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Highly spin polarized electron beams produced from GaAs photocathodes within DC high voltage photoguns have been critical to many accelerator-based nuclear and particle physics experiments. This chapter describes polarized photoemission from GaAs, the main requirements for constructing a DC high voltage electron source, and techniques to control and measure the polarization of the electron beam.

Photo-cathodes based on GaAs can be used in photo-electron sources to supply spin-polarized, high-current electron beams for various applications. An activation, adding a thin surface layer, is needed to achieve negative electron affinity (NEA) for such cathodes. Typically, Cs is used in combination with an oxidant. Previous studies have suggested that the addition of Li to this process can increase the quantum efficiency $\eta$ of the cathode as well as the lifetime $\tau$ of the cathode surface layer, both crucial parameters for photo-electron source operation. Charge lifetime studies of bulk GaAs photo-cathodes activated with Cs, NF$_3$, and Li have been conducted using the photo-electron gun of the Upgraded Injector Test Facility (UITF) at the Thomas Jefferson National Accelerator Facility (JLab), extracting beam currents of up to 100 µA. Evidence for significant charge lifetime enhancement with Li in the activation process is found.

This paper presents modeling results of Mie-type GaAs nanopillar array resonant structures and the design of negative electron affinity photocathodes based on Spicer’s three-step model. For direct-bandgap GaAs with high intrinsic absorption coefficient in the 500 ∼ 850 nm spectral range, photoelectrons were found to be highly localized inside the nanopillars near the top and side surfaces where electrons can be efficiently transported and emitted into vacuum, and the light reflectance can be reduced to ∼1% level at resonance wavelengths. Predictions of spectrally resolved photoemission indicate that these nanophotonics resonators, when properly optimized, can increase the photo-electron emission quantum efficiency at resonance wavelengths to levels limited only by the surface-electron escape probability, significantly outperforming traditional flat wafer photocathodes. Ultrafast photoelectric response is also expected from these nanostructured photocathodes due to the much shorter photoelectron transport distance in nanopillars compared to flat wafers. Given these unique optoelectronic properties, GaAs nanophotonic resonance structured photocathodes represent a very promising alternative to photocathodes with flat surfaces that are widely used in many applications today.

A particular type of semiconductor photocathode with a nanostructured surface is shown to increase photoemission yield by more than a factor of three, compared to a flat photocathode. This improvement stems from the excitation of Mie resonances, which serve to reduce reflectivity and enhance light absorption near the surface, where electrons are more efficiently emitted. Nanostructured photocathodes, which can be described as ``electrically bright'' yet ``optically dark'', could benefit many applications, including high-current electron cooling of hadron beams in particle accelerators.

Nuclear physics experiments performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at the Jefferson Lab require a DC high voltage photogun to generate polarized electron beams from GaAs photocathodes. The photogun uses a tapered ceramic insulator that extends into the vacuum chamber and mechanically holds the cathode electrode. Increasing the operating voltage from nominal -130 kV to -200 kV will provide lower beam emittance, better transmission through injector apertures, and improved photocathode lifetime. This desire to increase the photogun operating voltage led to the design of a triple-point-junction shield electrode which minimizes the electric field at the delicate insulator-metal-vacuum interface and linearizes the potential across the insulator, thus reducing the risk of arcing along the ceramic insulator. This work describes the results obtained using COMSOL® electrostatic-field simulation software and presents the high voltage conditioning results of the upgraded -200 kV CEBAF photogun.

The degree of polarization of photoemitted electrons extracted from bulk unstrained GaAs photocathodes is usually considerably less than the theoretical maximum value of 50%, as a result of depolarization mechanisms that originate within the photocathode material and at the vacuum surface interface. This paper provides a comprehensive review of depolarization mechanisms and presents a systematic experimental evaluation of polarization sensitivities to temperature, dopant density, quantum efficiency, and crystal orientation. The highest measured polarization was ∼50%, consistent with the maximum theoretical value, obtained from a photocathode sample with relatively low dopant concentration and cooled to 77 K. In general, measurements indicate electron spin polarization can be enhanced at the expense of photoelectron yield (or quantum efficiency).

