Uncertainties in estimating <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> hadronic productionand comparisons of the production at TEVATRON and LHC

The uncertainties in estimating the hadronic production of the B _c meson are studied in the framework of the complete approach of perturbative QCD and the gluon-gluon fusion mechanism. Quantitative comparisons of the production at TEVATRON and LHC are made. Considering the detectors at TEVATRON and LHC, we have also estimated the production with proper kinematic cuts. Based on the results, we conclude that the experimental studies of the B _c meson at the two colliders will be complementary and mutually stimulative. We find that as the CM energy is increasing from RUN-I to RUN-II at TEVATRON, the production cross section increases by about .Received: 21 July 2004, Published online: 18 November 2004PACS: 12.38.Bx, 13.85.Ni, 14.40.Nd, 14.40.Lb     

Spin structure function of deuteron g<Subscript>1</Subscript><Superscript>d</Superscript> from COMPASS

New results on the longitudinal inclusive spin asymmetry A ₁ ^d in the range 1 < Q ² < 100(GeV/c)^2 and 0.004 < x < 0.7 are presented. From these results we derive the spin-dependent structure function g ₁ ^d which we use to evaluate the scale-invariant flavor-singlet axial charge . The contribution of the measured region is evaluated by a QCD fit of the world data. The data were obtained by the COMPASS experiment at CERN using a 160GeV polarized muon beam scattered off a large double-cell polarized ⁶LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region x < 0.03.     

Extraction of the neutron charge form factor G<Superscript>n</Superscript><Subscript>E</Subscript>(Q<Superscript>2</Superscript>) from the charge form factor of deuteron G<Superscript>d</Superscript><Subscript>C</Subscript>(Q<Superscript>2</Superscript>)

We extract the neutron charge form factor G ⁿ _E(Q ²) from the charge form factor of deuteron G ^d _C(Q ²) obtained from T ₂₀(Q ²) data at 0≤Q ²≤ 1.717 (GeV/c)². The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics. Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose a fit for the whole set (36 points) taking into account the data for the slope of the form factor at Q ² = 0. Received: 26 July 2002 / Accepted: 18 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: krutov@ssu.samara.ru RID="b" ID="b"e-mail: troitsky@theory.sinp.msu.ru Communicated by V.V. Anisovich     

Long-range magnetic order in quasi-one-dimensional NaCrSi<Subscript>2</Subscript>O<Subscript>6</Subscript> and NaCrGe<Subscript>2</Subscript>O<Subscript>6</Subscript> metal oxides

Formation of a long-range magnetic order is observed at low temperatures in NaCrSi₂O₆ and NaCrGe₂O₆ quasi-one-dimensional metal oxide compounds with a pyroxene structure. The first of these compounds, NaCrSi₂O₆, is an antiferromagnet with the Néel temperature T _N =3 K, while the second, NaCrGe₂O₆, is a ferromagnet with the Curie temperature T _C =6 K. From the measurements of magnetization and specific heat of these compounds, the main parameters of their magnetic subsystems are determined. In NaCrSi₂O₆, a spin-flip transition is observed. A change in the type of magnetic order that accompanies the replacement of Si by Ge can be attributed to a change in the parameters of the competing direct antiferromagnetic Cr-Cr and indirect ferromagnetic Cr-O-Cr interactions in isolated chains of CrO₆ octahedra.     

Dynamics of the first-order magnetostructural transition in Gd<Subscript>5</Subscript>(Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>4</Subscript>

For a given crystal structure, say body-centred-cubic, the many-body Hamiltonian H in which nuclear and electron motions are to be treated from the outset on the same footing, has parameters, for the elements, which can be classified as (i) atomic mass M, (ii) atomic number Z, characterizing the external potential in which electrons move, and (iii) bcc lattice spacing, or equivalently one can utilize atomic volume, . Since the thermodynamic quantities can be determined from H, we conclude that T _c , the superconducting transition temperature, when it is non-zero, may be formally expressed as T _c = . One piece of evidence in support is that, in an atomic number vs. atomic volume graph, the superconducting elements lie in a well defined region. Two other relevant points are that (a) T _c is related by BCS theory, though not simply, to the Debye temperature, which in turn is calculable from the elastic constants C ₁₁, C ₁₂, and C ₄₄, the atomic weight and the atomic volume, and (b) T _c for five bcc transition metals is linear in the Cauchy deviation C ^* = (C ₁₂ - C ₄₄ )/(C ₁₂ + C ₄₄ ). Finally, via elastic constants, mass density and atomic volume, a correlation between C ^* and the Debye temperature is established for the five bcc transition elements.Received: 13 May 2004, Published online: 23 July 2004PACS: 74.62.-c Transition temperature variations - 74.70.Ad Metals; alloys and binary compounds     

