Proton Polarization Research Articles

Precision, absolute proton polarization measurements at 200 MeV beam energy

A new polarimeter for absolute proton beam polarization measurements at 200 MeV to accuracy better than ±0.5% has been developed as a part of the RHIC polarized source upgrade. The polarimeter is based on the elastic proton-carbon scattering at 16.2° angle, where the analyzing power is close to 100% and was measured with high accuracy. The elastically and in-elastically scattered protons are clearly identified by the difference in the propagation through variable copper absorber and energy deposition of the protons in the detectors. The elastic scattering polarimeter was used for calibration of a high rate inclusive 12° polarimer for the on-line polarization tuning and monitoring. This technique can be used for accurate polarization measurements in energy range of at least 160–250 MeV.

SINGLE-SPIN AZIMUTHAL ASYMMETRY IN EXCLUSIVE ELECTROPRODUCTION OF ɸ AND ω VECTOR MESONS ON TRANSVERSELY POLARIZED PROTONS

The hard exclusive electro-production of ɸ and ω vector mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target. The single-spin azimuthal asymmetry with respect to the transverse proton polarization was measured.

Polarization observables in deuteron photodisintegration below 360 MeV

High precision measurements of induced and transferred recoil proton polarization in d(γ→,p→)n have been performed for photon energies of 277–357 MeV and θcm=20°–120°. The measurements were motivated by a longstanding discrepancy between meson–baryon model calculations and data at higher energies. At the low energies of this experiment, theory continues to fail to reproduce the data, indicating that either something is missing in the calculations and/or there is a problem with the accuracy of the nucleon–nucleon potential being used.

Nucleon polarizabilities from deuteron Compton scattering within a Green’s function hybrid approach

We examine elastic Compton scattering from the deuteron for photon energies ranging from zero to 100MeV, using state-of-the-art deuteron wave functions and NN potentials. Nucleon-nucleon rescattering between emission and absorption of the two photons is treated by Green’s functions in order to ensure gauge invariance and the correct Thomson limit. With this Green’s function hybrid approach, we fulfill the low-energy theorem of deuteron Compton scattering and there is no significant dependence on the deuteron wave function used. Concerning the nucleon structure, we use the chiral effective field theory with explicit $ \Delta$ (1232) degrees of freedom within the small-scale expansion up to leading-one-loop order. Agreement with available data is good at all energies. Our 2-parameter fit to all elastic $ \gamma$ d data leads to values for the static isoscalar dipole polarizabilities which are in excellent agreement with the isoscalar Baldin sum rule. Taking this value as additional input, we find $ \alpha_{E}^{s}$ = (11.3±0.7(stat)±0.6(Baldin)±1(theory)).10-4 fm^3 and $ \beta_{M}^{s}$ = (3.2±0.7(stat)±0.6(Baldin)±1(theory)).10-4 fm^3 and conclude by comparison to the proton numbers that neutron and proton polarizabilities are the same within rather small errors.

ChemInform Abstract: An Intramolecular Hydrogen-Bonded System with Large Proton Polarizability - A Model with Regard to the Proton Pathway in Bacteriorhodopsin and Other Systems with Collective Proton Motion.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Features of chemical nuclear polarization (CNP) in photolysis of 8-hydroxy-6-phenyldibenzofurandeuteromethanol system

In this work photolysis of 8-hydroxy-6-phenyldibenzofuran (PDF) was carried out in benzene, acetonitrile, and water media directly in the probe of the NMR spectrometer (all of the solvents were deuterated). The H NMR spectra do not differ virtually from the spectra recorded in the dark conditions. On adding methanol into the reaction mixture, the strong negative polarization is observed on the meta-protons (7.9) of the initial compound (PDF) (δ7 = 7.46 ppm; δ9 = 7.18 ppm). Proton polarization peaks with polarization coefficient 700–750 were maximum at 20% (by volume) concentration of alcohol. After a transition period (15–20 s) the signal value remains constant and continues on the same level for many hours. Thus, a virtually constant radio-frequency radiation takes place in the course of the reversible photochemical reaction. On switching off the light the proton polarization in the initial PDF disappears.

