Hadron formation in deep-inelastic positron scattering in a nuclear environment

The influence of the nuclear medium on the production of charged hadrons in semi-inclusive deep-inelastic scattering has been studied by the HERMES experiment at DESY using a 27.5 GeV positron beam. The differential multiplicity of charged hadrons and identified charged pions from nitrogen relative to that from deuterium has been measured as a function of the virtual photon energy and the fraction z of this energy transferred to the hadron. There are observed substantial reductions of the multiplicity ratio at low and at high z, both of which are well described by a gluon-bremsstrahlung model of hadronization. A significant difference of the -dependence of is found between positive and negative hadrons. This is interpreted in terms of a difference between the formation times of protons and pions, using a phenomenological model to describe the - and z-dependence of . Received: 20 February 2001 / Revised version: 3 May 2001 / Published online: 8 June 2001     

Transverse energy flow in meson-proton and meson-nucleus interactions at 250 GeV/c

The transverse energy carried by charged hadrons and by mesons is studied in interactions of and K mesons with protons and nuclei at 250 GeV/c. The data obtained on transverse energy flow at mid-rapidity can be described by the FRITIOF7.0 model with tuned parameters. Received: 7 May 2001 / Revised version: 9 May 2001 / Published online: 19 July 2001     

Multiplicity of charged and neutral pions in deep-inelastic scattering of 27.5 GeV positrons on hydrogen

Measurements of the individual multiplicities of and produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion multiplicity is the same as for neutral pions, up to , where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below ) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is (syst.) and , respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer and the Bjorken variable x. The observed dependence on agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected -dependence. Received: 2 April 2001 / Revised version: 27 June 2001 / Published online: 7 September     

CP violation and the absence of second class currents in charmless B decays

The absence of second class currents together with the assumption of the factorization for non-leptonic B decays provide new constraints on CP observables in the decay . The kinematics of this decay does not allow for interference between the oppositely charged resonances in the Dalitz plot as in . Nonetheless, under the assumption of factorization, the two-body time-dependent isospin analysis leads to a more robust extraction of the angle than in the isospin-pentagon analysis. The absence of second class currents might lead to enhanced direct CP violation and/or allows for a test of some assumptions made in the analysis in other decays like , and . The effects from non-factorizable contributions on the determination of are estimated by means of a numerical study. Received: 3 July 2001 / Revised version: 19 September 2001 Published online: 21 November 2001     

Measurement of neutral and charged current cross sections in electron-proton collisions at high Q^2

The inclusive single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA, in the range of four-momentum transfer squared between 150 and 30 000 GeV, and Bjorken x between 0.002 and 0.65. The data were taken in 1998 and 1999 with a centre-of-mass energy of 320 GeV and correspond to an integrated luminosity of 16.4 pb. The data are compared with recent measurements of the inclusive neutral and charged current cross sections. For clear evidence is observed for an asymmetry between and neutral current scattering and the generalised structure function is extracted for the first time at HERA. A fit to the charged current data is used to extract a value for the W boson propagator mass. The data are found to be in good agreement with Standard Model predictions. Received: 21 December 2000 / Published online: 15 March 2001     

Threshold Laws for Multiparticle Fragmentation

 The threshold behaviour of the cross section for break-up of an atomic particle into N charged fragments is described by a power law, , where E is the energy excess above the threshold. The threshold index μ reflects the dynamics of long-range Coulomb correlation. The general features of the theory are discussed. The charge and mass dependence of the threshold index is analyzed for some particular systems. Received October 29, 2001; accepted for publication November 9, 2001     

Fermion masses in a model for spontaneous parity breaking

In this paper we discuss a left–right symmetric model for elementary particles and their connection with the mass spectrum of elementary fermions. The model is based on the group . New mirror fermions and a minimal set of Higgs particles that break this symmetry down to are proposed. The model can accommodate a consistent pattern for charged and neutral fermion masses as well as neutrino oscillations. An important consequence of the model is that the connection between the left and right sectors can be implemented by the neutral vector gauge boson Z and a new heavy Z'. Received: 15 June 2000 / Revised version: 14 September 2000 / Published online: 5 February 2001     

Rotational viscosity enhancement in nematic liquid crystal near a charged surface

The effective rotational viscosity coefficient and flow alignment angle are investigated for polar liquid crystals (LCs), such as 4-n-octyloxy- 4^′-cyanobiphenyl (8OCB), in the vicinity of a charged bounding surface. is calculated using the Ericksen-Leslie theory, both for stationary and nonstationary regimes. Calculations of , both for homeotropic and planar alignment of 8OCB molecules, at a charged indium tin oxide(ITO)-coated glass plate show an additional contribution to up to 7.8%. The nonequilibrium flow alignment angle (τ) is also calculated for the surface region bounded by 0.1≤y≤3.0 μm. Transition from a tumbling situation to a flow aligning regime can occur near the charged boundary surface. Received 22 November 2001 and Received in final form 31 January 2002     

