the six leading-twist Transverse-Momentum–Dependent distributions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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