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Combination of CDF and D0 measurements of the $W$ boson helicity in top quark decays

Description: We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7-5.4 fb{sup -1} of p{bar p} collisions collected during Run II of the Fermilab Tevatron Collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f{sub 0}) and right-handed (f{sub +}) helicities, we find f{sub 0} = 0.722 {+-} 0.081 [{+-} 0.062 (stat.) {+-} 0.052 (syst.)] and f{sub +} = -0.033 {+-} 0.046 [{+-} 0.034 (stat.) {+-} 0.031 (syst.)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f{sub 0} = 0.682 {+-} 0.057 [{+-} 0.035 (stat.) {+-} 0.046 (syst.)] and f{sub +} = ?0.015 {+-} 0.035 [{+-} 0.018 (stat.) {+-} 0.030 (syst.)]. The results are consistent with standard model expectations.
Date: February 1, 2012
Creator: Aaltonen, T.; Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Determination of the strong coupling constant from the inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV

Description: We determine the strong coupling constant {alpha}{sub s} and its energy dependence from the p{sub T} dependence of the inclusive jet cross section in p{bar p} collisions at {radical}s = 1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < p{sub T} < 145 GeV. Using perturbative QCD calculations to order {Omicron}({alpha}{sub s}{sup 3}) combined with {Omicron}({alpha}{sub s}{sup 4}) contributions from threshold corrections, we obtain {alpha}{sub s}(M{sub Z}) = 0.1173{sub -0.0049}{sup +0.0041}. This is the most precise result obtained at a hadron-hadron collider.
Date: November 1, 2009
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 t anti-t production cross section and top quark mass extraction using dilepton events in p anti-p collisions

Description: We present a measurement of the top quark pair production cross section in p{bar p} collisions at {radical}s = 1.96 TeV using approximately 1 fb{sup -1} of data collected with the D0 detector. We consider decay channels containing two high p{sub T} charged leptons where one lepton is identified as an electron or a muon while the other lepton can be an electron, a muon or a hadronically decaying {tau} lepton. For a mass of the top quark of 170 GeV, the measured cross section is 7.5{sub -1.0}{sup +1.0}(stat){sub -0.06}{sup +0.7}(syst){sub -0.5}{sup 0.6}(lumi) pb. Using {ell}{sub {tau}} events only, they measure: {sigma}{sub t{bar t}} x B(t{bar t} {yields} {ell}{sub {tau}}b{bar b}) = 0.13{sub -0.08}{sup +0.09}(stat){sub -0.06}{sup 0.06}(syst)+{sub -0.02}{sup +0.02}(lumi) pb. Comparing the measured cross section as a function of the mass of the top quark with a partial next-to-next-to leading order Quantum Chromodynamics theoretical prediction, we extract a mass of the top quark of 171.5{sub -8.8}{sup +9.9} GeV, in agreement with direct measurements.
Date: January 1, 2009
Creator: Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Evidence of WW+WZ production with lepton + jets final states in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We present the first evidence of WW+WZ production with lepton+jets final states at a hadron collider. The data correspond to 1.07 inverse femtobarns of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider in proton-antiproton collisions at sqrt(s)=1.96 TeV. The observed cross section for WW+WZ production is 20.2 +/- 4.5 pb, consistent with the SM prediction of 16.1 +/- 0.9 pb. The probability for background fluctuations to produce an excess equal to or larger than that observed is estimated to be 5.4e-6, corresponding to a significance of 4.4 standard deviations.
Date: October 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

Search for squark production in events with jets, hadronically decaying tau leptons and missing transverse energy at s**(1/2) = 1.96-TeV

Description: A search for supersymmetric partners of quarks is performed in the topology of multijet events accompanied by at least one tau lepton decaying hadronically and large missing transverse energy. Approximately 1 fb-1 of ppbar collision data from the Fermilab Tevatron Collider at a center of mass energy of 1.96 TeV recorded by the D0 detector is analyzed. Results are combined with the previously published D0 inclusive search for squarks and gluinos. No evidence of physics beyond the standard model is found and lower limits on the squark mass up to 410 GeV are derived in the framework of minimal supergravity with tan(beta)=15, A{sub 0}=-2m{sub 0} and mu<0, in the region where decays to tau leptons dominate. Gaugino masses m{sub 1/2} are excluded up to 172 GeV.
Date: May 1, 2009
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 production of charginos and neutralinos in the trilepton final state using 2.3 fb**-1 of data

Description: We report the results of a search for associated production of charginos and neutralinos using a data set corresponding to an integrated luminosity of 2.3 fb{sup -1} collected with the D0 experiment during Run II of the Tevatron proton-antiproton collider. Final states containing three charged leptons and missing transverse energy are probed for a signal from supersymmetry with four dedicated trilepton event selections. No evidence for a signal is observed, and we set limits on the product of production cross section and leptonic branching fraction. Within minimal supergravity, these limits translate into bounds on m{sub 0} and m{sub 1/2} that are well beyond existing limits.
Date: January 1, 2009
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 admixture of scalar top quarks in the t anti-t lepton+jets final state at s**(1/2) = 1.96-TeV

Description: A search for pair production of the lightest supersymmetric partner of the top quark, {tilde t}{sub 1}, is performed in the lepton+jets channel using 0.9 fb{sup -1} of data collected by the D0 experiment. Kinematic differences between {tilde t}{sub 1}{bar {tilde t}}{sub 1} and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark ({tilde t}{sub 1} {yields} {tilde {chi}}{sub 1}{sup +} b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.
Date: January 1, 2009
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 Pair Production of long-lived particles decaying to b anti-b in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: We report on a first search for production of Higgs bosons decaying into neutral long-lived particles (NLLP) which each decay to a b{bar b} pair, using 3.6 fb{sup -1} of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.
Date: June 1, 2009
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 differential cross section $d\sigma/dt$ in elastic $p\bar{p}$ scattering at $\sqrt{s}=1.96$ TeV

