T-violation neutron experiment and polarized3He

An experimental scheme of the spin detailed balance in polarized neutron transmission through a polarized nuclear target is discussed for the T-violation test. The value of the spin detailed balance is estimated by using the data of the scattering amplitudes. The nuclear polarizations of proton,³He and¹³⁹La are discussed for the T-violation experiment.     

Nuclear spin species,spin statistical weights and rovibronic tunnelling splittings of non-rigid water hexamer

Powerful multinomial generating functions together with the character table of the six-dimensional hyperoctahedral wreath product group S₆[S₂] of the non-rigid water hexamer are employed to obtain the nuclear spin species, nuclear spin multiplets and the total nuclear spin statistical weights of the rovibronic-tunnelling levels for both deuterated and regular forms. The methods are composed of algebraic generating functions involving 531,441 nuclear spin functions for (D₂O)₆ in a group of 46,080 operations and 65 irreducible representations of the S₆[S₂] group. Although the deuterated form of the non-rigid water hexamer possesses nuclear spin populations in 58 of the 65 possible symmetries of tunnelling levels, for the regular water hexamer only 23 of the 65 symmetries are populated with nuclear spin functions. The tunnelling splitting correlations of rovibronic levels of the water hexamer have been obtained from the Saykally's semi-rigid (G₄) model to the fully non-rigid limit (G₄₆₀₈₀). The computed nuclear spin statistical weights for protonated form of (H₂O)₆ call for a reinterpretation of the previous assignment of the observed spectra. The results can also be applied to enumerate the hyperfine patterns using the nuclear spin multiplets and intensities in semi-rigid to fully non-rigid limits.     

Present status of the 129Xe comagnetometer development for neutron EDM measurement

A ¹²⁹Xe comagnetometer designed for the measurement of neutron electric dipole moment (nEDM) as precisely as 1 × 10^?27e cm is presented. Highly nuclear spin polarized ¹²⁹Xe are introduced into an EDM cell where the ¹²⁹Xe spin precession is detected by means of the two-photon transition. The geometric phase effect (GPE) which generates the false nEDM was quantitatively discussed and the systematic error of nEDM from the GPE was estimated considering the buffer-gas suppression due to Xe atomic collisions. Research and development are in progress to construct the ¹²⁹Xe comagnetometer with a field sensitivity of 0.3 fT. At present, about 70 % nuclear spin polarized ¹²⁹Xe atoms have been obtained in a spin exchange opitial pumping cell, that are in the process of being transferred into the EDM cell via a cold trap.     

Quasi-free (e,e'N) reactions on polarized targets

The quasi-free nucleon knockout by the electron is studied in the general case of both polarized beams and polarized targets. The coincidence cross section involves nine structure functions which give detailed information on the nuclear current operator. However, their measurement requires out-of-plane experiments. Results on ⁷Li and ³⁹K obtained within the nonrelativistic DWIA framework indicate that some structure functions, very sensitive to final state interactions, are probably too small to be separated. On the other side, cross sections, asymmetries and electron polarization ratios in coplanar kinematics have measurable size. They add complementary information to the unpolarized quasi-free nucleon knockout because of their sensitivity to spin degrees of freedom which are averaged out without target polarization. In the particular case of a nucleon ejected along the direction of the momentum transfer from a target with spin oriented in the same direction (superparallel kinematics) only three structure functions survive and can be simply separated.     

Transverse spin and momentum correlations in quantum chromodynamics

The naive time reversal odd (‘T-odd’) parton distribution and fragmentation functions are explored. We use the spectator model framework to study flavour dependence of the Boer-Mulders (h ₁^⊥ ) and Sivers (f _1T^⊥) functions as well as the ‘T-even’ but chiral odd function h _1L^⊥. These transverse momentum-dependent parton distribution functions are of significance for the analysis of azimuthal asymmetries in semi-inclusive deep inelastic scattering, as well as for the overall physical understanding of the distribution of transversely polarized quarks in unpolarized hadrons. In this context we also consider the Collins mechanism and the fragmentation function H ₁^⊥. As a by-product of this analysis we calculate the leading twist unpolarized cos(2ϕ) asymmetry, and sin(2ϕ) single spin asymmetry for a longitudinally polarized target in semi-inclusive deep inelastic scattering.      

