41 Matching Results

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Multivariate searches for single top quark production with the D0 detector

Description: We present a search for electroweak production of single top quarks in (p{bar p} {yields} t{bar b} + X) and t-channel (p{bar p} {yields} tq{bar b} + X) modes. We have analyzed 230 pb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron collider at a center-of-mass energy of {radical}s = 1.96 TeV. Two separate analysis methods are used: neural networks and a cut-based analysis. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections using Bayesian statistics, based on event counts and binned likelihoods formed from the neural network output. The limits from the neural network (cut-based) analysis are 6.4 pb (10.6 pb) in the s-channel and 5.0 pb (11.3 pb) in the t-channel.
Date: April 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

Measurement of B(t ---> Wb)/B(t ---> Wq) at s**(1/2) = 1.96-TeV

Description: The authors present the measurement of R = {Beta}(t {yields} Wb)/{Beta}(t {yields} Wq) in p{bar p} collisions at {radical}s = 1.96 TeV, using 230 pb{sup -1} of data collected by the D0 experiment at the Fermilab Tevatron Collider. They fit simultaneously R and the number (N{sub t{bar t}}) of selected top quark pairs (t{bar t}), to the number of identified b-quark jets in events with one electron or one muon, three or more jets, and high transverse energy imbalance. To improve sensitivity, kinematical properties of events with no identified b-quark jets are included in the fit. They measure R = 1.03{sub -0.17}{sup +0.19}(stat+syst), in good agreement with the standard model. They set lower limits of R > 0.61 and |V{sub tb}| > 0.78 at 95% confidence level.
Date: March 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

Measurement of the ratios of the Z/gamma* + >= n jet production cross sections to the total inclusive Z/gamma* cross section in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We present a study of events with Z bosons and jets produced at the Fermilab Tevatron Collider in p{bar p} collisions at a center of mass energy of 1.96 TeV. The data sample consists of nearly 14,000 Z/{gamma}* {yields} e{sup +}e{sup -} candidates corresponding to the integrated luminosity of 340 pb{sup -1} collected using the D0 detector. Ratios of the Z/{gamma}* + {ge} n jet cross sections to the total inclusive Z/{gamma}* cross section have been measured for n = 1 to 4 jet events. Our measurements are found to be in good agreement with a next-to-leading order QCD calculation and with a tree-level QCD prediction with parton shower simulation and hadronization.
Date: August 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

First direct two-sided bound on the B0(s) oscillation frequency

Description: The authors report the first direct two-sided bound on the B{sub s}{sup 0} oscillation frequency using a large sample of B{sub s}{sup 0} semileptonic decays corresponding to approximately 1 fb{sup -1} of integrated luminosity collected by the D0 experiment in 2002-2006 during Run II of the Fermilab Tevatron Collider. The flavor (i.e., B{sub s}{sup 0} or B{sub s}{sup 0}) of the B{sub s}{sup 0} meson at the time of production was found using an opposite-side tagging technique, and the flavor at the time of decay was determined from the charge of the muon in the partially reconstructed decay B{sub s}{sup 0} {yields} {mu}{sup +} D{sub s}{sup -}X, D{sub s}{sup -} {yields} {phi}{pi}{sup -}, {phi} {yields} K{sup +}K{sup -}. A likelihood scan over the oscillation frequency, {Delta}m{sub s}, gives a most probable value of 19 ps{sup -1} and a range of 17 < {Delta}m{sub s} < 21 ps{sup -1} at the 90% C.L. At {Delta}m{sub s} = 19 ps{sup -1}, the amplitude method yields a result that deviates from the hypothesis of an oscillation amplitude of zero by 2.5 standard deviations, corresponding to a two-sided C.L. of 1%.
Date: March 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 Standard Model Higgs Boson in the p anti-p ---> ZH ---> nu anti-nu b anti-b channel

