Measurement Of Beam Polarization Research Articles

Correcting systematic errors in high-sensitivity deuteron polarization measurements

This paper reports deuteron vector and tensor beam polarization measurements taken to investigate the systematic variations due to geometric beam misalignments and high data rates. The experiments used the In-Beam Polarimeter at the KVI-Groningen and the EDDA detector at the Cooler Synchrotron COSY at Jülich. By measuring with very high statistical precision, the contributions that are second-order in the systematic errors become apparent. By calibrating the sensitivity of the polarimeter to such errors, it becomes possible to obtain information from the raw count rate values on the size of the errors and to use this information to correct the polarization measurements. During the experiment, it was possible to demonstrate that corrections were satisfactory at the level of 10 −5 for deliberately large errors. This may facilitate the real time observation of vector polarization changes smaller than 10 −6 in a search for an electric dipole moment using a storage ring.

Measurement of Electron Beam Polarization from Unstrained Bulk GaAs via Two Photon Photoemission

This paper describes measurements of the beam polarization and quantum efficiency for photoemission using two-photon excitation from unstrained bulk GaAs illuminated with pulsed, high intensity 1560nm laser light. Quantum efficiency is linearly proportional to 1560nm peak laser intensity, which was varied in three independent ways, indicating that the emitted electrons are promoted from the valence to the conduction band via two-photon absorption. Beam polarization was measured using a microMott polarimeter, with a value of 16.8(4)% polarization at 1560nm, which is roughly half the measured value of 33.4(8)% using 778 nm light.

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.

Measurement of the neutron beam polarization of BL05/NOP beamline at J-PARC

We measured the neutron beam polarization of the BL05/NOP (Neutron Optics and Physics) beamline at J-PARC with an accuracy of less than 10−3 using polarized 3He gas as a neutron spin analyzer. Precise polarimetry of the neutron beam is necessary to understand the beamline optics as well as for the asymmetry measurements of the neutron beta decay, which are planned in this beamline.

A new method for improving polarizing neutron coatings

Nanolayers with a negative neutron potential at the interfaces of magnetic and nonmagnetic layers in neutron coatings may suppress reflection of neutrons with undesired spin direction by one or even two orders of magnitude [N.K. Pleshanov, Nucl. Instr. and Meth. A 613 (2010) 15]. Thus, nanotechnology opens the possibility to build neutron optical polarizers and analyzers of new generation. New experiments with CoFe/Ti/TiZr/Ti (m=2.5) supermirrors verify the high potential of the method for improving polarizing neutron coatings. Superpolarizing coatings not only will improve the performance and thus widen the range of applications of the polarizing devices but may also be the basis for designing novel neutron instrumentation. The use of transmission polarizers on the basis of a ferromagnetic film and a substrate transparent for neutrons is suggested for precise measurements of beam polarization, flipper efficiencies and contributions of NSF and SF scattering into the portion of neutrons reflected with the undesired spin from the polarizing coating.

Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio

Reflectance versus incidence angle measurements have been performed from 5 to 152 nm on samples of SiC with a different C/Si ratio deposited with rf magnetron sputtering. The optical constants of the material at different wavelengths have been determined by using a curve-fitting technique of reflectance values versus incidence angle. Complementary measurements of the incident beam polarization, film thickness, surface roughness, and stoichiometry were performed to complete the analysis of the samples.

Improved measurement of double helicity asymmetry in inclulsive midrapidityπ0production for polarizedp+pcollisions ats=200 GeV

We present an improved measurement of the double helicity asymmetry for pi(0) production in polarized proton-proton scattering at root s=200 GeV employing the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The improvements to our previous measurement come from two main factors: Inclusion of a new data set from the 2004 RHIC run with higher beam polarizations than the earlier run and a recalibration of the beam polarization measurements for the earlier run, which resulted in reduced uncertainties and increased beam polarizations. The results are compared to a Next to Leading Order (NLO) perturbative Quantum Chromodynamics (pQCD) calculation with a range of polarized gluon distributions.

