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University of Nebraska - Lincoln

2007

Gregory Snow Publications

Articles 1 - 16 of 16

Full-Text Articles in Physics

Correlation Of The Highest-Energy Cosmic Rays With Nearby Extragalactic Objects, J. Abraham, Gregory Snow, Pierre Auger Collaboration Nov 2007

Correlation Of The Highest-Energy Cosmic Rays With Nearby Extragalactic Objects, J. Abraham, Gregory Snow, Pierre Auger Collaboration

Gregory Snow Publications

Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 × 1019 electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic ...


Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Nov 2007

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters Kgc/ Λ and Kgu/ Λ, where Kg define the strength of tcg and tug couplings, and Λ defines the scale of new physics ...


Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Nov 2007

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters Kgc/ Λ and Kgu/ Λ, where Kg define the strength of tcg and tug couplings, and Λ defines ...


Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Nov 2007

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters Kgc/ Λ and Kgu/ Λ, where Kg define the strength of tcg and tug couplings, and Λ defines ...


Search For A Higgs Boson Produced In Association With A Z Boson In Pp̅ Collisions, V. M. Abazov, Kenneth A. Bloom, Gregory Snow Nov 2007

Search For A Higgs Boson Produced In Association With A Z Boson In Pp̅ Collisions, V. M. Abazov, Kenneth A. Bloom, Gregory Snow

Gregory Snow Publications

We describe a search for the Standard Model Higgs boson with a mass of 105 GeV/c2 to 145 GeV/c2 in data corresponding to an integrated luminosity of approximately 450 pb-1 collected with the DØ detector at the Fermilab Tevatron p̅p collider at a center-of-mass energy of 1.96 TeV. The Higgs boson is required to be produced in association with a Z boson, and the Z boson is required to decay to either electrons or muons with the Higgs boson decaying to a b̅b pair. The data are well described by the expected ...


Measurement Of The ΛB0 Lifetime Using Semileptonic Decays, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Nov 2007

Measurement Of The ΛB0 Lifetime Using Semileptonic Decays, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report a measurement of the Λb0 lifetime using a sample corresponding to 1.3 fb-1 of data collected by the D0 experiment in 2002–2006 during run II of the Fermilab Tevatron collider. The Λb0 baryon is reconstructed via the decay Λb0 → μν̅Λc+ X. Using 4437 ± 329 signal candidates, we measure the Λb0 lifetime to be τ(Λb0) = 1.290-0.110+0.119 (stat) -0.091+0.087 (syst) ps, which is among the most precise measurements in semileptonic Λb0 decays. This result ...


Search For BS0→ Μ+ Μ- Decays At D0, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Nov 2007

Search For BS0→ Μ+ Μ- Decays At D0, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report results from a search for the decay Bs0 → μ+μ- using 1.3 fb-1 of pp̅ collisions at √s= 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron Collider.We find two candidate events, consistent with the expected background of 1.24 ± 0.99, and set an upper limit on the branching fraction of Ɓ(Bs0 → μ+μ-) < 1.2 x 10-7 at the 95% C.L.


Properties Of L = 1 B1 And B2* Mesons, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Oct 2007

Properties Of L = 1 B1 And B2* Mesons, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

This Letter presents the first strong evidence for the resolution of the excited B mesons B1 and B2* as two separate states in fully reconstructed decays to B+(*). The mass of B1 is measured to be 5720.6 ± 2.4 ± 1.4 MeV=c 2 and the mass difference ΔM between B2* and B1 is 26.2 ± 3.1 ± 0.9 MeV/c 2, giving the mass of the B2* as 5746.8 ± 2.4 ± 1.7 MeV/c 2. The production rate for B1 and B2* mesons is determined to ...


Measurement Of The Top Quark Mass In The Dilepton Channel, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Oct 2007

Measurement Of The Top Quark Mass In The Dilepton Channel, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Gregory Snow Publications

We present a measurement of the top quark mass in the dilepton channel based on approximately 370 pb-1 of data collected by the DØ 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 DØ Monte Carlo simulation. We combine the results from the two methods to obtain a top quark mass mt = 178.1 ± 8.2 GeV. The statistical uncertainty is 6.7 GeV and the systematic uncertainty is 4.8 ...


Measurement Of The Pp̅Tt̅ + X Production Cross Section At √S = 1.96 Tev In The Fully Hadronic Decay Channel, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Oct 2007

Measurement Of The Pp̅→ Tt̅ + X Production Cross Section At √S = 1.96 Tev In The Fully Hadronic Decay Channel, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

A measurement of the top quark pair production cross section in proton antiproton collisions at an interaction energy of √s= 1.96 TeV is presented. This analysis uses 405 ± 25 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. Fully hadronic tt̅ decays with final states of six or more jets are separated from the multijet background using secondary vertex tagging and a neural network. The tt̅ cross section is measured as σ tt̅= 4.5-1.9+2.0(stat)-1.1+1.4(syst) ± 0.3(lumi) pb for a top quark mass ...