Description: We report a search for the standard model (SM) Higgs boson based on data collected by the D0 experiment at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 260 pb{sup -1}. We study events with missing transverse energy and two acoplanar b-jets, which provide sensitivity to the ZH production cross section in the {nu}{bar {nu}}B{bar b} channel and to WH production, when the lepton from the W {yields} {ell}{nu} decay is undetected. The data are consistent with the SM background expectation, and we set 95% C.L. upper limits on {sigma}(p{bar p} {yields} ZN/WH) x B(H {yields} b{bar b}) from 3.4/8.3 to 2.5/6.3 pb, for Higgs masses between 105 and 135 GeV.
Date: July 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 resonant second generation slepton production at the Tevatron

Description: The authors present a search for supersymmetry in the R-parity violating resonant production and decay of smuons and muon-sneutrinos in the channels {tilde {mu}} {yields} {tilde {chi}}{sub 1}{sup 0} {mu}, {tilde {mu}} {yields} {tilde {chi}}{sub 2,3,4}{sup 0} {mu}, and {tilde {nu}}{sub {mu}} {yields} {tilde {chi}}{sub 1,2}{sup {+-}} {mu}. They analyzed 0.38 fb{sup -1} of integrated luminosity collected between April 2002 and August 2004 with the D0 detector at the Fermilab Tevatron Collider. The observed number of events is in agreement with the standard model expectation, and we calculate 95% C.L. limits on the slepton production cross section times branching fraction to gaugino plus muon, as a function of slepton and gaugino masses. In the framework of minimal supergravity, we set limits on the coupling parameter {lambda}'{sub 211}, extending significantly previous results obtained in Run I of the Tevatron and at the CERN LEP collider.
Date: May 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 R-parity violating supersymmetry via the LL anti-E couplings lambda(121), lambda(122) or lambda(133) in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: A search for gaugino pair production with a trilepton signature in the framework of R-parity violating supersymmetry via the couplings {lambda}{sub 121}, {lambda}{sub 122}, or {lambda}{sub 133} is presented. The data, corresponding to an integrated luminosity of L {approx} 360 pb{sup -1}, were collected from April 2002 to August 2004 with the D0 detector at the Fermilab Tevatron Collider, at a center-of-mass energy of {radical}s = 1.96 TeV. This analysis considers final states with three charged leptons with the flavor combinations ee{ell}, {mu}{mu}{ell}, and ee{tau} ({ell} = e or {mu}). No evidence for supersymmetry is found and limits at the 95% confidence level are set on the gaugino pair production cross section and lower bounds on the masses of the lightest neutralino and chargino are derived in two supersymmetric models.
Date: May 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 particles decaying into a Z boson and a photon in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: The authors present the results of the first search for a new particle X produced in p{bar p} collisions at {radical}s = 1.96 TeV and subsequently decaying to Z{gamma}. The search uses 0.3 fb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron Collider. They set limits on the production cross section times the branching fraction {sigma}(p{bar p} {yields} X) x B(X {yields} Z{gamma}) that range from 0.4-3.5 pb at the 95% C.L. for X with invariant masses between 100 and 1000 GeV/c{sup 2} over a wide range of X decay widths.
Date: May 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

A Precise measurement of the B0(s) lifetime

Description: The authors report a measurement of the B{sub s}{sup 0} lifetime in the semileptonic decay channel B{sub s}{sup 0} {yields} D{sub s}{sup -}{mu}{sup +}{nu}X (and its charge conjugate), using approximately 0.4 fb{sup -1} of data collected with the D0 detector during 2002-2004. They have reconstructed 5176 D{sub s}{sup -} {mu}{sup +} signal events, where the D{sub s}{sup -} is identified via the decay D{sub s}{sup 0} {yields} {phi}{pi}{sup -}, followed by {phi} {yields} K{sup +}K{sup -}. Using these events, they have measured the B{sub s}{sup 0} lifetime to be {tau}(B{sub s}{sup 0}) = 1.398 {+-} 0.044 (stat){sub -0.025}{sup +0.028}(syst) ps. This is the most precise measurement of the B{sub s}{sup 0} lifetime to date.
Date: April 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 a heavy resonance decaying into a Z+jet final state in p anti-p collisions at s**(1/2) = 1.96-TeV using the D0 detector

