Proton Polarization Measurements Research Articles

Systematic error analysis in the absolute hydrogen gas jet polarimeter at RHIC

The Polarized Atomic Hydrogen Gas Jet Target polarimeter (HJET) is operated at the Relativistic Heavy Ion Collider (RHIC) since 2004 to measure the absolute polarization of each colliding proton beam. Polarimeter detectors and data acquisition were upgraded in 2015 to increase the solid angle, energy range, and to improve the energy and time resolution. These upgrades along with an improved beam intensity and polarization allowed us to greatly reduce the statistical and systematic errors for the proton polarization measurements in RHIC Runs15 (Ebeam=100GeV) and 17 (255GeV). For a typical 8 h RHIC store, the measured proton beam average polarization was about Pbeam∼55±2.0stat±0.3syst%. The elastic pp analyzing power, AN(t)∼0.04, was determined with a precision of about |δAN(t)|∼0.0002 in the momentum transfer squared range 0.001<−t<0.020GeV2. In this paper we present a detailed systematic error analysis of the polarization measurements at HJET. Perspectives of using the HJET based absolute polarimeters in the future Electron Ion Collider (EIC) will be also discussed.

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 proton polarization in the 208Pb(d, p) 209Pb reaction at an incident energy of 20 MeV

Angular distribution measurements of proton polarization in the 208Pb(d, p) 209Pb reaction to the ground g 9/2 state were made at an incident deuteron energy of 20 MeV using a high efficiency proton polarimeter. Distorted wave Born approximation analysis and continuum discretized coupled channel analysis were performed on the data and compared with measurements of the angular distribution of the vector analyzing power for the same reaction. The result of the calculations predict that the angular distribution of the vector analyzing power should be similar to that of the polarization. However, the experimental data gives different angular distributions. The measured vector analyzing power is well reproduced by the calculations, while the polarization is not well reproduced.

Measurement of proton and nitrogen polarization in ammonia and a test of equal spin temperature

The 1996 data taking of the SMC experiment used polarized protons to measure the spin-dependent structure function g 1 of the proton. Three liters of solid granular ammonia were irradiated at the Bonn electron linac in order to create the paramagnetic radicals which are needed for polarizing the protons. Proton polarizations of ±(90±2.5)% were routinely reached. An analysis based on a theoretical line shape for spin-1 systems with large quadrupolar broadening was developed which allowed the nitrogen polarization in the ammonia to be determined with a 10% relative error. The measured quadrupolar coupling constant of 14N agrees well with earlier extrapolated values. The polarization of the nitrogen nuclei was measured as a function of the proton polarization in order to provide a test of the equal spin temperature (EST) hypothesis. It was found to be closely valid under the dynamic nuclear polarization conditions with which the protons are polarized. Large deviations from EST could be induced by cross relaxing the proton and nitrogen spin systems at low fields. Nitrogen polarizations up to 40% were reached by these means.

Ion sources at the KVI (abstract)

At the KVI there are presently four ion sources available: POLIS, for polarized protons and deuterons, to be injected in the new superconducting cyclotron AGOR ECRIS3, to produce highly charged ions for AGOR, ECRIS4, to produce highly charged ions for the Atomic and Surface Physics research facility (essentially a copy of ECRIS3), and CUSP, for high intensity AGOR beams of protons, deuteron, or alpha particles. We will report here on the performance and status of POLIS and ECRIS3. POLIS is an atomic beam type polarized ion source, according to the well known scheme with a cryo cooled dissociator, watercooled hexapole magnets, “strong field” and “weak field” radio frequency (rf) transitions for hydrogen and deuterium, and a 2.45 GHz electron cyclotron resonance (ECR) type ionizer. The source was constructed in a joint effort with the Forschungszentrum Karlsruhe, Cyclotron department. The ionizer section was modified and can be operated up to 40 kV. Following successful tests and deuteron polarization measurements at low energies, POLIS was connected to AGOR in November 1996. Most parts are now adapted to the AGOR-KVI control system. The first experiments with proton beams (190 MeV) from AGOR were done with polarized beams. As a consequence, the first measurement of proton polarization could be done only during these experiments, and all efforts to improve the polarization had to take place also during experiments. Efforts to get the weak field transition in operation have given a present best value of polarization of 70%±0.5% of the theoretical value. This value is deduced from an assumed analyzing power of the applied reaction. The strong field unit is not perfect; the best value which has been observed is 56%±0.5%. However, the difference between the given polarizations could be the result of a systematic error in the measurement of polarization “zero.” The output of POLIS is in the order of 50 μÅ. The running time is usually 1–2 weeks (with nozzle at 53 K) until the dissociator and nozzle become contaminated; with a nitrogen layer (nozzle at 35 K) the polarization degree tends to be higher, but the running time is reduced to 3–5 days. POLIS has been in operation during more than 70% of the 33 weeks scheduled for experiments with AGOR since November 1996. Present activities concentrate on the improvement of the strong field unit, increasing the ionizer efficiency and the running time. ECRIS3 is a room temperature ECR ion source, with rf and gas feed according to the CAPRICE scheme. Its performance has been reported earlier (RIKEN 95). Gas mixing is important for the production of highly charged ions. Like in other sources, the anomaly for oxygen isotopes has also been measured. One new observation concerning gas mixing, in particular for the production of argon beams, is the following: For medium charge states, e.g., Ar8+, there is a slight preference for helium as a mixing gas, as compared to pure argon. In fact, oxygen is not good here. On the contrary, for high charge states like Ar14+, oxygen is a very good mixing gas, helium has only a small effect, but the best results have been obtained with isotopic O18 as a mixing gas. Recently, the same has been observed with CAPRICE 10 GHz at CEN-Grenoble, and to some extent with ECRIS4.

