Evidence for exclusive ηc production in γγ interactions

We observe for evidence for γγ → η_c production in the reaction e⁺e⁻ → e⁺e⁻K_S⁰K^±π^∓. The product Γ_γγ(η_c)·B(η_c → K_S⁰K^±π^∓) is measured to be 0.5_−0.15^+0.2±0.1 keV.     

Discrete levels in 154Dy above spin 30ħ: Evidence for terminating band structures

High-spin states in ¹⁵⁴Dy have been studied using the TESSA2 γ-rays spectrometer following the ¹¹⁰Pd(⁴⁸Ca,4n)¹⁵⁴Dy reaction at a beam energy of 210 MeV. States up to 44⁺ and 37⁻ have been observed. Below spin 30 the data display regular rotational behaviour which can be interpreted in terms of the cranked shell model. Above spin 30, sequences of levels connected by stretched E2 transitions, which show large gains in energy when compared to a rotating liquid drop reference, are lowest in energy for both parities. Particularly low energy levels are observed for spin I^π = 36⁺ and 42⁺ and in addition dipole transitions are found connecting negative-parity states around spin I = 35. The experimental data for I ≳ 30 are compared with calculations, based on the Nilsson-Strutinsky cranking formalism, in which it is possible to trace fixed configurations through a sequence of spins. For the high-spin positive-parity sequence, the similarity with the ¹⁵⁶Er spectrum is discussed.     

Gluonic transverse spin structure functions and their possible measurement inχ 2 production

Gluonic parton distributions in a transversely polarized proton are identified and their classification according to twist is discussed. We find that there are two twist-three transverse spin gluonic structure functions, called hereinH ₁(x, Q ²) andH ₂(x, Q ²). These are potentially measureable in ₂ production in hard polarizedp-p collisions. Crossection formulae are calculated for a variety of polarization states, assuming a simple effective interaction for ₂ production from gluon fusion.     

Models for μ+ depolarization in spin glasses reflecting dynamical processes

The muon spin depolarization function is calculated for different dynamical processes. Muon diffusion is shown to cause motional narrowing at high temperatures (TT_f=freezing temperature of the spin glass) as well as at low temperatures (Tf), where the static line is essentially lorentzian due to the randomness of the spin distribution of the dilute system. Different models for ⁺ depolarization reflecting the freezing process of the spin glass system above T_f consider single correlation times as well as wide distributions of correlation times. It will be shown that the SR depolarization investigated in transverse external fields does not enable us to distinguish between single correlation times and wide correlation time distributions. Therefore, an interpretation of the spin dynamics requires a comparison of TF-SR with results of different measuring methods.     

Software package for modeling spin–orbit motion in storage rings

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 10⁶–10⁹ particles in a beam during 10⁹ turns in an accelerator (about 10¹²–10¹⁵ integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin–orbit dynamics.     

ρ-Meson dominance and spin correlations in pion photopair production at nucleons near nucleon resonances

The pion photopair production cross section near nucleon resonances of spin 3/2 has been calculated in the-meson dominance model, including particle spin correlation; the expressions for the angular and energy distribution have been derived, as well as the invariantmass distribution for the system, together with an expression for the asymmetry coefficient arising from the linear polarization of the photon. These results are compared with measurements at-ray energies of 1, 2.8, and 4.7 GeV. At these energies, the agreement with experiment is satisfactory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 103–108, June, 1976.     

A measurement of the spin correlation parameter CNN (θ) in n-p scattering at 181 MeV

The spin correlation parameter C_NN has been measured for n-p elastic scattering at 181 MeV. A comparison with predictions from various phase shift sets and potential models reveals sizeable deviations from the for the data Paris potential and Saclay phase shifts. For the Paris potential the deviations are directly related to an overprediction of the ³D₂ phase shift parameter.     

NMR spin–spin coupling constants in microhydrated ortho-aminobenzoic acid

The influence of the hydrogen-bond formation on the NMR spin–spin coupling constants, including the Fermi contact, the diamagnetic spin–orbit, the paramagnetic spin–orbit and the spin dipole term, has been investigated for the ortho-aminobenzoic acid microhydrated with up to three water molecules. The one-bond and two-bond spin–spin coupling constants for several intra-molecular and across-the-hydrogen-bond atomic pairs are calculated employing high-level density functional theory in combination with the B3LYP functional with two different types of extended basis sets for each level of microhydration. The spin–spin coupling constants, in general, vary inversely with the hydrogen bond length. The Fermi contact term is found to be the dominant contributor to the total value of spin–spin coupling constant followed by the paramagnetic spin–orbit term. The variations of Fermi contact term and atomic charge distribution with size of microhydration follow quite similar trend. The effect of explicit solvation provided by microhydration has also been compared briefly with that of bulk implicit solvation obtained through polarised continuum model and mixed microhydration/continuum approach.     