Polarized electron-nucleon scattering at TESLA

Measurements of polarized electron-nucleon scattering can be realized at the TESLA linear collider facility with projected luminosities that are about two orders of magnitude higher than those expected of other experiments at comparable energies. Longitudinally polarized electrons, accelerated as a small fraction of the total current in the e⁺ arm of TESLA, can be directed onto a solid state target that may be either longitudinally or transversely polarized. A large variety of polarized parton distribution and fragmentation functions can be determined with unprecedented accuracy, many of them for the first time. A main goal of the experiment is the precise measurement of the x- and Q²-dependence of the unknown transversity distributions that will provide us with the full information on the nucleon's quark spin structure as relevant for high energy processes. Comparing their Q²-evolution to that of the corresponding helicity distributions constitutes an important precision test of the predictive power of QCD in the spin sector. The additional possibilities of using unpolarized targets and of experiments with a real photon beam turn TESLA-N into a versatile next-generation facility at the intersection of particle and nuclear physics.     

The transient EPR spectra and spin dynamics of coupled three-spin systems in photosynthetic reaction centres

The concept of introducing an additional, stable paramagnetic species into photosynthetic reaction centres to increase the information content of their spin polarized transient EPR spectra is investigated theoretically. The light-induced electron transfer in such systems generates a series of coupled three-spin states consisting of sequential photoinduced radical pairs coupled to the stable spin which acts as an “observer”. The spin polarized transient EPR spectra are investigated using the coupled three-spin system P⁺I⁻Q⁻ _A in pre-reduced bacterial reaction centres as a specific example which has been studied experimentally. The evolution of the spin system and the spin polarized EPR spectra of P⁺I⁻Q⁻ _A and Q⁻ _A following recombination of the radical pair (P = primary donor, I = primary acceptor, Q_A = quinone acceptor) are calculated numerically by solving the equations of motion for the density matrix. The net polarization of the observer spin is also calculated analytically by perturbation theory for the case of a single, short-lived, charge-separated state. The result bears a close resemblance to the chemically induced nuclear polarization (CIDNP) generated in photolysis reactions in which a nuclear spin plays the role of the observer interacting with the radical pair intermediates. However, because the Zeeman frequencies of the three electron spins involved are usually quite similar, the polarization of the electron observer spin in strong magnetic fields can reflect features of the CIDNP effect in both, high and low magnetic fields. The dependence of the quinone spin polarization on the exchange couplings in the three-spin system is investigated by numerical simulations, and it is shown that the observed emissive polarization pattern is compatible with either sign, positive or negative, for a range of exchange couplings, J_PI, in the primary pair. The microwave frequency and orientation dependence of the spectra are discussed as two of several possible criteria for determining the sign of J_PI.     

Spin physics and more with HERMES

A review of recent results obtained by the HERMES experiment is given. Inclusive measurements on polarized and unpolarized targets provide precise information on the polarized structure functions g₁^d and g₁^p and the isoscalar unpolarized structure function ratio F₂^A/F₂^d. The geometrical acceptance of the HERMES detector and the good particle identification capabilities allow the study of semi-inclusive reactions as well. Using polarized targets, the polarized quark distribution functions can be extracted as well as a first indication of the transversity distributions . On unpolarized heavy targets, hadron formation in a nuclear environment is studied. Finally, data on Deeply Virtual Compton Scattering, the hard exclusive electroproduction of real photons, are presented, which are closely linked to the novel framework of Generalised Parton Distributions. For this reaction HERMES has measured the asymmetry main beam charge as well as in-beam spin.Received: 1 November 2002, Published online: 15 July 2003PACS: 13.60.Hb Total and inclusive cross-sections (including deep-inelastic processes) - 13.60.Le Meson production - 24.85.+p Quarks, gluons, and QCD in nuclei and nuclear processes - 25.30.Mr Muon scattering (including the EMC effect)B. Seitz: For the HERMES Collaboration     