Irradiation-induced suppression of the critical temperature in high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> superconductors: Pair breaking versus phase fluctuations

Experiments on the irradiation-induced suppression of the critical temperature in high-T _c superconductors are analyzed within the mean-field Abrikosov-Gor’kov-like approach. It is shown that the experimental data for YBa₂Cu₃O_7-δ single crystals can be quantitatively explained by the pair-breaking effects under the assumption of the combined effect of potential and spin-flip scattering on the critical temperature and with an accounting for a nonpure d-wave superconducting order parameter.     

Investigation of quasielastic muon-neutrino scattering on nuclei at <Emphasis Type="Italic">E</Emphasis><Subscript>v</Subscript> < 1 GeV

Quasielastic muon-neutrino scattering on nuclei of propane-Freon mixture at energies in the range E _v < 1 GeV is studied. The multiplicity, momentum, and emission-angle distributions of final protons are measured along with the dependence of the mean values for these distributions on the neutrino energy in the range 0.2 < E _v < 1 GeV.     

Magnetic structure of Er<Subscript>5</Subscript>Ge<Subscript>3</Subscript> at 4.2 K

A symmetry analysis of the possible magnetic structures of Er₅Ge₃ in the ground state is performed using the results of measurements of elastic magnetic neutron scattering at 4.2 K. It is shown that the minimum discrepancy factor R _m ≈9.5% corresponds to a modulated collinear magnetic structure in which the magnetic moments of erbium atoms are oriented along the a ₃ axis of the unit cell of the crystal structure and induce an antiferromagnetic longitudinal spin wave (AFLSW). The magnetic structure is characterized by the wave vector k=2π(0, 0, μ /a ₃) (where μ≈0.293) and the modulation period λ≈3.413a ₃. The magnetic ordering temperature T _N ≈38 K is determined from the temperature dependence of the intensity of magnetic reflections. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 9, 2003, pp. 1653–1659. Original Russian Text Copyright ? 2003 by Vokhmyanin, Dorofeev.     

The synthesis of graphene-TiO<Subscript>2</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> super-thin heterojunctions with enhanced visible-light photocatalytic activities

In this paper, an efficient strategy for the synthesis of graphene nanobelt-titanium dioxide/graphitic carbon nitride (graphene-TiO₂/g-C₃N₄) heterostructure photocatalyst was applied to fabricate a kind of visible-light-driven photocatalyst. The heterostructure shows higher absorption edge towards harvesting more solar energy compared with pure TiO₂ and pure g-C₃N₄ respectively. Furthermore, the as-prepared graphene-TiO₂/g-C₃N₄ heterostructure can show enhanced photocatalytic activity under visible-light irradiation. These outstanding performances of photocatalytic activities for graphene-TiO₂/g-C₃N₄ composites can be attributed to the heterojunction interfaces which can separate the electron-hole pairs and impede the recombination of electrons and holes more efficiently. This study conclusively demonstrates a facile and environmentally friendly new strategy to design highly efficient graphene-TiO₂/g-C₃N₄ heterostructure photocatalytic materials for potential applications under visible-light irradiation.

Open image in new window

Graphical abstract ?

     

Measurement of dijet production at low <Emphasis Type="Italic">Q</Emphasis><Superscript>2</Superscript> at HERA

Triple differential dijet cross sections in interactions are presented in the region of photon virtualities 2 < Q ² < 80 GeV², inelasticities 0.1 < y < 0.85, jet transverse energies E ^* _{T 1} > 7 GeV, E ^* _{T 2} > 5 GeV, and pseudorapidities . The measurements are made in the centre-of-mass frame, using an integrated luminosity of 57 pb^-1. The data are compared with NLO QCD calculations and LO Monte Carlo programs with and without a resolved virtual photon contribution. NLO QCD calculations fail to describe the region of low Q ² and low jet transverse energies, in contrast to a LO Monte Carlo generator which includes direct and resolved photon interactions with both transversely and longitudinally polarised photons. Initial and final state parton showers are tested as a mechanism for including higher order QCD effects in low E _T jet production.Received: 13 January 2004, Revised: 21 July 2004, Published online: 18 August 2004     

