24 Matching Results

Search Results

Advanced search parameters have been applied.

A measurement of the top-antitop production cross section in the dimuon final state with the D0 detector for proton-antiproton collisions as s**(1/2) = 1.96 TeV

Description: A measurement of the top pair production cross section in the dimuon final state for proton-antiproton collisions at ps = 1:96 TeV is presented. Approximately 420 pb{sup -1} of data collected with the Run II D{O} detector are used for this measurement. Two data events are observed with a total expected signal plus background yield of 3.6 events. Assuming a top mass of 175 GeV, the measured cross section is: {sigma}{sub {bar u}} = 3.13{sup +4.17}{sub -2.60}(stat){sup +0.92}{sub -0.86}(sys){+-}0.19(lumi)pb, which is consistent with a NNLO prediction of 6.77 {+-} 0.42 pb.
Date: December 1, 2006
Creator: Burke, Susan Elizabeth & U., /Arizona
Partner: UNT Libraries Government Documents Department

Measurement of the W boson helicity in top quark decays

Description: A measurement of the fraction, f{sup +}, of right-handed W bosons produced in top quark decays is presented. This analysis is based on a sample 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. The helicity angle, {theta}*, is reconstructed for each lepton. f{sup +} is determined by comparing the cos {theta}* distribution from the data with that for the expected background and signal for various values of f{sup +}. The fraction of longitudinal W bosons, f{sup 0}, is assumed to be 0.7 as predicted by the standard model. This yields f{sup +} = 0.109 {+-} 0.094 (stat) {+-} 0.063 (syst), consistent with the standard model prediction of f{sup +} = 3.6x 10{sup -4}. The possibility that both f{sup +} and f{sup 0} stray from standard model values is also investigated. In this case cos {theta}* distributions for each possible W helicity state, along with the backgrounds, are fit to the cos {theta}* distribution for the data. The best fit values are f{sup +} = 0.82 {+-} 0.30(stat) and f{sup 0} = -0.58 {+-} 0.50(stat).
Date: August 1, 2007
Creator: Gmyrek, Bryan David & U., /Arizona
Partner: UNT Libraries Government Documents Department

Time-integrated charge asymmetries at D0

Description: We have measured the time-integrated charge asymmetries in dimuon events and semileptonic B{sub s} decays. These results are the most precise semileptonic charge asymmetries in B decays to date. We combine these results with measurements from the decay B{sub s} {yields} J/{psi}{phi} to determine the CP-violating phase {phi}{sub s}. They find {phi}{sub s} = -0.56{sub -0.41}{sup +0.44}.
Date: October 1, 2006
Creator: Cheu, E. & U., /Arizona
Partner: UNT Libraries Government Documents Department

Measurement of top quark properties at the Tevatron

Description: We highlight the most recent top quark properties measurements performed at the Tevatron collider by the CDF and D0 experiments. The data samples used for the analyses discussed correspond to an integrated luminosity varying from 360 pb{sup -1} to 760 pb{sup -1}.
Date: July 1, 2006
Creator: Leveque, Jessica & U., /Arizona
Partner: UNT Libraries Government Documents Department

Study of the Rare Decay K(L) ---> pi0 gamma gamma at KTeV

Description: The authors study on the rare decay K{sub L} {yields} {pi}{sup 0}{gamma}{gamma}, measure a{sub V}, and branching ratio by analyzing 96, 97 and 99 data. The measurements were taken by KTeV at Fermi National Accelerator Laboratory. After all cuts, they have 1982 K{sub L} {yields} {pi}{sup 0}{gamma}{gamma} candidate. The background level is estimated as 30%. K{sub L} {yields} {pi}{sup 0}{gamma}{gamma} branching ratio is measured as (1.29 {+-} 0.03(stat) {+-} 0.04(sys)) x 10{sup -6}. By using D'Ambrosio's theory to fit a{sub V}, a{sub V} = -(-0.31 {+-} 0.05(stat) {+-} 0.07(sys)).
Date: August 1, 2007
Creator: Wang, Jianbo & U., /Arizona
Partner: UNT Libraries Government Documents Department

Top quark production at the Tevatron

Description: The Fermilab Tevatron has, until recently, been the only accelerator with sufficient energy to produce top quarks. The CDF and D0 experiments have collected large samples of top quarks. We report on recent top quark production measurements of the single top and t{bar t} production cross sections, as well as studies of the t{bar t} invariant mass distribution and a search for highly boosted top quarks.
Date: September 1, 2010
Creator: Varnes, Erich W. & U., /Arizona
Partner: UNT Libraries Government Documents Department