Hydrogen spectroscopy with a Lamb-shift polarimeter

A Lamb-shift polarimeter, which has been built for a fast determination of the polarization of protons and deuterons of an atomic-beam source and which is frequently used in the ANKE experiment at COSY-J\"ulich, is shown to be an excellent device for atomic-spectroscopy measurements of metastable hydrogen isotopes. It is demonstrated that magnetic and electric dipole transitions in hydrogen can be measured as a function of the external magnetic field, giving access to the full Breit-Rabi diagram for the $2^2S_{1/2}$ and the $2^2P_{1/2}$ states. This will allow the study of hyperfine structure, $g$ factors and the classical Lamb shift. Although the data are not yet competitive with state-of-the-art measurements, the potential of the method is enormous, including a possible application to anti-hydrogen spectroscopy.

Proton hyperpolarisation preserved in long-lived states

The polarisation of abundant protons, rather than dilute nuclei with low gyromagnetic ratios, can be enhanced in less than 10 min using dissolution DNP and converted into a long-lived state delocalised over an ensemble of three coupled protons. The process is more straightforward than the hyperpolarisation of heteronuclei followed by magnetisation transfer to protons.

Predictive powers of chiral perturbation theory in Compton scattering off protons

We study low-energy nucleon Compton scattering in the framework of baryon chiral perturbation theory (B$\chi$PT) with pion, nucleon, and $\Delta$(1232) degrees of freedom, up to and including the next-to-next-to-leading order (NNLO). We include the effects of order $p^2$, $p^3$ and $p^4/\varDelta$, with $\varDelta\approx 300$ MeV the $\Delta$-resonance excitation energy. These are all "predictive" powers in the sense that no unknown low-energy constants enter until at least one order higher (i.e, $p^4$). Estimating the theoretical uncertainty on the basis of natural size for $p^4$ effects, we find that uncertainty of such a NNLO result is comparable to the uncertainty of the present experimental data for low-energy Compton scattering. We find an excellent agreement with the experimental cross section data up to at least the pion-production threshold. Nevertheless, for the proton's magnetic polarizability we obtain a value of $(4.0\pm 0.7)\times 10^{-4}$ fm$^3$, in significant disagreement with the current PDG value. Unlike the previous $\chi$PT studies of Compton scattering, we perform the calculations in a manifestly Lorentz-covariant fashion, refraining from the heavy-baryon (HB) expansion. The difference between the lowest order HB$\chi$PT and B$\chi$PT results for polarizabilities is found to be appreciable. We discuss the chiral behavior of proton polarizabilities in both HB$\chi$PT and B$\chi$PT with the hope to confront it with lattice QCD calculations in a near future. In studying some of the polarized observables, we identify the regime where their naive low-energy expansion begins to break down, thus addressing the forthcoming precision measurements at the HIGS facility.

Non-spherical proton shape and hydrogen hyperfine splittingThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at University of Windsor, Windsor, Ontario, Canada on 21–26 July 2008.

We show that the non-spherical charge distribution of the proton manifests itself in hydrogen hyperfine splitting as an increase (in absolute value) of the proton Zemach radius and polarization contributions.

Small-angle neutron scattering study of dynamically polarized polyethylenes

Abstract We carried out a small-angle neutron scattering (SANS) study of dynamically polarized polyethylene (PE) samples doped with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). The transmission of the PE with almost fully polarized neutrons (98.5%) increased with increasing the proton polarization, P . The incoherent scattering cross section decreased with increasing P . The effect of P on the polarized neutrons’ transmission and the incoherent scattering cross section agreed well with the theory. The q -dependence of the coherent scattering, which reflects a two-phase structure of PE composed of crystalline and amorphous domains, was kept unchanged by the proton polarization, but the intensity increased by a factor of 3 and 6 for P =+23% and −23%, respectively. The results mean that the contrast between the two phases was successfully enhanced by a dynamic nuclear polarization (DNP) technique. However, the enhancement is only 1/13–1/16 of the enhancement calculated by assuming a homogeneous polarization through the PE sample. The discrepancy suggests that P in amorphous domains (25%) should be higher than that in crystalline domains (22%) by 3%, which in turn may suggest the partial depolarization of proton spins on the way of the spin diffusion from amorphous domains, where TEMPO radicals localize, to crystalline domains.

