A Fixed-Order Calculation of the Heavy-Quark Fragmentation Function in e+e- Collisions

We use a recently completed O(alpha_s^2) fixed-order calculation of the heavy-flavour production cross section in e+e- collisions to compute the heavy-quark fragmentation function. We fit the result of our calculation, convoluted with a Peterson fragmentation function, to available data for charm production, and thus obtain a value for the parameter epsilon in the Peterson function. We discuss the relevance of mass effects and of subleading terms in our calculation.Comment: 7 pages, 2 eps figure

Renewable electricity production with some wasted second-life components

Renewable energy systems are playing an important role to reduce CO2 emission and provide electricity for daily use in rural areas. But brand new components with up-to-date technology could be far too expensive for many potential users (rural communities in many developing countries. As a consequence, turning waste components into energy production systems could be a good opportunity to reach these two goals simultaneously. In this paper, a disposal induction motor, a car battery and an Uninterrupted Power Supply (UPS) are combined together in order to generate electrical energy from pico-hydro power. The control of the RMS output voltage and frequency is presented with a comprehensive state-space model, simulation and experimental validation results are provided

QCD Mechanisms for Double Quarkonium and Open Heavy Meson Hadroproduction

Double $J/\psi$ production on the order of 20-30 pb has been observed by the NA3 collaboration. These $\psi \psi$ pairs, measured in $\pi^- N$ interactions at 150 and 280 GeV$/c$ and in $pN$ interactions at 400 GeV$/c$, carry a large fraction of the projectile momentum, $x_{\psi \psi} \geq 0.6$ for the 150 GeV$/c$ beam and $\geq 0.4$ at 280 GeV$/c$. We examine several sources of $\psi \psi$ pair production within QCD, including ${\cal O}(\alpha_s^4)$ $\psi \psi$ production, leading-twist $b \overline b$ production and decay, and the materialization of heavy-quark Fock states in the projectile. We estimate the production cross section and the single and double $J/\psi$ momentum and mass distributions for each, comparing the results with the NA3 data, and predict $\psi \psi$ production in $pN$ interactions at 800 GeV$/c$, accessible to current fixed-target experiments. We also discuss the observable implications of open heavy meson pair production from the intrinsic heavy quark Fock states.Comment: Revtex, APS style, 16 pages, 15 figures available as uuencoded postscript files (or ps files) from the Autho

Differential Distributions for Heavy Flavour Production at HERA

We compute pseudorapidity and transverse momentum distributions for charm and bottom production at HERA. We examine the effect of next-to-leading order QCD corrections, the effect of possible intrinsic transverse momenta of the incoming partons, and of fragmentation. We compare our results with full Monte Carlo simulation using HERWIG. The importance of the hadronic component of the photon is also studied. We examine the possibility to distinguish among different parametrizations of the photon parton densities using charm production data, and the possibilty to extract information about the small-$x$ behaviour of the gluon density of the proton. We also give a prediction for the transverse momentum and pseudorapidity distributions for bottom production at HERA.Comment: 25 pages, Latex, epsfig, 19 tar-gzip-uuencoded figures. Also available from http://surya11.cern.ch/users/nason/mis

Perturbative Prediction for Parton Fragmentation into Heavy Hadron

By expanding functions of parton fragmentation into a heavy hadron in the inverse of the heavy quark mass $m_Q$ we attempt to factorize them into perturbative- and nonperturbative parts. In our approach the nonperturbative parts can be defined as matrix elements in heavy quark effective theory, the shape of the functions is predicted by perturbative QCD. In this work we neglect effect at order of $m_Q^{-2}$ and calculate the perturbative parts at one-loop level for heavy quark- and gluon fragmentation. We compare our results from leading log approximation with experimental results from $e^+e^-$ colliders and find a deviation below or at 10% level. Adding effect of higher order in $\alpha_s$ it can be expected to reduce the deviation. The size of matrix elements appearing at the order we consider for several types of heavy hadrons is determined.Comment: 21 pages + 3 pages figures, plain te

Hadron multiplicity induced by top quark decays at the LHC

The average charged hadron multiplicities induced by top quark decays are calculated in pQCD at LHC energies. Different modes of top production are considered. Proposed measurements can be used as an additional test of pQCD calculations independent on a fragmentation model.Comment: 12 pages, 12 figures, to be published elsewher

Heavy-Quark Correlations in Direct Photon-Photon Collisions

In two-photon collisions at LEP2 and a future $e^+e^-$ linear collider heavy quarks (mainly charm) will be pair-produced rather copiously. The production via direct and resolved photons can be distinguished experimentally via a remnant-jet tag. We study correlations of the heavy quarks at next-to-leading order in QCD in the direct channel, which is free from phenomenological parton densities in the photon. These correlations are therefore directly calculable in perturbative QCD and provide a stringent test of the production mechanism.Comment: 10 pages, LaTeX, epsfig, 5 figures appended as uuencoded file (hardcopy can be obtained upon request from [email protected] or [email protected]

Is There a Significant Excess in Bottom Hadroproduction at the Tevatron?

We discuss the excess in the hadroproduction of B mesons at the Tevatron. We show that an accurate use of up-to-date information on the B fragmentation function reduces the observed excess to an acceptable level. Possible implications for experimental results reporting bottom quark cross sections, also showing an excess with respect to next-to-leading order theoretical predictions, are discussed.Comment: 5 pages, Latex, 4 figures. Submitted to Phys. Rev. Let