Transverse spin asymmetries for W-production in proton–proton collisions

We study parity-even and parity-odd polarization observables for the process pp→l^±X$pp\to l^{\pm }X$, where the lepton comes from the decay of a W-boson. By using the collinear twist-3 factorization approach, we consider the case when one proton is transversely polarized, while the other is either unpolarized or longitudinally polarized. These observables give access to two particular quark–gluon–quark correlation functions, which have a direct relation to transverse momentum dependent parton distributions. We present numerical estimates for RHIC kinematics. Measuring, for instance, the parity-even transverse single spin correlation would provide a crucial test of our current understanding of single spin asymmetries in the framework of QCD.     

Evidence for direct impact damage in metamict titanite CaTiSiO?

We have measured the dose dependence of the degree of amorphization of titanite, CaTiSiO(5). Titanite is an often metamict mineral which has been considered as a matrix for the encapsulation of radiogenic waste, such as Pu. The amorphous fraction p of geologically irradiated samples (ages between 0.3 and 1 Ga) follows p = 1 - exp(-B(a)D) where D is the total dose and the characteristic amorphization mass is B(a) = 2.7(3) × 10(-19) g. Amorphization follows the direct impact mechanism where each α-decay leads to a recoil of the radiogenic atoms (mostly Th and U), which then, in turn, displaces some 5000 atoms of the titanite matrix. The amorphization behaviour is almost identical with that of zircon, ZrSiO(4), which has a similar molecular mass. While the recrystallization mechanism and elastic behaviour of the two minerals are very different, we do not find significant differences for the amorphization mechanism. Our samples have undergone little reheating over their geological history, since heating over 800 K would lead to rapid recrystallization for which we have found no evidence.     

Electron–electron interaction induced spin thermalization in quasi-low-dimensional spin valves

We study the spin thermalization, i.e., the inter-spin energy relaxation mediated by electron–electron scattering in small spin valves. When one or two of the dimensions of the spin valve spacer are smaller than the thermal coherence length, the direct spin energy exchange rate diverges and needs to be regularized by the sample dimensions. Here we consider two model systems: a long quasi-1D wire and a thin quasi-2D sheet.     

Theory of spin polarization in mesoscopic spin–orbit coupling systems

We establish a general formalism of the bulk spin polarization (BSP) and the current-based spin polarization (CSP) for mesoscopic ferromagnetic and spin–orbit interaction (SOI) semiconducting systems. Based on this formalism, we reveal the basic properties of BSP and CSP and their relationships. The BSP describes the intrinsic spin polarized properties of devices. The CSP depends on both intrinsic parameters of device and the incident current. For the non-spin-polarized incident current with the in-phase spin-phase coherence, CSP equals to BSP. We give analytically the BSP and CSP of several typical nanodevice models, ferromagnetic nanowire, Rashba nanowire and rings. These results provide basic physical behaviors of BSP and CSP and their relationships.     

Quantum communication in spin star configuration

This paper considers a generalized spin star system which can be solved exactly, with the central spin-1/2 system embedded in an outer ring of N spin-1/2 particles（denoted as spin bath）. In this model, in addition to the central-outer interaction, each pair of nearest neighbour of the bath interacts within themselves. The general expressions of the eigenstates as well as the eigenvalues of the model are derived with the use of the symmetries of system. It analyses the quantum state transfer and the dynamical behaviour of entanglement created during quantum communication. It also analyses the efficiency of the configuration regarded as quantum phase covariant clone or decoherence model. Some interesting results are discovered concerning the properties of quantum communication in this model.     

Evidence for the production of thermal muon pairs with masses above 1 GeV/c 2 in 158 A GeV indium-indium collisions

The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c ² produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c ², rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c ² to be of largely partonic origin, when radial flow has not yet built up.     

Feynman propagator for an arbitrary half-integral spin

Based on the solution to Bargmann-Wigner equation for a particle with arbitrary half-integral spin, a direct derivation of the projection operator and propagator for a particle with arbitrary half-integral spin is worked out. The projection operator constructed by Behrends and Fronsdal is re-deduced and confirmed and simplified, the general commutation rules and Feynman propagator with additional non-covariant terms for a free particle with arbitrary half-inteRzal spin are derived, and explicit expressions for the propagators for spins 3/2, 5/2 and 7/2 are provided.