Dynamic nuclear polarization system for the SANS-J-II spectrometer at JAEA

We have developed a dynamic nuclear polarization (DNP) system for the SANS-J-II spectrometer at the JRR-3 atomic research reactor of Japan Atomic Energy Agency (JAEA). The DNP system is composed of a split-type horizontal superconducting magnet (3.3 T), a Gunn oscillator as a microwave source (94 GHz), and a cryostat (1.2 K). In particular, a sample cell with ∅40 in inner diameter and the magnet with a field homogeneity of 5×10−5 in a volume of ∅25 mm×8 mm were employed to polarize samples with a diameter of ∅20 mm for the ultra small-angle scattering experiment using the magnetic lens installed at the SANS-J-II spectrometer [S. Koizumi, H. Iwase, J. Suzuki, T. Oku, R. Motokawa, H. Sasao, H. Tanaka, D. Yamaguchi, H.M. Shimizu, T. Hashimoto, J. Appl. Crystallogr. 40 (2007) s474]. We obtained the proton polarization |P|=32% in the polyethylene doped with 2,2,6,6-tetra-methyl-piperidine-1-oxyl (TEMPO).

Three-nucleon force effects in theH1(d→,p→p)nreaction at 135 MeV/nucleon

The deuteron to proton polarization transfer coefficients ${K}_{\mathit{yy}}^{{y}^{'}}$ and ${K}_{y}^{{y}^{'}}$ together with the deuteron analyzing powers are measured in three coplanar configurations of the deuteron-proton breakup reaction with a 135-MeV/nucleon polarized deuteron beam at the RIKEN Accelerator Research Facility. The data are compared with theoretical predictions based on exact solutions of the three-nucleon ($3N$) Faddeev equations with high-precision nucleon-nucleon ($\mathit{NN}$) forces, alone or combined with two $3N$ force (3NF) models, the $2\ensuremath{\pi}$-exchange Tucson-Melbourne${}^{'}(99)$ (${\mathrm{TM}}^{'}99$) and Urbana IX. Large 3NF effects have been found for all the measured observables. Predicted effects are supported by the data, with the exception of the vector analyzing power ${A}_{y}^{d}$. For this observable, theory based on only $\mathit{NN}$ forces is sufficient to explain the data. The behavior of the breakup analyzing powers is found to be different from the corresponding observables in elastic nucleon-deuteron scattering.

Double resonance experiments in low magnetic field: Dynamic polarization of protons by 14N and measurement of low NQR frequencies

The possibilities of dynamically polarizing proton spin system via the quadrupole 14N spin system in low magnetic field are analyzed. The increase of the proton magnetization is calculated. The polarization rate of the proton spin system is related to the transition probabilities per unit time between the 14N quadrupole energy levels and proton energy levels. The experiments performed in 1,3,5-triazine confirm the results of the theoretical analysis. A new double resonance technique is proposed for the measurement of nuclear quadrupole resonance frequencies ν Q of the order of 100 kHz and lower. The technique is based on magnetic field cycling between a high and a low static magnetic field and observation of the proton NMR signal in the high magnetic field. In the low magnetic field the quadrupole nuclei and protons resonantly interact at the proton Larmor frequency ν H = ν Q/2. The quadrupole nuclei are simultaneously excited by a resonant rf magnetic field oriented along the direction of the low static magnetic field. The experimental procedure is described and the sensitivity of the new technique is estimated. Some examples of the measurement of low 14N and 2H nuclear quadrupole resonance frequencies are presented.

Dynamic nuclear polarization of high- and low-crystallinity polyethylenes

We carried out a dynamic nuclear polarization (DNP) study of high- and low-crystallinity polyethylene films defined as HPE and LPE, respectively, which were doped with TEMPO (2,2,6,6-tetra-methyl-piperidine-1-oxyl) by the same amount (1×1019spins/cm3). The proton polarization of 32±3% was obtained for LPE and 23±4% for HPE at 3.35T and 1.4K. With increase in the concentration of TEMPO, the electron spin resonance (ESR) linewidth of TEMPO in HPE increased more steeply than that in LPE, indicating that TEMPO did not incorporated into the crystalline part, and was localized only at the amorphous part, hence the local concentration of TEMPO in the amorphous regions of HPE varied more steeply than that of LPE with the net amount of TEMPO fed into the film. We suggest that the smaller nuclear polarization for HPE is related to the localization of TEMPO in the smaller amorphous regions.

Polarization of the large COMPASS 14NH3 target

The COMPASS experiment in the CERN M2 beam line is using 1508 cm3 granular solid 14NH3 as polarized proton target material to study the nuclear spin with deep inelastic scattering of polarized muons. The target consists of 2.5 T solenoid and 0.63 T dipole magnets, microwave cavity and large dilution cryostat. Continuous wave NMR is used to determine the polarization of the nuclei that are polarized with dynamic nuclear polarization method using 4 mm microwaves. Determination of the target proton polarization with thermal equilibrium NMR signals at temperatures 1.0 - 1.6 K is discussed.

