Browsing by Subject "SUSY"
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Item Search for New Physics in the Exclusive $\gamma_{Delayed}$ + Missing Transverse Energy Channel in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV(2012-08-15) Asaadi, JonathanThis dissertation presents the results of a search in the exclusive photon plus missing transverse energy (gamma + E/_T) final state in proton antiproton collisions at center of mass energy of 1.96 TeV using the Collider Detector at Fermilab experiment. The strategy used here is to search for delayed photons coming from gauge mediated supersymmetric events with the exclusive production of ~X(0 1) -> gamma~G. In these models the ~X(0 1) is the lightest neutralino and has nanosecond lifetime before decaying to a photon (gamma) and gravitino (~G) which exits the detector unrecorded. In order to search for this process we select collisions that have a single photon plus missing transverse energy and little other activity in the detector and examine the arrival time of the photon. This arrival time is then compared against expectations from a data driven background of the standard model sources. In the data collected from the Fermilab Tevatron collider from December 2004 to June 2010, representing 6.3 fb^-1 of data, we observe 322 events in the photon arrival timing region from 2 nanoseconds to 7 nanoseconds with a data driven background prediction of 257 +/- 35. An excess of 65 events is observed, equivalent to a standard deviation (N_sigma) of 1.65 from the null hypothesis.Item Search for pair production of scalar top quarks decaying to a tau lepton and a b quark in 1.96-tev ppbar collisions(2009-05-15) Khotilovich, Vadim GennadyevichI present the results of a search for pair production of scalar top quarks (~t1) in an R-parity violating supersymmetric scenario using 322 pb_1 of pp collisions at ps = 1.96 TeV collected by the upgraded Collider Detector at Fermilab. I assume each ~t1 decays into a tau lepton and a b quark, with branching ratio B, and search for final states containing either an electron or a muon from a leptonic tau decay, a hadronically decaying tau lepton, and two or more jets. Two candidate events pass my final selection criteria, consistent with the expectation from standard model processes. I present upper limits on the cross section times branching ratio squared (~t1~t1)B2 as a function of the stop mass m(~t1). Assuming B = 1, I set a 95% confidence level limit m(~t1) > 153 GeV=c2. These limits are also fully applicable to the case of a pair produced third generation scalar leptoquark that decays into a tau lepton and a b quark.