Description: We have searched for a heavy resonance decaying into a Z+jet final state in p{bar p} collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370 pb{sup -1}. We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.
Date: June 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 associated Higgs boson production WH ---> WWW* ---> l+- nu l-prime+- nu-prime + X in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: The authors present a search for associated Higgs boson production in the process p{bar p} {yields} WH {yields} WWW* {yields} {ell}{sup {+-}}{nu} {ell}{prime}{sup {+-}} {nu}{prime} + X in final states containing two like-sign isolated electrons or muons (e{sup {+-}}e{sup {+-}}, e{sup {+-}} {mu}{sup {+-}}, or {mu}{sup {+-}} {mu}{sup {+-}}). The search is based on D0 Run II data samples corresponding to integrated luminosities of 360-380 pb{sup -1}. No excess is observed over the predicted standard model background. They set 95% C.L. upper limits on {sigma}(p{bar p} {yields} WH) x Br(H {yields} WW*) between 3.2 and 2.8 pb for Higgs masses from 115 to 175 GeV.
Date: July 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 excited muons in p anti-p collisions at s**(1/2) = 1.96- TeV

Description: We present the results of a search for the production of an excited state of the muon, {mu}*, in proton antiproton collisions at {radical}s = 1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb{sup -1}. We search for {mu}* in the process p{bar p} {yields} {mu}*{nu}, with the {mu}* subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes {mu}* production by four-fermion contact interactions and {mu}* decay via electroweak processes, we exclude production cross sections higher than 0.057 pb-0.112 pb at the 95% confidence level, depending on the mass of the excited muon. Choosing the scale for contact interactions to be {Lambda} = 1 TeV, excited muon masses below 618 GeV are excluded.
Date: April 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 neutral Higgs bosons decaying to tau pairs in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: A search for the production of neutral Higgs bosons {Phi} decaying into {tau}{sup +}{tau}{sup -} final states in p{bar p} collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of approximately 325 pb{sup -1}, were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for {Phi}b({bar b}) {yields} b{bar b}b({bar b}) and are interpreted in the minimal supersymmetric standard model.
Date: May 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 scalar leptoquarks in the acoplanar jet topology in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: A search for leptoquarks has been performed in 310 pb{sup -1} of data from p{bar p} collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider. The topology analyzed consists of acoplanar jets with missing transverse energy. The data show good agreement with standard model expectations, and a lower mass limit of 136 GeV has been set at the 95% C.L. for a scalar leptoquark decaying exclusively into a quark and a neutrino.
Date: July 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

Measurement of the top quark mass in the lepton+jets final state with the matrix element method

Description: We present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the Matrix Element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty.
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 W-prime boson production in the top quark decay channel

Description: We present a search for the production of a new heavy gauge boson W' that decays to a top quark and a bottom quark. We have analyzed 230 pb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron collider at a center-of-mass energy of 1.96 TeV. No significant excess of events is found in any region of the final state invariant mass distribution. We set upper limits on the production cross section of W bosons at the 95% confidence level for several different W' boson masses. We exclude masses below 610 GeV for a W' boson with standard-model-like couplings, below 630 GeV for a W' boson with right-handed couplings that is allowed to decay to both leptons and quarks, and below 670 GeV for a W' boson with right-handed couplings that is only allowed to decay to quarks.
Date: July 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 pair production of scalar bottom quarks in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: A search for direct production of scalar bottom quarks ({bar b}) is performed with 310 pb{sup -1} of data collected by the D0 experiment in p{bar p} collisions at {radical}s = 1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos ({tilde {chi}}{sub 1}{sup 0}), with {tilde {chi}}{sub 1}{sup 0} assumed to be the lightest supersymmetric particle. They find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m{sub {tilde b}}, m{sub {tilde {chi}}}) mass plane, improving significantly upon the results from Run I of the Tevatron.
Date: August 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 pair production of second generation scalar leptoquarks in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: The authors report on a search for the pair production of second generation scalar leptoquarks (LQ{sub 2}) in p{bar p} collisions at the center-of-mass energy {radical}s = 1.96 TeV, using data corresponding to an integrated luminosity of 294 {+-} 19 pb{sup -1} recorded with the D0 detector. No evidence for a leptoquark signal in the LQ{sub 2} {ovr LQ}{sub 2} {yields} {mu}q{mu}q channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of m{sub LQ{sub 2}} > 247 GeV for {beta} = {Beta}(LQ{sub 2} {yields} {mu}q) = 1 and m{sub LQ{sub 2}} > 182 GeV for {beta} = 1/2. Combining these limits with previous D0 results, the lower limits on the mass of a second generation scalar leptoquark are m{sub LQ{sub 2}} > 251 GeV and m{sub LQ{sub 2}} > 204 GeV for {beta} = 1 and {beta} = 1/2, respectively.
Date: January 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

