Polarized 3He Target Research Articles

Metastability exchange optical pumping of 3He at low pressure and high magnetic field

Systematic studies on metastability exchange optical pumping of 3He nuclei have been performed at Jefferson Lab using a 1-torr sealed cell at magnetic fields from 2 to 4T. The effects of the discharge intensity, pump laser power and pumping transition schemes on achievable nuclear polarization and pumping rate have been investigated. A maximum steady-state nuclear polarization of about 75% has been obtained. This work provides a baseline for the development of the novel polarized 3He target for CLAS12 at Jefferson Lab.

A concept for polarized [formula omitted]He targets for high luminosity scattering experiments in high magnetic field environments

We present the conceptual design of a polarized 3He target to be used for high luminosity scattering experiments within high magnetic field environments. This two-cell target will take advantage of advancements in optical pumping techniques at high magnetic field to create 60% longitudinally polarized 3He gas in a pumping cell within a uniform magnetic field above 1T. By transferring the polarized gas to a cryogenic target cell, the gas density is increased to create a target thickness suitable for high luminosity applications. We discuss the general design of this scheme, and plans for its application in Jefferson Lab’s CLAS12 detector.

Measurement of the 3He spin-structure functions and of neutron (3He) spin-dependent sum rules at 0.035 ≤ Q2 ≤ 0.24 GeV2

The spin-structure functions g1 and g2, and the spin-dependent partial cross-section σTT have been extracted from the polarized cross-sections differences, Δσ∥(ν,Q2) and Δσ⊥(ν,Q2) measured for the He3→(e→,e′)X reaction, in the E97-110 experiment at Jefferson Lab. Polarized electrons with energies from 1.147 to 4.404 GeV were scattered at angles of 6∘ and 9∘ from a longitudinally or transversely polarized 3He target. The data cover the kinematic regions of the quasi-elastic, resonance production and beyond. From the extracted spin-structure functions, the first moments Γ1‾(Q2), Γ2(Q2) and ITT(Q2) are evaluated with high precision for the neutron in the Q2 range from 0.035 to 0.24GeV2. The comparison of the data and the chiral effective field theory predictions reveals the importance of proper treatment of the Δ degree of freedom for spin observables.

Triple Coincidence Beam Spin Asymmetry Measurements in Deeply Virtual Compton Scattering

The Generalized Parton Distributions (GPDs) provides hitherto the most complete information about the quark structure of hadron. GPDs are accessible through hard-exclusive reactions, among which Deeply Virtual Compton Scattering (DVCS) is the cleanest reaction. A dedicated DVCS experiment on Hydrogen (E00-110) ran in the Hall A at Jefferson Laboratory in Fall 2004. I present here Beam Spin Asymmetry (BSA) results for the ep → epγ reaction studied in the E00-110 experiment with fully exclusive triple coincidence H(e, e'γp ) detection. I present a re-calibration of the electromagnetic calorimeter used to detect the high energy photon. This calibration is necessary to account for the effects of pile-up. The results show a 1-sigma disagreement with the double coincidence H(e, e'γ )p results, I also presents a feasibility study for measurements of neutron GPDs via the 3→He (e, e'γ)ppn reaction on a polarized 3He target with JLab at 12 GeV. These measurements offer the prospect of a determination of all four GPDs.

Precision measurements of [formula omitted] in the deep inelastic regime

We have performed precision measurements of the double-spin virtual-photon asymmetry A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277≤x≤0.548 at an average Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of an A1n zero crossing near x=0.5. We find no evidence of a transition to a positive slope in (Δd+Δd¯)/(d+d¯) up to x=0.548.

Towards an Improved Description of SiDIS by a Polarized 3He Target

The possibility of improving the description of the semi-inclusive deep inelastic electron scattering off polarized 3He, that provides information on the neutron single spin asymmetries, is illustrated. In particular, the analysis at finite momentum transfers in a Poincare' covariant framework is outlined and a generalized eikonal approach to include final state interaction is presented.

Meson photoproduction and baryon resonances at MAMBO experiment

Photoproduction of mesons within the framework of the MAMBO experiment (BGO-OD at Bonn plus MAMI at Mainz) was studied. The results on the operative work of the cryogenic H2/D2 target system during the last commissioning beam times at the March and June 2012 are shown. Investigation of the single charged pion photoproduction was provided using a polarized 3He target at the tagged photon facility of the MAMI accelerator. Unpolarized and helicity dependent cross sections are presented for channels γN → π±X in the Δ(1232) baryon resonance region.

