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Observation of Single Top Quark Production

Description: The author reports on the observation of electroweak production of single top quarks in p{bar p} collisions at {radical}s = 1.96 Tev using 2.3 fb{sup -1} of data collected with the D0 detector at the fermilab Tevatron Collider. Using events containing an isolated electron or muon, missing transverse energy, two, three or four jets, with one or two of them identified as originating from the fragmentation of a b quark, the measured cross section for the process p{bar p} {yields} tb + X, tqb + X is 3.94 {+-} 0.88 pb (for a top quark mass of 170 GeV). the probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10{sup -7}, corresponding to a 5.0 standard deviation significance. Using the same dataset, the measured cross sections for the t- and the s-channel processes when determined simultaneously with no assumption on their relative production rate are 3.14{sub -0.80}{sup +0.94} pb and 1.05 {+-} 0.81 pb respectively, consistent with standard model expectations. The measured t-channel cross section has a significance of 4.8 standard deviations, representing the first evidence for the production of an individual single top process to be detected.
Date: September 1, 2009
Creator: Gerber, Cecilia E. & /Illinois U., Chicago
Partner: UNT Libraries Government Documents Department

A search for the Higgs boson in the zh channel with the D0 detector at the Fermilab Tevatron collider

Description: This analysis describes a search for a standard model Higgs boson produced in association with a Z boson through the decay mode ZH {yields} e{sup +}e{sup -}b{bar b} in p{bar p} collisions at {radical}s = 1.96 TeV at the Fermilab Tevatron Collider. The data sample used in this analysis corresponds to 452 pb{sup -1} of integrated luminosity accumulated with the D{null} detector. Agreement between data and standard model predictions is observed. A 95% confidence level upper exclusion limit for the {sigma}(p{bar p} {yields} ZH) x BR(H {yields} b{bar b}) channel is set between 3.2-8.2 pb for Higgs masses of 105 to 145 GeV.
Date: November 1, 2006
Creator: Heinmiller, James Matthew & /Illinois U., Chicago
Partner: UNT Libraries Government Documents Department

High pt jets and photons at the Tevatron

Description: The authors present recent results on high p{sub T} jets and photon production in {bar p}p collisions at a center of mass energy of 1.96 TeV. The measurements were performed by the CDF and D0 collaborations using between 150 and 300 pb{sup -1} of data taken during Run II at the Tevatron.
Date: September 1, 2005
Creator: Gerber, Cecilia E. & /Illinois U., Chicago
Partner: UNT Libraries Government Documents Department

Measurement of the Z/Gamma* (--> e+e-) + >=n Jet Production Cross Sections

Description: A study of events with Z={gamma}* bosons and hadronic jets produced at the Tevatron in p{bar p} collisions at a center of mass energy of 1.96 TeV is presented. The data consist of approximately 14,000 Z/{gamma}* {yields} e{sup +}e{sup -} decay candidates from 343 pb{sup -1} of integrated luminosity collected with the D0 detector. Cross sections and jet production properties have been measured for Z/{gamma}* + {ge} 0 to 5 jet events. This measurement represents a significant improvement over previous measurements at the Tevatron, and it is the first at this center of mass energy with the D0 detector. The results are in good agreement with QCD predictions.
Date: July 1, 2005
Creator: Buehler, Marc & /Illinois U., Chicago
Partner: UNT Libraries Government Documents Department

Studies of top quark production at D0

Description: I present recent results on top quark production in pp collisions at a center of mass energy of 1.96 TeV. The studies were performed by the D0 collaboration using approximately 5 fb{sup -1} of data taken during Run II at the Fermilab Tevatron accelerator. The top quark is the heaviest known elementary particle and completes the quark sector of the three-generation structure of the standard model (SM). It differs from the other quarks not only by its much larger mass, but also by its lifetime which is too short to build hadronic bound states. The SM predicts that top quarks are created via two independent production mechanisms at hadron colliders. The primary mode, in which a t{bar t} pair is produced from a gtt vertex via the strong interaction, was used by the D0 and CDF collaborations to establish the existence of the top quark in 1995. The second production mode of top quarks at hadron colliders is the electroweak production of a single top quark from a Wtb vertex. The predicted cross section for single top quark production is about half that of t{bar t} pairs but the signal-to-background ratio is much worse; observation of single top quark production has therefore until recently been impeded by its low rate and difficult background environment compared to the top pair production. In the following sections I will present results for the measurement of the t{bar t} pair and the single top quark production cross section using respectively 5.3 fb{sup -1} and 5.4 fb{sup -1} of data taken by the D0 experiment.
Date: July 1, 2011
Creator: Gerber, Cecilia E. & /Illinois U., Chicago
Partner: UNT Libraries Government Documents Department

