Limits on the neutrino magnetic moment from solar neutrino experiments

If neutrinos have non-vanishing mass and non-vanishing magnetic moments, then electron neutrinos emitted in nuclear reactions in the solar interior may undergo flavour oscillations, spin precession or resonant spin-flavour precession. Assuming equal values for the magnetic moments of all neutrino flavours and using the data from Homestake and SuperKamiokande we obtain an upper limit on the neutrino magnetic moment and find μ_νe ≤ (2.2 − 2.3) × 10⁻¹⁰μ_B, within four standard solar models. We also point out that this limit may be further reduced if the detector threshold energy for the ν_e,χe⁻ scattering is decreased.     

Period doubling effects in the oscillations of persistent currents in discretized Aharonov–Bohm rings

One shows that the oscillations with respect to the magnetic flux in the one-dimensional discretized Aharonov–Bohm rings are sensitive with respect to the parity of the number of electrons N_e. Resorting to basic flux intervals of unit length indicates that the period of such oscillations is given by the flux quantum Φ₀=hc/e and by 2Φ₀ if N_e is odd and even, respectively. Accordingly, one deals with a period doubling effect when passing from odd N_e-values to even ones, which may be useful in the design of further nanodevices. Interaction free limits of the Drude weight are also discussed.     

Electron and hole μτ-products in a-Si:H/a-SiNχ:H multilayers

In this work the influence of the interface defect density on the a-Si:H/a-SiN_χ:H multilayers is investigated through photoconductivity, ambipolar diffusion length, dark conductivity activation energy, and defect density measurements. The results show a strong asymmetric dependence of (μτ)_e and μτ)_h on the interface defect density: As the thickness of the well decreases, (μτ)_e decreases strongly, whereas (μτ)_h remains constant. The asymmetry is consistently explained by a simple model, in which recombination of free carriers occurs via midgap defect states (in the bulk and at interfaces) and via trapping of electrons (holes) into their respective deep tail states below (above) their respective demarcation levels. Since the samples are slightly n-type and due to the asymmetric density-of-state distribution we can show analytically that (μτ)_h is indeed insensitive to the midgap defect density. Finally, when fitting the measured mobility-lifetime products to an exponentially decaying defect density profile we can conclude that the interface region is about 5 Åwide.     

Further evidence for neutrino oscillations from LSND: the νμ → νe decay-in-flight channel

A search for ν_μ → ν_e oscillations has been conducted at the Los Alamos Meson Physics Facility (LAMPF) using ν_μ from π⁺ decay in flight. An excess in the number of beam-related events from the ν_e C → e⁻ X inclusive reaction is observed. The excess is too large to be explained by normal ν_e contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 ± 1.3 ± 0.5) × 10⁻³ is consistent with the previously reported oscillation evidence from LSND.     

Final results from the ντ appearance search in the NOMAD experiment

An updated analysis of the full NOMAD data corresponding to 1.35 × 10⁶ charged current interactions has been performed to search for neutrino oscillations through ν_τ appearance. This document updates the recently published results on the ν_μ → ν_τ and ν_μ → ν_e oscillations search in NOMAD [1] with a unified analysis of the hadronic channels.     

Argon matrix absorption spectra of ClO, BrO, and IO and emission spectra of IO

Absorption spectra of ClO, BrO, and IO and the emission spectrum of IO have been observed from argon matrix samples prepared by microwave discharging the reagent mixture before condensation. Vibronic progressions were observed for each system. The spectroscopic scopic constants T_e, ω′_e, ω_ex′_e, ω″_e, and ω_ex″_e were evaluated from the absorption and emission data for comparison with gas-phase constants. Very good agreement is found for ClO. The argon matrix observations dictate a revision of the gas-phase vibronic assignments for BrO. The ground-state vibrational fundamental and T_e for argon matrix isolated IO are similar to the gas-phase values, but a lower excited-state spacing is found in the matrix.     

