SPIN STRUCTURE AT LONG DISTANCE: Workshop Proceedings
1155(2009); http://dx.doi.org/10.1063/1.3203300View Description Hide Description
The Gerasimov‐Drell‐Hearn sum rule and related dispersive integrals connect real and virtual Compton scattering to inclusive photo‐ and electroproduction. Being based on universal principles as causality, unitarity, and gauge invariance, these relations provide a unique testing ground to study the internal degrees of freedom that hold a system together. The present contribution reviews the spin‐dependent sum rules and cross sections of the nucleon. At small momentum transfer, the data sample information on the long range phenomena (Goldstone bosons and collective resonances), whereas the primary degrees of freedom (quarks and gluons) become visible at large momentum transfer (short distance). The rich body of new data covers a wide range of phenomena from coherent to incoherent processes, and from the generalized spin polarizabilities on the low‐energy side to higher twist effects in deep inelastic scattering.
1155(2009); http://dx.doi.org/10.1063/1.3203297View Description Hide Description
We discuss a precise determination of the polarizability and other proton structure dependent contributions to the hydrogen hyperfine splitting, based heavily on the most recent published data on proton spin dependent structure functions from the EG1 experiment at the Jefferson Laboratory. As a result, the total calculated hyperfine splitting now has a standard deviation slightly under 1 part‐per‐million, and is about 1 standard deviation away from the measured value.
1155(2009); http://dx.doi.org/10.1063/1.3203298View Description Hide Description
Polarized structure functions at low have the physical interpretation of (generalized) spin polarizabilities. At high the polarized parton distribution provides access to quark‐gluon correlations in the nucleon. We discuss the interpretation of the moment of as an average transverse force on quarks in deep‐inelastic scattering from a transversely polarized target. Qualitative connections with generalized parton distributions are emphasized. The moment of the chirally‐odd twist‐3 parton distribution e(x) provides information on the dependence of the average transverse force on the transversity of the quark.
1155(2009); http://dx.doi.org/10.1063/1.3203299View Description Hide Description
We review the study the Wandzura—Wilczek relation for the structure function with a particular attention on the connection with the framework of Transverse Momentum Dependent factorization. We emphasize that the relation is broken by two distinct twist‐3 terms. In the light of these findings, we clarify what can be deduced from the available experimental data on which indicate a breaking of the order 20–40%, and how to individually measure the twist‐3 terms.
1155(2009); http://dx.doi.org/10.1063/1.3203301View Description Hide Description
We apply chiral effective field theory with explicit Δlpar;1232) degrees of freedom to study double virtual Compton scattering at the photon point. Generalized spin polarizabilities are calculated up to order in the covariant small scale expansion. Systematic inclusion of Δ degrees of freedom drasticaly improves the theoretical predictions.
1155(2009); http://dx.doi.org/10.1063/1.3203302View Description Hide Description
A new iterative method is presented for extracting neutron structure functions from inclusive structure functions of nuclei, focusing specifically on the resonance region. Unlike earlier approaches, this method is applicable to both spin‐averaged and spin‐dependent structure functions. We show that in numerical tests, this method is able to reproduce known input functions of nearly arbitrary shape after only 5–10 iterations. We illustrate the method on extractions of and from data, and discuss the treatment of systematic errors from this extraction procedure.
1155(2009); http://dx.doi.org/10.1063/1.3203303View Description Hide Description
Nucleon spin structure has been an active, exciting and intriguing subject of interest for the last three decades. Recent precision spin‐structure data from Jefferson Lab have significantly advanced our knowledge of nucleon structure at low In particular, it has improved our understanding of spin sum rules and higher‐twist effects. First, results of neutron spin sum rules and polarizabilities in the low to intermediate region are presented. Comparison with theoretical calculations, in particular with Chiral Perturbation Theory (ChPT) calculations, are discussed. Surprising disagreements of ChPT calculations with experimental results on the generalized spin polarizability, were found. Results of precision measurements of the structure function to study higher‐twist effects are presented. The data indicate a significant higher‐twist (twist‐3 or higher) effect. The second moment of the spin structure functions and the twist‐3 matrix element results were extracted. The high result was compared with a Lattice QCD calculation. Finally, other neutron spin structure results, such as the resonance data for quark‐hadron duality study and a precision measurement of the neutron spin asymmetry in the valence quark (high‐x) region are briefly discussed.
1155(2009); http://dx.doi.org/10.1063/1.3203304View Description Hide Description
Measurements of the spin‐difference cross sections entering the Gerasimov‐Drell‐Hearn (GDH) sum rule are reviewed. Results on the proton from Mainz and Bonn exceeded the GDH prediction by 22 μb, requiring as yet unmeasured canceling high‐energy components. Recent experiments with frozen‐spin HD at BNL reveal a different angular dependence for production than what was assumed in Mainz analyses in lieu of direct measurements and integrate to a value that is 18 μb lower, suggesting a rapid convergence. Results for deuterium over limited energy ranges are consistent with large canceling contributions but differ from existing state of the art calculations.
