Search results for "Nucleon"
showing 10 items of 1041 documents
Nucleon Structure Functions and Light-Front Dynamics
1999
We present a quark-parton model to describe polarized and unpolarized nucleon structure functions. The twist-two matrix elements for the QCD evolution analysis of lepton-hadron scattering are calculated within a light-front covariant quark model. The relativistic effects in the three-body wave function are discussed for both the polarized and unpolarized cases. Predictions are given for the polarized gluon distributions as will be seen in future experiments.
Parity violating electron scattering at MAMI
2012
The investigation of the structure of the nucleon can help to understand the non-pertubative regime of the QCD. In the viewpoint of QCD, the nucleon is made up of constituent quarks, sea quarks and gluons. The nucleon structure can be described by the electromagnetic form factors. Parity violating electron scattering offers a tool to investigate the strange quark contribution to the nucleon form factors. Such measurements are carried out at the electron accelerator facility MAMI at Mainz. Recent results are presented here.
ASYMMETRIES IN POLARIZED ELECTRON SCATTERING AND THE STRANGENESS CONTENT OF THE NUCLEON
2009
In the viewpoint of QCD, the nucleon is made up of constituent quarks, sea quarks and gluons. Concerning the quark sea, also strange quarks can contribute to the nucleon properties. Parity violating electron scattering offers a tool to investigate the strange quark contribution to the nucleon form factors. The measurements of different experiments are discussed and the recent results from the A4 collaboration at MAMI is presented. Altogether the existing data allow to give constraints on the strangeness contribution.
Pionic effects in deep inelastic scattering off nuclei
1992
The structure functions calculated in the Chiral bag model reproduce quite well, after appropriate perturbative evolution to large energy scales, the experimental data. We use these results to interpret the structure of the $EMC$ data as a quenching of the pion decay constant due to the in medium behavior of the nucleon. This explanation supports recent proposals of this phenomenon whose origin is the scale invariance of the $QCD$ lagrangian.
Diffractive dijet production and Wigner distributions from the color glass condensate
2019
Experimental processes that are sensitive to parton Wigner distributions provide a powerful tool to advance our understanding of proton structure. In this work, we compute gluon Wigner and Husimi distributions of protons within the Color Glass Condensate framework, which includes a spatially dependent McLerran-Venugopalan initial configuration and the explicit numerical solution of the JIMWLK equations. We determine the leading anisotropy of the Wigner and Husimi distributions as a function of the angle between impact parameter and transverse momentum. We study experimental signatures of these angular correlations at a proposed Electron Ion Collider by computing coherent diffractive dijet p…
Dark matter in the Sun: scattering off electrons vs nucleons
2017
The annihilation of dark matter (DM) particles accumulated in the Sun could produce a flux of neutrinos, which is potentially detectable with neutrino detectors/telescopes and the DM elastic scattering cross section can be constrained. Although the process of DM capture in astrophysical objects like the Sun is commonly assumed to be due to interactions only with nucleons, there are scenarios in which tree-level DM couplings to quarks are absent, and even if loop-induced interactions with nucleons are allowed, scatterings off electrons could be the dominant capture mechanism. We consider this possibility and study in detail all the ingredients necessary to compute the neutrino production rat…
Light-front transverse charge densities
2010
We discuss the recent interpretation of quark-distribution functions in the plane transverse to the light-cone direction. Such a mapping is model independent and allows one to build up multidimensional pictures of the hadron and to develop a semi-classical interpretation of the quark dynamics. We comment briefly the results obtained from the form factors of the nucleon. We show that a generalization to a target with arbitrary spin leads to a set of preferred values for the electromagnetic coupling characterizing structureless particles. Finally, we present the Wigner distribution for an unpolarized quark in an unpolarized proton and we propose an interpretation of the observed distortion as…
Imaging the nucleus with high-energy photons
2019
In the 1930's, nuclear physicists developed the first realistic atomic models, showing that nuclei were made up of protons and neutrons. In the 1960's, Deep Inelastic Scattering experiments showed that protons and neutrons had internal structure: quarks and gluons (collectively, partons), and later experiments showed that the parton momentum distributions are different in heavy nuclei, compared to those in free nucleons. This difference is not surprising; partons are sensitive to their environment, and two gluons from different nucleons may fuse together, for example. Understanding how quarks and gluons behave in the nuclear environment is a significant focus of modern nuclear physics. Rece…
Medium effects in DIS from polarized nuclear targets
2014
The behavior of the nucleon structure functions in lepton nuclei deep inelastic scattering, both polarized and unpolarized, due to nuclear structure effects is reanalyzed. The study is performed in two schemes: an x-rescaling approach, and one in which there is an increase of sea quark components in the in medium nucleon, related to the low energy N-N interaction. In view of a recent interesting experimental proposal to study the behavior of the proton spin structure functions in nuclei we proceed to compare these approaches in an effort to enlighten the possible phenomenological interest of such difficult experiment.
Dirac and Pauli form factors from lattice QCD
2011
We present a comprehensive analysis of the electromagnetic form factors of the nucleon from a lattice simulation with two flavors of dynamical O(a)-improved Wilson fermions. A key feature of our calculation is that we make use of an extensive ensemble of lattice gauge field configurations with four different lattice spacings, multiple volumes, and pion masses down to m_\pi ~ 180 MeV. We find that by employing Kelly-inspired parametrizations for the Q^2-dependence of the form factors, we are able to obtain stable fits over our complete ensemble. Dirac and Pauli radii and the anomalous magnetic moments of the nucleon are extracted and results at light quark masses provide evidence for chiral …