A Twin Higgs Model from Left-Right Symmetry

Description: We present twin Higgs models based on the extension of the Standard Model to left-right symmetry that protect the weak scale against radiative corrections up to scales of order 5 TeV. In the ultraviolet the Higgs sector of these theories respects an approximate global symmetry, in addition to the discrete parity symmetry characteristic of left-right symmetric models. The Standard Model Higgs field emerges as the pseudo-Goldstone boson associated with the breaking of the global symmetry. The parity symmetry tightly constrains the form of radiative corrections to the Higgs potential, allowing natural electroweak breaking. The minimal model predicts a rich spectrum of exotic particles that will be accessible to upcoming experiments, and which are necessary for the cancellation of one-loop quadratic divergences. These include right-handed gauge bosons with masses not to exceed a few TeV and a pair of vector-like quarks with masses of order several hundred GeV.
Date: December 14, 2005
Creator: Chacko, Z.; Goh, Hock-Seng; U., /Arizona; Harnik, Roni & /SLAC /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department

Efficient Modeling of PIN Diode Switches Employing Time-Domain Electromagnetic-Physics-Based Simulators

Description: This paper presents an efficient full-wave time-domain simulator for accurate modeling of PIN diode switches. An equivalent circuit of the PIN diode is extracted under different bias conditions using a drift-diffusion physical model. Net recombination is modeled using a Shockley-Read-Hall process, while generation is assumed to be dominated by impact ionization. The device physics is coupled to Maxwell's equations using extended-FDTD formulism. A complete set of results is presented for the on and off states of the PIN switch. The results are validated through comparison with independent measurements, where good agreement is observed. Using this modeling approach, it is demonstrated that one can efficiently optimize PIN switches for better performance.
Date: September 20, 2005
Creator: Hussein, Y.A.; Spencer, J.E.; /SLAC; El-Ghazaly, S.M.; U., /Tennessee; Goodnick, S.M. et al.
Partner: UNT Libraries Government Documents Department

Quantum Vacuum Structure and Cosmology

Description: Contemporary physics faces three great riddles that lie at the intersection of quantum theory, particle physics and cosmology. They are: (1) The expansion of the universe is accelerating - an extra factor of two appears in the size; (2) Zero-point fluctuations do not gravitate - a matter of 120 orders of magnitude; and (3) The 'True' quantum vacuum state does not gravitate. The latter two are explicitly problems related to the interpretation and the physical role and relation of the quantum vacuum with and in general relativity. Their resolution may require a major advance in our formulation and understanding of a common unified approach to quantum physics and gravity. To achieve this goal we must develop an experimental basis and much of the discussion we present is devoted to this task. In the following, we examine the observations and the theory contributing to the current framework comprising these riddles. We consider an interpretation of the first riddle within the context of the universe's quantum vacuum state, and propose an experimental concept to probe the vacuum state of the universe.
Date: December 5, 2011
Creator: Rafelski, Johann; Labun, Lance; Hadad, Yaron; U., /Arizona U. /Munich; Chen, Pisin & /Taiwan, Natl. Taiwan U. /KIPAC, Menlo Park /SLAC
Partner: UNT Libraries Government Documents Department

Fe Emission And Ionized Excess Absorption in the Luminous Quasar 3C109 With XMM-Newton

