Polarized gas targets

Steffens, E.; Haeberli, W.

doi:10.1088/0034-4885/66/11/r02

Cited by 67 publications

(74 citation statements)

References 152 publications

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“…Much progress is observed in the art of building and maintaining a high degree of polarisation in targets, see, e.g., [271] for the history and [272] for the recent developments.…”

Section: Discussionmentioning

confidence: 99%

Spin observables and spin structure functions: Inequalities and dynamics

et al. 2009

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Model-independent identities and inequalities which relate the various spin observables of collisions in nuclear and particle physics are reviewed in a unified formalism. Their physical interpretation and their implications for dynamical models are also discussed. These constraints between observables can be obtained in several ways: from the explicit expression of the observables in terms of a set of helicity or transversity amplitudes, a non-trivial algebraic exercise which can be preceded by numerical simulation with randomly chosen amplitudes, from anticommutation relations, or from the requirement that any polarisation vector is less than unity. The most powerful tool is the positivity of the density matrices describing the spins in the initial or final state of the reaction or its crossed channels. The inequalities resulting from positivity need to be projected to single out correlations between two or three observables. The quantum aspects of the information carried by spins, in particular entanglement, are considered when deriving and discussing the constraints Several examples are given, with a comparison with experimental data in some cases. For the exclusive reactions, the cases of the strangeness-exchange proton-antiproton scattering and the photoproduction of pseudoscalar mesons are treated in some detail: all triples of observables are constrained, and new results are presented for the allowed domains. The positivity constraints for total cross-sections and for the simplest observables of single-particle inclusive reactions are reviewed. They also apply to spin-dependent structure functions and parton distributions, both integrated or transverse-momentum dependent. The corresponding inequalities are shown to be preserved by the evolution equations of quantum chromodynamics.Inequalities on spin observables 3

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“…Much progress is observed in the art of building and maintaining a high degree of polarisation in targets, see, e.g., [271] for the history and [272] for the recent developments.…”

Section: Discussionmentioning

confidence: 99%

Spin observables and spin structure functions: Inequalities and dynamics

et al. 2009

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“…In the third mechanism the high frequency fields generated by the passage of the very short HERA beam bunches can cause a depolarization in the target atoms under certain conditions [13]. Spin relaxation of atomic hydrogen by wall or spin exchange collisions with various types of wall coatings has been under study for many years in the context of a hydrogen maser for low holding fields [6]. For the HERMES target further studies of the magnetic field dependence of spin relaxation as well as studies of the temperature dependence and density dependence of the transition spectra have been carried out [16,30,31,32,33].…”

Section: Spin Relaxationmentioning

confidence: 99%

“…A target employing a cold storage cell fed by a a polarized atomic beam source was proposed and implemented. Polarized gas targets for storage rings were reviewed recently by Steffens and Haeberli [6].…”

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confidence: 99%

The HERMES polarized hydrogen and deuterium gas target in the HERA electron storage ring

Airapetian¹,

Акопов²,

Akopov³

et al. 2005

Nuclear Instruments and Methods in Physics Research Section A:

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The HERMES hydrogen and deuterium nuclear-polarized gas targets have been in use since 1996 with the polarized electron beam of HERA at DESY to study the spin structure of the nucleon. Polarized atoms from a Stern-Gerlach Atomic Beam Source are injected into a storage cell internal to the HERA electron ring. Atoms diffusing from the center of the storage cell into a side tube are analyzed to determine the atomic fraction and the atomic polarizations. The atoms have a nuclear polarization, the axis of which is defined by an external magnetic holding field. The holding field was longitudinal during 1996-2000, and was changed to transverse in 2001. The design of the target is described, the method for analyzing the target polarization is outlined, and the performance of the target in the various running periods is presented.

