Bose-Einstein and colour interference in W-pair decays

We study effects on the W mass measurements at LEP2 from non-perturbative interference effects in the fully hadronic decay channel. Based on a model for Bose-Einstein interference, which is in agreement with LEP1 data, we argue that there are no Bose-Einstein correlations between bosons coming from the different W's. For small reconnection probabilities we rule out the possible experimental signal of colour interference at LEP2, suggested in [1]. The conclusions from this paper are that the theoretical uncertainties in the W mass determination should be smaller than the experimental statistical error. Received: 3 November 1997 / Published online: 10 March 1998     

Bose-einstein correlations and color reconnection in W-pair production

We propose a systematic study of Bose-Einstein correlations between identical hadrons coming from different W decays. Experimentally accessible signatures of these correlations as well as of possible color reconnection effects are discussed on the basis of two-particle inclusive densities. Received: 7 July 1998 / / Published online: 19 November 1998     

Colour confinement in hadron-nucleus collisions

We study the evolution of colour confinement in hadron-nucleus collisions and determine the resultingx _F dependence for the suppression of quarkonium production on nuclear targets. The Landau-Pomeranchuk effect applied to colour bremsstrahlung is shown to play a considerable role in the from of the suppression.     

Four-quark final state in W-pair production: Case of signal and background

We discuss theoretical predictions for -pair production and decay at LEP2 and higher energies in a form suitable for comparison with raw data. We present a practical framework for calculating uncertainties of predictions given by the KORALW and grc4f Monte Carlo programs. As an example we use observables in the decay channel: the total four-quark (four-jet) cross section and two-quark/jet invariant-mass distribution and cross section, in the case when the other two may escape detection. Effects of QED bremsstrahlung, effective couplings, running and widths, Coulomb interaction and the complete tree level set of diagrams are discussed. We also revisit the question of technical precision of the new version 1.21 of the KORALW Monte Carlo code as well as of version 1.2(26) of the grc4f one. Finally we find predictions of the two programs to have an overall physical uncertainty of 2%. As a side result we show, on the example of an invariant mass distribution, the strong interplay of spin correlations and detector cut-offs in the case of four-fermion final states. Received: 18 March 1997 / Revised version: 4 July 1997     

Evaluation of the LEP centre-of-mass energy above the W-pair production threshold

Knowledge of the centre-of-mass energy at LEP2 is of primary importance to set the absolute energy scale for the measurement of the W-boson mass. The beam energy above 80 GeV is derived from continuous measurements of the magnetic bending field by 16 NMR probes situated in a number of the LEP dipoles. The relationship between the fields measured by the probes and the beam energy is calibrated against precise measurements of the average beam energy between 41 and 55 GeV made using the resonant depolarisation technique. The linearity of the relationship is tested by comparing the fields measured by the probes with the total bending field measured by a flux loop. This test results in the largest contribution to the systematic uncertainty. Several further corrections are applied to derive the centre-of-mass energies at each interaction point. In addition, the centre-of-mass energy spread is evaluated. The beam energy has been determined with a precision of 25 MeV for the data taken in 1997, corresponding to a relative precision of . This is small in comparison to the present uncertainty on the W mass measurement at LEP. However, the ultimate statistical precision on the W mass with the full LEP2 data sample should be around 25 MeV, and a smaller uncertainty on the beam energy is desirable. Prospects for improvements are outlined. Received: 14 December 1998 / Published online: 3 November 1999     

Quantization and confinement effects in superconducting nanostructures

The confinement of the flux lines by a lattice of submicron holes (‘antidots’) has been studied in nanostructured superconducting Pb/Ge multilayers. By introducing regular arrays of sufficiently large antidots, multi-quanta vortex lattices have been stabilized. Sharp cusp-like magnetization (M) anomalies, appearing at matching fieldsH_m=mφ₀/Sin superconducting films with the antidot lattices having a unit cell areaS, are successfully explained. These anomalies are, analogues of the well-knownM(H) cusp atH_c1, but for the onset of multi-quanta (m+1)φ₀-vortices penetration at each subsequent matching fieldH_m. It is shown that theM(H) curve between the matching fieldsH_m<H<H_m+1follows a simpleM∝ln(H−H_m) dependence. These experimental observations have revealed an unusual expansion of validity of the London limit in superconductors with lattices of relatively large antidots. The successful high quality fit of theM(H,T) curves convincingly demonstrates that a new type of the critical stateB=const (‘single-terrace critical state’) can be realized in superconductors with the antidot lattices.     

Colour effects in Drell-Yan process

We examine the predictions of gauge theories with colour excitation for the processpp →μ ⁺ μ ⁻ X. Relative to the predictions of quark parton model (with three colours) we find enhancements as large as a factor 3 – 4 for the cross-sectionM ³ d ² σ/dMdy|_y=0 in the region 0·03 ≲M/√s ≲ 0·2 at √s=62 GeV,M being the invariant mass andy the rapidity of the muon pair. We study the sensitivity of this result to the colour gluon mass and the underlying parametrisation of the quark and gluon distribution functions.     