Description: We present a measurement of the elastic differential cross section differential cross section d{sigma}(p{bar p}{yields}p{bar p})/dt as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of {approx}31 nb{sup -1} collected with the D0 detector using dedicated Tevatron p{bar p} Collider operating conditions at {radical}s = 1.96 TeV and covers the range 0.26 < |t| < 1.2 GeV{sup 2}. For |t| < 0.6 GeV{sup 2}, d{sigma}/dt is described by an exponential function of the form Ae{sup -b|t|} with a slope parameter b = 16.86 {+-} 0.10 (stat) {+-} 0.20 (syst) GeV{sup -2}. A change in slope is observed at |t| {approx} 0.6 GeV{sup 2}, followed by a more gradual |t| dependence with increasing values of |t|.
Date: June 1, 2012
Creator: Abazov, V.M.; Abazov, V.M.; Abbott, B.; Acharya, B.S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Search for quirks at the Fermilab Tevatron Collider

Description: We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in 2.4 fb{sup -1} of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron p{bar p} collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like SU(N) sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107 GeV for the mass of a charged quirk with strong dynamics scale {Lambda} in the range from 10 keV to 1 MeV.
Date: August 1, 2010
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 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

Depleted argon from underground sources

Description: Argon is a powerful scintillator and an excellent medium for detection of ionization. Its high discrimination power against minimum ionization tracks, in favor of selection of nuclear recoils, makes it an attractive medium for direct detection of WIMP dark matter. However, cosmogenic {sup 39}Ar contamination in atmospheric argon limits the size of liquid argon dark matter detectors due to pile-up. The cosmic ray shielding by the earth means that Argon from deep underground is depleted in {sup 39}Ar. In Cortez Colorado a CO{sub 2} well has been discovered to contain approximately 500ppm of argon as a contamination in the CO{sub 2}. In order to produce argon for dark matter detectors we first concentrate the argon locally to 3-5% in an Ar, N{sub 2}, and He mixture, from the CO{sub 2} through chromatographic gas separation. The N{sub 2} and He will be removed by continuous cryogenic distillation in the Cryogenic Distillation Column recently built at Fermilab. In this talk we will discuss the entire extraction and purification process; with emphasis on the recent commissioning and initial performance of the cryogenic distillation column purification.
Date: September 1, 2011
Creator: Back, H.O.; U., /Princeton; Alton, A.; Coll., /Augustana U.; Calaprice, F.; Galbiati, C. 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

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

Direct measurement of the W boson width

Description: We present a direct measurement of the width of the W boson using the shape of the transverse mass distribution of W {yields} e{nu} candidates selected in 1 fb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron collider in p{bar p} collisions at {radical}s = 1.96 TeV. We use the same methods and data sample that were used for our recently published W boson mass measurement, except for the modeling of the recoil, which is done with a new method based on a recoil library. Our result, 2.028 {+-} 0.072 GeV, is in agreement with the predictions of the standard model and is the most precise direct measurement result from a single experiment to date.
Date: September 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

Search for Higgs boson production in dilepton and missing energy final states with 5.4 fb-1 of p-pbar collisions at sqrt(s) =1.96 TeV

Description: A search for the standard model Higgs boson is presented using events with two charged leptons and large missing transverse energy selected from 5.4 fb{sup -1} of integrated luminosity in p{bar p} collisions at {radical}s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. No significant excess of events above background predictions is found, and observed (expected) upper limits at 95% confidence level on the rate of Higgs boson production are derived that are a factor of 1.55 (1.36) above the predicted standard model cross section at m{sub H} = 165 GeV.
Date: January 1, 2010
Creator: Abazov, V.M.; /Dubna, JINR; Abbott, B.; U., /Oklahoma; Abolins, M.; U., /Michigan State et al.
Partner: UNT Libraries Government Documents Department

Double parton interactions in photon+3 jet events in ppbar collisions sqrt{s}=1.96 TeV

Description: We have used a sample of photon+3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb{sup -1} to determine the fraction of events with double parton scattering (f{sub DP}) in a single ppbar collision at {radical}s = 1.96 TeV. The DP fraction and effective cross section (sigma{sub eff}), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in p{sub T}) jet transverse momentum pT{sub jet2} within the range 15 < pT{sub jet2} < 30 GeV. In this range, f{sub DP} varies between 0.23 < f{sub DP} < 0.47, while sigma{sub eff} has the average value sigma{sub effave} = 16.4 {+-} 0.3(stat) {+-} 2.3(syst) mb.
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

Precise measurement of neutrino and anti-neutrino differential cross sections

Description: The NuTeV experiment at Fermilab has obtained a unique high statistics sample of neutrino and anti-neutrino interactions using its high-energy sign-selected beam. We present a measurement of the differential cross section for charged-current neutrino and anti-neutrino scattering from iron. Structure functions, F{sub 2}(x,Q{sup 2}) and xF{sub 3}(x,Q{sup 2}), are determined by fitting the inelasticity, y, dependence of the cross sections. This measurement has significantly improved systematic precision as a consequence of more precise understanding of hadron and muon energy scales.
Date: September 1, 2005
Creator: Tzanov, M.; Naples, D.; Boyd, S.; McDonald, J.; Radescu, V.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department