Polarized 3He targets in medium energy physics at MAMI

Experiments with polarized 3He targets at the Mainz Microtron (MAMI) involve double polarized photoabsorption or the extraction of the electric form factor of the neutron Ge,n via electron scattering, respectively. Polarized 3He with an initial polarization of up to 70% at the experimental areas is provided by a polarizer based on the principle of metastability exchange optical pumping (MEOP). In this article both target setups for the photon- and the electron beamlines will be described and a status of the data analysis will be given.

A polarized 3He target for the photon beam at MAMI

A polarized 3He target has been installed for the first time inside the 4π Crystal Ball detector at the tagged photon beam of the MAinz MIcrotron (MAMI). It has been demonstrated that the system works reliably and that the polarization losses during handling of the polarized gas are under control. Initial polarization values up to 70% and total relaxation times up to 20h could be obtained during a first test beam time devoted to the measurement of the double polarized photoabsorption cross-section in the Δ(1232) baryon resonance region.

Energy levels of light nuclei [formula omitted

A compilation of experimental and theoretical information is presented on the mass 3 systems 3n, 3H, 3He and 3p. Emphasis is on advances since the previous evaluation Tilley et al. (1987) [1987TI07] such as, (1) detailed calculations of the vector and tensor analyzing powers for neutron and proton scattering by deuterium which led to the discovery of the still unresolved analyzing power puzzle, (2) the wide spread use of polarized 3He targets which allowed for the experimental study of sum rules among other things and (3) the ability to include the Coulomb interaction in three-body calculations. As stated in the 1987 evaluation and is still the case, there is no firm evidence for either excited states of 3H or 3He nuclei or for the existence of the trineutron or triproton.

Nucleon transversity study using a polarized 3He target in Hall A at JLab

A first measurement of Single target Spin Asymmetry (SSA) from semi-inclusive electro-production of charged pions from a transversely polarized 3He target in Deep-Inelastic-Scattering kinematics was completed in Hall A at Jefferson Lab in early 2009. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. Future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is being planned.

Precision measurement of the neutron- 3He spin-dependent scattering length using neutron interferometry

There is strong theoretical interest in the study of few-body nucleon systems. Experimental measurements of neutron scattering lengths are able to perform precise tests of nucleon–nucleon models. Neutron interferometry provides some of the most precise values of spin-independent neutron scattering lengths, b c , including measurements for n-H, n-D, and n- 3He to better than a percent relative uncertainty. The spin-dependent neutron scattering length, b i , of n- 3He has been measured once before by Zimmer et al. using a polarized 3He target inside a spin echo apparatus. Their result along with measurements of the spin-independent scattering length of n- 3He disagree with current theoretical models. An experiment to measure b i in n- 3He to less than 1% relative uncertainty has been conducted at the Neutron Interferometer and Optics Facility at the National Institute of Standards and Technology using small, flat-windowed 3He cells. This experiment has different systematics than that of the spin echo measurement, and is the first use of a polarized gas target in a neutron interferometer.

Quark-Hadron Duality in Neutron (He3) Spin Structure

We present experimental results of the first high-precision test of quark-hadron duality in the spin-structure function g_{1} of the neutron and 3He using a polarized 3He target in the four-momentum-transfer-squared range from 0.7 to 4.0 (GeV/c);{2}. Global duality is observed for the spin-structure function g_{1} down to at least Q;{2}=1.8 (GeV/c);{2} in both targets. We have also formed the photon-nucleon asymmetry A1 in the resonance region for 3He and found no strong Q2 dependence above 2.2 (GeV/c);{2}.

Nitrogen dilution effect for small angle GDH experiment in JLab Hall-A**Supported by NSFC (10605022), China Postdoctoral Science Foundation and Natural Science Foundation of Anhui Educational Committee(KJ2007B028,2006kj272B)

In the GDH sum rule measurement in JLab Hall-A, to obtain the cross section of electron scattering on polarized 3He and its asymmetry in different helicity states, the dilution effect from unpolarized nitrogen mixed in the polarized 3He target were calculated at different kinematic settings.

