Search

Measurement of single (SSA) and double spin asymmetries (DSA) in semi-inclusive DIS reactions using polarized targets provide a powerful method to probe transverse momentum dependent parton distribution functions (TMDs). In particular, the experimentally measured SSA on nucleon targets can help in extracting the transversity and Sivers distribution functions of u and d-quarks. Similarly, the measured DSA are sensitive to the quark spin-orbital correlations, and provide an access to the TMD parton distribution function (g1T ). A recent experiment conducted in Hall-A Jefferson Lab using transversely polarized ³He provide first such measurements on "effective" neutron target. The measurement was performed using 5.9 GeV beam from CEBAF and measured the target SSA/DSA in the SIDIS reaction ³He↑ (e, e' π±)X. The kinematical range, x = 0.19 - 0.34, at Q² = 1.77 - 2.73 (GeV/c)², was focused on the valence quark region. The results from this measurement along with our plans for future high precision measurements in Hall-A are presented. [ABSTRACT FROM AUTHOR]

The double spin asymmetry ALT for 3He was measured for the first time at Jefferson Lab Hall A in the semi-inclusive 3He↑(→,e[acute_underaccent]π+/-X reactions, using a 6 GeV polarized electron beam on a transversely polarized 3He target. The produced charged pions were detected in coincidence with the scattered electrons by the high-resolution spectrometer and the BigBite spectrometer, respectively. The kinematic coverage was focused on the valence quark region, x ∼ 0.13-0.41, Q2 ∼ 1.31-3.10 (GeV/c)2. When combined with the world data, this new data will provide constraints on the g1Tq distribution functions, which describe the longitudinal polarization of quarks in a transversely polarized nucleon. The status of the current analysis and the preliminary results are presented. [ABSTRACT FROM AUTHOR]

Polarized 3He targets have been widely used in nuclear and particle physics experiments to study neutron structure in the spin degree of freedom, as most of the 3He spin is carried by the unpaired neutron. The Spin-Exchange Optical Pumping (SEOP) process is used in Jefferson Lab Hall A to polarize its 3He target. In recent years, both the performance and corresponding polarimetry of such a target have been greatly improved. Several experiments recently carried out in Hall A have achieved record high figure of merit using this target. [ABSTRACT FROM AUTHOR]

It is an experimental evidence that all baryons are created polarized from unpolarized p—nucleus collisions. So far, the origin of this polarization remains unexplained in spite of the experimental evidences accumulated in the past thirty years. Up to these days, Λ0 is the most studied baryon for polarization, for it is copiously produced in p—nucleus collisions at the energies of the principal high energy physics accelerators of the world. This paper is an overview of the experimental evidences accumulated on the polarization of Λ0 from unpolarized exclusive pp collisions as function of xF, PT, and M(Λ0K+) in the past fifteen years inside Fermilab e690 experiment, in the particular reactions pp→pΛ0K0π+, pp→ppΛ0Λ-0, pp→pΛ0K+, produced at 800 GeV. [ABSTRACT FROM AUTHOR]

The COMPASS experiment has been taking data since 2002. Its polarized target was upgraded during the 2005 CERN SPS shutdown. With the high acceptance magnet we obtained +56.0% and -53.0% deuteron polarization in 6LiD. In 2007 ammonia is used as a proton target which has a relaxation time of ∼4000 h at 0.6 T. [ABSTRACT FROM AUTHOR]

Examples are given of dynamically polarized targets in use today and how the subsystems have changed to meet the needs of todays experiments. Particular emphasis is placed on target materials such as ammonia and lithium deuteride. Recent polarization studies of irradiated materials such as butanol, deuterated butanol, polyethylene, and deuterated polyethylene are presented. The operation of two non-DNP target systems as well as applications of traditional DNP targets are briefly discussed. [ABSTRACT FROM AUTHOR]

The production of tensor polarization in an unpolarized deuteron beam after passage through unpolarized carbon targets, which includes the effect of deuteron spin dichroism, has been observed for the first time. Theoretical background, experimental setup, and results of the experiment are presented. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