1155(2009); http://dx.doi.org/10.1063/1.3203305View Description Hide Description
The Jefferson Lab Hall C spin physics program started in 2002 with an inclusive measurement of the nucleon spin structure in the resonances at intermediate (RSS—E01‐006). A second inclusive experiment in the DIS and resonances region covering the four‐momentum transfer from to the Spin Asymmetries of the Nucleon Experiment (SANE—E07003) took data starting in October 2008 and was completed in March 2009. Highlights of both experiments are presented in this report.
1155(2009); http://dx.doi.org/10.1063/1.3203306View Description Hide Description
Experiment E97‐110 was performed at the Thomas Jefferson National Accelerator Facility to provide a precise measurement of the spin structure functions at low from 0.02 to A longitudinally‐polarized electron beam was scattered from a longitudinally or transversely polarized target. From these data, we have extracted moments of the neutron and spin structure functions at very low momentum transfers. These data allow us to make a benchmark check of Chiral Perturbation Theory calculations in a region where they are expected to be valid. In these proceedings, the experimental details are discussed and preliminary results on the first moments of the and structure functions are presented.
1155(2009); http://dx.doi.org/10.1063/1.3203291View Description Hide Description
Jefferson Lab experiment E01‐012 measured the spin‐structure functions and virtual photon asymmetries in the resonance region in the momentum transfer range Our data, when compared with existing deep inelastic scattering data, were used to test quark‐hadron duality in and for and the neutron. In addition, preliminary results on the spin‐structure function on the Burkhardt‐Cottingham sum rule and on higher twist effects through the ‐weighted moment of the neutron were presented.
1155(2009); http://dx.doi.org/10.1063/1.3203292View Description Hide Description
We present recent results on the Bjorken and the generalized forward spin polarizability sum rules from Jefferson Lab Hall A and CLAS experiments, focusing on the low part of the measurements. We then discuss the comparison of these results with Chiral Perturbation theory calculations. In the second part of this paper, we show how the Bjorken sum rule with its connection to the Gerasimov‐Drell‐Hearn sum, allows us to conveniently define an effective coupling for the strong force at all distances.
1155(2009); http://dx.doi.org/10.1063/1.3203293View Description Hide Description
JLab has been at the forefront of a program to measure the nucleon spin‐dependent structure functions over a wide kinematic range, and data of unprecedented quality has been extracted in all three experimental halls. Moments of these quantities have proven to be powerful tools to test QCD sum rules and provide benchmark tests of Lattice QCD and Chiral Perturbation Theory. Precision measurements of and have been performed as part of the highly successful ‘extended GDH program’, but data on the structure function remain scarce. We discuss here JLab experiment E08‐027, which will measure in the resonance region at low These data will be used to test the Burkhardt‐Cottingham sum rule and to extract the higher moments and Data in the range will provide unambiguous benchmark tests of calculations on the lower end, while probing the transition region at the high end where parton‐like behaviour begins to emerge. This data will also have a significant impact on our theoretical understanding of the hyperfine structure of the proton, and reduce the systematic uncertainty of previous experiments which extracted the structure from purely longitudinal measurements.
1155(2009); http://dx.doi.org/10.1063/1.3203294View Description Hide Description
The main physics goal of the CLAS EG4 experiment at Jefferson Lab is to measure the generalized GDH sum for the proton and the neutron at very low down to (inclusive channels). The same data can be used to extract asymmetries of pion electroproduction in the resonance region (exclusive channels). An overview of the experiment is presented here, as well as the analysis status of both inclusive and exclusive analyses. Some preliminary results on the single‐target and the beam‐target asymmetries of charged pion electroproductions are presented.
1155(2009); http://dx.doi.org/10.1063/1.3203295View Description Hide Description
We discuss two Jefferson Lab measurements of the spin structure function and the higher twist reduced matrix element on the neutron. The first, E06‐014, just completed its run in March 2009 and will reduce the uncertainty on the neutron by a projected factor of four. The second experiment to be described, E12‐06‐121, is targeted to run shortly after the JLab 12 GeV upgrade is completed (est. 2014–5) and will focus on precision measurements of over the region and The latter experiment will also provide the first explicit measurement of the evolution of for
1155(2009); http://dx.doi.org/10.1063/1.3203296View Description Hide Description
We plan to make definitive measurements of the deuteron spin structure function in the deep‐inelastic kinematics accessible with a 6 GeV beam at JLab. The principal goal is to provide the low anchor points for NLO pQCD plus higher twist fits to which is particularly sensitive to ΔG(x) (the polarized gluon density of the nucleon) and the sum of up and down quark polarizations. By spanning a factor of typically two in the ‐range at nine values of x, the new data will strongly constrain the higher twist contribution to the fits, with a corresponding reduction in the polarized PDF uncertainties. The proposed measurements, when combined with existing and planned world data at higher will provide the theoretically cleanest determination of ΔG(x) in the moderate to high x region, and will provide a necessary complement to the low x program of RHIC‐spin.
The experiment will use both and as a source of polarized deuterons, with approximately equal running times for both to constrain the nuclear effects in the target used by the higher experiments at SLAC and CERN. Both the target and low current (nA scale) 6 GeV electron beam will be longitudinally polarized. Electrons scattered at angles from about 18° to 45° will be detected. Additional measurements at lower will be made using a 4.8 GeV beam energy.