EMC and polarized EMC effects in nuclei

We determine nuclear structure functions and quark distributions for ⁷Li, ¹¹B, ¹⁵N and ²⁷Al. For the nucleon bound state we solve the covariant quark–diquark equations in a confining Nambu–Jona-Lasinio model, which yields excellent results for the free nucleon structure functions. The nucleus is described using a relativistic shell model, including mean scalar and vector fields that couple to the quarks in the nucleon. The nuclear structure functions are then obtained as a convolution of the structure function of the bound nucleon with the light-cone nucleon distributions. We find that we are readily able to reproduce the EMC effect in finite nuclei and confirm earlier nuclear matter studies that found a large polarized EMC effect.     

Improving results on transverse double spin asymmetries in the CNI region at STAR

Double spin effects in polarized pp-elastic scattering in the Coulomb nuclear interference (CNI) region are sensitive to small contributions to the nuclear amplitude in addition to Pomeron exchange dominating at high energies. Measurements of double spin asymmetries require external luminosity normalization using collision counts for all spin combinations. Several possible sources of such data from various STAR subsystems were thoroughly analyzed to make the best choice. BBC arrays were found to be free of double spin effects to the level of ～ 2 × 10^?4 thus leading to the systematic uncertainty ～10^?3 in the value of (A _NN + A _SS )/2.     

Parity violating effects in the coherent scattering of neutrons by 209Bi

We study the rotation of the spin in the coherent scattering of polarized thermal neutrons by ²⁰⁹Bi. Contributions due to direct weak scattering by the nucleus, parity admixtures into the nuclear wave functions and scattering by the electrons are calculated. We use a parity violating potential derived in the framework of the Salam-Weinberg model and several other semi-empirical potentials. The results show that the direct scattering on nuclei is the dominant contribution and some potentials predict results up to an order of magnitude larger than expected on dimensional grounds. The sign of the effect depends on the isospin properties of the potential and can distinguish between potentials with large isotensor or large isovector contributions.     

Nuclear Spin Maser Oscillation of 129Xe by Means of Optical-Detection Feedback

We have developed the nuclear spin maser oscillating at a low frequency of 34 Hz with highly polarized nuclear spins of the noble gas element ¹²⁹Xe. The system is advantageous for detecting a small frequency shift of the nuclear spin precession. We are thus planning to apply this system to the search for an atomic electric dipole moment of ¹²⁹Xe. We here report the development of the system and its performance.     

Surface SelectiveH/Si CP NMR by NOE Enhancement from Laser Polarized Xenon

The surface proton spin polarization created by the spin-polarization-induced nuclear Overhauser effect from optically polarized xenon can be transferred in a subsequent step by solid-state cross polarization to another nuclear spin species such as²⁹Si. The technique exploits the dipolar interactions of xenon nuclear spins with high γ nuclei such as¹H, and is experimentally simpler than direct polarization transfer from¹²⁹Xe to heteronuclei such as¹³C and²⁹Si.     

COMPASS results on transverse spin asymmetries in identified two-hadron production in SIDIS

COMPASS is a fixed target experiment at CERN where nucleon spin structure and hadron spectroscopy are investigated using a 160 GeV/c polarized μ⁺ beam. An important part of its physics program are the measurements of single spin asymmetries (SSA) in semi-inclusive deep inelastic scattering (SIDIS) on transversely polarized targets. Data on a deuteron target (⁶LiD) were taken in 2002–04. After taking the first data on a transversely polarized proton target (NH₃) in 2007, a full year of data taking followed in 2010 to increase precision. The SSA of identified hadron pairs consisting of charged pions and/or kaons from the 2010 data are shown for the first time and compared to model predictions and results from HERMES.     