Accurate measurement of the electron beam polarization in JLab Hall A using Compton polarimetry

A major advance in accurate electron beam polarization measurement has been achieved at Jlab Hall A with a Compton polarimeter based on a Fabry–Perot cavity photon beam amplifier. At an electron energy of 4.6 GeV and a beam current of 40 μ A, a total relative uncertainty of 1.5% is typically achieved within 40 min of data taking. Under the same conditions monitoring of the polarization is accurate at a level of 1%. These unprecedented results make Compton polarimetry an essential tool for modern parity-violation experiments, which require very accurate electron beam polarization measurements.

Project of Neutron Beta-Decay A-Asymmetry Measurement With Relative Accuracy of (1-2)×10(-3).

We are going to use a polarized cold neutron beam and an axial magnetic field in the shape of a bottle formed by a superconducting magnetic system. Such a configuration of magnetic fields allows us to extract the decay electrons inside a well-defined solid angle with high accuracy. An electrostatic cylinder with a potential of 25 kV defines the detected region of neutron decays. The protons, which come from this region will be accelerated and registered by a proton detector. The use of coincidences between electron and proton signals will allow us to considerably suppress the background. The final accuracy of the A-asymmetry will be determined by the uncertainty of the neutron beam polarization measurement which is at the level of (1–2) × 10−3, as shown in previous studies.

Project of neutron β-decay A-asymmetry measurement with relative accuracy of (1–2)×10 −3

We are going to use a polarized cold neutron beam and an axial magnetic field in the shape of a bottle formed by the superconducting magnetic system. Such configuration of magnetic field allows to extract the decay electrons inside a well-defined solid angle with a high accuracy. The electrostatic cylinder with a potential of 25 kV defines the detected region of neutron decays. The protons, which come from this region will be accelerated and registered by a proton detector. The use of coincidences between the electron and proton signals allows in considerably suppressing the background. The final accuracy of A-asymmetry will be determined by the accuracy of the neutron beam polarization measurement, which is at the level of (1–2)×10 −3 as it was shown in previous studies.

Møller polarimetry with atomic hydrogen targets

A novel proposal of using polarized atomic hydrogen gas, stored in an ultra-cold magnetic trap, as the target for electron beam polarimetry based on Moller scattering is discussed. Such a target of practically 100% polarized electrons could provide a superb systematic accuracy of about 0.5% for beam polarization measurements. Feasibility studies for the CEBAF electron beam have been performed. PACS: 07.60.Fs Polarimeters – 29.25.Pj Polarized targets – 67.65.+z Spin-polarized hydrogen and helium

Moller polarimetry with atomic hydrogen targets

A novel proposal of using polarized atomic hydrogen gas, stored in an ultracold magnetic trap, as the target for electron-beam polarimetry based on Moller scattering is discussed. Such a target of practically 100% polarized electrons could provide a superb systematic accuracy of about 0.5% for beam polarization measurements. Feasibility studies for the CEBAF electron beam have been performed.

The GDH-M øller-Polarimeter at ELSA

The design, setup and performance of a new two-arm coincidence, large acceptance and variable energy M øller-Polarimeter used within the GDH-Experiment at the Electron Stretcher Accelerator Facility (ELSA) in Bonn is described. The polarimeter employs a dipole magnetic spectrometer and lead glass detectors to detect both M øller scattered electrons in coincidence. A target system consisting of three different pairs of coils provides the magnetic field to magnetize Vacoflux foils in three different space orientations. This allows to measure all beam polarization components. The variable geometry of the detector system enables adjustments to the kinematic conditions between 0.8 and 3.5 GeV electron beam energy. A large center of mass acceptance of θ ̄ =[65°;115°] provides the measurement of the longitudinal electron beam polarization, for example at 1.9 GeV with a statistical precision of 1% within 10 min ( I e ≈500 pA ). Unprecedented systematic studies of M øller polarimetry as well as direct measurements of the transversal beam polarization components have been performed with this device.