Quantum confinement and surface-state effects in bismuth nanowires

Bulk bismuth is an efficient thermoelectric material. Assuming intrinsic conditions, the theory of quantum confinement of bismuth nanowires by Hicks and Dresselhaus predicts a semimetal-to-semiconductor transformation for critical diameters of around 50 nm. For nanowires of diameters below the critical diameter, electronic states can be considered to be one dimensional and therefore the thermopower can be very large. However, angle-resolved photoemission spectroscopy (ARPES) studies of Bi planar surfaces present direct evidence of heavy mass surface states that can inhibit the semimetal-to-semiconductor transformation. We present a study of the Fermi surface of Bi nanowires of diameters ranging between 200 and 30 nm employing the Shubnikov–de Haas method. Our results can be understood in terms of the model of surface states. For 30 nm nanowires we find that the Fermi surface is spherical, that the carriers have high effective mass, and that the number of carriers corresponds to that inferred from ARPES measurements.     

Chromoelectric and chromomagnetic effects in the confinement of gluons

Results are presented from a new variational calculation of quantized SU(3) Yang-Mills fields. The Hamiltonian formalism is applied to the continuum theory, with a truncated momentum expansion in a finite volume, using the Coulomb gauge. The relative importance of electrical and magnetic effects is examined, using an improved treatment of paramagnetic effects. The results depend on the value of the interaction constant, with a transition at0.4. For>0, there is a mass gap between the first excited state and the vacuum state, arising from properties of the Faddeev-Popov determinant. For0·4, properties of the Coulomb energy operator lead to a second mass gap between the first and the higher excited states.This work was supported by the U.S. Dept. of Energy under contract No. DE-AC 02-76 ER-03066. Support for computation on the CRAY X-MP/48 at the Pittsburgh Supercomputing Center has been provided by the NSF through grant No. PSCA-195, and by Cray Research, Inc. through grant No. CRI-8703. The calculation ofF andG _KL was done in collaboration with K. C. Wang. J. Mahdavi assisted with programming.     

Inelastical effects in classical field-theoretical models with confinement

Solitons in a class of relativistic field-theoretical models with confinement of spreading waves are considered and their stability is proven under certain conditions for any space dimension. Njmerical studies are presented about the collision of solitons and antisolitons in one spatial dimension. In these processes different types of localized structures are generated which are pulsating in time and appear to be stable. The interaction of these new objects, called ss- and sa-breathers, with solitons and antisolitons is also studied.     

Disorder and suppression of quantum confinement effects in Pd nanoparticles

Size-selectable ligand-passivated crystalline and amorphous Pd nanoparticles (<4 nm) are synthesized by a novel two-phase process and verified by high-resolution transmission electron microscopy. Scanning tunneling spectroscopy preformed at 5 K on these two types of nanoparticles exhibits clear Coulomb blockade and Coulomb staircases. Size dependent multipeak spectral features in the differential conductance curve are observed for the crystalline Pd particles but not for the amorphous particles. Theoretical analysis shows that these spectral features are related to the quantized electronic states in the crystalline Pd particle. The suppression of the quantum confinement effect in the amorphous particle arises from the reduction of the degeneracy of the eigenstates and the level broadening due to the reduced lifetime of the electronic states.     

Extra interference effects in SEXAFS

Following the analysis of Abraham et al., Phys. Rev. B18 (1978) 6702, we have derived the consequences for SEXAFS of treating the photoexcitation and the decay (Auger or fluorescence) as a one-step process. The detected current is not simply proportional to the absorption cross section. The two cases of extra-atomic and intra-atomic interferences are studied and shown to give non-negligible contributions to the amplitude of the oscillations of the current with the photon frequency. A correct study of the coordination number of an atom should thus take them into account.     

Quantum confinement effects and source-to-drain tunneling in ultra-scaled double-gate silicon n-MOSFETs

By using the linear combination of bulk band (LCBB) method incorporated with the top of the barrier splitting (TBS) model, we present a comprehensive study on the quantum confinement effects and the source-to-drain tunneling in the ultra-scaled double-gate (DG) metal-oxide-semiconductor field-effect transistors (MOSFETs). A critical body thickness value of 5 nm is found, below which severe valley splittings among different X valleys for the occupied charge density and the current contributions occur in ultra-thin silicon body structures. It is also found that the tunneling current could be nearly 100% with an ultra-scaled channel length. Different from the previous simulation results, it is found that the source-to-drain tunneling could be effectively suppressed in the ultra-thin body thickness (2.0 nm and below) by the quantum confinement and the tunneling could be suppressed down to below 5% when the channel length approaches 16 nm regardless of the body thickness.     

The process of multi-hadron production and the problem of colour confinement

A new possibility of interpreting the multiple production characteristics is discussed based on the results obtained in a large number of papers. It is shown that assuming the mechanism of dynamic-confinement of “colour”, one can consistently construct a model of multiple hadron production at high energies containing the thermodynamics mechanism as an essential element. This model accounts for the basic characteristics of this process in the hadron interactions, e⁺e⁻-annihilation. deep inelastic lepton-nucleon scattering and in the reactions followed by the production of particles with large transverse momenta as well. It does not contradict the data on the multiple production in the interaction of hadrons and of nuclei with nuclei.