The contribution of off-shell gluons to the longitudinal structure function F<Subscript>L</Subscript>

We present the results for the structure function for a gluon target having a non-zero transverse momentum square at order . The results of a double convolution (with respect to the Bjorken variable x and the transverse momentum) of the perturbative part and the unintegrated gluon densities are compared with recent experimental data for at low x values and with the predictions of other approaches. Received: 21 August 2002 / Revised version: 31 October 2002 Published online: 24 January 2003     

Spin glass and ferromagnetism in Kondo lattice compounds

The Kondo lattice model has been analyzed in the presence of a random inter-site interaction among localized spins with non zero mean J₀ and standard deviation J. Following the same framework previously introduced by us, the problem is formulated in the path integral formalism where the spin operators are expressed as bilinear combinations of Grassmann fields. The static approximation and the replica symmetry ansatz have allowed us to solve the problem at a mean field level. The resulting phase diagram displays several phase transitions among a ferromagnetically ordered region,a spin glass one, a mixed phase and a Kondo state depending on J₀, J and its relation with the Kondo interaction coupling J_K. These results could be used to address part of the experimental data for the CeNi _{1 - x} Cu _x compound, when x ⩽ 0.8. Received 24 June 2002 Published online 31 December 2002     

A simple model for nuclear structure functions at small x in the dipole picture

A simple model for nuclear structure functions in the region of small x and small and moderate Q² is presented. It is a parameter-free extension, in the Glauber-Gribov approach to nuclear collisions, of a saturation model for the nucleon. A reasonable agreement with experimental data on the ratios of nuclear structure functions is obtained. Nuclear effects in the longitudinal-to-transverse cross section ratios are found to be small. Predictions of the model for values of x smaller than those available to present experiments are given. The unintegrated gluon distribution and the behaviour of the saturation scale which result from this model are shown and discussed. Received: 5 June 2002 / Revised version: 27 June 2002 / Published online: 16 October 2002     

Theoretical total ionization cross-sections of CH x,CF x,SiH x,SiF x ( ) and CCl 4 targets by electron impact

Total ionization cross-sections of electron impact are calculated for the molecular targets CH_x, CF_x, SiH_x, SiF_x (x = 1-4) and CCl₄ at incident energies 20-3 000 eV. The calculation is based on Complex Scattering Potential approach, as developed by us recently. This leads to total inelastic cross-sections, from which the total ionization cross-sections are extracted by reasonable physical arguments. Extensive comparisons are made here with the previous theoretical and experimental data. The present results are satisfactory except for the CF_x and SiF_x (x = 1-3) radicals, for which the experimental data are lower than most of the theories by more than 50%. Received 23 May 2002 / Received in final form 24 October 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: knjoshipura@yahoo.com     

Inclusive production of antihyperons in nC-interactions

The inclusive production cross-sections of , , and in neutron-carbon interactions at GeV mean energy of neutrons have been measured. The parameters n and b of differential cross-section parametrisation , where x_F is the Feynman variable, p_t is the transverse momentum, have been obtained. The kinematic region of validity of the parametrisation has been defined. Results are compared with published experimental data. Received: 7 June 2002 / Revised version: 23 January 2003 / Published online: 3 March 2003     

Charmonium production in deep inelastic scattering at HERA

The electroproduction of and mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers and photon-proton centre of mass energies GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic production is measured as a function of and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic and meson production is measured as a function of . The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions. Received: 10 March 1999 / Published online: 8 September 1999     

Delineating the polarized and unpolarized photon distributions of the nucleon in <Emphasis Type="Italic">eN</Emphasis> collisions

The production rates of lepton-photon and dimuon pairs at the HERA collider and the HERMES experiment are evaluated in the leading order equivalent photon approximation. It is shown that the production rates are sufficient to facilitate the extraction of the polarized and unpolarized equivalent photon distributions of the proton and neutron in the available kinematical regions. It is pointed out that these results indicate the possibility of additional, independent, tests concerning the unpolarized and polarized structure functions F _1,2 ^N and g _1,2 ^N , respectively, of the nucleon. Received: 2 October 2002 / Revised version: 9 December 2002 / Published online: 14 February 2003     

Measurement of the $b\overline{b}$ production cross section in 920 GeV fixed-target proton-nucleus collisions

