Hadronization corrections to helicity components of the fragmentation function

In the hadronic decays of Z, gluon emission leads to the appearance of the longitudinal component of the fragmentation function, F_L. Measurement of F_L and the transverse component, F_T, could thus provide an insight into the gluon fragmentation function. However, hadronization corrections at low x can be significant. Here we present a method of accounting for such corrections, using the JETSET event generator as illustration.Comment: 11 pages, 5 figure

Measurement of inclusive π0\pi^{0} production in hadronic Z0Z^{0} decays

An analysis is presented of inclusive \pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \pi^0 decays are reconstructed by \linebreak using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to x_p = 2 \cdot p_{\pi}/\sqrt{s} = 0.75) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for {q\overline q} and {b \bar b} events. The number of \pi^0's per hadronic Z^0 event is N(\pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{(stat)} \pm 1.0 \mbox{(syst)} and for {b \bar b}~events the number of \pi^0's is {\mathrm N(\pi^0)/ b \overline b} = 10.1 \pm 0.4 \mbox{(stat)} \pm 1.1 \mbox{(syst)} . The ratio of the number of \pi^0's in b \overline b events to hadronic Z^0 events is less affected by the systematic errors and is found to be 1.09 \pm 0.05 \pm 0.01. The measured \pi^0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the \mathrm \xi_p = \ln(1/x_p) distribution is \xi_p^{\star} = 3.90^{+0.24}_{-0.14}. The average number of \pi^0's from the decay of primary \mathrm B hadrons is found to be {\mathrm N} (B \rightarrow \pi^0 \, X)/\mbox{B hadron} = 2.78 \pm 0.15 \mbox{(stat)} \pm 0.60 \mbox{(syst)}

Luminosity evaluation and fragmentation studies for the DELPHI experiment at LEP

The first subject addressed in this thesis is the contribution of the VSAT luminosity to the lineshape analysis, i.e. to the extraction of the mass and width of the Z0 boson from LEP1 DELPHI data. The VSAT detector has contributed to the lineshape parameter determination by providing a relative luminosity measurement of high accuracy. The second subject of the thesis is the extraction of the helicity components of the fragmentation function. The analysis is performed on data collected by the DELPHI detector from 1992 to 1995. The study concentrates on the correction required for the hadronization process. Hadronization mainly affects the longitudinal component of the fragmentation function. The corrected measurement is used for the extraction of the strong coupling constant

Monte Carlo simulation with Geant4 for verification of rotational total skin electron therapy (TSET)

Detta arbete handlar om en behandlingsteknik för hudterapi där lågenergetiska elektroner utnyttjas för strålbehandling där patienten står eller sitter på en roterande plattform. För att behandlingen skall få ett lyckat resultat krävs en viss stråldos (den absorberade energin per massenhet) till patientens hud. För att kontrollera att dosen är rätt används normalt mätningar med olika detektorer. Dessa detektorer fungerar optimalt när de är riktade mot strålkällan men har en obestämd känslighet när de roteras. För att uppskatta den totala dosen under en rotation användes i stället ett datorsimuleringsprogram (Geant4). Programmet Geant4, för simulering av transport av partiklar i materia, utnyttjas av ett brett spektrum av användare inom högenergifysiken, rymdfysiken och för medicinska ändamål. Programmet har nyligen uppdaterats med nya rutiner för elektromagnetisk strålning (jonisation, bromsstrålning och multipelspridning) vilket har ökat precisionen av simuleringar för rymd- och medicinska applikationer. Ett stort antal användare i Europa utnyttjar nu programmet för beräkningar av lågenergetiska elektromagnetiska processer och i denna studie har vi använt programmet för att simulera behandlingstekniken som nämndes ovan. Resultaten av denna undersökning visar att Geant4 programmet ger god överensstämmelse i en stillastående referensgeometri när man gämnför med mätningar och med ett annat simuleringsprogram (VMC++). Resultaten visar också att Geant4 kan optimeras för beräkningar även vid mycket låga energier, och att programmet kan användas för att bestämma dosfördelningen när patienten roterar.Background and purpose: This study refers to a rotational radiotherapy technique for the treatment of mycosis fungoides. Patients are irradiated by a high dose-rate low-energy electron beam while they stand on a rotating platform. This report presents a first effort to use the Geant4 simulation program to calculate the relation between the stationary and rotational depth dose distributions in an ellipsoid phantom along the central beam axis. The absorbed dose delivered in one rotation can then be inferred from dose rate measurements performed in a stationary geometry. Method: Percentage depth dose and ionisation chamber measurements along the central beam axis were done at SSD = 100 cm and 250 cm (treatment distance). The measurement at SSD = 100 cm was used 1. to extract the beam characterization using VMC++ calculated percentage depth dose distributions and 2. to select the physics model of Geant4. A set of simulations were subsequently performed at the treatment distance in order to determine the following parameters in the simulation: 1. the number of primary electrons that are needed for the calculation of the ratio between the stationary and rotational depth dose distributions, R, to have a given level of statistical uncertainty (2%), 2. the distance off the central beam axis within which the energy should be scored, r, and 3. the step in beam incidence angle, . The rotational depth dose and R distributions were then calculated for one elliptical and one cylindrical phantom. The cylindrical phantom calculations were done for two production thresholds for the electrons, 10 keV and 100 keV. Results: This simulation study has contributed to the theoretical background of a rotational technique for total skin electron therapy (TSET). It was found that the low production threshold simulations give results that agree better with the measurements and the VMC++ calculation at SSD = 100 cm and also with the expected shape of the depth dose distribution for one rotation. Conclusion: The Monte Carlo calculations presented in this report were used to determine the the relation between the stationary and rotational depth dose distributions and thus contributed to a more accurate evaluation of the absorbed dose delivered at the prescription depth during treatment