Description: We report results from an XMM-Newton observation of the broad-line radio galaxy 3C 109 (z=0.3056). Previous ASCA data revealed the presence of a broad iron line from the accretion disc with which the XMM-Newton spectrum is fully consistent. However, although improving the ASCA constraints on the line parameters, the quality of the data is not high enough to distinguish between an untruncated accretion disc extending down to small radii close to the black hole and a scenario in which the innermost 20-30 gravitational radii are missing. For this reason, our results are model-dependent and the hard data can be modeled equally well by considering an absorption scenario in which a large column of neutral gas partially covers the X-ray continuum source. However, the absorber would have to comprise hundreds/thousands very compact clouds close to the X-ray source, which seems rather extreme a requirement. The 2-10 keV intrinsic luminosity of 3C 109 is of the order of 2-3 x 10{sup 45} erg s{sup -1} regardless of the adopted model. A recent black hole mass estimate of {approx} 2 x 10{sup 8} M{sub {circle_dot}} implies that L{sub bol}/L{sub Edd} > 1. If partial covering is excluded, the observed reflection fraction (of the order of unity), steep photon index (1.86), and Fe line equivalent width (about 100 eV) all suggest to exclude that the X-ray continuum is strongly beamed indicating that the large Eddington ratio is associated with a radiatively efficient accretion process and making it unlikely that the innermost accretion disc is replaced by a thick radiatively inefficient medium such as in advection-dominated accretion models. We also confirm previous findings on the detection of low energy absorption in excess of the Galactic value, where we find excellent agreement with previous results obtained in X-rays and at other wavelengths (optical and infrared). The ...
Date: June 9, 2006
Creator: Miniutti, Giovanni; /Cambridge U., Inst. of Astron.; Ballantyne, D.R.; U., /Arizona; Allen, S.W.; /KIPAC, Menlo Park et al.
Partner: UNT Libraries Government Documents Department

ORKA: Measurement of the $K^ \to \pi^+ \nu \bar{\nu}$ decay at Fermilab

Description: A high precision measurement of the ultra-rare K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} decay at Fermilab would be one of the most incisive probes of quark flavor physics this decade. Its dramatic reach for uncovering new physics is due to several important factors: (1) The branching ratio is sensitive to most new physics models which extend the Standard Model to solve its considerable problems. (2) The Standard Model predictions for the K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} and K{sub L}{sup 0} {yields} {pi}{sup 0} {nu}{bar {nu}} branching fractions are broadly recognized to be theoretically robust at the 5-10% level. Only a precious few accessible loop-dominated quark processes can be predicted with this level of certainty. (3) The K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} branching fraction is highly suppressed in the Standard Model to the level < 10{sup -10} (<1 part in 10 billion). This suppression allows physics beyond the Standard Model to contribute dramatically to the branching fraction with enhancements of up to factors of 5 above the Standard Model level. (4) The certainty with which the Standard Model contribution to K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} can be predicted will permit a 5{sigma} discovery potential for new physics even for enhancements of the branching fraction as small as 35%. This sensitivity is unique in quark flavor physics and allows probing of essentially all models of new physics that couple to quarks within the reach of the LHC. Furthermore, a high precision measurement of K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} is sensitive to many models of new physics with mass scales well beyond the direct reach of the LHC. The experimental challenge of suppressing backgrounds to enable measurement of K{sup +} {yields} {pi}{sup +} {nu}{bar {nu}} at the 1 in 10-billion Standard Model rate has ...
Date: November 28, 2011
Creator: Comfort, Joseph; U., /Arizona State; Bryman, Douglas; Doria, Luca; Numao, Toshio; Sher, Aleksey et al.
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

Measurement of direct photon emission in the K(L) ---> pi+ pi- gamma decay mode

Description: In this paper the KTeV collaboration reports the analysis of 112.1 x 10{sup 3} candidate K{sub L} {yields} {pi}{sup +}{pi}{sup -}{gamma} decays including a background of 671 {+-} 41 events with the objective of determining the photon production mechanisms intrinsic to the decay process. These decays have been analyzed to extract the relative contributions of the Cp violating bremsstrahlung process and the CP conserving M1 and CP violating E1 direct photon emission processes. The M1 direct photon emission amplitude and its associated vector form factor parameterized as |{bar g}{sub M1}|(1 + a{sub 1}/a{sub 2}/(M{sub {rho}}{sup 2}-M{sub K}{sup 2}) + 2M{sub K}E{sub {gamma}}) have been measured to be |{bar g}{sub M1}| = 1.198 {+-} 0.035(stat) {+-} 0.086(syst) and a{sub 1}/a{sub 2} = =0.738 {+-} 0.007(stat) {+-} 0.018(syst) GeV{sup 2}/c{sup 2} respectively. An upper limit for the CP violating E1 direct emission amplitude |g{sub E1}| {le} 0.1 (90%CL) has been found. The overall ratio of direct photon emission (DE) to total photon emission including the bremsstrahlung process (IB) has been determined to be DE/(DE + IB) = 0.689 {+-} 0.021 for E{sub {gamma}} {ge} 20 MeV.
Date: April 1, 2006
Creator: Abouzaid, E.; /Chicago U., EFI; Arenton, M.; U., /Virginia; Barker, A.R.; U., /Colorado et al.
Partner: UNT Libraries Government Documents Department