Using the HERA - B detector, the production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The production was tagged via inclusive bottom quark decays into by exploiting the longitudinal separation of decay vertices from the primary proton-nucleus interaction. Both e ⁺ e ^- and channels have been reconstructed and the combined analysis yields the cross section . Received: 6 June 2002 / Revised version: 2 September 2002 / Published online: 8 November 2002     

Elementary excitations in multiple quantum wire structures

We calculate the plasmon dispersion of electrons in multiple quantum wire structures. Wave function overlapping effects between different wires are neglected. The Coulomb interaction potential is calculated for a model with circular wire area. Analytical results for the excitation spectrum of electron multiple quantum wire structures are obtained within an one-subband model. Landau damping of intrasubband plasmons is discussed. Results for an electron superlattice within a two-subband model are presented and the coupling of intersubband plasmons with intrasubband plasmons is calculated. We compare the theoretical results with recent Raman measurements of intrasubband plasmons in Al _x Ga_1–x As/GaAs wire superlattices. The plasmon dispersion for boson multiple quantum wire structures also is calculated.     

Double-spin asymmetries in electron-nucleon scattering in Halls B and C at JLab

Three experiments at JLab have measured the double polarization asymmetries ) in the nucleon resonance region, using polarized electron beams incident on polarized proton and deuteron targets. The analysis for the first experiment, eg1a in Hall B, is nearly finished and preliminary values of the spin structure function g₁(x, Q²) and the first moment (x) have been extracted. The other two experiments, one in Hall B and one in Hall C, are still analysing data. Some results are presented.Received: 1 November 2002, Published online: 15 July 2003PACS: 24.70.+s Polarization phenomena in reactions     

Towards a new global QCD analysis: low <Emphasis Type="Italic">x</Emphasis> DIS data from non-linear evolution

A new approach to global QCD analysis is developed. The main ingredients are two QCD-based evolution equations. The first one is the Balitsky-Kovchegov non-linear equation, which sums higher twists while preserving unitarity. The second equation is linear and it is responsible for the correct short distance behavior of the theory, namely it includes the DGLAP kernel. Our approach allows for extrapolation of the parton distributions to the very high energies available at the LHC as well as very low photon virtualities, . All existing low x data on the F₂ structure function are reproduced using two fitting parameters, the other parameters were taken as constants. The result is . Analyzing the parameter at very low x and Q² well below we find -0.1. This is a result which agrees with the “soft pomeron” intercept without involving soft physics. Received: 9 September 2002 / Revised version: 15 November 2002 / Published online: 14 February 2003     

Exactly solvable models through the generalized empty interval method,for multi-species interactions

Multi-species reaction-diffusion systems, with nearest-neighbor interaction on a one-dimensional lattice are considered. Necessary and sufficient constraints on the interaction rates are obtained, that guarantee the closedness of the time evolution equation for E _n(t)'s, the expectation value of the product of certain linear combination of the number operators on n consecutive sites at time t. The constraints are solved for the single-species left-right-symmetric systems. Also, examples of multi-species system for which the evolution equations of E _n(t)'s are closed, are given. Received 25 September 2002 / Received in final form 3 December 2002 Published online 14 February 2003 RID="a" ID="a"e-mail: mamwad@iasbs.ac.ir     

Partial reduction of graphene oxide upon intercalation into exfoliated manganese thiophosphate

Abstract

We have prepared novel nanohybrid Li_2xMn_1?xPS₃/GO films consisting of graphene oxide (GO) and exfoliated MnPS₃ nanosheets via an easy mixing protocol at room temperature. These films were investigated by SEM and AFM, as well as XRD, Raman and XPS spectroscopies, obtaining information about the nature of the interaction between MnPS₃ and GO. In particular, the dark colour of the nanocomposite film and, more to the point, the analysis of (i) the C1s core level XPS spectra, (ii) the interlayer spacing obtained by XRD measurements and (iii) the increment in the intensity ratio I_D/I_G of the two bands typical of the carbon region of GO Raman spectra, suggest that a partial reduction of GO can be obtained right upon intercalation into Li_2xMn_1?xPS₃.     

From Regge behavior to DGLAP evolution

We study the interface between Regge behavior and DGLAP evolution in a non-perturbative model for the nucleon structure function based on a multipole pomeron exchange. This model provides the input for a subsequent DGLAP evolution that we calculate numerically. The soft input and its evolution give a good fit to the experimental data in the whole available range of x and . Received: 4 January 2002 / Revised version: 19 February 2002 / Published online: 5 April 2002