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Subcycle Dynamics in the Laser Ionization of Molecules

Description: The time and momentum distributions of electron emission from a molecule during a single laser cycle are calculated by solving a two-dimensional time-dependent Schr{umlt o}dinger equation. The momentum distributions strongly depend on the orbital symmetry and orientation of the molecular axis. Field-induced internal dynamics of the molecule can shift electron emission and recollision times through a large part of the laser cycle, which leads to corresponding variations of high-harmonic emission times and to the appearance of even harmonics.
Date: October 23, 2007
Creator: Xie, X.H.; Wickenhauser, M.; /Vienna, Tech. U.; Boutu, W.; /Saclay; Merdji, H. et al.
Partner: UNT Libraries Government Documents Department

Searches for gauge mediated supersymmetry at the Tevatron

Description: We report the results of searches for new physics in events with two photons and large missing transverse energy collected with both detectors at the Fermilab Tevatron collider. Several models of physics beyond the Standard Model motivate searches in this final state, in particular supersymmetry (SUSY) with gauge-mediated supersymmetry breaking. The D0 collaboration interprets also its search in the framework of universal extra dimensions (UED) with gravity-mediated Kaluza-Klein excitation decays. The results presented use 2.6 fb{sup -1} (CDF) and 6.3 fb{sup -1} (D0) of data collected at the Fermilab Tevatron collider.
Date: January 1, 2010
Creator: Lutz, Pierre & /Saclay
Partner: UNT Libraries Government Documents Department

Hard diffraction at the LHC and the Tevatron using double pomeron exchange

Description: We use a Monte Carlo implementation of recently developed models of inclusive and exclusive diffractive W, top, Higgs and stop productions to assess the sensitivity of the LHC experiments. We also discuss how the Tevatron experiments could test the models and measure the gluon density in the pomeron, which is needed to make precise predictions at the LHC.
Date: January 1, 2006
Creator: Royon, C. & /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

Top quark pair production cross section at Tevatron

Description: An overview of the recent measurements of the top antitop quark pair production cross section in proton antiproton collisions at {radical}s = 1.96 TeV in lepton + jets and dilepton final states is presented. These measurements are based on 1-2.8 fb{sup -1} of data collected with the D0 and CDF experiments at the Fermilab Tevatron collider. The cross section is measured with a precision close to 8 % and found to be compatible with the standard model prediction. Interpretations of the cross-section measurements for charge higgs search and for top quark mass measurement are also discussed.
Date: May 1, 2009
Creator: Shary, V. & /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

Higgs results from the Tevatron Run II

Description: The data taken at the Tevatron experiments have been analyzed to search for Higgs bosons. For the Standard Model Higgs searches, no excess is observed, the data are in good agreement with the expectations, so that limits are set on the production rates. For various theoretical models beyond the Standard Model, there is no excess either, which allows to derive constraints in their respective parameter spaces.
Date: January 1, 2005
Creator: Tuchming, B. & /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