A Proposal to Study Beauty Production and Other Heavy Quark Physics Associated with Dimuon Production in 800 (925) GeV/C pp Interactions

Description: The presence of dimuons in final states produced in hadronic interactions has proved to be a valuable indicator that interesting hard physics processes have taken place. These muon pairs provide a mechanism for selecting these relatively rare processes from interactions due to the total cross section. In particular, processes involving heavy quarks are flagged by the presence of muon pairs. We are proposing to use the high rate E705 spectrometer and its dimuon trigger processor which have already functioned well in Experiments E-537 and E-705 to detect and measure several heavy quark phenomena which result in a final state containing a pair of muons. This experiment will use the primary proton beam from the Tevatron at the maximum energy available at the time of execution of the experiment. The spectrometer will be augmented by the addition of a silicon tracker similar to those used in other experiments at the Fermilab. The present P-West High Intensity Laboratory secondary beams will need to be upgraded by addition of sufficient bending power to allow the transport of the 800 to 925 GeV/c primary proton beam to the experiment target (see Appendix A).
Date: May 1, 1986
Creator: Arenton, M.; Chen, T.Y.; Lai, K.W.; Yao, N.; U., /Arizona; Anassontzis, S.E. et al.
Partner: UNT Libraries Government Documents Department

Determination of the Parity of the Neutral Pion via the Four-Electron Decay

Description: We present a new determination of the parity of the neutral pion via the double Dalitz decay {pi}{sup 0} {yields} e{sup +}e{sup -}e{sup +}e{sup -}. Our sample, which consists of 30 511 candidate decays, was collected from K{sub L} {yields} {pi}{sup 0}{pi}{sup 0}{pi}{sup 0} decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative {pi}{sup 0} parity, and place a limit on scalar contributions to the {pi}{sup 0} {yields} e{sup +}e{sup -}e{sup +}e{sup -} decay amplitude of less than 3.3% assuming CPT conservation. The {pi}{sup 0}{gamma}*{gamma}* form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase space distribution. Additionally, we have measured the branching ratio of this mode to be B({pi}{sup 0} {yields} e{sup +}e{sup -}e{sup +}e{sup -}) = (3.26 {+-} 0.18) x 10{sup -5}.
Date: February 1, 2008
Creator: Abouzaid, E.; U., /Chicago; Arenton, M.; U., /Virginia; Barker, A.R.; U., /Colorado et al.
Partner: UNT Libraries Government Documents Department

Implementation And Performance of the ATLAS Second Level Jet Trigger

Description: ATLAS is one of the four major LHC experiments, designed to cover a wide range of physics topics. In order to cope with a rate of 40MHz and 25 interactions per bunch crossing, the ATLAS trigger system is divided in three different levels. The jet selection starts at first level with dedicated processors that search for high E{sub T} hadronic energy depositions. At the LVL2, the jet signatures are verified with the execution of a dedicated, fast jet reconstruction algorithm, followed by a calibration algorithm. Three possible granularities have been proposed and are being evaluated: cell based (standard), energy sums calculated at each Front-End Board and the use of the LVL1 Trigger Towers. In this presentation, the design and implementation of the jet trigger of ATLAS will be discussed in detail, emphasazing the major difficulties of each selection step. The performance of the jet algorithm, including timing, efficiencies and rates will also be shown, with detailed comparisons of the different unpacking modes.
Date: November 9, 2011
Creator: Conde Muino, Patricia; /Lisbon, LIFEP; Aracena, I.; /SLAC; Brelier, B.; U., /Montreal et al.
Partner: UNT Libraries Government Documents Department

