Order \alpha_s^2 Contributions to charm production in charged-current deep-inelastic lepton-hadron scattering

The most important part of the order $\alpha_s^2$ corrections to the charm component of the charged-current structure functions $F_2(x,Q^2)$ and $F_3(x,Q^2)$ have been calculated. This calculation is based on the asymptotic form of the heavy-quark coefficient functions corresponding to the higher order corrections to the W-boson-gluon fusion process. These coefficient functions which are in principle only valid for $Q^2 \gg m^2$ can be also used to estimate the order $\alpha_s^2$ contributions at lower $Q^2$ values provided $x < 0.1$. It turns out that the above corrections are appreciable in the large $Q^2$-region and they explain the discrepancy found for the structure functions between the fixed-flavour scheme (FFS) and the variable-flavour-number scheme (VFNS). These corrections also hamper the extraction of the strange-quark density from the data obtained for the charged-current and the electromagnetic-current processes.Comment: 45 pages LaTeX, 17 Postscript Figure

Dynamical NNLO parton distributions

Utilizing recent DIS measurements (\sigma_r, F_{2,3,L}) and data on hadronic dilepton production we determine at NNLO (3-loop) of QCD the dynamical parton distributions of the nucleon generated radiatively from valencelike positive input distributions at an optimally chosen low resolution scale (Q_0^2 < 1 GeV^2). These are compared with `standard' NNLO distributions generated from positive input distributions at some fixed and higher resolution scale (Q_0^2 > 1 GeV^2). Although the NNLO corrections imply in both approaches an improved value of \chi^2, typically \chi^2_{NNLO} \simeq 0.9 \chi^2_{NLO}, present DIS data are still not sufficiently accurate to distinguish between NLO results and the minute NNLO effects of a few percent, despite of the fact that the dynamical NNLO uncertainties are somewhat smaller than the NLO ones and both are, as expected, smaller than those of their `standard' counterparts. The dynamical predictions for F_L(x,Q^2) become perturbatively stable already at Q^2 = 2-3 GeV^2 where precision measurements could even delineate NNLO effects in the very small-x region. This is in contrast to the common `standard' approach but NNLO/NLO differences are here less distinguishable due to the much larger 1\sigma uncertainty bands. Within the dynamical approach we obtain \alpha_s(M_Z^2)=0.1124 \pm 0.0020, whereas the somewhat less constrained `standard' fit gives \alpha_s(M_Z^2)=0.1158 \pm 0.0035.Comment: 44 pages, 15 figures; minor changes, footnote adde

Bottom quark electroproduction in variable flavor number schemes

Two variable flavor number schemes are used to describe bottom quark production in deep inelastic electron-proton scattering. In these schemes the coefficient functions are derived from mass factorization of the heavy quark coefficient functions presented in a fixed flavor number scheme. Also one has to construct a parton density set with five light flavors (u,d,s,c,b) out of a set which only contains four light flavors (u,d,s,c). In order $\alpha_s^2$ the two sets are discontinuous at $\mu=m_b$ which follows from mass factorization of the heavy quark coefficient functions when it is carried out in the ${\bar {\rm MS}}$-scheme. Both variable flavor number schemes give almost identical predictions for the bottom structure functions $F_{2,b}$ and $F_{L,b}$. Also they both agree well with the corresponding results based on fixed order four-flavor perturbation theory over a wide range in $x$ and $Q^2$.Comment: Latex with seventeen PostScript figure

A Variable-Flavour Number Scheme for NNLO

At NNLO it is particularly important to have a Variable-Flavour Number Scheme (VFNS) to deal with heavy quarks because there are major problems with both the zero mass variable-flavour number scheme and the fixed-flavour number scheme. I illustrate these problems and present a general formulation of a Variable-Flavour Number Scheme (VFNS)for heavy quarks that is explicitly implemented up to NNLO in the strong coupling constant alpha_S, and may be used in NNLO global fits for parton distributions. The procedure combines elements of the ACOT(chi) scheme and the Thorne-Roberts scheme. Despite the fact that at NNLO the parton distributions are discontinuous as one changes the number of active quark flavours, all physical quantities are continuous at flavour transitions and the comparison with data is successful.Comment: 17 pages, 5 figures included as .ps files, uses axodraw. One additional explanatory sentence after eq. (25). Correction of typos and updated references. To be published in Phys. Rev.

Caracterização da colheita florestal em Cabinda, Angola.