Analysis and interpretation of new low-energy \pi\pi scattering data

The recently published E865 data on charged decays and phases are reanalyzed to extract values of the two S-wave scattering lengths, of the subthreshold parameters and , of the low-energy constants and as well as of the main two-flavour order parameters: and in the limit taken at the physical value of the strange quark mass. Our analysis is exclusively based on direct experimental information on phases below 800 MeV and on the new solutions of the Roy equations by Ananthanarayan et al. The result is compared with the theoretical prediction relating 2a ₀ ⁰-5a ₀ ² and the scalar radius of the pion, which was obtained in two-loop Chiral Perturbation Theory. A discrepancy at the 1- level is found and commented upon. Received: 11 December 2001 / Revised version: 28 March 2002 / Published online: 7 June 2002     

Heterolytic dissociation under hot-electron bombardment of the silanic bond at the Si-SiO2 interface

An atomistic model is proposed to account for the threshold-voltage instability of mos transistors under hot-electron bombardment. High-level density-functional-theory calculations for a set of model molecules simulating the Si-SiO₂ interface show that in the presence of one adsorbed water molecule the diradical center (resulting from the homolytic cleavage by hot-electron impact of the silanic bond at the hydrogen-passivated interface trap) evolves spontaneously to the formation of a positively charged defect at the oxide side of the Si-SiO₂ interface. Received: 10 January 2001 / Accepted: 19 June 2001 / Published online: 30 August 2001     

Scattering of Heavy Charged Particles on Hydrogen Atoms

 Low-energy scattering of heavy positively charged particles on hydrogen atoms (H) is investigated by solving Faddeev equations in configuration space. A resonant value of the pH scattering length, a = 750 ± 5 a.u., in the pp antisymmetric state was found. This large value indicates the existence of a first excited state with a binding energy B = 1.14 × 10⁻⁹ a.u. below the H ground state. Resonances for non-zero angular-momenta states are predicted. Received November 4, 2001; accepted for publication November 12, 2001     

Nanoparticles superficial density of charge in electric double-layered magnetic fluid: A conductimetric and potentiometric approach

We analyze potentiometric and conductimetric measurements simultaneously performed on Electric Double-Layer Magnetic Fluid based on cobalt ferrite nanoparticles, in order to obtain the pH-dependence of the particle surface charge density. We propose a mechanism for the charging of the particle surface. This model considers the ferrofluid solution as a mixture of strong and weak diprotic acids. We show how an exact analytical treatment involving proton transfer between the particle surface and the bulk solution allows the construction of a speciation diagram of the charged superficial sites. The saturation value of the superficial density of charge is found to be equal to 0.326 ± 0.065 C m^-2. Received 9 May 2001 and Received in final form 17 July 2001     

Spectroscopy of the regenerative soot

The mechanisms and processes of the formation of the regenerative soot in a graphite hollow cathode discharge that produces and emits carbon clusters are presented. Mass spectrometry with a specially designed E×B velocity filter analyzes the entire range of the charged clusters from C ₁ to ∼C ₄₃₀₀. The state of the carbon vapour within the source is evaluated by using the characteristic line emissions from the carbonaceous discharge whose formative mechanisms depend upon the kinetic and potential sputtering of the sooted cathode. The carbonaceous discharge generates atomic and ionic C and its clusters C _m (m≥ 2), noble gas metastable atoms and ions, energetic electrons and photons in the cavity of the graphite hollow cathode. The parameters of soot formation and its recycling depend critically on the discharge parameters, the geometry of the hollow cathode and 3D profile of the cusp magnetic field contours. Received 2nd July 2001 and Received in final form 10 September 2001     

The linkage between macroscopic gettering mechanisms and electronic configuration of 3d-elements in p/p+ epitaxial silicon wafers

We have measured the gettering efficiencies for Cr, Mn, Fe, Co, Ni and Cu in p/p+ epitaxial wafers. The gettering test started with a reproducible spin-on contamination on the front side of the wafers in the 10¹²–10¹⁴ atoms/cm² range, followed by thermal treatment to redistribute the metallic impurities in the wafer. The gettering efficiencies were measured by a novel wet chemical stratigraphic etching technique in combination with inductively-coupled plasma mass spectrometry. The residual bulk metal contamination was also measured by this method. This procedure led to global distributions of the 3d elements on the wafer’s front side, in the bulk of the wafer and on the wafer’s back side. Recovery rates were found to be 34%, 2.3%, 100%, 85%, 100% and 100% for Cr, Mn, Fe, Co, Ni and Cu, respectively. An impurity segregation effect in the wafer bulk was measured for Cu (100%) and Cr (34%), while no detectable segregation-induced gettering mechanisms were detected for the other elements in the applied concentration range. The segregation-induced gettering mechanisms were interpreted from the electronic structure of the metallic impurities. For segregation gettering by increased solubility in p+ silicon, the metallic species must form donors. Only Cu⁺ (3d ¹⁰) and Cr⁺ (3d ⁵) can form singly positively charged species that exhibit a spherical electronic distribution. It is well known from spinell structures that 3d ¹⁰ and, to a smaller extent 3d ⁵, are stable configurations in tetrahedral structures like the silicon lattice. Thus, we link the segregation-induced gettering mechanism in p/p+ epitaxial wafer to the electronic configuration of the 3d elements. Received: 19 January 2001 / Accepted: 31 January 2001 / Published online: 20 June 2001     

