Heavy Quark Production Asymmetries

In the hadroproduction of charm (or heavy flavours in general) in the context of string fragmentation, the pull of a beam remnant at the other end of a string may give a charm hadron more energy than the perturbatively produced one. The collapse of a low-mass string to a single hadron is the extreme case in this direction, and gives rise to asymmetries between leading and non-leading charm hadrons. We study these phenomena within the Lund string fragmentation model and improve the modelling in part by a consideration of hadroproduction data. Applications include heavy quark production in any collision between hadron-like particles such as \gamma p at HERA and pp at HERA-B or the LHC.Comment: 6 pages, 6 figures, to appear in the Proceedings of the International Europhysics Conference on High Energy Physics, Tampere, Finland, 15-21 July 1999, edited by K. Huitu, H. Kurki-Suonio and J. Maalamp

Production and Hadronization of Heavy Quarks

Heavy long-lived quarks, i.e. charm and bottom, are frequently studied both as tests of QCD and as probes for other physics aspects within and beyond the standard model. The long life-time implies that charm and bottom hadrons are formed and observed. This hadronization process cannot be studied in isolation, but depends on the production environment. Within the framework of the string model, a major effect is the drag from the other end of the string that the c/b quark belongs to. In extreme cases, a small-mass string can collapse to a single hadron, thereby giving a non-universal flavour composition to the produced hadrons. We here develop and present a detailed model for the charm/bottom hadronization process, involving the various aspects of string fragmentation and collapse, and put it in the context of several heavy-flavour production sources. Applications are presented from fixed-target to LHC energies.Comment: 40 pages, 25 figure

Drag Effects in Charm Photoproduction

We have refined a model for charm fragmentation at hadron colliders. This model can also be applied to the photoproduction of charm. We investigate the effect of fragmentation on the distribution of produced charm quarks. The drag effect is seen to produce charm hadrons that are shifted in rapidity in the direction of the beam remnant. We also study the importance of different production mechanisms such as charm in the photon and from parton showers.Comment: 6 pages, 5 figures, Proc. of DESY Workshop "Monte Carlo Generators for HERA Physics

Is the real dollar rate highly volatile?

This note s the real exchange rate behavior observed by Lothian (1998). Specifically, we investigate the volatility of the U.S. dollar relative to other major currencies using d data, and reestimate the real exchange rate using alternative currency baskets. The results confirm Lothian's suggestion that the dollar is highly volatile. However, other major currencies also have high volatility. In fact, the DM is surprisingly calm relative to most major currencies. Thus the use of the DM as a numeraire would be preferred to any other major currency.

Heavy Quark Fragmentation

I present the main aspects of open charm production in \pi^-\p collisions in the context of the Lund String Fragmentation Model as implemented in the Monte Carlo program PYTHIA. The emphasis is on the transition from large to small strings and the dependence on model parameters. A modified version is presented and compared with experimental results both on asymmetries, single-charm spectra and correlations.Comment: 10 pages, 6 figures, to appear in the proceedings of the Workshop on Heavy Quarks at Fixed Target, editors H.W.K. Cheung and J.N. Butle

The Sources of b-Quarks at the Tevatron and their Correlations

The leading-log order QCD hard scattering Monte-Carlo models of HERWIG, ISAJET, and PYTHIA are used to study the sources of b-quarks at the Tevatron. The reactions responsible for producing b and bbar quarks are separated into three categories; flavor creation, flavor excitation, and parton-shower/fragmentation. Flavor creation corresponds to the production of a b-bbar pair by gluon fusion or by annihilation of light quarks, while flavor excitation corresponds to a b or bbar quark being knocked out of the initial-state by a gluon or a light quark or antiquark. The third source occurs when a b-bbar pair is produced within a parton shower or during the fragmentation process of a gluon or a light quark or antiquark (includes gluon splitting). The QCD Monte-Carlo models indicate that all three sources of b-quarks are important at the Tevatron and when combined they qualitatively describe the inclusive cross-section data. Correlations between the b and bbar quark are very different for the three sources and can be used to isolate the individual contributions.Comment: RevTex4, 14 pages, 20 figures, submitted to Phys. Rev.

Transverse Momentum as a Measure of Colour Topologies

Several distinct colour flow topologies are possible in multiparton configurations. A method is proposed to find the correct topology, based on a minimization of the total transverse momentum of produced particles. This method is studied for three-jet $Z^0 \to q\overline{q} g$ and four-jet $W^+W^- \to q_1\overline{q}_2q_3\overline{q}_4$ events. It is shown how the basic picture is smeared, especially by parton-shower activity. The method therefore may not be sufficient on its own, but could still be a useful complement to others, and e.g. help provide some handle on colour rearrangement effects.Comment: 1+8 pages, LaTeX2e, 6 eps figures included in file using filecontents environment

How Much Is Purchasing Power Parity Worth?

Updating Bilson \u27s (1984) investment strategy using an out-of-sample forecast procedure, we find much smaller profits from a trading strategy based on purchasing power parity. Though the total profit is significant at a 5 percent level, it is substantially lower than what Bilson found. Our results suggest Bilson\u27s excess profits are due to the sample of data used and the in-sample nature of the tests. Hence, this paper demonstrates that the simple investment strategy leads to the same conclusion that econometric testing does; namely, that purchasing power parity is only marginally useful in forecasting exchange rates