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“…A Letter-of-Intent for spin-physics experiments has been submitted by the PAX collaboration [6] to employ a polarized antiproton beam incident on a polarized internal storage cell target [7]. A beam of polarized antiprotons would enable new experiments, such as the first direct measurement of the transversity distribution of the valence quarks in the proton, a test of the predicted opposite sign of the Sivers-function -related to the quark distribution inside a transversely polarized nucleon -in Drell-Yan as compared to semi-inclusive deep-inelastic scattering, and a first measurement of the moduli and the relative phase of the time-like electric and magnetic form factors G E,M of the proton [6].…”

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confidence: 99%

“…The density d t of a storage cell target depends on the flow of atoms q into the feeding tube of the cell, its length along the beam L beam , and the total conductance C tot of the storage cell d t = 1 2 L beam ·q Ctot [7]. The conductance of a cylindrical tube C • for a gas of mass M in the regime of molecular flow (mean free path large compared to the dimensions of the tube) as function of its length L, diameter d, and temperature T , is given by…”

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confidence: 99%

A Method to Polarize Stored Antiprotons to a High Degree

et al. 2005

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Polarized antiprotons can be produced in a storage ring by spin-dependent interaction in a purely electron-polarized hydrogen gas target. The polarizing process is based on spin transfer from the polarized electrons of the target atoms to the orbiting antiprotons. After spin filtering for about two beam lifetimes at energies T ≈ 40−170 MeV using a dedicated large acceptance ring, the antiproton beam polarization would reach P = 0.2 − 0. . Unfortunately, both approaches do not allow efficient accumulation in a storage ring, which would greatly enhance the luminosity. Spin splitting using the Stern-Gerlach separation of the given magnetic substates in a stored antiproton beam was proposed in 1985 [3]. Although the theoretical understanding has much improved since then [4], spin splitting using a stored beam has yet to be observed experimentally.Interest in the polarization of antiprotons has recently been stimulated by a proposal to build a High Energy Storage Ring (HESR) for antiprotons at the new Facility for Antiproton and Ion Research (FAIR) at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt [5]. A Letter-of-Intent for spin-physics experiments has been submitted by the PAX collaboration [6] to employ a polarized antiproton beam incident on a polarized internal storage cell target [7]. A beam of polarized antiprotons would enable new experiments, such as the first direct measurement of the transversity distribution of the valence quarks in the proton, a test of the predicted opposite sign of the Sivers-function -related to the quark distribution inside a transversely polarized nucleon -in Drell-Yan as compared to semi-inclusive deep-inelastic scattering, and a first measurement of the moduli and the relative phase of the time-like electric and magnetic form factors G E,M of the proton [6].In 1992 an experiment at the Test Storage Ring (TSR) at MPI Heidelberg showed that an initially unpolarized stored 23 MeV proton beam can be polarized by spindependent interaction with a polarized hydrogen gas target [8,9,10]. In the presence of polarized protons of magnetic quantum number m = , which eventually caused the stored beam to acquire a polarization parallel to the proton spin of the hydrogen atoms during spin filtering. In an analysis by Meyer three different mechanisms were identified, that add up to the measured result [11]. One of these mechanisms is spin transfer from the polarized electrons of the hydrogen gas target to the circulating protons. Horowitz and Meyer derived the spin transfer cross section p + e → p + e (using c = = 1) [12],where α is the fine-structure constant, a is the anomalous magnetic moment of the proton, m e and m p are the rest mass of electron and proton, p is the momentum in the CM system, a 0 = 52900 fm is the Bohr radius and C 2 0 = 2πη/[exp(2πη) − 1] is the square of the Coulomb wave function at the origin. The Coulomb parameter η is given by η = −zα/v (for antiprotons, η is positive). z is the beam charge number and v the relative velocity of particle and projectile in ...

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Polarized gas targets

Cited by 67 publications

References 152 publications

Spin observables and spin structure functions: Inequalities and dynamics

Spin observables and spin structure functions: Inequalities and dynamics

The HERMES polarized hydrogen and deuterium gas target in the HERA electron storage ring

A Method to Polarize Stored Antiprotons to a High Degree

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