On the fragmentation of multiply charged sodium clusters

The fragmentation of multiply charged atomic sodium clusters of mass 200 is investigated using the Micro-canonical Metropolis Monte Carlo (MMMC) statistical technique for excitation energies up to 200 eV and for cluster charges up to +9e. In this work we present caloric curves and charged and uncharged fragment mass distributions for clusters with charges 0, 2, and 4. The caloric curves show a dip at the critical point implying a negative specific heat, as expected for finite systems, while the fragment mass distributions corroborate the picture of a phase transition from one dominant liquid-like cluster to complete vaporization. Received 7 November 2001 / Received in final form 4 April 2002 Published online 28 June 2002     

Radiative return at NLO and the measurement of the hadronic cross-section in electron–positron annihilation

Electron–positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process and the emission of two real hard photons: . A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DANE, CLEO-C and B-meson factories. Received: 14 December 2001 / Published online: 5 April 2002     

On the Motion of a Charged Particle Interacting with an Infinitely Extended System

 We study the time evolution of a charged particle moving in a medium under the action of a constant electric field E. In the framework of fully Hamiltonian models, we discuss conditions on the particle/medium interaction which are necessary for the particle to reach a finite limit velocity. We first consider the case when the charged particle is confined in an unbounded tube of ℝ³. The electric field E is directed along the symmetry axis of the tube and the particle also interacts with an infinitely many particle system. The background system initial conditions are chosen in a set which is typical for any reasonable thermodynamic (equilibrium or non-equilibrium) state. We prove that, for large E and bounded interactions between the charged particle and the background, the velocity v(t) of the charged particle does not reach a finite limit velocity, but it increases to infinite as: |v(t)−Et|≤C ₀ (1+t), where C ₀ is a constant independent of E. As a corollary we obtain that, if the initial conditions of the background system are distributed according to any Gibbs state, then the average velocity of the charged particle diverges as time goes to infinite. This result is obtained for E large enough in comparison with the mean energy of the Gibbs state. We next study the one-dimensional case, in which the estimates can be improved. We finally discuss, at an heuristic level, the existence of a finite limit velocity for unbounded interactions, and give some suggestions about the case of small electric fields. Received: 7 March 2002 / Accepted: 23 September 2002 Published online: 8 January 2003 RID="*" ID="*" Work partially supported by the GNFM-INDAM and the Italian Ministry of the University. Communicated by J.L. Lebowitz     

Heavy-light current correlators at order \alpha_\mathrm{s}^2 in QCD and HQET

The non-diagonal correlators of vector and scalar currents are considered at three-loop order in QCD. The full mass dependence is computed in the case where one of the quarks is massless and the other one carries mass M. We exploit the decoupling relations between the full theory and the heavy quark effective theory (HQET) in order to obtain the logarithmic parts of the leading threshold terms. With the help of conformal mapping and Padé approximation numerical estimates for the non-logarithmic terms are extracted which in turn lead to a prediction of the correlator in HQET at order . As applications of the vector and scalar correlator we consider the single-top-quark production via the process and the decay rate of a charged Higgs boson into hadrons, respectively. In both cases the computed NLO corrections are shown to be numerically much less important than the leading ones. On the contrary, the NLO order QCD corrections to the HQET sum rule for the leptonic decay rate of a heavy-light meson proves to be comparable to the leading one. Received: 19 June 2001 / Published online: 10 August 2001     

Kinetic arrest in polyion-induced inhomogeneously charged colloidal particle aggregation

Polymer chains adsorbed onto oppositely charged colloidal particles can significantly modify the particle-particle interactions. For sufficient amounts of added polymers, the original electrostatic repulsion can even turn into an effective attraction and relatively large aggregates can form. The attractive interaction contribution between two particles arises from the correlated adsorption of polyions at the oppositely charged particle surfaces, resulting in a non-homogeneous surface charge distribution. Here, we investigate the aggregation kinetics of polyion-induced colloidal complexes through Monte Carlo simulation, in which the effect of charge anisotropy is taken into account by a DLVO-like inter-particle potential, as recentely proposed by Velegol and Thwar (Langmuir 17, 7687 (2001)). The results reveal that the aggregation process slows down due to the progressive increase of the potential barrier height upon clustering. Within this framework, the experimentally observed cluster phases in polyelectrolyte-liposome solutions can be interpreted as a kinetic arrested state.     

The quantum harmonic oscillator on a circle and a deformed Heisenberg algebra

We show that the Heisenberg-type algebra describing the first levels of the quantum harmonic oscillator on a circle of large length L is a deformed Heisenberg algebra. The successive energy levels of this quantum harmonic oscillator on a circle of large length L are interpreted, similarly to the standard quantum one-dimensional harmonic oscillator on an infinite line, as being obtained by the creation of a quantum particle of frequency w at very high energies. Received: 29 March 2001 / Revised version: 17 July 2001 / Published online: 31 August 2001