In the spring of 2006, Jefferson Lab experiment 02–013 successfully collected data to measure the neutron elastic form factor GEn at the four-momentum transfer values Q2 = 1.2, 1.8, 2.6, and 3.5(GeV/c)2. This measurement of the quasi-elastic semi-exclusive 3Hvector e(evector ,e′n) reaction used the polarized CEBAF beam (Pb ≈ 85%) and a highly polarized 3He target (Pt ≈ 50%). Neutrons were detected in a large array of scintillators with an efficiency of 35–40%. The electrons were detected by the newly commissioned BigBite spectrometer with a solid angle of 76msr and a momentum resolution of 1%. From the transverse asymmetry of the cross section, GEn will be extracted. A statistical accuracy of ΔGEn/GEn ≈ 0.14 is expected. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Vector analyzing power was measured for the proton elastic scattering on 6He at 71 MeV/u. We applied a solid polarized proton target, which was operated in a low magnetic field of 88 mT and at high temperature of 100 K, to a radioactive-isotope beam experiment. Low energy recoil protons were successfully detected due to the modest operation conditions of the target. Selection of pvector +6He elastic scattering events was clearly carried out with detected protons. Absolute values of the analyzing power were determined for the first time. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

At the SpinLab laboratory (University of Ferrara, Italy), a three stage cooling system was installed along the dissociator tube of an atomic beam source (ABS). With this tool, it is possible to observe correlations between the measured temperatures and the atomic beam intensity. The existence of such correlations is suggested by the larger intensity of the RHIC ABS, the only other source with additional cooling stages. An increased intensity at lower cooling temperatures was observed in SpinLab, while no change in the beam’s velocity distribution was observed. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The setup of the polarized target for the spin filtering studies at COSY and AD will be shown together with the planned measurements. The target fulfills all the requirements coming from the experiment. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The design and operation of the polarized hydrogen and deuterium gas target internal to the HERA 27.5 GeV polarized electron ring is described. The target has been employed to measure the spin structure of the nucleon, using beams of electrons and positrons, both polarized and unpolarized. The various components of the target system will be described and the operation summarized. The target was removed in November 2005, after 10 years of successful running. It will be utilized in preparation of the PAX experiment at FAIR (Darmstadt) for spin filtering studies of protons and antiprotons. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Due to its spin structure polarized 3He serves as a suitable substitute for a polarized neutron target. The 3He-gas is polarized at pressures of about 1 mbar via the metastability exchange optical pumping method. After compression to 5 bar and filling to target cells the gas is used as a target for scattering experiments at the electron accelerator MAMI in Mainz. The polarizer can provide polarized 3He with a polarization of more than 70 % at a yield of 2 bar·1/h. The total relaxation time of the target cells in the electron beam is about 50 h. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

For future few-nucleon interactions studies with polarized beams and targets at COSY-Jülich, a polarized internal storage cell gas target was implemented at the magnetic spectrometer ANKE in summer 2005. First commissioning of the polarized Atomic Beam Source (ABS) at ANKE was carried out and some improvements of the system have been done. At the same time, storage-cell tests to determine the COSY beam dimensions have been performed. In February 2005, a first storage cell prototype was implemented. It was made from an aluminum foil covered by a special PTFE suspension. In November 2005, tests were carried out with a storage cell using a polarized hydrogen beam from the ABS, electron cooling and stacking injection of the COSY beam at different deflection angles of the ANKE spectrometer magnet. An average target polarization of P=0.44±0.03 (November 2005 beamtime) was measured, while we expected about P=0.51–0.55 due to the availability of rf-transition units in the ABS. The jet target thickness was measured as (1.5±0.1)·1011 atoms/cm2. In March 2006, measurements with unpolarized protons at T=831 MeV and an unpolarized H2 beam injected from a gas feeding system into the aluminum storage cell were carried out. The analysis of the pp → ppπ0 and pp → pnπ+ reactions showed that events from the extended target can be clearly identified in the ANKE forward detector system. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Since the polarization relaxation time of polarized targets quickly decreases with increasing temperature, the choice of size and shape of the target, and in particular of its thickness, must be based on the evaluation of the temperature profile inside the target for the specific experimental conditions. This evaluation is particularly important when designing a target for scattering experiments for which a high beam intensity and collimation are required, as localized beam heating causes inhomogeneous depolarization of the target. The efficiency of the thermal transport in the target material for dissipating the heat deposited by the beam toward the cryogenic bath depends not only on the thermal conductivity of the material itself but it is also strongly limited by the Kapitza thermal impedance on the boundary. We present a new finite element model to study the thermal transport properties as a function of size and shape of the target and of the thermal conductivity parameters. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We discuss the status and prospects of an experimental program of parity-violating asymmetry measurements in the scattering of longitudinally polarized electrons off unpolarized fixed targets. One thrust is the measurements of nucleon neutral weak form factors at intermediate four-momentum transfer (0.1 < Q2 < 1) (GeV/c)2 which provide information about the role of virtual strange quarks on the charge and current distributions inside nucleons. A new topic is the elastic neutral weak amplitude from scattering off a heavy spinless nucleus, which is sensitive to the presence of a neutron skin. Finally, we discuss the neutral current elastic amplitude at very low Q2, which allows precision measurements of the weak mixing angle at low energy and is thus sensitive to new physics at the TeV scale. The physics implications of recent results, potential measurements from experiments under construction as well as new ideas at future facilities are discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have measured the spin structure functions g[sub 2][sup p] and g[sub 2][sup d] over the kinematic range 0.02 ≤ x ≤ 0.8 and 0.7 ≤ Q2 ≤ 20 GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and 6LiD targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d[sub 2][sup p] and d[sub 2][sup n] are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