A gain-switched diode laser was used to injection modelock a Ti-sapphire laser. The pulse repetition rate of the modelocked Ti-sapphire laser was varied by setting the diode laser pulse repetition rate equal to different multiples of the Ti-sapphire laser cavity fundamental frequency. Pulse repetition rates from 223 MHz (fundamental) to 1.56 GHz (seventh harmonic) were observed. No intracavity modelocking device was required and the Ti-sapphire laser cavity length was not changed. Maximum average output power at 854 nm was 700 mW for all pulse repetition rates when pumped with 6 W from an argon-ion laser. Pulsewidths ranged from 21 to 39 ps (FWHM). Phase noise measurements indicate that timing jitter was 2.5 ps at a pulse repetition rate of 223 MHz. Pulse-to-pulse amplitude fluctuations however, were significant and suggest that active cavity length stabilization may be required for reliable photoinjector applications.

The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6x109 e−, a width of 100 ps and a repetition rate of 2 GHz. A peak current of 10 A in the micro-bunch is a challenge for the surface charge limit of the photo-cathode. Two options are feasible to generate the 2 GHz e− bunch train: 100 ps micro-bunches can be extracted from the photo-cathode either by a 2 GHz laser system or by generating a macro-bunch using a ~200 ns laser pulse and a subsequent RF bunching system to produce the appropriate micro-bunch structure. Recent results obtained by SLAC, for the latter case, are presented. The polarized positron source is based on a positron production scheme in which polarized photons are produced by a laser Compton scattering process. The resulting circularly-polarized gamma photons are sent onto a target, producing pairs of longitudinally polarized electrons and positrons. The Compton backscattering process occurs either in a Compton ring, where a 1 GeV electron beam interacts with circularly-polarized photons in an optical resonator or in a 1.8 GeV Compton Energy Recovery Linac (ERL) or in a 6 GeV Linac with several optical cavities. The undulator scheme is also studied. The nominal CLIC e+ bunch population is 6.7x109 particles per bunch at 200 MeV. The tradeoff between e+ yield and level of polarization is an important topic. The overal l scheme for both polarized electron and positron beams is described.

Exclusive pi0 electroproduction from nucleons at large photon virtuality can be described in terms of Generalized Parton Distributions, particularly the chiral odd subset. Chiral odd GPDs are related to transversity and can be accessed experimentally for various special choices of observables. This is accomplished by choosing C-parity odd and chiral odd combinations of t-channel exchange quantum numbers. These GPDs are calculated in a spectator model, and are constrained by boundary functions. Alternatively, the production amplitudes correspond to C-odd Regge exchanges with final state interactions. The helicity structure of the virtual photoproduction amplitudes provides relations between the partonic description via GPDs and the hadronic, Regge description of C-odd processes, all via quark helicity flip. GPDs, in general, are analytic functions of energy variables. Their integrals over unobservable parton momenta thereby satisfy Dispersion Relations (DR). Using DR's could allow the real part of the amplitudes, the integrated GPDs, to be extracted from the more easily measured imaginary parts. However, at non-zero momentum transfer DRs require integration over unphysical regions of the variables. We show that the relevant unphysical region of the non-forward DRs is considerable. This will vitiate the efforts to avoid the actual measurement of the real parts more directly., 5 pages, 4 figures, Spin 2008 contribution, to be published in Proceedings

The Relativistic Heavy Ion Collider (RHIC) has brought the study of spin effects in hadronic collisions to a new energy regime. In conjunction with other experiments at facilities around the world, much can be learned from the high-energy polarized proton collisions RHIC provides, allowing the collider to serve as a powerful tool to continue to understand the rich subtleties and surprises of spin effects in QCD, some of which were originally discovered more than three decades ago., 6 pages, 7 figures, to appear in the proceedings of the 18th International Symposium on Spin Physics (SPIN2008)

Using as basic observable an angular-integrated asymmetry to be measured in Drell-Yan lepton-pair production at the LHC, we discuss the identification reach on the spin-2 of the lowest-lying Randall-Sundrum resonance predicted by gravity in one warped extra dimension, against the spin-1 and spin-0 hypotheses. Numerical results indicate that, depending on the graviton coupling strength to the standard model particles, such a spin-2 identification can extend up to mass scales of 1.0-1.6 TeV and 2.4-3.2 TeV for LHC integrated luminosities of 10 and 100 fb^{-1}, respectively., 6 pages, 2 figures, talk presented at the 18th International Symposium on Spin Physics (SPIN 2008), Charlottesville, VA, October 6-11, 2008

