Search

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.

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.

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.

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.

We construct the ERBL region of the unpolarized Generalized Parton Distributions using the phenomenological constraints obtained from recent measurements of the ep{yields}e'{gamma}p reaction, from the nucleon form factor data, and from deep inelastic inclusive measurements.

We report on a calculation of the chiral odd generalized parton distributions (GPDs) for non-zero skewness $\zeta$ in transverse and longitudinal position spaces by taking Fourier transform with respect to the transverse and longitudinal momentum transfer respectively using overlaps of light-front wave functions (LFWFs)., Comment: Presented at the 18 th International Spin Physics Symposium, University of Virginia, Charlottesville, Virginia, USA, October 6-11, 2008

Spin dependent sum rules from the current algebra on the null‐plane both from the current commutation and the current anti‐commutation relations are given. By regularizing these sum rules, we explain that the Born term, resonances and the continuum are constrained severely by the sum rules. This fact explains why the sign change of the Gerasimov‐Drell‐Hearn (GDH) sum occurs in the very small Q2. Further, combined with the regularized Burkhart and Cottingham(BC) sum rule, we find that g2ep has a similar behavior as g1ep. The method has been applied to the deuteron target.

We have suggested that a small momentum spread of photoelectrons and high quantum efficiency can be obtained concurrently by a photocathode using a semiconductor with a superlattice instead of a bulk. We have begun to search for the suitable semiconductor material of a superlattice photocathode for maintaining the surface with a negative electron affinity state for a long time. We measured quantum efficiency degradation of photocathodes using GaAs and AlGaAs semiconductors with various electron affinities. The AlGaAs semiconductor had a quantum efficiency lifetime of 10 times long compared with the GaAs semiconductor. We found that the AlGaAs semiconductor was the suitable material for the superlattice photocathode with the surface maintaining a negative electron affinity state for a long time.

The Standard Model is only a few decades old and has been successfully confirmed by experiment, particularly at the high energy frontier. This will continue with renewed vigor at the LHC. However, many important elements of the Standard Model remain poorly understood. In particular, the exploration of the strong interaction theory Quantum Chromodynamics is in its infancy. How does the spin‐1/2 of the proton arise from the fundamental quark and gluon constituents? Can we understand the new QCD world of virtual quarks and gluons in the nucleon? Using precision measurements can we test the limits of the Standard Model and look for new physics? To address these and other important questions, physicists have developed a concept for a new type of accelerator, namely a high luminosity, polarized electron‐ion collider. Here the scientific motivation is summarized and the accelerator concepts are outlined.

Generalised Parton Distributions (GPDs) have grown into one of the main topics in hadron physics. They are playing a central role in the physics of the JLab 12 GeV upgrade as well as in the future physics programme of the COMPASS experiment at CERN. This paper explores the future of GPD measurements in the short, medium and long term. The short term includes the analysis of already existing data from HERMES and JLab and planned measurements at JLab before the 12 GeV upgrade. In the medium term this concerns the JLab programme after the upgrade, measurements at COMPASS and at PANDA/FAIR. The EIC project or possible alternatives form the long term perspective. The main focus of the considerations lies on DVCS measurements and related experiments.

A transmission photocathode was fabricated based on GaAs‐GaAsP strained superlattice layers on a GaP substrate and a 20 kV‐gun was built to generate the polarized electron beams with the diameter of a few micro‐meter. As the results, the reduced brightness of 1.3×107 A/cm2/sr and the polarization of 90% were achieved.

K2CsSb is an attractive photocathode for high current applications. With a quantum efficiency of >4% at 532 nm and >10% at 355 nm, it is the only cathode to have demonstrated an average current of 35 mA in an accelerator environment. We describe ongoing cathode development work for the energy recovery linac being constructed at BNL. Several cathodes have been created on both copper and stainless steel substrates, and their spatial uniformity and spectral response have been characterized. Preliminary lifetime measurements have been performed at high average current densities (>1 mA/mm2).

The ERLP energy recovery linac prototype at Daresbury Laboratory has been rebranded, and is now called ALICE (Accelerators and Lasers In Combined Experiments). This paper gives an overview of the project and its status, outlines some of the challenges experienced during the commissioning of the photoinjector and superconducting accelerating systems, and presents our photoinjector gun commissioning results. An outline is given of the planned photon science program for ALICE, and its under‐pinning role in the EMMA NS‐FFAG project.

DC high voltage photoemission electron guns with GaAs photocathodes have been used to produce polarized electron beams for nuclear physics experiments for about 3 decades with great success. In the late 1990s, Jefferson Lab adopted this gun technology for a free electron laser (FEL), but to assist with high bunch charge operation, considerably higher bias voltage is required compared to the photoguns used at the Jefferson Lab Continuous Electron Beam Accelerator Facility. The FEL gun has been conditioned above 400 kV several times, albeit encountering non‐trivial challenges with ceramic insulators and field emission from electrodes. Recently, high voltage processing with krypton gas was employed to process very stubborn field emitters. This work presents a summary of the high voltage techniques used to high voltage condition the Jefferson Lab FEL photoemission gun.

Electric dipole moments (EDM) experiments are in the research frontier of CP‐violation beyond the standard model (SM). EDM experiments set the current limits on CP‐violation beyond the SM and are most likely to be the first ones to discover if nature has indeed chosen that path.

A Mott polarimeter operating at energies from 1 to 3.5 MeV and at backward scattering angle of 164 degree has been installed at the MAMI accelerator. Its detection system is based on magnetic spectrometers allowing for efficient background suppression. The useful range of primary currents is between 10 nA and 100 μA, hence adapted to the typical beam currents at MAMI. The reduction of analyzing power due to multiple scattering can be calculated directly from the cross sections with the help of Monte Carlo simulation.