KARMEN: Neutrino oscillation limits and new results with the upgrade

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS which provides ν_μ's, ν_e's and from the π⁺−μ⁺-decay at rest. The oscillation channels ν_{μ → νe} and are investigated with a 56 t liquid scintillation calorimeter. No evidence for oscillations could be found with KARMEN, resulting in 90% CL exclusion limits of sin²(2Θ) < 8.5 · 10⁻³ ( ) and sin²(2Θ) < 4.0 · 10⁻² (ν_μ → ν_e) for Δm² > 100 eV². In 1996, the experiment has been upgraded by an additional veto counting system with a total coverage of 300 m². The new system allows the identification of cosmic muons in the vicinity of the detector. Vetoing these muons suppresses energetic neutrons from deep inelastic scattering of muons as well as from μ-capture by a factor of 40. Up to 1996, these neutrons represented the main background for oscillation search. The experimental sensitivity for will be significantly enhanced towards sin²(2Θ) 1.0 · 10⁻³ after a further measuring period of 2–3 years.     

VUV emission model of REB-heated plasma

VUV emission model of a hygrogen plasma with oxygen impurity (T _e=tens of eV,n _e 10¹⁴–10¹⁶ cm^–3,ⁿimp=1–3 % n_e) is constructed in order to judge different possibilities of plasma diagnostics (especiallyT _e measurements) in the REBEX experiments. Two sets of calculations based on the nonstationary corona model are performed: time dependent continuous and line spectra in the range 5 eV—5 keV in the constantT _e approximation (discussion ofT _e measurements by the filter-method) and time dependent intensities of selected spectral lines (2s-2p type) of ionsO ²⁺–O⁵⁺ at variableT _e (including plasma heating by REB and radiative cooling). A possibility of plasma energy content determination from radiation losses is shown.We would like to acknowledge many helpful discussions with dr. P. unka; we thank also dr. J. Ullschmied for comparing our results with diamagnetic measurements.     

Update on the search for μ→ e oscillations by the 2 experiment

The neutrino experiment sets the most stringent exclusion limits for _μ→ _e oscillations. Analyzing the data set recorded from Feb.1997 up to March 2000 with the upgraded experimental configuration, the search of _e appearance via the p( _e, e⁺)n reaction yields no hints for neutrino oscillations. Applying a likelihood method to the measured event sample of 11 events (background expectation 12.3 events), we deduce an upper limit of sin² (2Θ) < 1.3 · 10⁻³ for large Δm² > 100 eV² and Δm² < 0.049 eV² for sin² (2Θ)=1.     

Study of radiative leptonic events with hard photons and search for excited charged leptons at GeV

During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of 5.9 pb⁻¹ at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events (e, μ, τ) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits m_e^* > 62.5 GeV/c², m_μ^* > 62.6 GeV/c² and m_τ^* > 62.2 GeV/c² at 95% confidence level were established. For single excited lepton production, upper limits on the ratio λ/m_l^* of the coupling of the excited charged lepton to its mass were derived.     

Condition for adiabatic passage in the earth’s-field NMR technique

The equation of motion dM/dt=γ M×B(t) is solved for the case B(t)=jB_p(t)+kB_e. The field B_e is a small static field, typically the earth’s field. The field B_p(t) decays exponentially toward zero with time constant T. This decay is produced by an overdamped switching transient that occurs near the end of the rapid cutoff of the coil current used to polarize the sample. It is assumed that B_p is initially large compared to B_e, and that magnetization M is initially along the resultant field B. Exact solutions are obtained numerically for several decay time constants of B_p, and the motion of M is depicted graphically. It is found that for adiabatic passage, the final cone angle β of the precession in field B_e is related to the decay time constant of B_p by β=2e^{−(π/2)ω_eT}. This is confirmed by measurements of the amplitudes of the ensuing free-precession signals for various decay rates of B_p. Near-perfect adiabatic passage (magnetization aligned within 2° of the earth’s field) can be achieved for time constants T2.6/ω_e. For the case of sudden passage, an approximate analytic solution is developed by linearizing the equation of motion in the laboratory frame of reference. For the adiabatic case, an approximate analytic solution is obtained by linearizing the equation of motion in a rotating frame of reference that follows the resultant field B=B_p+B_e.     

