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Flavor Changing Neutral Currents in ttbar Decays at D\O

Description: We present a search for flavor changing neutral currents (FCNC) in decays of top quarks. The analysis is based on a search for t{bar t} {yields} {ell}'{nu}{ell}{bar {ell}} + jets ({ell},{ell}' = e, {mu}) final states using 4.1 fb{sup -1} of integrated luminosity of p{bar p} collisions at {radical} s = 1.96 TeV. We extract limits on the branching ratio B(t {yields} Zq) (q = u, c quarks), assuming anomalous tuZ or tcZ couplings. We do not observe any sign of such anomalous coupling and set a limit of B < 3.2% at 95% C.L.
Date: September 1, 2011
Creator: McGivern, C.L. & U., /Kansas
Partner: UNT Libraries Government Documents Department

A Measurement of CP Asymmetry in b->sgamma Using a Sum ofExclusive Final States

Description: We perform a measurement of the CP asymmetry in b {yields} s{gamma} decays using a sample of 383 x 10{sup 6} B{bar B} events collected by the BABAR detector at the PEP-II asymmetric B factory. We reconstruct sixteen flavor-specific B decay modes containing a high-energy photon and a hadronic system X{sub s} containing an s quark. We measure the CP asymmetry to be -0.011 {+-} 0.030(stat) {+-} 0.014(syst) for a photon energy threshold at 1.6 GeV and the hadronic system mass between 0.6 and 2.8 GeV/c{sup 2}.
Date: August 7, 2008
Creator: Zao, M
Partner: UNT Libraries Government Documents Department

Measurement of the top quark mass in the dilepton channel

Description: We present a measurement of the top quark mass in the dilepton channel based on approximately 370 pb{sup -1} of data collected by the D0 experiment during Run II of the Fermilab Tevatron collider. We employ two different methods to extract the top quark mass. We show that both methods yield consistent results using ensemble tests of events generated with the D0 Monte Carlo simulation. We combine the results from the two methods to obtain a top quark mass m{sub t} = 178.1 {+-} 8.2 GeV. The statistical uncertainty is 6.7 GeV and the systematic uncertainty is 4.8 GeV.
Date: September 1, 2006
Creator: Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Search for the lightest scalar top quark in events with two leptons in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: Data collected by the D0 detector at a p{bar p} center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider have been used to search for pair production of the lightest supersymmetric partner of the top quark decaying into b{ell}{bar {nu}}. The search is performed in the {ell}{ell}{prime} = e{mu} and {mu}{mu} final states. No evidence for this process has been found in data samples of approximately 400 pb{sup -1}. The domain in the [M({bar t}{sub 1}),M({bar {nu}})] plane excluded at the 95% C.L. is substantially extended by this search.
Date: July 1, 2007
Creator: Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Top quark physics

Description: While the top quark was discovered in 1995 at the Fermilab Tevatron, a decade later they still have very little information about the top. As the heaviest particle yet discovered, the top quark is interesting in and of itself, but some speculate that it may play a special role in physics beyond the Standard Model. With Run 2 of the Tevatron well underway, they have the opportunity to study top quark properties with much better sensitivity, and to test whether top quarks behave as predicted by current theories. This article focuses on the basics of top quark physics at the Tevatron, highlighting only a sample of the many recent measurements, as new results are being released monthly, and constantly changing the landscape of our knowledge of top.
Date: October 1, 2005
Creator: Erbacher, Robin D. & /UC, Davis
Partner: UNT Libraries Government Documents Department

Top quark mass: Latest CDF results, Tevatron combination and electroweak implications

Description: A summary of the most up-to-date top quark mass measurements at CDF is presented. These analyses use top-antitop candidate events detected in the CDF experiment at the Tevatron collider with an integrated luminosity of up to {approx}3/fb. The combination of all those measurements together with the corresponding top mass measurements from the concurrently running D0 experiment at the Tevatron yields a world average of M{sub t} = [173.1 {+-} 0.6(stat.) {+-} 1.1(syst.)] GeV/c{sup 2}.
Date: October 1, 2009
Creator: Vellidis, Costas
Partner: UNT Libraries Government Documents Department