A high precision Q-meter for the measurement of proton polarization in polarised targets

Abstract A Q-meter system for the measurement of the proton polarisation in polarised targets is described, in which the real part of the output signal, rather than its magnitude, is used to obtain the polarisation. It uses a radio frequency phase sensitive detection technique. Calculations are presented which show that a very high linearity is obtained with this system when used under the experimental conditions obtained in typical polarised targets. A description of the electronic circuits used to implement such a system is given, together with measurements of their performance.

Polarization observables?,P y ,T 1 in the reaction $$\vec \gamma d \to \vec pn$$ at photon energies between 200 and 600 MeV and dibaryon resonances

The polarization observables Σ,Py,T1,Py⊥,Py∥ are derived in proton polarization measurements of the\(\vec \gamma d \to \vec pn\) reaction, using a linearly polarized photon beam of energies between 300 and 600 MeV for c.m.s. proton emission angles of 90° and 120°. A multipole analysis is performed in the framework of the gauge-invariant pole model considering theγN→πN amplitudes and the deuteron structure without dibaryon resonances and with different sets of isovector and isoscalar dibaryon resonances. It is shown that the inclusion of dibaryon resonances substantially improves agreement with experimental data.

Proton polarization in deuteron photodisintegration in the Δ(1232)-resonance region

We report the results from measurements of proton polarization P, in the γ+D→p+n reaction at photon energies ranging from 200 to 350 MeV. The data obtained are compared with the measured analysing power A, of the reverse reaction and with model calculations. The assumption of the dominant contribution of isobar configurations in this region is on the whole confirmed by the present proton polarization measurements.

A silicon polarimeter for proton energies below 4 MeV

A polarimeter using a silicon detector as the analyser has been designed for measurements of proton polarization over a range of energies from 2.6 to 4.0 MeV. In this range the effective analyzing power varies smoothly between −0.2 and −0.7. The mean registration efficiency of the polarimeter is about 2.5 × 10 −6.

Proton polarization in deuteron disintegration by linearly polarized photons and dibaryon resonances

The paper deals with proton polarization measurements in the deuteron disintegration γd → pn by linearly polarized photons and a theoretical description of the measured data on differential cross sections with unpolarized particles (dσ/dΩ) 0, the asymmetry due to the photon linear polarization Σ, the proton polarization P y , and the asymmetry due to the deuteron vector polarization T. At E γ = 300, 350, 400, 500 MeV and θ = 90° (θ being the angle between the c.m.s. proton and photon momenta), under the same experimental conditions, Σ, P y and the double-polarization observable, viz the T 1, asymmetry of the proton polarization with linearly polarized photons, are obtained. It is shown that the model without dibaryons fails to provide a satisfactory description of the collection of experimental data on ( dσ/ dΩ) 0, Σ, P y, T in the photon energy range between 160 and 400 MeV. The consideration of unit-isospin dibaryons 1 D 2(J π = 2 +), 3 F 3(J π = 3 −), 1 S 0(J π = 0 +), 3 P 1(J π = 1 −) essentially improves the agreement with experiment.

Irradiated ammonia (NH 3) as target material for polarized proton targets

Dynamic proton polarization measurements in irradiated NH 3 were performed at 1 K and 0.5 K in a magnetic field of 2.5 T. The paramagnetic radicals in the frozen ammonia beads were created by irradiation with 20 MeV electrons from the injection linac of the Bonn 2.5 GeV electron synchrotron. During the irradiation the ammonia beads were cooled in liquid argon at about 90 K. Electron paramagnetic resonance measurements identified the created radicals as NH 2. Samples of NH 3 yielded a maximum proton polarization of 35% at 1 K and 66% at a temperature of 0.5 K. They exhibited short polarization build-up times of 2 min at 1 K and 9 min at 0.5 K. The radiation resistance of the polarization of NH 3 is better than that of butanol. The radiation damage can be repaired by annealing.

