The evolution of parton distributions at small x

We investigate parton distributions at small x using moments of the Gribov-Lipatov-Altarelli-Parisi (GLAP) evolution equation with respect to x. In this representation the kernel of the GLAP equation contains singularities in the moment variable ω at ω = 0. We show that the importance of these singularities at small x depends on the form of the starting distributions. We examine the range of x in which the GLAP equation is valid. The restrictions on the range of x depend on the form of the starting distributions. We investigate whether the GLAP equation can be used to interpolate data in the HERA region. Results are given for the structure function F₂ at small x. A possible method of determining the gluon distribution from F₂ is discussed.     

x-distribution of non-singlet structure function at low and high x

In recent years, study of parton distribution function (PDF) has itself become a topic of significant interest. To overcome the shortcoming of the conventional PDF, several alternative methods have been proposed in recent years like neural network formalism. In the present work, x distribution of the non-singlet structure function is obtained using the recently reported complete solution of Taylor-approximated DGLAP equation. The results are compared with exact results as well as CCFR data.     

Saturation momentum at fixed and running QCD coupling

A relationship linking the saturation momentum in the case of fixed and running QCD coupling, respectively, is derived from the Balitsky-Kovchegov equation. It relies on the linear instability of the evolution equation in the dilute regime. The relationship can also be derived for the Balitsky-Kovchegov equation with a cutoff accounting for low-density effects. Arrival of the final proofs: 7 December 2005     

Simplified test of universality in lattice QCD

A simplified test of universality in lattice QCD is performed by analytically evaluating the continuous Euclidean time limits of various lattice fermion determinants, both with and without a Wilson term to lift the fermion doubling on the Euclidean time axis, and comparing them with each other and with the zeta-regularized fermion determinant in the continuous time-lattice space setting. The determinant relations expected from universality considerations are found to be violated by a certain gauge field-dependent factor; i.e., we uncover a "universality anomaly." The physical significance, or lack thereof, of this factor is a delicate question that remains to be settled.     

Low-x QCD studies with forward jets in p-p at 14 TeV

The Large Hadron Collider will provide hadronic collisions at energies in the multi-TeV range, never explored before. The parton fractional momenta probed at such energies can be as low as $ x \approx 2p_T /\sqrt {se^{ - y} } \approx 10^{ - 5} $ x \approx 2p_T /\sqrt {se^{ - y} } \approx 10^{ - 5} at large rapidities y, opening up attractive opportunities for low-x QCD studies. The combination of the CMS HF (3< |η| <5) and CASTOR (5.1< |η| <6.6) calorimeters allows one, in particular, to reconstruct very forward jets. We present generator-level studies of the CMS capabilities to measure the single inclusive forward jet spectrum and forward-backward (Mueller-Navelet) dijets in p-p collisions at 14 TeV. Both observables are sensitive to low-x gluon densities and non-linear QCD evolution.     

Saturation and BFKL dynamics in the HERA data at small-x

We show that the HERA data for the inclusive structure function F₂(x,Q²) for x10⁻² and 0.045Q²45 GeV² can be well described within the color dipole picture, with a simple analytic expression for the dipole–proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Q_s(x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger than 1/Q_s(x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x₀ of x at which the saturation scale Q_s equals 1 GeV, and the logarithmic derivative of the saturation momentum λ. The value of λ extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism.     

Two particle correlations: Saturation and issues with universality

We study the universality issue of the transverse momentum dependent parton distributions at small-x, by comparing the initial/final state interaction effects in di-jet correlation in pA collisions with those in deep inelastic lepton–nucleus scattering. We demonstrate the non-universality by performing an explicit calculation in a particular model where the multiple gauge boson exchange contributions are summed up to all orders. In addition, we generalize the model calculation to the CGC formalism, and find the non-universality for quark distributions in CGC.     

Electrical and photovoltaic properties of Cd1? x Zn x S/ p -GaAs heterojunctions

Cd_1−x Zn _x S/p-GaAs heterojunctions for solar cell applications have been prepared by growing single crystal Cd_1−x Zn _x S epitaxial layers on (111)GaAs substrates through a vapour phase chemical transport method using the close-spaced geometry and H₂ as a transport agent. Electrical and photovoltaic properties of the heterojunctions have been investigated and discussed in connection with the main features of the growth technique. AM1 power conversion efficiencies up to 6.2% have been measured and possible improvements have been examined.     

Distribution of valence quarks in hadrons at small x in QCD

Valence u- and d-quark distributions in nucleons and pions at small x corresponding to ? and ω Regge pole exchanges have been obtained on the basis of the QCD sum rule method.     

Enhancement of minority carrier lifetime in GaAs1? x P x ( x =0.4; 0.65) by nitrogen implantation

Minority carrier lifetimes in nitrogen implanted GaAs_1-x P _x (x=0.4; 0.65) were measured at 77K by an optical phase shift method as a function of nitrogen dose and annealing temperature in order to investigate the dependence of the lifetime on the concentration of nitrogen isoelectronic traps. A large increase in the lifetime was observed after nitrogen implantation followed by annealing at and above 800°C. The maximum lifetimes were 22ns for GaAs_0.35P_0.65 and 6.7 ns for GaAs_0.6P_0.4. They were obtained by implantation to a dose of 5×10¹³ cm⁻² in GaAs_0.35P_0.65 and 10¹³ cm⁻² in GaAs_0.6P_0.4. The lifetime after nitrogen implantation followed by annealing was longer by a factor of 6–7 than that of the unimplanted sample.     