Dynamic Star Formation in the Massive DR21 Filament

Description: The formation of massive stars is a highly complex process in which it is unclear whether the star-forming gas is in global gravitational collapse or an equilibrium state supported by turbulence and/or magnetic fields. By studying one of the most massive and dense star-forming regions in the Galaxy at a distance of less than 3 kpc, i.e. the filament containing the well-known sources DR21 and DR21(OH), we attempt to obtain observational evidence to help us to discriminate between these two views. We use molecular line data from our {sup 13}CO 1 {yields} 0, CS 2 {yields} 1, and N{sub 2}H{sup +} 1 {yields} 0 survey of the Cygnus X region obtained with the FCRAO and CO, CS, HCO{sup +}, N{sub 2}H{sup +}, and H{sub 2}CO data obtained with the IRAM 30m telescope. We observe a complex velocity field and velocity dispersion in the DR21 filament in which regions of the highest column-density, i.e., dense cores, have a lower velocity dispersion than the surrounding gas and velocity gradients that are not (only) due to rotation. Infall signatures in optically thick line profiles of HCO{sup +} and {sup 12}CO are observed along and across the whole DR21 filament. By modelling the observed spectra, we obtain a typical infall speed of {approx}0.6 km s{sup -1} and mass accretion rates of the order of a few 10{sup -3} M{sub {circle_dot}} yr{sup -1} for the two main clumps constituting the filament. These massive clumps (4900 and 3300 M{sub {circle_dot}} at densities of around 10{sup 5} cm{sup -3} within 1 pc diameter) are both gravitationally contracting. The more massive of the clumps, DR21(OH), is connected to a sub-filament, apparently 'falling' onto the clump. This filament runs parallel to the magnetic field. Conclusions. All observed kinematic features in the DR21 filament (velocity field, velocity dispersion, and infall), ...
Date: August 25, 2010
Creator: Schneider, N.; /Saclay; Csengeri, T.; /Saclay; Bontemps, S.; /OASU, Floirac et al.
Partner: UNT Libraries Government Documents Department

Precision measurements of the top quark mass and width with the D0 detector

Description: Since the discovery of the top quark in 1995 at the Fermliab Tevatron Collider, top quark properties have been measured with ever higher precision. In this article, recent measurements of the top quark mass and its width using up to 3.6 fb{sup -1} of D0 data are summarized. Different techniques and final states have been examined and no deviations within these measurements have been observed. In addition to the direct measurements, a measurement of the top quark mass from its production cross section and a measurement of the top-antitop quark mass difference are discussed. With a mass of 173.3 {+-} 1.1 GeV, the top quark is the heaviest of all known fundamental particles. Due to the high mass, its Yukawa coupling is close to unity suggesting that it may play a special role in electroweak symmetry breaking. Precise measurements of both, the W boson and the top quark mass, constrain the mass of the yet unobserved Higgs boson and allow to restrict certain extensions of the Standard Model. At the Tevatron collider with a center-of-mass energy of 1.96 TeV, 85% of the top quark pairs are produced in quark-antiquark annihilation; 15% originate from gluon fusion. Top quarks are predicted to decay almost exclusively to a W boson and a bottom quark. According to the number of hadronic W decays, top events are classified into all-jets, lepton+jets and dilepton events. The lepton+jets channel is characterized by four jets, one isolated, energetic charged lepton and missing transverse energy. With 30%, the branching fraction of the lepton+jets channel is about seven times larger than the one of the dilepton channel whereas the signal to background ratio is about three times smaller. The main background in this final state comes from W +jets events. Instrumental background arises from events in which a jet is ...
Date: January 1, 2010
Creator: Grohsjean, Alexander & /IRFU, SPP, Saclay
Partner: UNT Libraries Government Documents Department

Search for scalar bottom quarks and third-generation leptoquarks in $p\overline{p}$ collisions at $\sqrt{s}$ = 1.96 TeV

Description: We present the results of a search for pair production of scalar bottom quarks ({bar b}{sub 1}) and scalar third-generation leptoquarks (LQ{sub 3}) in a data sample of 5.2 f b{sup -1} collected by the D0 experiment at the Tevatron, the p{bar p} collider at Fermilab. We assume that sbottoms decay to a neutralino ({bar {chi}}{sub 1}{sup 0}) and a b quark, and we set 95% C.L. lower limits on their production in the (m{sub {bar b}{sub 1}}, m{sub {bar {chi}}{sub 1}{sup 0}}) mass plane such that m{sub {bar b}{sub 1}} > 247 GeV for m{sub {bar {chi}}{sub 1}{sup 0}} = 0 and m{sub {bar {chi}}{sub 1}{sup 0}} > 110 GeV for 160 < m{sub {bar b}{sub 1}} < 200 GeV. The leptoquarks are assumed to decay to a tau neutrino and a b quark, and we set a 95% C.L. lower limit of 247 GeV on the mass of a charge-1/3 third-generation leptoquark.
Date: January 1, 2010
Creator: Deterre, Cecile & /IRFU, SPP, Saclay
Partner: UNT Libraries Government Documents Department