Measurement of B(d) mixing using opposite-side flavor tagging

Description: We report on a measurement of the B{sub d}{sup 0} mixing frequency and the calibration of an opposite-side flavor tagger in the D0 experiment. Various properties associated with the b quark on the opposite side of the reconstructed B meson are combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance is tested with data, using a large sample of reconstructed semileptonic B {yields} {mu}D{sup 0} X and B {yields} {mu}D* X decays, corresponding to an integrated luminosity of approximately 1 fb{sup -1}. The events are divided into groups depending on the value of the combined tagging variable, and an independent analysis is performed in each group. Combining the results of these analyses, the overall effective tagging power is found to be {var_epsilon}{prime}D{sup 2} = (2.48 {+-} 0.21{sub -0.06}{sup +0.08})%. The measured B{sub d}{sup 0} mixing frequency {Delta}m{sub d} = 0.506 {+-} 0.020 (stat) {+-} 0.016 (syst) ps{sup -1} is in good agreement with the world average value.
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 Higgs boson in H ---> WW(*) decays in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We present a search for the standard model Higgs boson in H {yields} WW{sup (*)} decays with e{sup +}e{sup -}, e{sup {+-}}{mu}{sup {-+}} and {mu}{sup +}{mu}{sup -} final states in p{bar p} collisions at a center-of-mass energy of {radical}s = 1.96 TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300-325 pb{sup -1}, depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs production cross section times branching ratio {sigma} x BR(H {yields} WW{sup (*)}) are presented.
Date: August 1, 2005
Creator: Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al.
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

Measurement of the W boson helicity in top quark decay at D0

Description: The authors present a measurement of the fraction f{sub +} of right-handed W bosons produced in top quark decays, based on a candidate sample of t{bar t} events in the {ell}+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb{sup -1} collected by the D0 detector at the Fermilab Tevatron p{bar p} Collider at {radical}s = 1.96 TeV. They reconstruct the decay angle {theta}* for each lepton. By comparing the cos{theta}* distribution from the data with those for the expected background and signal for various values of f{sub +}, they find f{sub +} = 0.056 {+-} 0.080(stat) {+-} 0.057(syst). (f{sub +} < 0.23 at 95% C.L.), consistent with the standard model prediction of f{sub +} = 3.6 x 10{sup -4}.
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

Measurement of the CP-violation parameter of B0 mixing and decay with p anti-p ---> mu mu X data

Description: The authors measure the dimuon charge asymmetry A in p{bar p} collisions at a center of mass energy {radical}s 1960 GeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately 1.0 fb{sup -1}. Assuming that the asymmetry A is due to asymmetric B{sup 0} {leftrightarrow} {bar B}{sup 0} mixing and decay, they extract the CP-violation parameter of B{sup 0} mixing and decay: R({epsilon}{sub B{sup 0}}/1) + |{epsilon}{sub B{sup 0}}|{sup 2} = A{sub B{sup 0}}/4 = -0.0023 {+-} 0.0011(stat) {+-} 0.0008(syst). A{sub B{sup 0}} is the dimuon charge asymmetry from decays of B{sup 0}{bar B}{sup 0} pairs. The general case, with CP violation in both B{sup 0} and B{sub s}{sup 0} systems, is also considered. Finally they obtain the forward-backward asymmetry that quantifies the tendency of {mu}{sup +} to go in the proton direction and {mu}{sup -} to go in the anti-proton direction. The results are consistent with the standard model and constrain new physics.
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