Observation Of The Omegab Baryon And Measurement Of The Properties Of The Xib And Omegab Baryons

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ISBN 13 :
Total Pages : 119 pages
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Download or read book Observation of the Doubly Strange B-Baryon Omega(b)- written by and published by . This book was released on 2011 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis reports the first experimental evidence of the doubly strange b-baryon?{sub b}− (ssb) following the decay channel?{sub b}− → J/?(1S)??−?−? K− p?− in p{bar p} collisions at √s = 1.96 Tev. Using approximately 1.3 fb−1 of data collected with the D0 detector at the Fermilab Tevatron Collider, they observe 17.8 ± 4.9(stat) ± 0.8(syst)?{sub b}− signal events at 6.165 ± 0.010(stat) ± 0.013(syst) GeV/c2 with a corresponding significance of 5.4?, meaning that the probability of the signal coming from a fluctuation in the background is 6.7 x 10−8. The theoretical model we have to describe what we believe are the building blocks of nature and the interactions between them, is known as Standard Model. The Standard Model is the combination of Electroweak Theory and Quantum Chromodynamics into a single core in the attempt to include all interactions of subatomic particles except those due to gravity in a simple framework. This model has proved highly accurate in predicting certain interactions, but it does not explain all aspects of subatomic particles. For example, it cannot say how many particles there should be or what their masses are. The search goes on for a more complete theory, and in particular an unified field theory describing the strong, weak, and electromagnetic forces. Twelve elementary particles are known in the Standard Model: the Fermions. They have spin -1/2 and obey the Pauli Exclusion Principle. Fermions are divided into six Quarks: up u, down d, charm c, strange s, top t and, bottom b; and six Leptons: electron e, muon?, tau?, electron neutrino?{sub e}, muon neutrino?{sub {mu}} and, tau neutrino?{sub {tau}}. Quarks interact via the strong force because they carry color charge, electromagnetically because of their electric charge and via the weak nuclear interaction because of the weak isospin. Quarks form color-neutral composite particles known as Hadrons which are divided in Mesons, containing a quark and an antiquark and Baryons, made up three quarks. Leptons have no color charge and can not interact via the strong force. Only three of them have electric charge, hence interact electromagnetically. The motion of non-electrically charged leptons, the neutrinos, is influenced only by the weak nuclear interaction. Every fermion have an associated antiparticle. For quarks, the antiparticle carry opposite electric charge, color charge and baryon number. For leptons, the antiparticle carry opposite electric charge and lepton number. Fermions are suitably grouped together considering their properties and three generations of them are defined. A higher generation fermion have greater mass than those in lower generations. Charged members of the first generation do not decay and form the ultimate building blocks for all the baryonic matter we know about. Charged members of higher generations have very short half lives and are found normally in high-energy environments. Non-electrically charged fermions do not decay and rarely interact with baryonic matter. The way particles interact and influence each other in the Standard Model is result from matter particles exchanging other particles, known as Force Mediating Particles. They are believed to be the reason of the existence of the forces and interactions between particles observed in the laboratory and the universe. Force mediating particles have spin 1, i.e., they are Bosons, and do not follow the Pauli Exclusion Principle. The types of force mediating particles are: the photon?, three gauge bosons W{sup {+-}} and Z and, eight gluons g. Photons have no mass, the theory of Quantum Electrodynamics describe them very well and are responsible for mediation of the electromagnetic force between electrically charged particles. Gauge bosons are massive, being Z heavier than W{sup {+-}}. They are responsible for the mediation of the weak interactions between particles of different flavors but W{sup {+-}} act only on left-handed particles and right-handed antiparticles while Z with both left-handed particles and antiparticles. Due to the electric charge of W{sup {+-}}, they couple also to electromagnetic interactions. Photons and the three gauge bosons are grouped together and collectively mediate the electroweak interactions. Finally, gluons have no mass, the theory of Quantum Chromodynamics describe them and are responsible for the mediation of the strong interactions between particles with color charge. Having an effective color charge, gluons can interact among themselves. The Higgs Boson is the only particle in the SM without direct experimental evidence. Its detection would help in the explanation of the difference between massive bosons mediating the weak force and the massless photon mediating the electromagnetism.