I examine the uncertainty of perturbative QCD factorization for (un)polarized hadron structure functions in deep inelastic scattering at a large value of the Bjorken variable xB. The focus will be on Target Mass Corrections and Jet Mass Corrections in the collinear factorization framework., 4 pages, 1 figure. Talk given at "SPIN2008", University of Virginia, October 6-11 2008

The nuclear physics experiments at the Thomas Jefferson National Accelerator Facility often require longitudinally polarized electrons to be simultaneously delivered to three experimental halls. The degree of longitudinal polarization to each hall varies as function of the accelerator settings, making it challenging in certain situations to deliver a high degree of longitudinal polarization to all the halls simultaneously. Normally, the degree of longitudinal polarization the halls receive is optimized by changing the initial spin direction at the beginning of the machine with a Wien filter. Herein, it is shown that it is possible to further improve the degree of longitudinal polarization for multiple experimental halls by redistributing the energy gain of the CEBAF linacs while keeping the total energy gain fixed., 4 pages, 3 figures, to appear in the proceedings of the 18th International Symposium on Spin Physics (SPIN2008)

The longitudinal-transverse spin asymmetry $A_{LT}$ in the polarized Drell-Yan process depends on twist-3 quark distributions of nucleon. In addition to the contributions associated with the twist-3 operators, these distributions contain the "Wandzura-Wilczek (WW)" part, which is determined by a certain integral of twist-2 distributions. The recently obtained empirical information on the transversity allows a realistic estimate of the WW contribution to $A_{LT}$ for the polarized $p\bar{p}$ collisions. Our results indicate that rather large $A_{LT}$ ($\sim 10$%) can be observed in the proposed spin experiments at GSI, with novel pattern as a function of dilepton mass compared with $A_{TT}$ and $A_{LL}$., 4 pages, 2 figures; to appear in the proceedings of the 18th International Symposium on Spin Physics (SPIN20008), October 6 - 11, 2008, Charlottesville, Virginia, USA

Measurements of double‐spin asymmetries for single‐inclusive heavy flavor production and for heavy quark correlations are expected to provide valuable information about the spin structure of the nucleon, in particular, the elusive gluon polarization. We discuss progress towards a versatile parton‐level Monte‐Carlo code for the production and decay of heavy quarks in longitudinally polarized proton‐proton collisions at next‐to‐leading order accuracy of Quantum Chromodynamics (QCD). First phenomenological studies are presented for BNL‐RHIC.

AIP Conference Proceedings - AIP, 2009. - ISBN - doi:10.1063/1.3215743 18th International Spin Physics Symposium, SPIN 2008, Charlottesville, Virginia, USA, 6 Oct 2008 - 11 Oct 2008; AIP conference proceedings 1149, 709-714 (2009). doi:10.1063/1.3215743, Measurements at future electron accelerators will require unprecedented precision in the determination of electron beam polarization. Existing and novel electron beam polarization measurement schemes are examined, and ideas are being presented of how to to achieve sub‐1% precision in polarization determination., Published by Inst., Melville, NY

A quasi particle model for the diquark is suggested in an analogy with the quasi particle model in the crystal lattice. The magnetic moments of the exotics and the non exotic members of the baryon antidecuplet have been estimated considering the diquark‐diquark‐ antiquark picture for the baryons. The masses of the baryon antidecuplet have also been estimated. The results are found to be in agreement with the existing theoretical and experimental results.

Neural network (NN) algorithms have been recently applied to construct Parton Distribution Function (PDF) parametrizations, providing an alternative to standard global fitting procedures. Here we explore a novel technique using Self‐Organizing Maps (SOMs). SOMs are a class of clustering algorithms based on competitive learning among spatially‐ordered neurons. We train our SOMs with stochastically generated PDF samples. On every optimization iteration the PDFs are clustered on the SOM according to a user‐defined feature and the most promising candidates are used as a seed for the subsequent iteration using the topology of the map to guide the PDF generating process. Our goal is a fitting procedure that, at variance with the standard neural network approaches, will allow for an increased control of the systematic bias by enabling user interaction in the various stages of the process.

Hadron physics aims at a fundamental understanding of all particles and their interactions that are subject to the strong force. Experiments using hadronic probes could contribute to shed light on open questions on the structure of hadrons and their interaction as well as the symmetries of nature. The COoler SYnchrotron COSY at the Forschungszentrum Julich accelerates protons and deuterons with momenta up to 3.7 GeV/c. The availability of both an electron cooler as well as a stochastic beam cooling system allows for precision measurements, using polarized proton and deuteron beams in combination with polarized Hydrogen or Deuterium targets.This contribution summarizes the ongoing physics program at the COSY facility using ANKE, WASA and TOF detector systems with polarized hadronic probes, highlighting recent results and outlining the new developments.

