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Presented here are the results of a direct search for flavor changing neutral currents via the rare process Z° → bs and a measurement of R{sub bs} = [Lambda](Z° → bs)/[Lambda](Z° → hadrons). Because the decays Z° → b{bar b} and Z° → c{bar c} contribute significant backgrounds to Z° → bs, simultaneous measurements of R{sub b} = [Lambda](Z° → b{bar b})/[Lambda](Z° → hadrons) and R{sub c} = [Lambda](Z° → c{bar c})/[Lambda](Z° → hadrons) were also made. The standard double tag technique was extended and self calibrating tags were used for s, c, and b quarks. These measurements were made possible by the unique capabilities of the SLAC Large Detector (SLD) at the Stanford Linear Accelerator Center (SLAC): The b and c tags relied upon the SLD's VXD3 307 megapixel CCD vertex detector for topological and kinematic reconstruction of the B and D decay vertices; the s tag identified K{sup {+-}} mesons using the particle identification capabilities of SLD's Cherenkov Ring Imaging Detector (CRID), and K{sub S}° mesons and [Lambda] hadrons by kinematic reconstruction of their decay vertices in SLD's 5120 channel central drift chamber (CDC) particle tracking system.
This dissertation presents a blind search for the flavor changing neutral current decay of the top quark t → qZ in pp collisions at [special characters omitted] = 1.96TeV using a data sample corresponding to an integrated luminosity of 1.12 fb-1 collected by the Collider Detector at Fermilab (CDF), This decay is extremely rare in the standard model, and a signal at the Tevatron would be an indication of new physics. Dividing candidate events with a Z boson and four or more jets into a sample of those which have a heavy flavor jet identified by a secondary vertex algorithm and those which do not, we observe data yields consistent with background expectations. We set a 95% C.L. upper limit on the branching fraction B (t → qZ) of 11.3%, consistent with an expected upper limit of 7.8% ± 3.3%.
This PhD thesis focuses on the search for flavor-changing neutral currents in the decay of a top quark to an up-type quark (q = u, c) and the Standard Model Higgs boson, where the Higgs boson decays to bb. Further, the thesis presents the combination of this search for top quark pair events with other ATLAS searches – in the course of which the most restrictive bounds to date on tqH interactions were obtained. Following on from the discovery of the Higgs boson, it is particularly important to measure the Yukawa couplings of the Standard Model fermions; these parameters may provide crucial insights to help solve the flavor puzzle and may help reveal the presence of new physics before it is directly observed in experiments.
We report on a search for the flavor-changing neutral-current decays K/sub L/° .-->. .pi.°ee/sup /minus//, K/sub L/° .-->. ee/sup /minus// and K/sub L/° .-->. .mu./sup +-/e/sup /minus plus//. Limits obtained for these processes are BR(K/sub L/° .-->. .pi.°e+e/sup /minus//) 3.2 x 10/sup /minus/7/, BR(K/sub L/° .--. e+e/sup /minus//) 1.2 x 10/sup /minus/9/, BR(K/sub L/° .--. .mu./sup +-/e/sup /minus plus//)
From a February 1991 conference in Santa Monica, California, 22 papers by particle, theoretical, and accelerator physicists discuss flavor physics and novel flavor factories (aspects of the subatomic world). CP violation and the search for flavor-changing weak neutral currents are covered extensivel