Browsing by Subject "kaksoisryöppy"

Particle jets are formed in high energy proton-proton collisions and then measured by particle physics experiments. These jets, initiated by the splitting and hadronization of color charged quarks and gluons, serve as important signatures of the strong force and provide a view to size scales smaller than the size of an atom. So, understanding jets, their behaviour and structure, is a path to understanding one of the four fundamental forces in the known universe. But, it is not only the strong force that is of interest. Studies of Standard Model physics and beyond Standard Model physics require a precise measurement of the energies of final state particles, represented often as jets, to understand our existing theories, to search for new physics hidden among our current experiments and to directly probe for the new physics. As experimentally reconstructed objects the measured jets require calibration. At the CMS experiment the jets are calibrated to the particle level jet energy scale and their resolution is determined to achieve the experimental goals of precision and understanding. During the many-step process of calibration, the position, energy and structure of the jets' are taken into account to provide the most accurate calibration possible. It is also of great importance, whether the jet is initiated by a gluon or a quark, as this affects the jets structure, distribution of energy among its constituents and the number of constituents. These differences cause disparities when calibrating the jets. Understanding of jets at the theory level is also important for simulation, which is utilized heavily during calibration and represents our current theoretical understanding of particle physics. This thesis presents a measurement of the relative response between light quark (up, down and strange) and gluon jets from the data of CMS experiment measured during 2018. The relative response is a measure of calibration between the objects and helps to show where the difference of quark and gluon jets is the largest. The discrimination between light quarks and gluons is performed with machine learning tools, and the relative response is compared at multiple stages of reconstruction to see how different effects affect the response. The dijet sample that is used in this study provides a full view of the phase space in pT and |eta|, with analysis covering both quark and gluon dominated regions of the space. These studies can then be continued with similar investigations of other samples, with the possibility of using the combined results as part of the calibration chain.