We study the single transverse-spin asymmetry for open charm production in the semi-inclusive lepton-hadron deep inelastic scattering (SIDIS) and $pp$ collision. Within collinear factorization approach, we find that the asymmetry is sensitive to the twist-3 trigluon correlation functions in the proton. With a simple model for the trigluon correlation functions, we estimate the asymmetry in SIDIS for both COMPASS and eRHIC kinematics, as well as in $pp$ collision at RHIC energy. We discuss the possibilities of extracting the trigluon correlation functions in these experiments., Comment: 4 pages, 2 figures; to appear in the proceedings of the 18th International Symposium on Spin Physics (SPIN2008), October 6 - 11, 2008, Charlottesville, Virginia, USA

spink is a spin tracking code for spin polarized particles. The code tracks both trajectories in 3D and spin. It works using thick element modeling from MAD and thin element modeling based on the BMT equation to track spin. The code is written in Fortran and typically runs on a Linux platform, either sequentially or MPI‐parallel.

A new Quantum Chromodynamics (QCD) analysis framework of fragmentation and parton distribution functions has been developed by the TTAP (Team Towards global Analysis of the Proton and partons) collaboration. The Mellin transformation technique used in the analysis framework improved the computing speed, which allows us to perform further detailed analysis.

In this paper the method of beam depolarization compensation during spin resonance crossing is developed. This method is based on the restoration of the spin adiabatic invariant after the spin resonance crossing. The case when the restoration of spin adiabatic invariant occurs due to multiple crossing of the resonance effective area is considered. At the same time it is necessary to provide the certain difference of spin phases between the moments of crossing of the resonance effective area. The conditions of beam polarization preservation when the resonance effective area is repeatedly crossed are obtained. Numerical examples are presented.

The present status of the longitudinal polarized parton densities (PDFs) and the contribution of their first moments to the nucleon spin is discussed. Special attention is paid to the role of higher twist effects in determining the PDFs and to the polarized strange quark and gluon densities, which are still not well determined from the present data., Comment: 6 pages, 5 figures; to appear in the proceedings of the 18th International Symposium on Spin Physics (SPIN20008), October 6 - 11, 2008, Charlottesville, Virginia, USA

We have developed a prototype DC photoemission electron gun for a future energy recovery linac (ERL) based light source in Japan. The prototype gun is operated at up to 250 kV and is designed to deliver up to 50 mA beam current. A diagnostic beam line for emittance and bunch length measurements has been constructed. We have also designed a new 500 kV DC gun which is capable of producing up to 10 mA electron current with emittance lower than 1 mm‐mrad. The high voltage terminal will be isolated by ten ceramics stacked in series. The new gun will satisfy performance required as an injector for the compact ERL, which will be constructed at KEK site as a prototype of the future ERL light source.

In calculating the strengths of depolarizing resonances it may be convenient to reformulate the equations of spin motion in a coordinate system based on the actual trajectory of the particle, as introduced by Kondratenko, rather than the conventional one based on a reference orbit. It is shown that resonance strengths calculated by the conventional and the revised formalisms are identical. Resonances induced by radiofrequency dipoles or solenoids are also treated; with rf dipoles it is essential to consider not only the direct effect of the dipole but also the contribution from oscillations induced by it.

We complement the concept of the invariant spin field (ISF) in storage rings by defining the invariant polarisation‐tensor field (ITF) for spin‐1 particles and we suggest how to calculate it by stroboscopic averaging or directly from the invariant spin field. The ITF the ISF are used to construct equilibrium spin density‐matrix fields, and thereby offer a clean framework for describing equilibrium ensembles of spin‐1 particles such as deuterons in storage rings.

