Study of the production of the Σ <sub>b</sub><sup>*±</sup> with the CDF detector at the Tevatron

Abstract

The composition of matter is a topic in which the man has been interested throughout History. Since the introduction of the atom by Democritus in the 5th century BC until the establishment of the Standard Model, our successful theory that contains our current knowledge on the matter and their interactions, it has come a long way trying to solve this fundamental question. The efforts of many of the greatest minds to perform crucial experiments and develop theoretical models have helped to get deeper insight into the origin of the matter. Today we know that indivisible atoms postulated by Democritus are no longer true, and they are actually composed of a nucleus made of protons and neutrons (nucleons) with orbiting electrons through electromagnetic interactions. Also the nucleons are not fundamental particles but are composed of more fundamental ones called quarks. According to the present state of our knowledge, matter is composed of two types of particles: quarks and leptons. Leptons are believed to be fundamental particles and can occur freely in nature. Quarks are also fundamental particles, and there are no free in nature, but are confined to form hadrons. The hadrons may consist of a quark and an antiquark (mesons) or three quarks or three antiquarks (baryons). These quarks and leptons interact through the exchange of particles called bosons. Figure 1.1 summary the elementary particles in the Standard Model. Despite its enormous success we know that the Standard Model is incomplete. Some of the issues left unresolved by the Standard Model are the mechanism for electroweak symmetry breaking, the mass spectrum of the Standard Model or that the Universe is much more matter than antimatter. That means that it should exist a more general theory which include the Standard Model as a valid approximation for low energy. This more general theory must give answers to the previous unresolved questions. Accumulate more experimental information is crucial to get a deeper understanding of the Standard Model and its limitations. In particular, it is very important the measurement of those observables which they are not able to be calculated from theory by perturbation theory. Particle accelerators have played and play nowadays a major role for past and new physics discoverements and has been for many years the source of many precision measurements. Unprecedent discoveries have been made and are yet to come. These measurements allow to select the models that best fit the results and also they can be used as input for those models to get further predictions. Tevatron has been for many years the highest energy particle collider operational in the world. It is located in the high energy physics laboratory Fermilab in Batavia, in the State of Illinois (USA). Tevatron produce proton-antiproton collisions with an energy of 1.96 TeV at the center of the mass. This thesis is based on the data taken by the CDF II detector, one of the two multipurpose detectors located in the two interaction points at Tevatron. In this thesis a precise measurement of the mass and width of four heavy baryon states are performed. These states are described together by the symbol Σ b*±. They are built by two light quarks and one heavy b quark as it is shown in Fig. 1.2. Baryons containing one bottom quark and two light quarks are described by Heavy Quark Effective Theories (HQET).