Facility for the measurement of proton polarization in the range 50–70 MeV

A proton polarimetry facility based on silicon analyzers combined with high-purity germanium detectors is described. The scattering efficiency is 1.5 × 10−5 at 60 MeV with an effective analyzing power of 0.71 and the energy resolution is about 300 keV fwhm. The facility has succeeded in measuring the depolarization in p−13C elastic scattering separated clearly from inelastic events. In order to use a silicon detector as an analyzer target, measurements of cross sections and analyzing powers have been performed at proton energies of 65, 60, 55, 50 and 45 MeV.

Further measurement of proton polarization in deuteron photodisintegration at photon energies between 400 and 650 MeV: Possible evidence for dibaryon resonances

The proton polarization in deuteron photodisintegration has been measured at photon energies between 400 and 650 MeV at c.m. angles between 45° and 135°. To explain the polarization and differential cross-section data consistently, we have introduced dibaryon resonances and performed a partial-wave analysis at photon energies between 350 and 700 MeV. It has been shown that the existence of at least two dibaryon resonances is required in this energy range: one at ∼2380MeV with I( J P ) = 0(3 +) or 0(1 +), and the other at ∼2260 MeV with I( J P ) = 1(3 −) or 1(2 −).

Facility for the measurement of proton polarization in nuclear reactions

A polarimetry facility based on high resolution and high efficiency silicon polarimeters with on-line particle identification is described. It has proven its capability to measure polarizations in ( 3 He, p ) reaction with cross section levels of 40 μb/sr.

The crystal magnetic field in a proton-polarized lanthanum magnesium nitrate single crystal

Knowledge of the crystal magnetic fieldHc is necessary for proton polarization measurements in polarized targets by the internal field method [1, 2]. Because of the importance of lanthanum magnesium nitrate (LMN) single crystals for low-energy polarized proton targets [3],Hc has been calculated for LMN on the basis of new x-ray diffraction data. We find thatHc=ApP2(cosθ), wherep is the proton polarization andP2 the second Legendre polynomial depending onθ, the angle between crystalc-axis and external magnetic field, andA is a constant characteristic for LMN. Our result\(A = - \left( {0.242 \pm \begin{array}{*{20}c} {0.028} \\ {0.090} \\ \end{array} } \right) Oe\) leads to a field only about half as large as expected according to previous assumptions. The difference is due to the markedly different proton positions, revealed by the x-ray structure analysis.

The reaction3He(d, p)4He with a polarized target

The left-right asymmetry for the3He(d, p)4He reaction has been measured with a polarized3He target at a bombarding energy of 12 MeV. The experimental results are compared with proton polarization measurements for unpolarized target and beam. The construction of the optically pumped3He target is described. A special design has been chosen to overcome the difficulty that the target contamination caused by the bombarding particles destroys the polarization. The target can easily be purified without removing it from the experimental set-up.

Measurements of recoil proton polarization in photoproduction of pions off the nucleus12C

Preliminary results on the measurements of recoil photon polarization in photoproduction of pions off protons and neutrons bound in the nucleus carbon-12 at 0.8 and 0.9 GeV maximum energy for incident photons are presented. (JFP)

Dynamic Nuclear Polarization Investigations of (C6H5)3AsCH3+TCNQ Single Crystals

AbstractThe paramagnetic states occurring in the anion radical salt As‐TCNQ are not merely characterized by the value of their spin quantum numbers. The doublet states are strongly localized and have a static dipole coupling, with the protons. The thermal‐excited triplet states, however, show a great mobility even at low temperatures and me in fluctuating scalar interaction with the protons. These results are obtained from measurements of dynamic proton polarization.

Vector analysing power of the (d, p) reaction on 28Si, 52Cr and 88Sr AT 12 MeV

The vector analysing power of the (d, p) reaction leading to several states of the final nuclei 29Si, 53Cr and 89Sr was measured using a 12.3 MeV vector polarized deuteron beam. The data exhibit a distinct j-dependence which is in accordance with known spin and parity assignments of the final states. Present experimental results are compared with existing measurements of proton polarization. An extensive DWBA analysis confirms an applicability of the method for calculating the vector analysing power for most reactions involving orbital momentum transfer l = 1, 2, 3. It is less satisfactory in cases with l = 0. The effects of optical model parameters and particularly the spin-orbit distortion in the deuteron and proton channel are discussed.

Polarization and spin-correlation parameters in proton- 3He elastic scattering at 19.4 MeV

Using a polarized proton beam and a polarized 3He target, measurements of proton polarization, 3He polarization, and the spin correlation parameters A yy and A xx in p- 3He elastic scattering at 19.4 MeV have been obtained in a range of laboratory scattering angles from 38° to 115°. A phase-shift analysis, which is consistent with analyses at lower energies, is presented