Nucleon Electromagnetic Form Factors

There has been much activity in the measurement of the elastic electromagnetic proton and neutron form factors in the last decade, and the quality of the data has greatly improved by performing double polarization experiments, in comparison with previous unpolarized data. Here we review the experimental data base in view of the new results for the proton, and neutron, obtained at JLab, MAMI, and MIT-Bates. The rapid evolution of phenomenological models triggered by these high-precision experiments will be discussed, including the recent progress in the determination of the valence quark generalized parton distributions of the nucleon, as well as the steady rate of improvements made in the lattice QCD calculations

The Structure of the Nucleon: Elastic Electromagnetic Form Factors

Precise proton and neutron form factor measurements at Jefferson Lab, using spin observables, have recently made a significant contribution to the unraveling of the internal structure of the nucleon. Accurate experimental measurements of the nucleon form factors are a test-bed for understanding how the nucleon's static properties and dynamical behavior emerge from QCD, the theory of the strong interactions between quarks. There has been enormous theoretical progress, since the publication of the Jefferson Lab proton form factor ratio data, aiming at reevaluating the picture of the nucleon. We will review the experimental and theoretical developments in this field and discuss the outlook for the future.Comment: arXiv admin note: text overlap with arXiv:1301.0905, arXiv:hep-ph/0609004, arXiv:1411.6908 by other author

The Proton Form Factor Ratio Measurements at Jefferson Lab

The ratio of the proton form factors, GEp/GMp, has been measured from Q(2) of 0.5 GeV2 to 8.5 GeV2, at the Jefferson Laboratory, using the polarization transfer method. This ratio is extracted directly from the measured ratio of the transverse and longitudinal polarization components of the recoiling proton in elastic electron-proton scattering. The discovery that the proton form factor ratio measured in these experiments decreases approximately linearly with four-momentum transfer, Q(2), for values above approximate to 1 GeV2, is one of the most significant results to come out of JLab. These results have had a large impact on progress in hadronic physics; and have required a significant rethinking of nucleon structure. There is an approved experiment at JLab, GEp(5), to continue the ratio measurements to 12 GeV2. A dedicated experimental setup, the Super Bigbite Spectrometer (SBS), will be built for this purpose. In this paper, the present status of the proton elastic electromagnetic form factors and a number of theoretical approaches to describe nucleon form factors will be discussed

Feeling and hearing country as research method

This paper explains Feeling and Hearing Country as an Australian Indigenous practice whereby water is life, Country is responsive, and Elders generate wisdom for a communicative order of things. The authors ask, as a society of Indigenous people and those no longer Indigenous to place, can we walk together in the task of collectively healing Country? The research method uses experiential, creative, propositional, and practical ways of knowing and being in and with local places. Evidence may take many forms based upon engagement with an animate, sentient world. The research method can generate new meanings, implications and insights, and regenerate practical knowledge of Country. As an Indigenous tradition, Feeling and Hearing Country can enable the regeneration of healing life energies. It can help freshen up stories, knowledges, and help link ancestral wisdom to the present while co-creating healthy futures. Feeling and Hearing Country can enliven the human spirit, landscapes, and all beings via a participative, creative process that is helpful for the planet at this climate time, when many humans have forgotten their place in the world. As a research method, Feeling and Hearing Country can support the unlearning of epistemological errors for reinstating vitality in things

Determining the size of the proton

A measurement of the Lamb shift of 49,881.88(76) GHz in muonic hydrogen in conjunction with theoretical estimates of the proton structure effects was recently used to deduce an accurate but rather small radius of the proton. Such an important shift in the understanding of fundamental values needs reconfirmation. Using a different approach with electromagnetic form factors of the proton, we obtain a new expression for the transition energy, $\Delta = E_{2P_{{3}/{2}}}^{f=2} - E_{2S_{{1}/{2}}}^{f=1}$, in muonic hydrogen and deduce a proton radius, $r_p = 0.831$ fm.Comment: 20 pages LaTe

New Measurements of High-Momentum Nucleons and Short-Range Structures in Nuclei

We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate

Cross sections and transverse single-spin asymmetries in forward jet production from proton collisions at root s=500 GeV

Measurements of the production of forward jets from transversely polarized proton collisions at root s = 500 GeV conducted at the Relativistic Heavy Ion Collider (RHIC) are reported. Our measured jet cross section is consistent with hard scattering expectations. Our measured analyzing power for forward jet production is small and positive, and provides constraints on the Sivers functions that are related to partonic orbital angular momentum through theoretical models. (C) 2015 The Authors. Published by Elsevier B.V

Use of the calorimeter to improve analyzing power of the reactions, investigating secondary proton polarization

The reaction p + CH2 - \u3e forward charge particle + X is used for this aim traditionally. Analyzing power of this reaction falls off as 1/p, where p is the laboratory momentum. At the proton momenta of order 8 GeV/c, which are expected at the JLab experiment, the low analyzing power creates problems for off-line analysis of data. On the other hand, it is well known that the reaction p+p - \u3e p+p has the much more analyzing power. So, the calorimeter is predestinated for suppression of inelastic events in this reaction. In the report it is shown that the problem is solved quite well