Data Preservation in High Energy Physics

Description: Data from high-energy physics (HEP) experiments are collected with significant financial and human effort and are mostly unique. At the same time, HEP has no coherent strategy for data preservation and re-use. An inter-experimental Study Group on HEP data preservation and long-term analysis was convened at the end of 2008 and held two workshops, at DESY (January 2009) and SLAC (May 2009). This document is an intermediate report to the International Committee for Future Accelerators (ICFA) of the reflections of this Study Group. Large data sets accumulated during many years of detector operation at particle accelerators are the heritage of experimental HEP. These data sets offer unique opportunities for future scientific studies, sometimes long after the shut-down of the actual experiments: new theoretical input; new experimental results and analysis techniques; the quest for high-sensitivity combined analyses; the necessity of cross checks. In many cases, HEP data sets are unique; they cannot and most likely will not be superseded by data from newer generations of experiments. Once lost, or in an unusable state, HEP data samples cannot be reasonably recovered. The cost of conserving this heritage through a collaborative, target-oriented long-term data preservation program would be small, compared to the costs of past experimental projects or to the efforts to re-do experiments. However, this cost is not negligible, especially for collaborations close or past their end-date. The preservation of HEP data would provide today's collaborations with a secure way to complete their data analysis and enable them to seize new scientific opportunities in the coming years. The HEP community will benefit from preserved data samples through reanalysis, combination, education and outreach. Funding agencies would receive more scientific return, and a positive image, from their initial investment leading to the production and the first analysis of preserved data.
Date: April 3, 2012
Creator: Mount, Richard; Brooks, Travis; /SLAC; Le Diberder, Francois; /Orsay, LAL; Dubois-Felsmann, Gregory et al.
Partner: UNT Libraries Government Documents Department

Parametrization and Classification of 20 Billion LSST Objects: Lessons from SDSS

Description: The Large Synoptic Survey Telescope (LSST) will be a large, wide-field ground-based system designed to obtain, starting in 2015, multiple images of the sky that is visible from Cerro Pachon in Northern Chile. About 90% of the observing time will be devoted to a deep-wide-fast survey mode which will observe a 20,000 deg{sup 2} region about 1000 times during the anticipated 10 years of operations (distributed over six bands, ugrizy). Each 30-second long visit will deliver 5{sigma} depth for point sources of r {approx} 24.5 on average. The co-added map will be about 3 magnitudes deeper, and will include 10 billion galaxies and a similar number of stars. We discuss various measurements that will be automatically performed for these 20 billion sources, and how they can be used for classification and determination of source physical and other properties. We provide a few classification examples based on SDSS data, such as color classification of stars, color-spatial proximity search for wide-angle binary stars, orbital-color classification of asteroid families, and the recognition of main Galaxy components based on the distribution of stars in the position-metallicity-kinematics space. Guided by these examples, we anticipate that two grand classification challenges for LSST will be (1) rapid and robust classification of sources detected in difference images, and (2) simultaneous treatment of diverse astrometric and photometric time series measurements for an unprecedentedly large number of objects.
Date: November 10, 2011
Creator: Ivezic, Z.; /Washington U., Seattle, Astron. Dept.; Axelrod, T.; /Large Binocular Telescope, Tucson; Becker, A.C.; /Washington U., Seattle, Astron. Dept. et al.
Partner: UNT Libraries Government Documents Department

Sdssj103913.70+533029.7: a super star cluster in the outskirts of a galaxy merger

Description: We describe the serendipitous discovery in the spectroscopic data of the Sloan Digital Sky Survey of a star-like object, SDSSJ103913.70+533029.7, at a heliocentric radial velocity of +1012 km s{sup -1}. Its proximity in position and velocity to the spiral galaxy NGC 3310 suggests an association with the galaxy. At this distance, SDSSJ103913.70+533029.7 has the luminosity of a super star cluster and a projected distance of 17 kpc from NGC 3310. Its spectroscopic and photometric properties imply a mass of > 10{sup 6} M{sub {circle_dot}} and an age close to that of the tidal shells seen around NGC 3310, suggesting that it formed in the event which formed the shells.
Date: November 1, 2005
Creator: Knapp, Gillian R.; Tremonti, Christy A.; Rockosi, Constance M.; Schlegel, David J.; Yanny, Brian; Beers, Timothy C. et al.
Partner: UNT Libraries Government Documents Department

Boosted Objects: A Probe of Beyond the Standard Model Physics

Description: We present the report of the hadronic working group of the BOOST2010 workshop held at the University of Oxford in June 2010. The first part contains a review of the potential of hadronic decays of highly boosted particles as an aid for discovery at the LHC and a discussion of the status of tools developed to meet the challenge of reconstructing and isolating these topologies. In the second part, we present new results comparing the performance of jet grooming techniques and top tagging algorithms on a common set of benchmark channels. We also study the sensitivity of jet substructure observables to the uncertainties in Monte Carlo predictions.
Date: June 12, 2012
Creator: Abdesselam, A.; U., /Oxford; Kuutmann, E.Bergeaas; /DESY; Bitenc, U.; U., /Freiburg et al.
Partner: UNT Libraries Government Documents Department