We present studies of the transverse momentum dependence of valence quark transverse and longitudinal spin distributions through measurements of spin‐azimuthal asymmetries in Semi‐Inclusive Deep Inelastic Scattering (SIDIS) of kaons using the upgraded JLab 11 GeV polarized electron beam and the CLAS12 detector with longitudinally polarized proton and deuteron targets. Measurements with kaons are complementary to measurements with pions and will provide additional information on the Collins fragmentation mechanism. The PT dependence of the double spin asymmetry provides additional information on the flavor and polarization dependence of transverse‐momentum‐dependent helicity distributions of quarks, which provides complementary to the Single‐Spin Asymmetry (SSA) measurements access to spin‐orbit correlations. The large acceptance of CLAS12 would allow simultaneous detection of scattered electrons and leading hadrons, providing information on the struck quark’s flavor and transverse momentum.

International audience; A polarized 3He ion source has been developed at RCNP for intermediate and high energy spin physics. Though we started with an OPPIS (Optical Pumping Polarized Ion Source), it could not provide highly polarized 3He beam because of fundamental difficulties. Subsequently to this unhappy result, we examined novel types of the polarized 3He ion source, i.e., EPPIS (Electron Pumping Polarized Ion Source), and ECRPIS (ECR Polarized Ion Source) experimentally or theoretically, respectively. However, attainable 3He polarization degrees and beam intensities were still insufficient for practical use. A few years later, we proposed a new idea for the polarized 3He ion source, SEPIS (Spin Exchange Polarized Ion Source) which is based on enhanced spin-exchange cross sections at low incident energies for 3He++Rb, and its feasibility was experimentally examined.Recently, we started a project on polarized 3He gas generated by the brute force method with low temperature (~4 mK) and strong magnetic field (~17 T), and rapid melting of highly polarized solid 3He followed by gasification. When this project will be successful, highly polarized 3He gas will hopefully be used for a new type of the polarized 3He ion source.

Designs of future electron‐ion colliders (EIC) are presently under development at BNL and TJNAF. Polarized beams of electrons, protons and light ions are essential feature of those designs. The talk reviews approaches and techniques used in the EIC designs for delivering high‐energy polarized beams and describes existing challenges.

We present a comprehensive formalism for dilepton production from the collision of two polarized spin−12 hadronsby identifying the general angular distribution of the cross section in combination with a complete set of structure functions. The various structure functions are computed in the parton model approximation where we mainly consider the case when the transverse momentum of the dilepton pair is much smaller than its invariant mass. In this kinematical region dilepton production can be described in terms of transverse momentum dependent parton distributions.

Measurements of beam‐spin asymmetries from semi‐inclusive pion electro‐production in deep inelastic scattering (DIS) have been performed. Data were taken with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 5.7 GeV longitudinally polarized electron beam and an unpolarized liquid hydrogen target. All three pion channels (π+, π0 and π−) were measured simultaneously over a large range of kinematics at the intermediate Q2 range (Q2≈1–3 GeV2). We present our preliminary studies of single‐spin azimuthal asymmetries of the two charged pion channels as functions of z and PT. This new high statistical data will provide important means of studying physics underlying the spin structure of the nucleon.

An ultra cold electron target with a cryogenic GaAs photocathode source, developed for the Heidelberg TSR, delivers electron currents up to a few mA with typical kinetic energies of few keV and provides unprecedented energy resolution below 1 meV for electron‐ion recombination merged‐beam experiments. For the new generation of low‐energy electrostatic storage rings, cold electron beams from a photocathode source can bring additional benefits, improving the cooling efficiency of stored ions and making it possible to cool even heavy, slow molecules by electron beams of energies of only a few eV or even below.

A spinfilter, the most important component of a Lamb‐shift polarimeter, is used to produce a beam of metastable hydrogen (deuterium) atoms in one hyperfine state (HFS)(α1, α2 and together with the Sona transition β3). As function of a magnetic field separated transitions between the 2s1/2 metastable Zeeman states seem to be observable as well as single transitions into the short‐lived 2P1/2 and 2P3/2 states. The Breit‐Rabi diagrams for these states and, therefore, the g factors can be measured with good precision. Furthermore, the hyperfine splittings and the Lamb shift can be observed as well. Application of this method to anti‐hydrogen atoms is suggested.

Transverse-momentum-dependent parton distribution and fragmentation functions describe the partonic structure of the nucleon in a three-dimensional momentum space. They are subjects of flourishing theoretical and experimental activity. They provide novel and intriguing information on hadronic structure, including evidence of the presence of partonic orbital angular momentum., Proceedings of SPIN2008, 6-11 October 2008, Charlottesville, VA, USA

RF photoinjectors for next generation spin‐polarized electron accelerators require photo‐cathodes capable of surviving RF gun operation. Free electron laser photoinjectors can benefit from more robust visible light excited photoemitters. A negative electron affinity gallium arsenide activation recipe has been found that diminishes its background gas susceptibility without any loss of near bandgap photoyield. The highest degree of immunity to carbon dioxide exposure was achieved with a combination of cesium and lithium. Activated amorphous silicon photocathodes evince advantageous properties for high current photoinjectors including low cost, substrate flexibility, visible light excitation and greatly reduced gas reactivity compared to gallium arsenide.

An experiment is under way to prove the feasibility of a super‐conducting RF gun for the production of polarized electrons. We report on the progress of the experiment and on simulations predicting the possibility of success.

The polarized gluon distribution function Δg(x) is presently studied at various deep inelastic scattering and pp experiments. The goal is to eventually determine the contribution of the gluon spin ΔG to the overall spin‐1/2 of the proton, given that the quark spins are known to only contribute at the level of 30%. A review of the present status and prospects will be given.