Dynamical mechanism for varying light velocity as a solution to cosmological problems

A dynamical model for varying light velocity in cosmology is developed, based on the idea that there are two metrics in spacetime. One metric g_μν describes the standard gravitational vacuum, and the other describes the geometry through which matter fields propagate. Matter propagating causally with respect to can provide acausal contributions to the matter stress-energy tensor in the field equations for g_μν, which, as we explicitly demonstrate with perfect fluid and scalar field matter models, provides a mechanism for the solution of the horizon, flatness and magnetic monopole problems in an FRW universe. The field equations also provide a ‘graceful exit' to the inflationary epoch since below an energy scale (related to the mass of ψ_μ) we recover exactly the standard FRW field equations.     

Quantitative assessment of solid oxide electrochemical doping

Quantitative analysis of metal cation doping by solid oxide electrochemical doping (SOED) has been performed under galvanostatic doping conditions. A M–β″-Al₂O₃ (M=Ag, Na) microelectrode (contact radius: about 10 μm) was used as cation source to attain a homogeneous solid–solid contact between the β″-Al₂O₃ and doping target. In Ag doping into alkali borate glass, the measured dopant amount closely matched the theoretical value. High Faraday efficiencies of above 90% were obtained. This suggests that the dopant amount can be precisely controlled on a micromole scale by the electric charge during electrolysis. On the other hand, current efficiencies of Na doping into Bi₂Sr₂CaCu₂O_y (BSCCO) ceramics depended on the applied constant current. Efficiencies of above 80% were achieved at a constant current of 10 μA (1.6 A cm⁻²). The relatively low efficiencies were explained by the saturation of BSCCO grain boundaries with Na. By contrast, excess Na was detected on the anodic surface of ceramics at a constant current of 100 μA (16 A cm⁻²). In the present study, we demonstrate that SOED enables micromole-scale control over dopant amount.     

Physical processes of current gain in InAs bipolar junction transistors

InAs bipolar junction transistors (BJTs), grown by molecular beam epitaxy, are reported with common emitter current gains (β's) as large as 400. The factors affecting the common emitter current gain have been studied by estimating the magnitudes of the base transport factor (α_T) and emitter injection efficiency (γ). This has been accomplished by studying a sequence of InAs BJTs with varying emitter doping densities, N_E. Minority carrier diffusion length in the base (L_B), α_T, and γ have been extracted from measured electrical characteristics. The results of the study of these InAs BJTs are as follows: L_B≈0.4 μm, α_T≈98% and γ ranges from 92% to nearly 100% depending on N_E. This knowledge of the magnitudes of the injection efficiencies suggests when it would be useful to move from the simple BJT structure to the more advanced heterojunction bipolar transistor (HBT) structure. Lower γ BJTs would be improved, however high-γ BJTs would benefit little, by the use of the widegap emitters of HBTs. The method developed here to estimate γ, α_T and L_B is not specific to InAs BJTs, but should be useful for study of BJTs and HBTs in any material system.     

Spin-dependent magnetotransport through one or more rings in the presence of the Rashba and Dresselhaus terms of the spin–orbit interaction