During the last years the HERMES collaboration has measured inclusive and semi-inclusive double-spin asymmetries in deep inelastic scattering on polarised hydrogen and deuterium targets in the kinematic range 0.02 < x < 0.6 and 1 GeV2 < Q2 < 10 GeV2. With the installation of a Ring Imaging Cˇerenkov detector in 1998, charged pions and kaons could be identified and for the first time allowed to separately determine the polarisations of all valence and sea quark distributions. Of special interest are the difference between the polarisation of the u- and d- sea quarks where various phenomenological models predict a significant flavour asymmetry and the polarisation of the strange quarks which have been suggested to have a negative contribution to the nucleon spin. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

At PSI polarized scintillating targets are available since 1996. Proton polarizations of more than 80%, and deuteron polarizations of 25% in polystyrene-based scintillators can be reached under optimum conditions in a vertical dilution refrigerator with optical access, suited for nuclear and particle physics experiments. New preparation procedures allow to provide very thin polarizable scintillating targets and widen the spectrum of conceivable experiments. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

The dynamically polarized solid state nucleon target has played a very important role in the experiments to study the spin structure of the nucleon which have been carried out over the last two decades. The quality of the data obtainable is critically dependent the properties of the target materials used. The developments which have been made to improve both target materials and overall target performance during this period are reviewed. The effects that these developments have had on present and future experiments is discussed. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

During the RHIC Au-Au runs in 2000 and 2001 as well as in the polarized proton run in 2001 no transverse damping system existed. To overcome residual injection jitter and to maintain transverse beam emittances a transverse injection damping system is foreseen for the 2002/2003 run. This report describes the realization of the injection damping system and outlines the future upgrade into a bunch-to-bunch transverse instability damping system, which is expected to be required for increasing bunch intensities. [ABSTRACT FROM AUTHOR]

We study parametrization of polarized parton distribution functions in the α[sub s] leading order (LO) and in the next-to-leading order (NLO). Prom xsup2; fitting to the experimental data on A[sub 1], optimum polarized distribution functions are determined. The quark spin content ΔΣ is very sensitive to the small-x behavior of antiquark distributions which suggests that small-x data are needed for precise determination of ΔΣ. We propose three sets of distributions and also provide FORTRAN library for our distributions. [ABSTRACT FROM AUTHOR]

Experiments utilizing polarized internal gas targets will be reviewed. Since a few years these targets are being used at electron and proton machines and the progress made in operating these targets on a routinely basis has been pronounced. This paper will focus on experimental aspects, such as the design and construction of storage cells and different methods employed for polarimetry. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

High energy polarized beam collisions will open up the unique physics opportunities of studying spin effects in hard processes. However, the acceleration of polarized beams in circular accelerators is complicated by the numerous depolarizing spin resonances. Using a partial Siberian Snake and a rf dipole that ensure stable adiabatic spin motion during acceleration has made it possible to accelerate polarized protons to 25 GeV at the Brookhaven AGS. Full Siberian Snakes and polarimeters are being developed for RHIC to make the acceleration of polarized protons to 250 GeV possible. Spin rotators around two RHIC interaction regions will allow for the collision of longitudinally polarized protons at the STAR and PHENIX detectors. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]