The injector for the ALICE machine (Accelerators and Lasers In Combined Experiments) at Daresbury Laboratory is based around a 350 kV DC photocathode electron gun. An upgrade is proposed to introduce a load‐lock GaAs photocathode preparation facility to allow rapid transfer of photocathodes to the gun without breaking the vacuum system. In the current design this requires side‐loading of the photocathodes into the cathode ball. An alternative is to relocate the ceramic insulator vertically which will allow back‐loading and also backillumination of the photocathodes. 3D electrostatic simulations of the gun chamber are presented for both options along with 3D beam dynamic simulations for an off‐axis photocathode, introduced to increase photocathode lifetime by reducing damage by ion backbombardment. Beam dynamic simulations are also presented for the entire injector beamline as well as for a proposed extension to the injector beamline to include a diagnostic section.

The completion of the planned 12 GeV upgrade at Jefferson Lab will open a new avenue for precision studies of the high‐x structure of the nucleon through parity‐violation in deeply‐inelastic scattering (PV‐DIS). PV‐DIS would be a clean technique for studying quark‐level charge symmetry violation, probing higher‐twist effects and for a measurement of the structure function ratio d/u at high x. In addition to these topics in hadronic physics, these measurements would also provide access to a linear combination of the poorly measured axial electron‐quark weak couplings C2u and C2d, thus provide an important test of the electroweak Standard Model.

Polarized {sup 3}He obtained from metastability exchange optical pumping is used for various double polarized experiments at the Mainz Microtron (MAMI). At the experimental area more than 70% initial target polarization is available. Besides a description of the target setup and its performance under electron beam conditions, the status of the polarized {sup 3}He target for the tagged photon beam at MAMI will be given.

We have developed a 200 keV polarized electron source for generating high bunch charge of >3.2 nC within ∼1 ns bunch duration for the International Linear Collider (ILC) and >7.7 pC within 30 ps bunch duration for a basic source study of an Energy Recovery Linac (ERL). In order to improve gun operation voltage and an operational lifetime, we have employed new electrode materials of molybdenum and titanium to eliminate field emission dark current, and restructured a beam transport vacuum systems. As a beam generation for the ERL, bunch charge of up to 28 pC was generated by irradiating with sliced laser pulse trains. The details are described in this report.

Ion pumps are common vacuum pumps on DC high voltage photoguns and baked-accelerator beamlines. Commercial ion pump power supplies provide a measure of the electrical current drawn by the pump, but typically have resolution to only {approx}0.1 uA, which corresponds to pressure {approx}10{sup -9} Torr, a value considerably higher than the minimum pressure required by photoguns and nearby beamline. This submission describes a very sensitive in-house-built ion pump power supply with current monitoring capability good to less than 1 nA, and corresponding pressure in the low-minus;10{sup -11} Torr range. Besides providing 'free' pressure monitoring on a scale equivalent to the best available commercial pressure gauges, the ion pump power supply also serves as a sensitive diagnostic for detecting field emission from the photogun cathode electrode and bad electron beam orbits that could diminish photogun operating lifetime. Since its inception, this ion pump power supply has become an invaluable tool for operating the CEBAF polarized electron source. It is also a very useful low-cost diagnostic for ultrahigh vacuum studies in the laboratory.

We present first results from our analysis of the most general quark‐quark correlator of the nucleon, which can be parameterized in terms of so‐called generalized transverse momentum dependent parton distributions. These results include the first complete parameterization of the nucleon GPDs and TMDs as well as new results on possible nontrivial relations between them.

It is a challenge to generate full charge electrons from the electron sources without compromising polarization for the proposed ILC and CLIC. It is essential to advance polarized photocathodes to meet the requirements. SLAC has worldwide unique dedicated test facilities, Cathode Test System and dc‐Gun Test Laboratory, to fully characterize polarized photocathodes. Recent systematic measurements on a strained‐well InAlGaAs/AlGaAs cathode at the facilities show that 87% polarization and 0.3% QE are achieved. The QE can be increased to ∼1.0% with atomic hydrogen cleaning. The surface charge limit at a very low current intensity and the clear dependence of the polarization on the surface charge limit are observed for the first time. Ongoing programs to develop photocathodes for the ILC and CLIC are briefly introduced.

Since the introduction of hyperpolarized 3He and 129Xe as gaseous MRI contrast agents more than a decade ago, a rich variety of imaging techniques and medical applications have been developed. Magnetic resonance imaging of the inhaled gas depicts ventilated lung airspaces with unprecedented detail, and allows one to track airflow and pulmonary mechanics during respiration. Information about lung structure and function can also be obtained using the physical properties of the gas, including spin relaxation in the presence of oxygen, restricted diffusion inside the alveolar airspaces, and the NMR frequency shift of xenon dissolved in blood and tissue.