Radiative Corrections and Polarization Effects to Møller Scattering

Polarization effects including radiative corrections have been considered. Exact lowest-order covariant calculation of QED RC has been carried out and detailed numerical analysis is given. The hard photon contribution is calculated analytically. Exponentation procedure is used to consider multi-soft-photon contribution. Numerical analysis is perfomed for beam polarization measurements at Møller polarimeter.

First electron beam polarization measurements with a Compton polarimeter at Jefferson Laboratory

A Compton polarimeter has been installed in Hall A at Jefferson Laboratory. This Letter reports on the first electron beam polarization measurements performed during the HAPPEX experiment at an electron energy of 3.3 GeV and an average current of 40 μA. The heart of this device is a Fabry–Perot cavity which increased the luminosity for Compton scattering in the interaction region so much that a 1.4% statistical accuracy could be obtained within one hour, with a 3.3% total error.

A measurement of the absolute neutron beam polarization produced by an optically pumped [formula omitted] neutron spin filter

The capability of performing accurate absolute measurements of neutron beam polarization opens a number of exciting opportunities in fundamental neutron physics and in neutron scattering. At the LANSCE pulsed neutron source we have measured the neutron beam polarization with an absolute accuracy of 0.3% in the neutron energy range from 40 meV to 10 eV using an optically pumped polarized 3 He spin filter and a relative transmission measurement technique. 3 He was polarized using the Rb spin-exchange method. We describe the measurement technique, present our results, and discuss some of the systematic effects associated with the method.

Polarized Jet Target for Absolute Measurement of RHIC Proton Beam Polarization(5th Session: Strategy for the Long Range Plan,Polarized Partons at High Q^2 Region)

Polarized Jet Target for Absolute Measurement of RHIC Proton Beam Polarization(5th Session: Strategy for the Long Range Plan,Polarized Partons at High Q^2 Region)

Secondary standards for 7Li beam polarimetry

Primary standards for 7Li polarimetry requiring a measurement of the reaction p( 7 Li → ,α) at 0° to the beamline impose excessive radiation damage on the detectors. Eliminating this damage requires the establishment of secondary standards for the online measurement of beam polarization. A complete set of analyzing powers has been obtained for the scattering of polarized 7Li by 4He to the 4.63 MeV excited state of 7Li at a bombarding energy of 31.5 MeV. Certain angles at which both the differential cross-sections and analyzing powers are large are tabulated as secondary polarization standards.

Fabrication and tests of [formula omitted] and [formula omitted] targets for beam polarization measurement

3 He and 2 H targets were fabricated through implantation of 3 He and 2 H ions in 0.2–0.3 mm thick tantalum and titanium foils. The energy of 3 He and 2 H ions was 45–100 and 78 keV, respectively. Ions beams with typical current of 90–300 μA were used for implantation. Stability tests of 3 He and 2 H targets were carried out by monitoring the yield of 3 He d, p 4 He and 2 H d, p 3 H reactions. For the 3 He target, the reaction yield was stable for both tantalum and titanium foils but the most stabilized maximum yield was observed for the 100 keV tantalum target. In the case of 2 H targets, the yield increased with increasing total dose implanted on the target.

An experiment to measure λ= GA/ GV from a combination of angular correlation coefficients in the beta decay of polarized neutrons

A technique is described which allows us to measure the ratio λ= G A/ G V of the weak axial-vector and vector coupling constants in neutron decay without any measurement of the neutron beam polarization. λ is determined from a combination of the parity-odd angular correlations σ → · p → e and σ → · p → ν between the neutron spin σ → and the electron momentum p → e and the anti-neutrino momentum p → ν , respectively, both of which are measured in a single experiment using the same neutron beam. A description of the experiment and the results of the first run at the cold neutron beam facility at the Institut Laue–Langevin are presented.