Studies of top quark properties at the D0 experiment

Description: We present an overview of selected top quark properties in lepton + jets and dilepton final states based on 1-4.3 fb{sup -1} of data, collected with the D0 experiment at the Fermilab Tevatron collider. The recent measurement of theW boson helicity, a search for anomalous top quark couplings, and measurements of spin correlations and forward backward color charge asymmetry are discussed. Since the discovery of top quark in 1995 by CDF and D0, the discovered particle is considered as a standard model (SM) top quark, mainly because its cross-section is in a reasonable agreement with QCD calculations and its measured mass is in a agreement with indirect top quark mass determinations. However the limited precision of these comparisons doesn't exclude the possibility of non SM contributions in the top quark final states, so direct measurements of top quark properties are useful to confirm its SM nature. In this article we report several recent measurements done using 1-4.3 fb{sup -1} of data collected with the D0 detector at the Fermilab Tevatron collider.
Date: January 1, 2010
Creator: Shary, Viatcheslav & /IRFU, SPP, Saclay
Partner: UNT Libraries Government Documents Department

Bootstrapping Multi-Parton Loop Amplitudes in QCD

Description: The authors present a new method for computing complete one-loop amplitudes, including their rational parts, in non-supersymmetric gauge theory. This method merges the unitarity method with on-shell recursion relations. It systematizes a unitarity-factorization bootstrap approach previously applied by the authors to the one-loop amplitudes required for next-to-leading order QCD corrections to the processes e{sup +}e{sup -} {yields} Z, {gamma}* {yields} 4 jets and pp {yields} W + 2 jets. We illustrate the method by reproducing the one-loop color-ordered five-gluon helicity amplitudes in QCD that interfere with the tree amplitude, namely A{sub 5;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}) and A{sub 5;1}(1{sup -}, 2{sup +}, 3{sup -}, 4{sup +}, 5{sup +}). Then we describe the construction of the six- and seven-gluon amplitudes with two adjacent negative-helicity gluons, A{sub 6;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}) and A{sub 7;1}(1{sup -}, 2{sup -}, 3{sup +}, 4{sup +}, 5{sup +}, 6{sup +}, 7{sup +}), which uses the previously-computed logarithmic parts of the amplitudes as input. They present a compact expression for the six-gluon amplitude. No loop integrals are required to obtain the rational parts.
Date: July 6, 2005
Creator: Bern, Zvi; /UCLA; Dixon, Lance J.; /SLAC; Kosower, David A. & /Saclay, SPhT
Partner: UNT Libraries Government Documents Department

Measurement of the inclusive jet cross section in proton-antiproton collisions at the center-of-mass energy of 1.96 TeV

Description: This thesis studies the high-energy collisions of protons and antiprotons. The data used in the measurement were collected during 2004-2005 with the D0 detector at the Tevatron Collider of the Fermi National Accelerator Laboratory and correspond to 0.7 fb{sup -1} of integrated luminosity. High energy hadron collisions usually produce collimated sprays of particles called jets. The energy of the jets is measured using a liquid Argon-Uranium calorimeter and the production angle is determined with the help of silicon microstrip and scintillating fiber trackers. The inclusive jet cross section in proton-antiproton collisions is measured as a function of jet transverse momentum p{sub T} in six bins of jet rapidity at the center-of-mass energy {radical}s = 1.96 TeV. The measurement covers jet transerve momenta from 50 GeV up to 600 GeV and jet rapidities up to |y| = 2.4. The data are collected using a set of seven single jet triggers. Event and jet cuts are applied to remove non-physical backgrounds and cosmic-ray interactions. The data are corrected for jet energy calibration, cut and trigger efficiencies and finite jet p{sub T} resolution. The corrections are determined from data and the methods are tested with Monte Carlo simulation. The main experimental challenges in the measurement are the calibration of jet energies and the determination of the jet p{sub T} resolution. New methods are developed for the jet energy calibration that take into account physical differences between the {gamma}+jet and dijet calibration samples arising from quark and gluon jet differences. The uncertainty correlations are studied and provided as a set of uncertainty sources. The production of particle jets in hadron collisions is described by the theory of quantum chromodynamics (QCD). When the transverse jet momentum is large, the contributions from long-distance physics processes are small and the production rates of jets can be predicted ...
Date: July 1, 2008
Creator: Voutilainen, Mikko Antero & /Saclay, /Helsinki Inst. of Phys. /Helsinki U. of Tech. /Nebraska U.
Partner: UNT Libraries Government Documents Department

