A comparison of HREM and weak beam transmission electron microscopy for the quantitative measurement of the thickness of ferroelectric domain walls

In this paper we present two methods for the quantitative measurement of the thickness of ferroelectric domain walls, one using high-resolution electron microscopy (HREM) and the other weak beam transmission electron microscopy (WBTEM). These techniques can be used to determine the thickness of domain walls at room temperature as well as close to the ferroelectric to paraelectric phase transition. The first method allows a direct visualization of the lattice distortion across the domain wall, by measuring the continuous deviation of a set of planes with respect to the undistorted lattice. The second method consists in a quantitative analysis of the thickness fringes that appear on weak beam images of inclined domain walls. By fitting simulated fringe profiles to experimental ones, we can extract the thickness of the domain walls in a quantitative way. These two complementary techniques lead to a complete characterization of the thickness of ferroelectric domain walls over a wide range of specimen thicknesses at different magnifications. As an example we apply these methods to ferroelectric domain walls in PbTiO3 The domain wall thickness at room temperature is found to be 1.5 ± 0.3 nm using HREM (in very thin samples≈10 nm) and 2.1 ± 0.7 nm using WBTEM (in samples thicker than 30 nm

Impact of the tip radius on the lateral resolution in piezoresponse force microscopy

We present a quantitative investigation of the impact of tip radius as well as sample type and thickness on the lateral resolution in piezoresponse force microscopy (PFM) investigating bulk single crystals. The observed linear dependence of the width of the domain wall on the tip radius as well as the independence of the lateral resolution on the specific crystal-type are validated by a simple theoretical model. Using a Ti-Pt-coated tip with a nominal radius of 15 nm the so far highest lateral resolution in bulk crystals of only 17 nm was obtained

A Measurement of the K0 Charge Radius and a CP Violating Asymmetry Together with a Search for CP Violating E1 Direct Photon Emission in the Rare Decay KL->pi+pi-e+e-

Using the complete KTeV data set of 5241 candidate KL->pi+pi-e+e- decays (including an estimated background of 204+-14 events), we have measured the coupling gCR=0.163+- 0.014(stat)+-0.023(syst) of the CP conserving charge radius process and from it determined a K0 charge radius of (K0)=(-0.077+-0.007(stat)+-0.011(syst)) fm**2. We have also determined a first experimental upper limit of 0.04 (90% CL) for the ratio |g_{E1}|/|g_{M1}| of the coupling for the E1 direct photon emission process relative to the coupling for M1 direct photon emission process. We also report the measurement of its associated vector form factor |gM1`|(1+ (a_1/a_2)/(M(rho)**2-M(K)**2)+2M(K)E(gamma*)) where |gM1`|=(1.11+- 0.12(stat)+-0.08(syst) and a_1/a_2 = (-0.744+-0.027(stat)0.032(syst)) GeV**2/c**2. In addition, a measurement of the manifestly CP violating asymmetry of magnitude (13.6+- 1.4+-(stat)+-1.5(syst))% in the CP and T odd angle phi between the decay planes of the e+e- and pi+pi- pairs in the KL center of mass system is reported

Measurement and Interpretation of Fermion-Pair Production at LEP energies above the Z Resonance

This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the e+e- -> ffbar process for centre-of-mass energies above the Z resonance, from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study a variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering and several models which include physics beyond the Standard Model: the exchange of Z' bosons, contact interactions between fermions, the exchange of gravitons in large extra dimensions and the exchange of sneutrino in R-parity violating supersymmetry.Comment: 79 pages, 16 figures, Accepted by Eur. Phys. J.

A Determination of the Centre-of-Mass Energy at LEP2 using Radiative 2-fermion Events

Using e+e- -> mu+mu-(gamma) and e+e- -> qqbar(gamma) events radiative to the Z pole, DELPHI has determined the centre-of-mass energy, sqrt{s}, using energy and momentum constraint methods. The results are expressed as deviations from the nominal LEP centre-of-mass energy, measured using other techniques. The results are found to be compatible with the LEP Energy Working Group estimates for a combination of the 1997 to 2000 data sets.Comment: 20 pages, 6 figures, Accepted by Eur. Phys. J.

Determination of the b quark mass at the M_Z scale with the DELPHI detector at LEP

An experimental study of the normalized three-jet rate of b quark events with respect to light quarks events (light= \ell \equiv u,d,s) has been performed using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are found to agree with theoretical predictions treating mass corrections at next-to-leading order. Measurements of the b quark mass have also been performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data are found to be better described when using the running mass. The measurement yields: m_b(M_Z) = 2.85 +/- 0.18 (stat) +/- 0.13 (exp) +/- 0.19 (had) +/- 0.12 (theo) GeV/c^2 for the CAMBRIDGE algorithm. This result is the most precise measurement of the b mass derived from a high energy process. When compared to other b mass determinations by experiments at lower energy scales, this value agrees with the prediction of Quantum Chromodynamics for the energy evolution of the running mass. The mass measurement is equivalent to a test of the flavour independence of the strong coupling constant with an accuracy of 7 permil.Comment: 24 pages, 10 figures, Accepted by Eur. Phys. J.

A Measurement of the Tau Hadronic Branching Ratios

The exclusive and semi-exclusive branching ratios of the tau lepton hadronic decay modes (h- v_t, h- pi0 v_t, h- pi0 pi0 v_t, h- \geq 2pi0 v_t, h- \geq 3pi0 v_t, 2h- h+ v_t, 2h- h+ pi0 v_t, 2h- h+ \geq 2pi0 v_t, 3h- 2h+ v_t and 3h- 2h+ \geq 1pi0 v_t) were measured with data from the DELPHI detector at LEP.Comment: 53 pages, 18 figures, Accepted by Eur. Phys. J.

Study of Inclusive J/psi Production in Two-Photon Collisions at LEP II with the DELPHI Detector

Inclusive J/psi production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction gamma gamma -> J/psi+X is seen. The number of observed N(J/psi -> mu+mu-) events is 36 +/- 7 for an integrated luminosity of 617 pb^{-1}, yielding a cross-section of sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the event shapes of different types of gamma gamma processes in the PYTHIA program, we conclude that (74 +/- 22)% of the observed J/psi events are due to `resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon.Comment: 13 pages, 8 figures, Accepted by Phys. Lett.

Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton

Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000. The corresponding integrated luminosity is 650 pb^{-1}. The values of the cross-section obtained are found to be in agreement with QED predictions. Limits on the anomalous magnetic and electric dipole moments of the tau lepton are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.

Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0

Soft photons inside hadronic jets converted in front of the DELPHI main tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the experimental data as compared to the Monte Carlo predictions is observed. This excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/- 0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected level of the inner hadronic bremsstrahlung (which is not included in the Monte Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8), which is similar in strength to the anomalous soft photon signal observed in fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.