Neutron transversity measurement at Jefferson Lab with a polarized 3He target

A first measurement of single target spin asymmetry (SSA) from semi-inclusive electroproduction of charged pions from a transversely polarized 3He target in deep-inelastic-scattering kinematics will take data in Hall A at Jefferson Lab in 2008. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. The experiment will be a coincidence measurement with the BigBite spectrometer detecting the scattered electrons and the left-arm HRS spectrometer detecting the charged pions. The prospect of future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is also discussed in this talk.

A high-pressure polarized 3He gas target for the High Intensity Gamma Source (HI [formula omitted]S) facility at Duke Free Electron Laser Laboratory

A new polarized 3He target has been developed for nuclear physics experiments utilizing the High Intensity Gamma Source (HI γ S) at the Duke Free Electron Laser Laboratory (DFELL). This target is designed for a broad program of physics employing high intensity polarized photons and a polarized 3He target as an effective polarized neutron target. We report the performance of this target based on the technique of spin-exchange optical pumping (SEOP). Due to the significantly larger photon beam size at the HI γ S facility than that of a typical electron beam at electron accelerator laboratories, the HI γ S 3He target contains a larger number of 3He nuclei than any polarized 3He targets reported previously. A target polarization on the order of 33–46% has been achieved from both a regular 3He–Rubidium (Rb) target and a hybrid target which contains a mixture of Rb and potassium. The target polarization has been determined within 3 % using both the Electron Paramagnetic Resonance (EPR) technique and the NMR–AFP (Adiabatic Fast Passage) technique.

Low Q2measurements of the neutron and 3He spin structure

Thomas Jefferson National Accelerator Facility experiment E97-110 was performed to provide a precise measurement of the extended Gerasimov-Drell-Hearn integral and of moments of the neutron and of the 3He spin structure functions. The momentum transfer range 0.02 < Q2 < 0.3 (GeV/c)2 will allow us to test predictions of Chiral Perturbation Theory, and chek the GDH sum rule by extrapolating the integral to the real photon point. The data have been taken in Hall A using a highly polarized electron beam and a polarized 3He target. The status of the data analysis is discussed, and preliminary results are shown.

Q2 evolution of 3He spin structure functions moments

Sum rules offer the opportunity to test our understanding of the structure of a system on general grounds. In this paper we investigate the 3He nucleus using the Gerasimov-Drell-Hearn and Burkhardt-Cottingham sum rules. We have previously used the polarized 3He target measurements to extract the neutron spin structure, our goal here is to investigate rather the 3He nucleus. We have determined for the first time the Q2 evolution of $\Gamma_1(Q^2)=\int_0^{1} g_1(x,Q^2) dx$ and $\Gamma_2(Q^2)=\int_0^1 g_2(x,Q^2) dx$ for 3He in the range 0.1 GeV2 ≤ Q2 ≤ 0.9 GeV2 with good precision. Γ1(Q2) displays a smooth variation from high to low Q2. However, we do not see yet its expected turnover toward the real photon limit value. On the other hand the Burkhardt-Cottingham sum rule holds at all measured Q2s within uncertainties due mainly to cancellations between the elastic, quasielastic and the Δ(1232) resonance contributions.

Neutron spin structure in the valence quark region

I present in this talk the latest results of the neutron spin physics program at Jefferson Laboratory in Hall A using the highly polarized electron beam and a high pressure polarized 3He target. This program includes among others experiment E99-117 in which the neutron spin asymmetry was measured in the deep inelastic region with high precision. This asymmetry is observed, for the first time, to change sign from negative to positive values between 0.3 < x < 0.6. Furthermore we perform a flavor decomposition of the spin-dependent to spin-independent quark distributions ratios in the nucleon and find that relativistic quark models are in better agreement than pQCD fits using the hadron helicity conservation constraint as x ® 1.

Transverse asymmetry of $^3\!\stackrel{\rightarrow}{\rm He}$ and the magnetic form factor of the neutron

Preliminary calculations of the inclusive electromagnetic responses by a polarized 3He target, including final state interaction effects, relativistic kinematics and a relativistic electron-nucleon cross section, are presented. The features of our approach will be briefly illustrated, in order to yield an insight on the model dependence affecting the extraction of the neutron magnetic form factor, G n M , from the inclusive scattering of polarized electrons by a polarized 3He target, recently explored at TJLAB for \(0.1 ~(GeV/c)^2 \le Q^2 \le 0.6 ~(GeV/c)^2\).