Investigation of Quark-Antiquark Interaction Properties using Leading Particle Measurements in e+e- Annihilation

Measurements of heavy quark production in electron-positron collisions are used to analyse the strong interactions between quarks and anti-quarks. A scaling behaviour is observed in distributions of the rapidity change of D*, B*, and B mesons. From these distributions information is obtained on the hadron formation time, effective quark masses, and the potential between quark-antiquark pairs. Predictions for fragmentation functions are presented.Comment: 10 pages, 4 figures, fig.2 references added, revised version accepted by Physics Letters

Elección del verso sobre la prosa en el De Rerum Natura de Lucrecio : La poesía al servicio de la enseñanza

Una acostumbrada y debatida concepción considera inadecuado expresar temas filosóficos por medio del uso de la poesía, pues en líneas generales la poesía no satisface el rigor y claridad necesarios para desarrollar temas científicos. Este conflicto entre contenido y forma es reconocido como una característica de la poesía didáctica que se manifiesta muy bien en el poema de Lucrecio. Sin embargo, Lucrecio no fue el primero en intentar este acercamiento poético a la filosofía con fines persuasivo-instructivos; esta elección, a pesar de contradecir los preceptos de Epicuro, estaba acorde con el modelo de discurso escrito empleado por algunos pensadores pre-socráticos para transmitir conocimientos sobre fenómenos naturales. El estudio de esta preferencia estilística en la obra de Lucrecio nos ayudará a comprender mejor la intención persuasivo-instructiva a la que apunta este controvertido texto y mostrar, a partir de ahí, nuevas luces que puedan ayudar a alcanzar una mejor interpretación del mismoA debated and usual conception considers inadequate to express philosophical subjects by means of poetry, for in a general sense, poetry do not satisfies the necessary rigor and clarity to develop scientific subjects. This conflict between form and content is well known as a didactic poetry feature, and easily recognizable in Lucretius?s poem. Nevertheless, Lucretius was not the first to attempt this poetic approach to philosophy with persuasive-instructive purposes; despite contradicting the Epicurean precepts, this choice was in consonance with the written discourse used by some of the pre Socratic thinkers to transmit knowledge about natural phenomena. The study of this stylistic preference in Lucretius?s work will help us reach a better understanding of the persuasive-instructive intention to which this controversial text aim

Symmetry restoration of the soft pion corrections for the light sea quark distributions in the small xx region

The soft pion correction at high energy may play a crucial role in non-perturbative parts of sea quark distributions. In this paper, we show that, while the soft pion correction for the strange sea qaurk distribution is suppressed in the large and the medium $x$ region compared with that for the up and the down sea quark one, it can become large and SU(3) flavor symmetric in the very small $x$ region. This gives us a good reason for the symmetry restoration of light sea quark distributions required by the mean charge sum rule for the light sea quarks. Then, by estimating this sum rule with the help of the results obtained by the soft pion correction, it is argued that there is a large symmetry restoration of the strange sea quark in the region from $x=10^{-2}$ to $10^{-6}$ at $Q^2\sim 1$ GeV.Comment: 22 pages including 4 eps figures, ReVTeX, to appear in Phys. Rev.

QCD at high energy (experiments)

Recent measurements of QCD interactions involving large momentum transfers are reviewed. The status of measurements of the strong coupling constant is summarised. Recent developments in the measurement and interpretation of deep inelastic scattering, proton-anti-proton collisions and two-photon processes are discussed. While QCD at next-to-leading order gives a qualitative description of many processes, next-to-NLO calculations are now required to allow quantitative information to be extracted from hadron-initiated multijet data. This is illustrated by a discussion of recent data on the photoproduction of dijet events at HERA.Comment: Talk presented at the $31^{\rm st}$ International Conference on High Energy Physics, Amsterdam, 24-31 July 2002. 18 pages, 30 figure

Strongly walk-regular graphs

We study a generalization of strongly regular graphs. We call a graph strongly walk-regular if there is an $\ell >1$ such that the number of walks of length $\ell$ from a vertex to another vertex depends only on whether the two vertices are the same, adjacent, or not adjacent. We will show that a strongly walk-regular graph must be an empty graph, a complete graph, a strongly regular graph, a disjoint union of complete bipartite graphs of the same size and isolated vertices, or a regular graph with four eigenvalues. Graphs from the first three families in this list are indeed strongly $\ell$-walk-regular for all $\ell$, whereas the graphs from the fourth family are $\ell$-walk-regular for every odd $\ell$. The case of regular graphs with four eigenvalues is the most interesting (and complicated) one. Such graphs cannot be strongly $\ell$-walk-regular for even $\ell$. We will characterize the case that regular four-eigenvalue graphs are strongly $\ell$-walk-regular for every odd $\ell$, in terms of the eigenvalues. There are several examples of infinite families of such graphs. We will show that every other regular four-eigenvalue graph can be strongly $\ell$-walk-regular for at most one $\ell$. There are several examples of infinite families of such graphs that are strongly 3-walk-regular. It however remains open whether there are any graphs that are strongly $\ell$-walk-regular for only one particular $\ell$ different from 3

Heavy Flavor Enhancement as a Signal of Color Deconfinement

We argue that the color deconfinement in heavy ion collisions may lead to enhanced production of hadrons with open heavy flavor (charm or bottom). We estimate the upper bound of this enhancement.Comment: 7 pages, LaTeX, 3 PS-figure

Lablab purpureus (L.) sweet soil-plant system towards the recovery of marginal lands

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