Magnetotransport through one or several quasi-one-dimensional rings, in the presence of the Rashba (RSOI) and Dresselhaus (DSOI) terms of the spin–orbit interaction (SOI) and of a magnetic field B, is investigated. The RSOI field and an effective DSOI field are taken as E_R=E_R(sinγ₁e_r+cosγ₁e_z) and E_D=E_D(sinγ₂e_r+cosγ₂e_z), their strengths are denoted by α and β, respectively. The exact one-electron eigenvalues and eigenfunctions are obtained and used to evaluate the transmission as a function of α, β, and of the angles γ₁,γ₂. Because the RSOI term couples the electronic orbit (along the θ direction) with the Pauli matrices σ_z and σ_r while the DSOI term couples it with σ_θ, they affect the electronic spin transport through a ring in distinctly different ways. The resulting transmission shows a considerable structure as a function of the angles γ₁ or γ₂. The same holds for the transmission, versus α or β, with the SOI present only in one arm of the ring and for that through two rings with the same or different radii. Various results of the literature, valid for β=0, are readily recovered. For weak magnetic fields the influence of the Zeeman term on the transmission, assessed by perturbation theory, is negligible.     

On the Casimir energy for a massive quantum scalar field and the cosmological constant

We present a rigorous, regularization-independent local quantum field theoretic treatment of the Casimir effect for a quantum scalar field of mass μ≠0 which yields closed form expressions for the energy density and pressure. As an application we show that there exist special states of the quantum field in which the expectation value of the renormalized energy–momentum tensor is, for any fixed time, independent of the space coordinate and of the perfect fluid form g_μ,νρ with ρ>0, thus providing a concrete quantum field theoretic model of the cosmological constant. This ρ represents the energy density associated to a state consisting of the vacuum and a certain number of excitations of zero momentum, i.e., the constituents correspond to lowest energy and pressure p0.     

The Electric Dipole Moment of the CO2–CO van der Waals Complex

Radiofrequency transitions withinK= 2 asymmetry doublets have been observed for the CO₂–CO van der Waals complex. A Stark effect measurement on theJ= 2,K= 2 transition provides an electric dipole moment of μ = 0.2493(1) D. Combining this result with the permanent moment of CO, μ_CO= 0.1098 D, gives a change of moment on complex formation of Δμ = 0.140 D. The sign of Δμ is such that the CO end of the complex is more positive than CO₂. The origin of Δμ should not be attributed to any single mechanism, and several different contributions to Δμ are discussed.     

Observation of χb production in the exclusive reaction ′→γγχb→γγ→γγ(eeorμμ−)

We report on the observation of 1 ³P_J (χ_b) production in the reaction ′→γχ_b→γγ→γγ(e⁺e⁻ or μ⁺μ⁻). The data were recorded with the nonmagnetic CUSB detector at the Cornell Electron Storage Ring, CESR. We observe 124 γγ events with either an electron or muon pair in the final state. In the γγ correlation plot about 40% of the events cluster around (120, 430) MeV.     

Search for anomalous production of single photons at and 136 GeV

This letter reports the results of the measurement of single photon production in the reaction e⁺e⁻ → γ+ invisible particles at centre-of-mass energies and 136 GeV and an integrated luminosity of 5.83 pb⁻¹, collected with the DELPHI detector at LEP. The signal is compatible with the prediction of the Standard Model for the process , and the number of neutrino families has been determined to be N_ν = 3.1 ± 0.6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specific model.     

Time evolution of initially localized states in two-dimensional quantum dot arrays in a magnetic field

The evolution of non-stationary localized states |Ψ(t=0) is investigated in two-dimensional tight binding systems of N potential wells with and without a homogeneous field perpendicular to the plane. Most results are presented in analytical form, what is almost imperative if the patterns are as complex as for rings in a magnetic field, where the qualitatively different features arise depending on rational or irrational numbers. The systems considered comprise finite linear chains (N=2,3), finite rings (N=3–6), infinite chains, finite rings (N=3–6) in a magnetic field, and rings with leads attached to each ring site. The position of the particle at time t is described by the projection of the wave function P_m(t)=|m|Ψ(t)|² onto the localized basis function at site m. For finite chains and rings with N=3,4,6 the time evolution is periodic, whereas it is non-periodic for N=5 and N greater then 6. Rings in a magnetic field show a rich spectrum of different features depending on N and the number of flux quanta through the ring, including periodic oscillation and rotation of the charge as well as non-periodic charge fluctuations.