Final Results from the KTeV Experiment on the Decay K(L) ---> pi0 gamma gamma

Description: The authors report on a new measurement of the branching ratio B(K{sub L} {yields} {pi}{sup 0}{gamma}{gamma}) using the KTeV detector. They reconstruct 1982 events with an estimated background of 608, that results in B(K{sub L} {yields} {pi}{sup 0}{Gamma}{gamma}) = (1.29 {+-} 0.03{sub stat} {+-} 0.05{sub syst}) x 10{sup -6}. They also measure the parameter, a{sub V}, which characterizes the strength of vector meson exchange terms in this decay. They find a{sub V} = -0.31 {+-} 0.05{sub stat} {+-} 0.07{sub syst}. These results utilize the full KTeV data set collected from 1997 to 2000 and supersede earlier KTeV measurements of the branching ratio and a{sub V}.
Date: May 1, 2008
Creator: Abouzaid, E.; /Illinois U., Chicago; Arenton, M.; U., /Virginia; Barker, A.R.; U., /Colorado et al.
Partner: UNT Libraries Government Documents Department

Inclusive Cross Sections for p n ---> p X between 50-GeV and 400-GeV

Description: The authors have measured the inclusive cross sections for the reaction p + d {yields} p + X in the region 0.14 < |t| < 0.38 GeV{sup 2}, 100 < s < 750 GeV{sup 2} and 0.80 < x < 0.93 using the acceleration ramp and deuterium gas jet target at Fermilab. These measurements are combined with the earlier measurements of p + p {yields} p + X to obtain invariant cross sections for p + n {yields} p + X.
Date: January 1, 1975
Creator: Robinson, B.; Abe, K.; Carr, J.; Keyne, J.; Pagnamenta, A.; Sannes, F. et al.
Partner: UNT Libraries Government Documents Department

Study of the Nuclear Antiquark Sea via p+N --> Dimuons

Description: We propose a precise measurement of the A dependence of the Drell-Yan process for 900 GeV protons on targets of deuterium and calcium using the E605 spectrometer. Emphasis will be placed on the kinematic region M > 4 GeV and x{sub F} > 0.2, where one is most sensitive to beam-valence-quark, target-antiquark annihilation. Such measurements will be very sensitive to the A dependence of the target sea quark distribution in the range 0.05 < x{sub 2} < 0.3, and hence provide important clues about the origin-of the EMC (European Muon Collaboration) effect, and unique information on the general issue of quark distributions in nuclear systems. Only minor modifications (liquid deuterium target, and reduced-size beam dump) of the E605 spectrometer will be required.
Date: January 1, 1986
Creator: Moss, J.; Garvey, G.; Peng, J-C.; Alamos, /Los; McCarthy, R.L.; Brook, /SUNY Stony et al.
Partner: UNT Libraries Government Documents Department

Evidence for production of single top quarks

Description: We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron p{bar p} collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top quark partner that is always produced from strong coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top quark production has been searched for in ever larger datasets. In this analysis, we select events from a 0.9 fb{sup -1} dataset that have an electron or muon and missing transverse energy from the decay of a W boson from the top quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W+jets and t{bar t} events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top quark production of {sigma}(p{bar p} {yields} tb + X, tqb + X) = 4.7 {+-} 1.3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa quark mixing matrix element that describes the Wtb coupling and find |V{sub tb}f{sub 1}{sup L}| = 1.31{sub -0.21}{sup +0.25}, where f{sub ...
Date: March 1, 2008
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Measurement of differential Z / gamma* + jet + X cross sections in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We present new measurements of differential cross sections for Z/{gamma}* ({yields} {mu}{mu})+jet+X production in a 1 fb{sup -1} data sample collected with the D0 detector in p{bar p} collisions at {radical}s = 1.96 TeV. Results include the first measurements differential in the Z/{gamma}* transverse momentum and rapidity, as well as new measurements differential in the leading jet transverse momentum and rapidity. Next-to-leading order perturbative QCD predictions are compared to the measurements, and reasonable agreement is observed, except in the region of low Z/{gamma}* transverse momentum. Predictions from two event generators based on matrix elements and parton showers, and one pure parton shower event generator are also compared to the measurements. These show significant overall normalization differences to the data and have varied success in describing the shape of the distributions.
Date: August 1, 2008
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Measurement of the forward-backward charge asymmetry and extraction of $sin^2Theta^{eff}_W$ in $p\bar{p} \to Z/\gamma^{*}+X \to e^+e^-+X$ events produced at $\sqrt{s}=1.96$ TeV