Made available in DSpace on 2011-10-13T14:29:05Z (GMT). No. of bitstreams: 1 Ufra4559.pdf: 359633 bytes, checksum: 50c870722483fa72e8a00abfa2c0107e (MD5) Previous issue date: 2007-09-1

Treatment of Heavy Quarks in Deeply Inelastic Scattering

We investigate a simplified version of the ACOT prescription for calculating deeply inelastic scattering from Q^2 values near the squared mass M_H^2 of a heavy quark to Q^2 much larger than M_H^2.Comment: 14 pages, 5 figure

Variable Flavor Number Parton Distributions and Weak Gauge and Higgs Boson Production at Hadron Colliders at NNLO of QCD

Based on our recent NNLO dynamical parton distributions as obtained in the `fixed flavor number scheme', we generate radiatively parton distributions in the `variable flavor number scheme' where also the heavy quark flavors (c,b,t) become massless partons within the nucleon. Only within this latter factorization scheme NNLO calculations are feasible at present, since the required partonic subprocesses are only available in the approximation of massless initial-state partons. The NNLO predictions for gauge boson production are typically larger (by more than 1 sigma) than the NLO ones, and rates at LHC energies can be predicted with an accuracy of about 5%, whereas at Tevatron they are more than 2 sigma above the NLO ones. The NNLO predictions for SM Higgs boson production via the dominant gluon fusion process have a total (pdf and scale) uncertainty of about 10% at LHC which almost doubles at the lower Tevatron energies; they are typically about 20% larger than the ones at NLO but the total uncertainty bands overlap.Comment: 28 pages, 3 tables, 6 figure

Deep-inelastic production of heavy quarks

Deep-inelastic production of heavy quarks at HERA, especially charm, is an excellent signal to measure the gluon distribution in the proton at small $x$ values. By measuring various differential distributions of the heavy quarks this reaction permits additional more incisive QCD analyses due to the many scales present. Furthermore, the relatively small mass of the charm quark, compared to the typical momentum transfer $Q$, allows one to study whether and when to treat this quark as a parton. This reaction therefore sheds light on some of the most fundamental aspects of perturbative QCD. We discuss the above issues and review the feasibility of their experimental investigation in the light of a large integrated luminosity.Comment: 10 pages, uses epsfig.sty, five ps figures included. To appear in the proceedings of the workshop Future Physics at HERA, eds. G. Ingelman, A. De Roeck and R. Klanner, DESY, Hamburg, 199

Experimental-confirmation and functional-annotation of predicted proteins in the chicken genome

<p>Abstract</p> <p>Background</p> <p>The chicken genome was sequenced because of its phylogenetic position as a non-mammalian vertebrate, its use as a biomedical model especially to study embryology and development, its role as a source of human disease organisms and its importance as the major source of animal derived food protein. However, genomic sequence data is, in itself, of limited value; generally it is not equivalent to understanding biological function. The benefit of having a genome sequence is that it provides a basis for functional genomics. However, the sequence data currently available is poorly structurally and functionally annotated and many genes do not have standard nomenclature assigned.</p> <p>Results</p> <p>We analysed eight chicken tissues and improved the chicken genome structural annotation by providing experimental support for the <it>in vivo </it>expression of 7,809 computationally predicted proteins, including 30 chicken proteins that were only electronically predicted or hypothetical translations in human. To improve functional annotation (based on Gene Ontology), we mapped these identified proteins to their human and mouse orthologs and used this orthology to transfer Gene Ontology (GO) functional annotations to the chicken proteins. The 8,213 orthology-based GO annotations that we produced represent an 8% increase in currently available chicken GO annotations. Orthologous chicken products were also assigned standardized nomenclature based on current chicken nomenclature guidelines.</p> <p>Conclusion</p> <p>We demonstrate the utility of high-throughput expression proteomics for rapid experimental structural annotation of a newly sequenced eukaryote genome. These experimentally-supported predicted proteins were further annotated by assigning the proteins with standardized nomenclature and functional annotation. This method is widely applicable to a diverse range of species. Moreover, information from one genome can be used to improve the annotation of other genomes and inform gene prediction algorithms.</p

Charm quark and D^* cross sections in deeply inelastic scattering at DESY HERA

A next-to-leading order Monte Carlo program for the calculation of heavy quark cross sections in deeply inelastic scattering is described. Concentrating on charm quark and D^*(2010) production at HERA, several distributions are presented and their variation with respect to charm quark mass, parton distribution set, and renormalization-factorization scale is studied.Comment: 15 pages including 8 figures. Uses Latex, Revtex, and psfig. References added - others updated. Several sentences/words added for clarity. Results/conclusions unchanged. To appear in Phys. Rev.