Measurement Of The ΛB Lifetime In The Exclusive Decay ΛBJ/Ψλ, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Oct 2007

Measurement Of The ΛB Lifetime In The Exclusive Decay ΛB→ J/Ψλ, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

Λ are identified via the decays J/ψ → μ+μ- and Λ →pπ, we measured the Λb lifetime to be 1.218-0.115+0.130 (stat) ± 0.042(syst) ps. We also measured the B0 lifetime in the decay B0J/ψ(μ+μ-)Ks2+π-) to be τ(B0) = 1.501-0.074+0.078 (stat) ± 0.050(syst) ps, yielding a lifetime ratio of τ(Λb)/τ(B0) = 0.811-0.087+0.096 (stat) ± 0.034(syst).


Search For Stopped Gluinos From Pp̅ Collisions At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Sep 2007

Search For Stopped Gluinos From Pp̅ Collisions At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

Long-lived, heavy particles are predicted in a number of models beyond the standard model of particle physics. We present the first direct search for such particles’ decays, occurring up to 100 h after their production and not synchronized with an accelerator bunch crossing. We apply the analysis to the gluino (g̃), predicted in split supersymmetry, which after hadronization can become charged and lose enough momentum through ionization to come to rest in dense particle detectors. Approximately 410 pb-1 of pp̅ collisions at √s = 1.96 TeV collected with the D0 detector during Run II of the Fermilab Tevatron collider ...


Measurement Of The Tt̅ Production Cross Section In Pp̅ Collisions Using Dilepton Events, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Sep 2007

Measurement Of The Tt̅ Production Cross Section In Pp̅ Collisions Using Dilepton Events, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present a measurement of the tt̅ pair production cross section in pp̅ collisions at √s = 1.96 TeV utilizing approximately 425 pb-1 of data collected with the D0 detector. We consider decay channels containing two high pT charged leptons (either ℯ or μ) from leptonic decays of both top-daughter W bosons. These were gathered using four sets of selection criteria, three of which required that a pair of fully identified leptons (i.e., ℯμ, ℯℯ, or μμ) be found. The fourth approach imposed less restrictive criteria on one of the lepton candidates and required that at least ...


Combined D0 Measurements Constraining The Cp-Violating Phase And Width Difference In The BS0 System, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Sep 2007

Combined D0 Measurements Constraining The Cp-Violating Phase And Width Difference In The BS0 System, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We combine the D0 measurement of the width difference between the light and heavy Bs0 mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the Bs0J/ψφ decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific Bs0 lifetime, we obtain ΔΓs ≡ (ΓL - ΓH) = 0.13 ± 0.09 ps-1 and ∣φs∣ = 2.44-0.39+0.47. The data sample corresponds to an integrated luminosity ...


The Cosmic Ray Observatory Project: A Statewide Outreach And Education Experiment In Nebraska, Daniel R. Claes, Gregory R. Snow Jul 2007

The Cosmic Ray Observatory Project: A Statewide Outreach And Education Experiment In Nebraska, Daniel R. Claes, Gregory R. Snow

Gregory Snow Publications

The Cosmic Ray Observatory Project (CROP) is a statewide education and research experiment involving Nebraska high school students, teachers and university undergraduates in the study of extensive cosmic-ray air showers. A network of high school teams construct, install, and operate school-based detectors in coordination with University of Nebraska physics professors and graduate students. The detector system at each school is an array of scintillation counters recycled from the Chicago Air Shower Array in weather-proof enclosures on the school roof, with a GPS receiver providing a time stamp for cosmic-ray events. The detectors are connected to triggering electronics and a data-acquisition ...


Correlation Of The Highest-Energy Cosmic Rays With Nearby Extragalactic Objects, J. Aberham, Gregory Snow, The Pierre Auger Collaboration Jan 2007

Correlation Of The Highest-Energy Cosmic Rays With Nearby Extragalactic Objects, J. Aberham, Gregory Snow, The Pierre Auger Collaboration

Gregory Snow Publications

Cosmic rays are particles and nuclei that bombard the Earth from space in all directions (1). A few have astounding energies—beyond 100 EeV (1 EeV = 1 exa-electron volt = 1018 eV)—orders of magnitude beyond even the future capabilities of any earthly particle accelerator. Such energies are so extreme that they could arise in only the most violent places in the universe. One possible location is within active galactic nuclei (AGN), galaxies hosting central black holes that feed on gas and stars and may eject vast plasma jets into intergalactic space.