Kaon Fragmentation Functions From Semi-Inclusive Deep Inelastic Scattering of Muons on an Isoscalar Target

Abstract

This thesis presents the analysis of K⁰_s multiplicities from COMPASS 2006 data, and the extraction of kaon fragmentation functions (FFs) including fits to K⁺ and K^- multiplicities available from previous analyses and the K⁰_s multiplicities from this thesis.<br /> The K⁰_s multiplicities, analyzed in the kinematical region of 0.004 < x < 0.4, Q^2 > 1 (GeV/c)^2, and 0.2 < z < 0.85, are complementary to the K⁺ and K^- multiplicities.The K⁰_s are identified by their decay into p⁺pi^- pairs, in contrast to the charged kaons which rely on the RICH detector for particle identification.This yields a larger coverage of z and different systematic uncertainties.Furthermore the FFs have a different weight on the multiplicities of charged and neutral kaons.<br /> The FFs are extracted from the multiplicities using a LO pQCD fit.Isospin and charge invariance allow for a simultaneous fit of K⁺, K^-, and K⁰_s multiplicities.To perform the fit, good knowledge of the parton distribution functions (PDFs) of the nucleon is necessary.The impact of the PDFs on the FFs is studied by performing the fits with different PDF sets.It is shown that the PDF sets have the largest contribution to the systematic uncertainties of the FFs.<br /> Furthermore it is shown that fits with the K⁰_s multiplicities included are able to constrain the FFs with more accuracy.<br /> The largest impact is found for the FF of strange quarks.The strange FFs of fits with the K⁰_s included ranging between 0.456-1.265 are larger and better constrained than the ones of fits with the K⁰_s excluded, ranging between 0.195-0.563.A comparison of kaon multiplicities from COMPASS and HERMES shows large differences between the two, which, in LO, cannot be explained by the different kinematics of the experiments.<br /> The K⁺ and K^- multiplicities, together with the K⁰_s multiplicities of this thesis, provide a full set of kaon multiplicities for further analyses, especially for more sophisticated extractions of FFs by theory groups.