Measurement of the Vertical Emittance and beta-Function at the PEP-II Interaction Point Using the BaBar Detector

Description: We present measurements of the effective vertical emittance and IP {beta}-function in the PEP-II asymmetric B Factory at SLAC. These beam parameters are extracted from fits to the longitudinal dependence of the luminosity and the vertical luminous size, measured using e{sup +}e{sup -} {yields} {mu}{sup +}{mu}{sup -} events recorded in the BABAR detector. The results are compared, for different sets of machine conditions, to accelerator-based measurements of the optical functions of the two beams.
Date: May 17, 2005
Creator: Thompson, J.M.; Roodman, A.; /SLAC; Kozanecki, W. & /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

Characterization of the PEP-II Colliding-Beam Phase Space by the Boost Method

Description: We present a novel approach to characterize the colliding-beam phase space at the interaction point of the energy-asymmetric PEP-II B-Factory. The method exploits the fact that the transverse-boost distribution of e{sup +}e{sup -} {yields} {mu}{sup +}{mu}{sup -} events reconstructed in the BABAR detector reflects that of the colliding electrons and positrons. The mean boost direction, when combined with the measured orientation of the luminous ellipsoid, determines the e{sup +}-e{sup -} crossing angles. The average angular spread of the transverse boost vector provides an accurate measure of the angular divergence of the incoming high-energy beam, confirming the presence of a sizeable dynamic-{beta} effect. The longitudinal and transverse dependence of the boost angular spread also allow to extract from the continuously-monitored distributions detailed information about the emittances and IP {beta}-functions of both beams during high-luminosity operation.
Date: July 19, 2006
Creator: Weaver, M.; /SLAC; Kozanecki, W.; /DAPNIA, Saclay; Viaud, B. & U., /Montreal
Partner: UNT Libraries Government Documents Department

20 - 50 GeV muon storage rings for a neutrino factory

Description: Muon decay rings are under study as part of an International Scoping Study (ISS) for a future Neutrino Factory. Both isosceles triangle- and racetrack-shaped rings are being considered for a 20 GeV muon energy, but with upgrade potentials of 40 or 50 GeV. Both rings are designed with long straights to optimize directional muon decay. The neutrinos from muon decay pass to one or two distant detectors; the racetrack ring has one very long production straight aligned with one detector while the triangular ring has two straights which can be aligned with two detectors. Decay ring specifications and lattice studies are the primary topic of this paper. Injection, collimation, and the RF system are covered in a second contribution to these proceedings.
Date: July 1, 2006
Creator: Rees, G.H.; /Rutherford; Johnstone, C.; /Fermilab; Meot, F. & /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

N >= 4 Supergravity Amplitudes from Gauge Theory at One Loop

Description: We expose simple and practical relations between the integrated four- and five-point one-loop amplitudes of N {ge} 4 supergravity and the corresponding (super-)Yang-Mills amplitudes. The link between the amplitudes is simply understood using the recently uncovered duality between color and kinematics that leads to a double-copy structure for gravity. These examples provide additional direct confirmations of the duality and double-copy properties at loop level for a sample of different theories.
Date: August 19, 2011
Creator: Bern, Z.; /UCLA; Boucher-Veronneau, C.; /SLAC; Johansson, H. & /Saclay
Partner: UNT Libraries Government Documents Department