Diffraction at small M^2/Q^2 in the QCD dipole picture

Using the QCD dipole picture of BFKL dynamics, the quasi-elastic component of the diffractive -dipole cross-section, dominating at small , is calculated. Received: 17 November 1998 / Revised version: 15 December 1998 / Published online: 7 April 1999     

Charge ordering in crystals of Pr1? x Sr x MnO3 ( x = 0.22, 0.24) ferromagnetic manganites

The structural and magnetic states of Pr_1−x Sr _x MnO₃ (x = 0.22, 0.24) manganite crystals were studied over a wide temperature range. Measurements of the magnetic susceptibility and electrical resistivity demonstrated that these manganites belong to the class of ferromagnetic semiconductors. Thermal neutron elastic scattering patterns revealed that, in the temperature range 4.2–350 K, the manganites have an orthorhombic structure (space group Pnma) with a well-pronounced cooperative Jahn-Teller effect. Major emphasis was placed on the nuclear magnetic superstructure with a wave vector q = (2π/2a, 0, 2π/2c). It was shown that this superstructure suggests 1/4-type charge ordering in the manganites under investigation. Original Russian Text ? S.F. Dubinin, S.G. Teploukhov, V.E. Arkhipov, V.D. Parkhomenko, é.A. Neĭfel’d, A.V. Korolev, N.A. Ugryumova, Ya.M. Mukovskiĭ, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 704–710.     

Properties of Hg implanted Hg1? x Cd x Te infrared detectors

Experimental performance parameters of Hg implanted Hg_1−x Cd _x Te photovoltaic detectors are analyzed. At 77K, for 8–14 μm band, a comparison is made between performances and theoretical ultimate diffusion limits in low frequency direct detection. Experimental features are well-explained by a model based on the Auger band-to-band process for carrier recombination. Peak detectivities exceeding 10¹¹ cm Hz^1/2W⁻¹, external quantum efficiencies as high as 90%, and zero-bias resistance-area products better than 1 Ω·cm² have been achieved in devices with 12 μm cutoff wavelengths. In the 3–5 μm band performances are far from the diffusion limit. Notwithstanding, at 77K zero-bias resistance-area products are better than 10⁴Ω·cm² and detectivities of the order of 10¹² cm Hz^1/2W⁻¹ were observed at 5 μm. Predominant generation-recombination contribution are present at room temperature in 1–1.3 μm photodiodes whose detectivities, primarily limited by the Johnson noise, at 1.3 μm are higher than 10¹¹ cm Hz^1/2W⁻¹ at 300 K. The high frequency response of the photodiodes is also discussed. Response times as low as 0.5 ns are reached despite some limitations arising from the implanted layer sheet resistance. Work supported by CNR-CISE contract No. 73.01435.     

Measurement of the proton structure function F 2 at low x and low Q 2 at HERA

We report on a measurement of the proton structure functionF ₂ in the range 3.5×10⁻⁵≤x≤4×10⁻³ and 1.5 GeV²≤Q ²≤15GeV² at theep collider HERA operating at a centre-of-mass energy of √s=300GeV. The rise ofF ₂ with decreasingx observed in the previous HERA measurements persists in this lowerx andQ ² range. TheQ ² evolution ofF ₂, even at the lowestQ ² andx measured, is consistent with perturbative QCD. supported by EU HCM contract ERB-CHRX-CT93-0376     

Formation of the polycrystalline FeSi phase with the CsCl structure in codeposited thin Fe x Si1 ? x films ( x = 0.5–0.6)

Specific features of the phase formation in the Fe-Si system within the Fe _x Si_{1 − x} (x = 0.5–0.6) concentration range have been investigated. The data obtained by conversion electron M?ssbauer spectroscopy suggest that, for the Fe-Si system in the concentration range x > 0.55, a polycrystalline FeSi phase with the CsCl structure is formed under thermodynamically equilibrium conditions upon annealing at T = 250°C; in this case, the excess (overstoichiometric) Fe atoms are incorporated into the Si sublattice. Previously, the CsCl-FeSi phase was observed only in epitaxially stabilized FeSi/Si(100) layers. Original Russian Text ? A.V. Zenkevich, D.E. Lauer, V.P. Filippov, 2007, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 9, pp. 1313–1315.     

Orbitally excited D and B mesons in the approach of the QCD string with quarks at the ends

In this Letter we discuss the masses and the splittings of 1^2S+1P_J states in the spectrum of D and B mesons, as they appear in the approach of the QCD string with quarks at the ends. We find good agreement of our predictions with those of other QCD-motivated models as well as with the lattice and experimental data, including recent experimental results. We discuss the ordering pattern for P levels in D- and B-mesonic spectrum.     

QCD predictions for polarized deep inelastic scattering accompanied by a forward jet in the low x region of possible HERA measurements

We estimate the cross-section and asymmetry relevant for the production of forward jets in polarized deep inelastic scattering in the region of small values of x which can be probed at possible polarized HERA measurements. The kinematical cuts implemented in our analysis are the same as those which were used in the unpolarized deep inelastic scattering at HERA. The calculations are based on the double ln²(1/x) resummation which controls the polarized deep inelastic scattering for small values of the Bjorken parameter x. We show that this resummation substantially enhances the corresponding cross-section and asymmetry. The predicted value of the asymmetry is found to vary between −0.01 and −0.04 within the small x region which can possibly be probed at polarized HERA measurements.