Description: We present a measurement of the forward-backward charge asymmetry (A{sub FB}) in p{bar p} {yields} Z/{gamma}* + X {yields} e{sup +}e{sup -} + X events at a center-of-mass energy of 1.96 TeV using 1.1 fb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron collider. A{sub FB} is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the A{sub FB} measurement to extract the effective weak mixing angle sin{sup 2} {theta}{sub W}{sup eff} = 0.2327 {+-} 0.0018 (stat.) {+-} 0.0006 (syst.).
Date: April 1, 2008
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Search for long-lived particles decaying into electron or photon pairs with the D0 detector

Description: In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, like hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.
Date: June 1, 2008
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Search for the standard model Higgs boson in the ZH->vvbb channel in 5.2 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV

Description: A search is performed for the standard model Higgs boson in 5.2 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV, collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered is a pair of b jets and large missing transverse energy, as expected from p{bar p} {yields} ZH {yields} {nu}{bar {nu}}b{bar b} production. The search is also sensitive to the WH {yields} {ell}{nu}b{bar b} channel when the charged lepton is not identified. For a Higgs boson mass of 115 GeV, a limit is set at the 95% C.L. on the cross section multiplied by branching fraction for (p{bar p} {yields} (Z/W)H) x (H {yields} b{bar b}) that is a factor of 3.7 larger than the standard model value, consistent with the factor of 4.6 expected.
Date: December 1, 2009
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Simultaneous measurement of the ratio B(t->Wb)/B(t->Wq) and the top quark pair production cross section with the D0 detector at s**(1/2) = 1.96-TeV

Description: The authors present the first simultaneous measurement of the ratio of branching fractions, R = {Beta}(t {yields} Wb)/{Beta}(t {yields} Wq), with q being a d, s, or b quark, and the top quark pair production cross section {sigma}{sub t{bar t}} in the lepton plus jets channel using 0.9 fb{sup -1} of p{bar p} collision data at {radical}s = 1.96 TeV collected with the D0 detector. they extract R and {sigma}{sub t{bar t}} by analyzing samples of events with 0, 1 and {ge} 2 identified b jets. They measure R = 0.97{sub -0.08}{sup +0.09} (stat+syst) and {sigma}{sub t{bar t}} = 8.18{sub -0.84}{sup +0.90}(stat+syst) {+-} 0.50 (lumi) pb, in agreement with the standard model prediction.
Date: January 1, 2008
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Results from irradiation tests on D0 Run 2a silicon detectors at the Radiation Damage Facility at Fermilab

Description: Several different spare modules of the D0 experiment Silicon Microstrip Tracker (SMT) have been irradiated at the Fermilab Booster Radiation Damage Facility (RDF). The total dose received was 2.1 MRads with a proton flux of {approx} 3 {center_dot} 10{sup 11} p/cm{sup 2} sec. The irradiation was carried out in steps of 0.3 or 0.6 MRad, with several days between the steps to allow for annealing and measurements. The leakage currents and depletion voltages of the devices increased with dose, as expected from bulk radiation damage. The double sided, double metal devices showed worse degradation than the less complex detectors.
Date: March 1, 2006
Creator: Gardner, J.; Cerber, C.; Ke, Z.; Korjanevsky, S.; Leflat, A.; Lehner, F. et al.
Partner: UNT Libraries Government Documents Department

Measurement of the polarization of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states in $p\bar{p}$ collisions at $\sqrt{s}=$1.96 TeV

Description: We present a study of the polarization of the {Upsilon}(1S) and {Upsilon}(2S) states using a 1.3 fb{sup -1} data sample collected by the D0 experiment in 2002-2006 during Run II of the Fermilab Tevatron Collider. We measure the polarization parameter {alpha} = ({sigma}{sub T} - 2{sigma}{sub L})/({sigma}{sub T} + 2{sigma}{sub L}), where {sigma}{sub T} and {sigma}{sub L} are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum (p{sub T}{sup {Upsilon}}) for the {Upsilon}(1S) and {Upsilon}(2S). Significant p{sub T}{sup {Upsilon}}-dependent longitudinal polarization is observed for the {Upsilon}(1S). A comparison with theoretical models is presented.
Date: April 1, 2008
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department