Evidence for single top quark production using Bayesian neural networks

Description: We present results of a search for single top quark production in p{bar p} collisions using a dataset of approximately 1 fb{sup -1} collected with the D0 detector. This analysis considers the muon+jets and electron+jets final states and makes use of Bayesian neural networks to separate the expected signals from backgrounds. The observed excess is associated with a p-value of 0.081%, assuming the background-only hypothesis, which corresponds to an excess over background of 3.2 standard deviations for a Gaussian density. The p-value computed using the SM signal cross section of 2.9 pb is 1.6%, corresponding to an expected significance of 2.2 standard deviations. Assuming the observed excess is due to single top production, we measure a single top quark production cross section of {sigma}(p{bar p} {yields} tb + X, tqb + X) = 4.4 {+-} 1.5 pb.
Date: August 1, 2007
Creator: Kau, Daekwang
Partner: UNT Libraries Government Documents Department

Measurement of top quark mass in the all hadronic channel in s**(1/2) = 1.96 TeF, ppbar collisions at D0

Description: A measurement of the top quark mass in proton-antiproton collisions at {radical}s = 1.96 TeV using 1040fb{sup -1} of data collected in D detector at Fermilab is presented. This analysis focuses on the all-hadronic decay mode of the top quark and therefore only events with six or more calorimeter jets in the final state are considered.
Date: May 1, 2008
Creator: Lam, David Wai Kui & U., /Notre Dame
Partner: UNT Libraries Government Documents Department

Tools for top physics at D0

Description: Top quark measurements rely on the jet energy calibration and often on b-quark identification. We discuss these and other tools and how they apply to top quark analyses at D0. In particular some of the nuances that result from D0's data driven approach to these issues are presented.
Date: July 1, 2008
Creator: Harel, Amnon
Partner: UNT Libraries Government Documents Department

Measurement of gamma + c + X and gamma + b + X production cross sections at s**(1/2) = 1.96-TeV

Description: The photon plus heavy-flavour quark (b, c) final state provides a unique and valuable window into both the sea quark content of the proton and the splitting of gluons into heavy-flavour quark pairs. A new combination of experimental techniques has provided the basis for the first measurements of the differential {gamma} + c + X and {gamma} + b + X production cross sections at {radical}s = 1.96 TeV. The measurements use {approx} 1 fb{sup -1} of data from p{bar p} collisions collected with the D0 detector.
Date: June 1, 2009
Creator: Duggan, Daniel & U., /Florida State
Partner: UNT Libraries Government Documents Department

Top Mass Measurements with the D0 Detector

Description: I present recent results related to the measurement of the top quark mass, using p{bar p} collisions recorded with the D0 Detector at the Tevatron. The results are: A direct measurement of the mass difference between top and anti-top quarks, Measurement of the top quark mass in the lepton+jets channel and in the dilepton channel.
Date: September 1, 2009
Creator: Boline, Daniel & U., /Boston
Partner: UNT Libraries Government Documents Department

Measurement of the t anti-t production cross section in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We measure the t{bar t} production cross section in p{bar p} collisions at {radical}s = 1.96 TeV in the lepton+jets channel. Two complementary methods discriminate between signal and background, b-tagging and a kinematic likelihood discriminant. Based on 0.9 fb{sup -1} of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure {sigma}{sub t{bar t}} = 7.62 {+-} 0.85 pb, assuming the current world average m{sub t} = 172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top quark mass of 170 {+-} 7 GeV.
Date: March 1, 2008
Creator: Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Rare B Decays

Description: Recent results from Belle and BaBar on rare B decays involving flavor-changing neutral currents or purely leptonic final states are presented. Measurements of the CP asymmetries in B {yields} K*{gamma} and b {yields} s{gamma} are reported. Also reported are updated limits on B{sup +} {yields} K{sup +}{nu}{bar {nu}}, B{sup +} {yields} {tau}{sup +}{nu}, B{sup +} {yields} {mu}{sup +}{nu} and the recent measurement of B {yields} X{sub s}{ell}{sup +}{ell}{sup -}.
Date: February 24, 2006
Creator: Jackson, P.D. & U., /Victoria
Partner: UNT Libraries Government Documents Department