Power-suppressed effects in heavy quark fragmentation functions

This talk summarizes the results of a phenomenological analysis of heavy quark fragmentation data published by the CLEO and BELLE collaborations at \sqrt{s} = 10.6 GeV and by the LEP collaborations at \sqrt{s} = 91.2 GeV. Several theoretical ingredients are employed: next-to-leading order initial conditions, evolution and coefficient functions; soft-gluon resummation to next-to-leading-log accuracy; a next-to-leading order matching condition for the crossing of the bottom threshold in the evolution. Important initial-state electromagnetic radiation effects in the CLEO and BELLE data are also accounted for. We find that with reasonably simple choices of a non-perturbative correction to the fixed-order initial condition for the evolution, the data from CLEO and BELLE can be fitted with remarkable accuracy. The fitted fragmentation function, when evolved to LEP energies, does not however represent fairly the D* fragmentation spectrum measured by ALEPH. Large non-perturbative corrections to the coefficient functions of the meson spectrum are needed in order to reconcile CLEO/BELLE and ALEPH results.Comment: Latex, 9 pages, talk given by M. Cacciari at FRIF workshop on first principles non-perturbative QCD of hadron jets, LPTHE, Paris, France, 12-14 Jan 200

Crossing Heavy-Flavour Thresholds in Fragmentation Functions

In analogy with parton distribution functions, also parton fragmentation functions obey matching conditions when crossing heavy-flavour thresholds. We compute these matching conditions at next-to-leading order in the strong coupling constant alpha_s in the MSbar scheme. Our results can be used for the dynamical generation of the heavy-flavour component in next-to-leading order fits to light-hadrons fragmentation functions. Furthermore, when computing perturbatively the charm fragmentation function from first principles and evolving it to higher scales, our matching conditions should be used for consistency when crossing the bottom threshold.Comment: 9 pages, 2 figure

Phenomenological study of charm photoproduction at HERA

We present predictions for single inclusive distributions of charmed mesons, relevant to the HERA experiments. Our results are based upon a computation that correctly incorporates mass effects up to the next-to-leading order level, and the resummation of transverse momentum logarithms up to next-to-leading-logarithmic level. We apply the same acceptance cuts as the H1 and Zeus experiments, and compare our results to their data. We perform a study of the sensitivity of our predictions on the charm mass, \LambdaQCD, factorization scale, renormalization scale, and fragmentation parameters.Comment: 15 pages Latex; 25 figures include

QCD Predictions for Charm and Bottom Production at RHIC

We make up-to-date QCD predictions for open charm and bottom production at RHIC in nucleon-nucleon collisions at \sqrt{S} = 200 GeV. We also calculate the electron spectrum resulting from heavy flavor decays to allow direct comparison to the data. A rigorous benchmark, including the theoretical uncertainties, is established against which nuclear collision data can be compared to obtain evidence for nuclear effects.Comment: 5 pages, 4 figure

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

Charm Cross Sections for the Tevatron Run II

We present a calculation of the D^{*+}, D^+ and D^0 meson single inclusive production cross section for the Tevatron Run II. We use the FONLL approach in perturbative QCD, which, besides including the known next-to-leading order corrections, also provides for the resummation at the next-to-leading logarithmic level of terms enhanced at large p_T by powers of log(p_T/m), where m is the charm mass and p_T is its transverse momentum. Non-perturbative effects in charm hadronization are extracted, in moment space, from recent ALEPH data for D^* fragmentation in e^+e^- collisions.Comment: 11 pages, 5 figures, LaTe

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

Electrophysiological correlates of idiom comprehension: semantic composition does not follow lexical retrieval

We investigated the extent to which the literal meanings of the words forming literally-plausible idioms (e.g., break the ice) are retrieved from memory and semantically composed during sentence comprehension. Idiom strings were embedded in highly predictable, literal and idiomatic contexts. EEG data showed that the integration of the idiom\u2019s conventional meaning occurred at the end of the expression and affected the Post-N400 Positivity. Time-Frequency Representation of the EEG clarified that prior to integrating the idiom\u2019s meaning, an increase in power of higher gamma frequency band was associated only with literal processing. We argue that idioms comprehension proceeds in discrete steps: idiom recognition hampers semantic composition processes so that readers wait until the end of the expression to integrate the idiom meaning with the representation of the sentence

Updated predictions for the total production cross sections of top and of heavier quark pairs at the Tevatron and at the LHC

We present updated predictions for the total production cross section of top-quark pairs at the Tevatron and at the LHC, and, at the LHC, of heavy-quark pairs with mass in the range 0.5-2 TeV. For t\bar{t} production at the LHC we also present results at \sqrt{S}= 10 TeV, in view of the expected accelerator conditions during the forthcoming 2008 run. Our results are accurate at the level of next-to-leading order in alpha_s, and of next-to-leading threshold logarithms (NLO+NLL). We adopt the most recent parametrizations of parton distribution functions, and compute the corresponding uncertainties. We study the dependence of the results on the top mass, and we assess the impact of missing higher-order corrections by independent variations of factorisation and renormalisation scales

Theoretical predictions for charm and bottom production at the LHC

We present predictions for a variety of single-inclusive observables that stem from the production of charm and bottom quark pairs at the 7 TeV LHC. They are obtained within the FONLL semi-analytical framework, and with two "Monte Carlo + NLO" approaches, MC@NLO and POWHEG. Results are given for final states and acceptance cuts that are as close as possible to those used by experimental collaborations and, where feasible, are compared to LHC data.Comment: 22 pages, 10 figure