Polarization in hyperon photo- and electro-production<Superscript>⋆</Superscript>

Multiple polarization observables must be measured to access the amplitude structure of pseudoscalar meson photoproduction off the proton. The hyperon-producing reactions are especially attractive to study, since the weak decays allow straightforward measurement of the induced and recoil polarization observables. In this paper we emphasize γ + p → K ⁺ + Λ , discussing recent measurements of C_x, C_z, and P for this reaction. An empirical constraint on the helicity amplitudes is obtained. A simplified model involving spin-flip and spin-non-flip amplitudes is presented. Finally, a semi-classical model of how the polarization may arise is presented.     

Radiative <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>3</Subscript> decays revisited

Motivated by recent experimental results and ongoing measurements, we review the chiral perturbation theory prediction for decays. Special emphasis is given to the stability of the inner bremsstrahlung-dominated relative branching ratio versus the K _e3 form factors, and on the separation of the structure-dependent amplitude in differential distributions over the phase space. For the structure-dependent terms, an assessment of the order p ⁶ corrections is given, in particular, a full next-to-leading order calculation of the axial component is performed. The experimental analysis of the photon energy spectrum is discussed, and other potentially useful distributions are introduced.Received: 9 December 2004, Published online: 21 February 2005PACS: 13.20.Eb, 11.30.Rd, 12.39.Fe     

Annealing study of electrodeposited CuInSe<Subscript>2</Subscript> and CuInS<Subscript>2</Subscript> thin films

In this study CuInSe₂ and CuInS₂ thin films were prepared onto ITO glass substrate using the electrodeposition technique in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis. The annealing effects on electrodeposited precursors were investigated. The chalcopyrite structure of CuInSe₂/CuInS₂ showed an enhancement of crystallinity after subsequent selenization/sulfurization treatment in Se/S atmosphere, respectively. XRD and SEM studies revealed a dramatic improvement of the crystalline quality of CIS films after annealing treatments. Mott–Schottky measurements were used to assess the conductivity type of the films and their carrier concentration. The prepared samples underwent an etching process to remove the binary accumulated Cu_2?x(Se,S) phases shown in FESEM pictures. This etching process has shown a noticeable decrease in both, the flat band potential, V_fb (V), and the number of acceptors, N_A (cm^?3) in selenized CuInSe₂ and sulfurized CuInS₂ samples.     

<Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>3</Subscript> decays and CKM unitarity

We present a detailed numerical study of the K_e3 decays to in chiral perturbation theory with virtual photons and leptons. We describe the extraction of the CKM matrix element |V_us| from the experimental K_e3 decay parameters. We propose a consistency check of the K ⁺ _e3 and K⁰_e3 data that is largely insensitive to the dominating theoretical uncertainties, in particular the contributions of . Our analysis is highly relevant in view of the recent high statistics measurement of the K ⁺ _e3 branching ratio by E865 at Brookhaven which does not indicate any significant deviation from CKM unitarity but rather a discrepancy with the present K⁰_e3 data.Received: 22 January 2004, Published online: 30 April 2004Work supported in part by IHP-RTN, Contract No. HPRN-CT2002-00311 (EURIDICE) and by Acciones Integradas, Project No. 19/2003 (Austria), HU2002-0044 (MCYT, Spain)     

<Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">K</Emphasis></Subscript> from the lattice with Wilson quarks

We report our results for the bag parameter B _K obtained from the quenched simulations on the lattice with Wilson fermions for three values of the lattice spacing. We implemented the method by which no subtraction of the mixing with other four-fermion operators is needed. Our final result, in terms of the renormalization group invariant bag parameter, is .Received: 9 July 2004, Revised: 27 July 2004, Published online: 21 September 2004     