We use the ponderomotive potential of the RF field to study the motion of ions in an RF gun. We apply this method to the BNL 1/2‐cell SRF photogun and demonstrate that a significant portion of the ions produced in the gun can reach the cathode if no special precautions are taken. Also, we propose simple mitigation techniques that can reduce the rate of ion bombardment.

Part of the future polarization program performed at the Bonn accelerator facility ELSA will rely on precision Compton polarimetry of the stored transversely polarized electron beam. Precise and fast polarimetry poses high demands on the light source and the detector which were studied in detail performing numerical simulations of the Compton scattering process. In order to experimentally verify these calculations, first measurements were carried out using an argon ion laser as light source and a prototype version of a counting silicon microstrip detector. Calculated and measured intensity profiles of backscattered photons are presented and compared, showing excellent agreement. Background originating from beam gas radiation turned out to be the major limitation of the polarimeter performance. In order to improve the situation, a new polarimeter was constructed and is currently being set up. Design and expected performance of this polarimeter upgrade are presented.

Jefferson Lab uses 100 kV DC high voltage photoguns with high polarization strained superlattice GaAs photocathodes to achieve electron beam polarization over 80%. The photocathode is subjected to back‐bombardment from ionized residual gasses during operation. We present surface analyses using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) to characterize photocathode damage.

Experiment E97‐110 was performed at the Thomas Jefferson National Accelerator Facility in Hall A to provide a precise measurement of the moments of the neutron and 3He spin structure functions. A longitudinally‐polarized electron beam was scattered from a longitudinally or transversely polarized 3He target. The extended Gerasimov‐Drell‐Hearn integral and other moments of the neutron and 3He spin structure functions were extracted at very low momentum transfers (0.02

Cross Insulated Core Transformer (CCT) technology improves on Insulated Core Transformer (ICT) implementations. ICT systems are widely used in very high voltage, high power, power supply systems. In an ICT transformer ferrite core sections are insulated from their neighboring ferrite cores. Flux leakage is present at each of these insulated gaps. The flux loss is raised to the power of stages in the ICT design causing output voltage efficiency to taper off with increasing stages. KSI’s CCT technology utilizes a patented technique to compensate the flux loss at each stage of an ICT system. Design equations to calculate the flux compensation capacitor value are presented. CCT provides corona free operation of the HV stack. KSI’s CCT based High Voltage power supply systems offer high efficiency operation, high frequency switching, low stored energy and smaller size over comparable ICT systems.

SVT Associates, in collaboration with SLAC, has investigated two novel photocathode design concepts in an effort to increase polarization and quantum efficiency. AlGaAsSb/GaAs superlattice photocathodes were fabricated to explore the effect of antimony on device operation. In the second approach, an internal electrical field was created within the superlattice active layer by varying the aluminum composition in AlGaAs/GaAs. A 25% increase in quantum efficiency as a result of the gradient was observed.

We studied spin manipulation of 1.85 GeV/c polarized deuteron beam stored in COSY obtaining a spin‐flip efficiency of 97±1%. We first discovered experimentally and then explained theoretically interesting behavior of the deuteron tensor polarization. We, for the first time, studied systematically spin resonance strengths induced by rf dipoles and solenoids. We found huge disagreements between the strengths measured in controlled Froissart‐Stora sweeps and the theoretical values calculated using the well‐known formulae. These data instigated re‐examination of these formulae. We tested Chao’s proposed new matrix formalism for describing the spin dynamics due to a single spin resonance, which may be the first fundamental improvement of the Froissart‐Stora equation in that it allows analytic calculation of the beam polarization’s behavior inside a resonance. Our measurements of the deuteron’s polarization near and inside the resonance agreed precisely with the Chao formalism’s predicted oscillations. We teste...

Measurements involving the gluon spin, ΔG(x, t) and the corresponding asymmetry, A(x,t) = ΔG(x,t)/G(x,t) play an important role in quantitative understanding of proton structure. We have modeled the asymmetry perturbatively and calculated model corrections to obtain information about non‐perturbative spin‐orbit effects. These models are consistent with existing COMPASS and HERMES data on the gluon asymmetry. The Jz = 12 sum rule is used to generate values of orbital angular momentum at LO and NLO. For models consistent with data, the orbital angular momentum is small. Our studies specify accuracy that future measurements should achieve to constrain theoretical models for nucleon structure.