Topics on fundamental symmetries in particle physics

Topics on the test of fundamental symmetries are shown. Comparison of the gravitational interactions between particle and anti-particle is one of the most important experiments for the test of the CPT-theorem. The measurement of K _L ⁰ →π⁰e^{+ -} is being carried out in order to find the direct CP-violating amplitude. Several experiments to search for the T-violation are being carried out. The muon polarization in K⁺→π⁰μ⁺υdecay and the electron polarization in the β-decay of polarized⁸Li are very interesting from the viewpoint of T-violation. Recent progress of the measurement of electric dipole moments of atoms and the neutron are mentioned. Studies of parity-violating processes in nucleon-nucleon scattering and nucleon-nucleus reactions are discussed. The results encourage us to measure the T-violation using polarized neutrons and a polarized nuclear target.     

Neutron polarization for P- and T-violation experiments

The polarization of neutron spin, target nucleus spin and He nuclear spin was developed at KEK for measuring the T-odd term in polarized neutron transmission through a polarized nuclear target. A method to measure the neutron spin rotation was developed for the T-violation experiment. This apparatus has been found to be quite useful for the P-violating neutron spin rotation experiment. The angular distribution of neutron-capture -rays was measured for the study of the enhancement mechanism of the P-violation. The results are also discussed.On leave from Tohoku University.     

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.     

Polarized quark distributions in bound nucleon and polarized EMC effect in Thermodynamical Bag Model

The polarized parton distribution functions (PDFs) and nuclear structure functions are evaluated by the phenomenological Thermodynamical Bag Model for nuclear media ⁷Li and ²⁷Al. The Fermi statistical distribution function which includes the spin degree of freedom is used in this statistical model. We predict a sizeable polarized EMC effect. The results of quark spin sum and axial coupling constant of bound nucleons are compared with theoretical predictions of modified Nambu–Jona-Lasinio (NJL) model by Bentz et al.     

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.     

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.     

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.     

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.     

Nuclear spin polarization produced by ion-beam-surface-interaction,its optical detection and use in an atomic quantum-beat experiment

It is shown that nuclear spin polarized ion beams can be generated by ion beam surface interaction at grazing incidence. An optical detection method for the nuclear polarization after foil excitation of such beams is described and used for a hyperfine structure quantum-beat measurement on the¹⁴N II ?2p 3p ³ D-state.     

Time-reversal,nuclear reactions and molecular beams

It is pointed out, that very accurate nuclear reaction detailed balance test could be done in a single experiment using molecular beams. The feasibility of these measurements is discussed for the case of the¹³C(d, t)¹²C reaction.     

Spin exchange polarization and hfs anomaly measurement of β-active37K

Rf-spectroscopic measurements in the atomic ground state of the 1.2 sec-isotope³⁷K yielded independent values of magnetic moment μ _I (³⁷K)=0.20320 (6) nm (diamagnetically corrected), hfs separation ΔW(³⁷K)=240.2672 (7) MHz and the resulting hfs anomaly³⁷Δ³⁹=(0.249±0.035) · 10^?2. The³⁷K was polarized by spin exchange scattering with optically pumped⁸⁷Rb; as a detector for rf transitions the asymmetry of the β-decay of the polarized³⁷K nuclei was used. A detailed analysis of the spin exchange mechanism under the conditions of experiments of this type was performed. This led to an explanation for the observed strong enhancement of the resonance signal heights by the spin bath. Furthermore the dependence of the nuclear polarization and relaxation time constants on the strength of the hfs coupling could be demonstrated.     

Ultrasensitive 3He magnetometer for measurements of high magnetic fields

We describe a ³He magnetometer capable to measure high magnetic fields (B> 0.1 T) with a relative accuracy of better than 10^-12. Our approach is based on the measurement of the free induction decay of gaseous, nuclear spin polarized ³He following a resonant radio frequency pulse excitation. The measurement sensitivity can be attributed to the long coherent spin precession time T₂ ^? being of order minutes which is achieved for spherical sample cells in the regime of “motional narrowing” where the disturbing influence of field inhomogeneities is strongly suppressed. The ³He gas is spin polarized in situ using a new, non-standard variant of the metastability exchange optical pumping. We show that miniaturization helps to increase T₂ ^? further and that the measurement sensitivity is not significantly affected by temporal field fluctuations of order 10^-4.     

129Xe NMR – highly polarized thin films

We studied the macroscopic effects of nuclear magnetization. Highly polarized xenon is often used to increase the sensitivity in NMR investigations of porous media, diluted liquids or for imaging in the gas phase. In the condensed phase, however, highly nuclear spin polarized xenon also possesses a sizable magnetization due to the nuclear spin density. This results in an additional magnetic field, that is used to measure the polarization of the sample, when only the particle density is known. Here we find P_z≈0.8 corresponding to a spin temperature of 0.5 mK. We use isotopically enriched xenon with a ¹²⁹Xe abundance of 0.71. At high abundance of ¹²⁹Xe and high nuclear polarization the dipolar linewidth is considerably reduced. We find for small angle excitation a reduction from 650 Hz to 400 Hz. We investigate this using a thin film geometry. The susceptibility effects of the substrate and the Xe film are treated. The macroscopic angle between the normal of the film and the external field strongly changes the polarization induced line shift and line width. The first follows an expected cos²θ dependence with an understood amplitude the latter however is not understood up to now. Relaxation of ¹²⁹Xe in the condensed film is observed to be T₁=15±1.8 min, much faster than expected. To cite this article: P. Gerhard et al., C. R. Physique 5 (2004).     

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.     

Measurement of the electric quadrupole moments of 26–29Na

The nuclear electric quadrupole moments of the isotopes ²⁶Na, ²⁷Na, ²⁸Na and ²⁹Na were measured by -NMR spectroscopy in single crystals of LiNbO₃ and NaNO₃. High degrees of nuclear polarization were produced by optical pumping of the sodium atoms in a fast beam with a collinear laser beam. The polarized nuclei were implanted into the crystals and NMR signals were observed in the -decay asymmetries. Preparatory measurements also yielded improved values for the magnetic moments of ^27-31Na and confirmed the spin I=3/2 for ³¹Na. The results are discussed in comparison with large-basis shell model calculations. Received: 1 February 2000 / Accepted: 3 April 2000     

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.     

Neutron diffraction study on the hyperfine-induced nuclear spin order in the antiferromagnet PrSn3

At several $\text{(h+}\text{1}\text{2}\text{0 0)}$ reciprocal lattice positions of PrSn₃, we observed Bragg scattering of neutrons which is purely due to the nuclear spin polarization of ¹⁴¹Pr, and could measure the temperature dependence of the polarization between 10 mK and 4.2 K. From the perfectly polarized state of the nuclear spins, the difference between the spin-dependent nuclear scattering lengths b⁺ and b^- has been determined to be b⁺ - b^- = -0.110 ± 0.006 × 10^-12 cm, which is significantly larger in magnitude than the previously reported value. An additional electronic polarization which is linearly proportional to the nuclear spin polarization has also been observed.     

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.     

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.