A nuclear-spin based rotation sensor using optical polarization and detection methods

We describe a rotation sensor that is based on the detection of the nuclear magnetic resonance signal of¹²⁹Xe in the gas phase. Under rotation shifts of the signal phase and Larmor frequency occur, which can be used to determine orientational angle variations with an accuracy of about 1^o and rotation rates of 0.4 mHz to 5 Hz with a precision of 0.4 mHz during the measurement time, which is of the order of 3×T ₂, the nuclear spin relaxation time. The nuclear spin species is polarized by spin-exchange collisions with optically pumped ground-state spins of Rb-gas atoms. The Rb atoms also present in the sample are used as a magnetometer to probe the free-induction decay of the nuclear spin ensemble. Polarization, detection, and data processing sheemes are described in detail and the current sensitivity and limitations of this Stuttgart nuclear magnetic resonance (NMR) gyroscope are discussed. Possibilities for further improvements are pointed out.     

Analyzing the nucleon spin in weak interaction processes at HERA energies

We investigate the possibility to measure the spin content carried by the different quark flavors in a nucleon by means of polarized deep inelastic scattering with W^± exchange at HERA. Such measurements require a polarized proton beam. The expected inclusive and semi-inclusive asymmetries are sizable and for realistic luminosites the expected statistical accuracies are good enough to extract new and relevant information on the valence quark and the strange sea distributions.     

The shape of polarized gluon distributions

The recent high precision SMC data on polarized μp scatterings have again confirmed that very little of the proton spin is carried by quarks. To unravel the mystery of the proton spin structure, it is quite important to know the behavior of the polarized gluon distribution. By using the positivity condition of distribution functions together with the unpolarized and polarized experimental data, we restrict thex dependence of the polarized gluon distribution.     

Large transient magnetic fields at high ion velocities in polarized iron

Nuclear spin precessions due to the transient magnetic field in polarized Fe have been measured as a function of the initial velocity of²⁸Si ions in the first-excited nuclear state. The transient field was found to increase linearly with the ion velocityv in the regionv/c=0.006–0.049. This is in contrast to the Lindhard and Winther model, which requires an inverse proportionality with ion velocity. Reanalysis of an earlier measurement on³⁰Si(2 ₁ ⁺ ) with the linear velocity dependence yields a reduced value for theg-factor ofg=0.37±0.12. Other available velocity-dependent data for²²Ne,⁵⁶Fe and¹⁹⁶Pt are consistent with a linear velocity dependence and suggest in addition a linear dependence on the nuclear charge Z of the moving ion. The increase of the transient field with recoil velocity can be explained semi-quantitatively by the capture of polarized Fe electrons into 1s and 2s vacancies in the moving ion. The velocity-dependent data and other discrepancies from the Lindhard and Winther model for¹⁶N,¹⁸O and very recently, for¹²C are also discussed in terms of the proposed microscopic model.     

Applications of He neutron spin filters at the NCNR

At the NIST Center for Neutron Research (NCNR), we have applied ³He neutron spin filters (NSFs) to the instruments where ³He NSFs are advantageous, such as thermal triple-axis spectrometry, small-angle neutron scattering, and diffuse reflectometry. We present the status of our development and application of this method, including polarized gas production by spin-exchange optical pumping, magnetostatic cavities for storage of the polarized gas on the beam line, and nuclear magnetic resonance (NMR)-based, on-line monitoring and reversal of the ³He polarization. We present the status of developing user-friendly interfaces incorporated into the instrument software to handle these ³He neutron spin filters while taking data and performing data analysis. Finally we discuss the status of development of a polarization capability on the multi-axis crystal spectrometer, which requires polarization analysis over a 220° angular range.     

Optimised adiabatic fast passage spin flipping for He neutron spin filters

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized ³He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the ³He nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500 ms we can spin flip a polarized ³He neutron spin filter with only 1.8×10⁻⁵ loss in ³He polarization. The small magnetic fields (10-15 G) used to house neutron spin filters mean the ³He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using ³He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters.