Report series ISSN 0284-2769 of THE SVEDBERG LABORATORY and DEPARTMENT OF RADIATION SCIENCES UPPSALA UNIVERSITY Box 533, S-75121 Uppsala, Sweden

TSL/ISV-2004-0278
March 2004

The Charm of Colour Octet Fields
A Study of Quark Production
in Fragmentation Processes

Magdalena Larfors

High Energy Physics, Uppsala University, Box 535, S-75121 Uppsala, Sweden

Abstract: This master thesis presents a model, similar to the Lund string model, where charmed hadrons are produced non-perturbatively in the fragmentation of colour octet strings. Octet strings have higher energy density than the Lund triplet strings, thus enhancing the non-perturbative charm production significantly. When combined with the standard Lund Monte Carlo {\sc Pythia}, the model reduces the need for 'string drag' effects and gives a better description of the experimental data of charmed meson production in fixed target $\pi^-p$ collisions ($E_{lab}$=500 GeV). These data also limits the model normalization. The model's impact on prompt atmospheric lepton fluxes was also studied. The impact is typically small, unless leading hypothetical charmed pentaquarks are formed. If these pentaquarks decay weakly and are short-lived ($\tau_{\Theta_c} \le 0.05$ ps), the resulting leptons will dominate the fluxes at high energies.