Thermoelectric Properties of the TlBiS<Subscript>2</Subscript>-PbS Alloys

High efficiency of thermoelectric conversion can be achieved by using materials with a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Mass-difference-scattering of the phonons is one of the most effective way for reducing the thermal conductivity in bulk thermoelectric materials. Investigations of transport phenomena in (TlBiS₂)_1-x (2PbS)_x alloys system have shown that in solid solutions of the (A³B⁵C ₂ ⁶ )_1-x (2A⁴B⁶)_x type at cation substitution according to scheme 2A⁴⁽⁺²⁾ A ³⁽⁺¹⁾ + B⁵⁽⁺³⁾ occurs a strong decrease of the lattice thermal conductivity. In the vicinity of x = 0. 50 the lattice part of thermal conductivity of (TlBiS₂)_1-x (2PbS)_x alloys decreases down to 0. 26 W/mK, i. e., it approaches the theoretical minimum. As a result, the thermoelectric figure of merit for these alloys ( 25%) exceeds the respective value for lead sulfide at room temperature.     

Behavior of the hadron potential at large distances and properties of the hadron spin-flip amplitude

The impact of the form of the hadron potential at large distances on the behavior of the hadron spin-flip amplitude at small angles is examined. The t-dependence of the spin-flip amplitude of high-energy hadron elastic scattering is analyzed under different assumptions on the hadron interaction. It is shown that the long tail of the nonGaussian form of the hadron potential of the hadron interaction in the impact parameter representation leads to a large value of the slope of the spin-flip amplitude (without the kinematical factor ) as compared with the slope of the spin-nonflip amplitude. This effect can explain the form of the differential cross-section and the analyzing power at small transfer momenta. The methods for the definition of the spin-dependent part of the hadron scattering amplitude are presented. A possibility to investigate the structure of the hadron spin-flip amplitude from the accurate measure of the differential cross-section and the spin correlation parameters is shown. Received: 14 December 2001 / Accepted: 17 January 2002     

Pressure-induced antiferromagnetism in La<Subscript>0.75</Subscript>Ca<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> manganite

The crystal and magnetic structures of La_0.75Ca_0.25MnO₃ manganite are studied under high pressures up to 4.5 GPa in the temperature range 12–300 K by the neutron diffraction method. At normal pressure and temperature T _C = 240 K, a ferromagnetic state is formed in La_0.75Ca_0.25MnO₃. At high pressures P ≥ 1.5 GPa and at temperatures T < T _N ≈ 150 K, a new A-type antiferromagnetic state appears. A further increase in pressure leads to an increase in the volume fraction of the antiferromagnetic phase, which coexists with the initial ferromagnetic phase. The effect of high pressure causes a considerable increase in T _C with the slope dT _C /dP ≈ 12 K/GPa. Calculations performed in the framework of the double exchange model with allowance for the electron-phonon interaction make it possible to explain this pressure dependence of T _C on the basis of experimental data.     

Superposition of M<Subscript>5</Subscript>X<Subscript>5</Subscript> superstructures and X-ray diffraction in TiO<Subscript>1.0</Subscript> titanium monoxide

The interpretation of diffraction spectra of ordered high-temperature phases of solid solutions and strongly nonstoichiometric compounds is discussed. It has been shown that variations of the intensities of superstructure reflections, which cannot be explained within simple ordering models, can be due to the superposition of superstructures with different symmetries in the matrix of the basis crystal structure. Using an example of atom–vacancy ordering in TiO_1.0 titanium monoxide, a model of the order–order transition state formed by the superposition of low-temperature monoclinic (space group A2/m (C2/m)) and high-temperature cubic (space group Pm3?m) M₅X₅ superstructures has been proposed. It has been shown that the transition state is thermodynamically equilibrium and should be implemented instead of the M₅X₅ cubic superstructure. The transition state model can be considered as an M_(5–i)X_(5–i) superstructure (i = 1, 14/18, 11/18) with the monoclinic symmetry (space group P1m1).     

Is there a hadron spin-flip contribution to the Coulomb-hadron interference at small momentum transfer and high energies?

The analysing power A_N is examined in the range of the Coulomb-hadron interference on the basis of the experimental data from p_L = 6 GeV/c up to 200 GeV/c taking account of a phenomenological analysis at p_L = 6 GeV/c and a dynamic high-energy spin model. The results are compared with the new RHIC data at p_L = 100 GeV/c. The new experimental data obtained at RHIC indicate small contributions of the hadron spin-flip amplitude.