Phenomenological insight into the space-like proton elastic form factor using the deuteron impulse approximation

The analysis of the JLab proton polarization data on the ratio {mu}{sub p}G{sub Ep}(t)/G{sub Mp}(t) in the framework of the unitary and analytic model of nucleon electromagnetic structure implicates surprising nondipole behavior of the proton electric form factor G{sub Ep}(t) in the space-like region with the zero around the momentum transfer squared value t=-Q{sup 2}=-13 GeV{sup 2}. This result differs from the unpolarized cross-section measurements giving the dipole behavior of G{sub Ep}(t) by means of the Rosenbluth technique. Recent investigations demonstrate that inclusion of a two-photon mechanism could solve the problem, which plays an important role for the unpolarized cross section, but it is negligible for the polarization ratio. Here, investigating a size of a difference in a prediction of the deuteron elastic structure functions A(t),B(t) by both, the nondipole and the old dipole, behaviors of G{sub Ep}(t) in space-like region through the nonrelativistic impulse approximation, we have come to the conclusion that the two-photon mechanism plays much less of a role for the unpolarized electron-deuteron elastic scattering than for the unpolarized electron-proton elastic scattering.

RHIC polarized proton status and plan

The Relativistic Heavy Ion Collider (RHIC) as the first high energy polarized proton collider has been providing collisions at a beam energy of 100 GeV since 2001. Equipped with two full Siberian snakes in each ring, polarization is preserved during the acceleration from injection to 100 GeV with careful control of the betatron tunes and the vertical orbit distortions. In the latest RHIC polarized proton run in 2006, a peak luminosity of 28 × 1030cm−2 s−1 with 60% average polarization at store was achieved. During the run, RHIC also demonstrated its capability in providing a combination of polarized proton collisions with longitudinal polarization and radial polarization were provided to the STAR experiment and PHENIX experiment with the local spin rotators installed on either side of the STAR detector and PHENIX detector. Polarized protons were also first accelerated to 250 GeV at the end of RHIC 2006 run with a 46% polarization measured at this new store energy in one of the RHIC accelerators. Currently, the luminosity in RHIC is limited by the beam-beam effect. The plan is to triple the luminosity. Plans to achieve polarized proton collision at 250 GeV are also reported.

Recent Progress in the Dynamic Nuclear Polarization of Solid Deuterated Butanol Targets

Polarized solid targets have been used in nuclear and particle physics experiments since the early 1960s, and with the development of superconducting magnets and 3He/4He dilution refrigerators in the early 1970s, proton polarization values of 80–100% have been achieved routinely in various target materials at two standard magnetic field and temperature conditions (2.5 T, <0.3 K and 5 T, 1 K). Due to the much lower magnetic moment of the deuteron compared with that of the proton, deuteron polarization values have been considerably lower, typically 30–40% in chemically doped alcohols (d-butanol), 40–45% in radiation-doped ammonia (ND3), and 50–55% in irradiated lithium-deuteride. Now, however, research at the University of Bochum – including systematical electron spin resonance (ESR) investigations in order to study the properties of the paramagnetic dopants (i.e., their ESR line width) – is yielding alcohol and diol materials with deuteron polarizations as high as 80%.

Dynamic nuclear polarization of small labelled molecules in frozen water–alcohol solutions

In recent years methods of creating ‘hyperpolarized’ substances have gained considerable attention in biomedical magnetic resonance and dynamic nuclear polarization (DNP) is one of the most promising, especially for imaging applications. Here we present results of DNP studies on protons and 13C nuclei in frozen solutions of sodium acetate and glycine, dissolved in water–ethanol and water–glycerol, doped with TEMPO free radicals and EHBA-CrV complexes. Up to 14% 13C polarization and close to 50% proton polarization were achieved at ∼1.2 K in a magnetic field of ∼3.5 T under irradiation with ∼97 GHz microwaves, which corresponds to an enhancement of more than 15 000 with respect to thermal equilibrium polarization in a 9.4 T magnet at room temperature. For all investigated samples the main DNP mechanism was found to be thermal mixing. The absolute polarization values achieved are mainly depending on the type of solvent, the water–alcohol ratio, its degree of deuteration and the concentration of paramagnetic centres. This allows application of the so-established sample preparation and DNP procedure to other molecules in future experiments. Two further examples of DNP of molecules in solution underline the general applicability of the method to a wide variety of organic compounds.