Top Quark Physics at the Tevatron

Description: The authors review the field of top-quark physics with an emphasis on experimental techniques. The role of the top quark in the Standard Model of particle physics is summarized and the basic phenomenology of top-quark production and decay is introduced. They discuss how contributions from physics beyond the Standard model could affect the top-quark properties or event samples. The many measurements made at the Fermilab Tevatron, which test the Standard model predictions or probe for direct evidence of new physics using the top-quark event samples, are reviewed here.
Date: October 1, 2010
Creator: Deliot, Frederic; /DAPNIA, Saclay; Glenzinski, Douglas A. & /Fermilab
Partner: UNT Libraries Government Documents Department

Results on inclusive jets and jet properties

Description: We report on a measurement of the inclusive jet cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0.70 fb{sup -1}. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.
Date: April 1, 2008
Creator: Voutilainen, Mikko Antero & /Nebraska U. /Helsinki Inst. of Phys. /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

Modeling Lost-Particle Backgrounds in PEP-II Using LPTURTLE

Description: Background studies during the design, construction, commissioning, operation and improvement of BaBar and PEP-II have been greatly influenced by results from a program referred to as LPTURTLE (Lost Particle TURTLE) which was originally conceived for the purpose of studying gas background for SLC. This venerable program is still in use today. We describe its use, capabilities and improvements and refer to current results now being applied to BaBar.
Date: May 17, 2005
Creator: Fieguth, T.; /SLAC; Barlow, R.; U., /Manchester; Kozanecki, W. & /DAPNIA, Saclay
Partner: UNT Libraries Government Documents Department

Summary of sessions B and F: High intensity linacs and frontend & proton drivers

Description: This paper summarizes the sessions B&F of the 33rd ICFA Advanced Beam Dynamics Workshop on High Intensity & High Brightness Hadron Beams held in Bensheim, Germany. It covers high intensity linacs, front ends and proton driver topics.
Date: January 1, 2005
Creator: Ferdinand, R.; /Saclay; Chou, W.; /Fermilab; Galambos, J. & Ridge, /Oak
Partner: UNT Libraries Government Documents Department

Isolated Attosecond Pulses using a Detuned Second-harmonic Field

Description: Calculations are presented for the generation of an isolated attosecond pulse in a multicycle two-color strong-field regime. We show that the recollision of the electron wave packet can be confined to half an optical cycle using pulses of up to 40 fs in duration. The scheme is proven to be efficient using two intense beams, one producing a strong field at {omega} and the other a strong field detuned from 2{omega}. The slight detuning {delta}{omega} of the second harmonic is used to break the symmetry of the electric field over many optical cycles and provides a coherent control for the formation of an isolated attosecond pulse.
Date: November 7, 2007
Creator: Merdji, Hamed; /Saclay /SLAC, PULSE; Auguste, Thierry; Boutu, Willem; Caumes, J.-Pascal; Carre, Bertrand et al.
Partner: UNT Libraries Government Documents Department

Higher-Order Corrections to Timelike Jets

Description: We present a simple formalism for the evolution of timelike jets in which tree-level matrix element corrections can be systematically incorporated, up to arbitrary parton multiplicities and over all of phase space, in a way that exponentiates the matching corrections. The scheme is cast as a shower Markov chain which generates one single unweighted event sample, that can be passed to standard hadronization models. Remaining perturbative uncertainties are estimated by providing several alternative weight sets for the same events, at a relatively modest additional overhead. As an explicit example, we consider Z {yields} q{bar q} evolution with unpolarized, massless quarks and include several formally subleading improvements as well as matching to tree-level matrix elements through {alpha}{sub s}{sup 4}. The resulting algorithm is implemented in the publicly available VINCIA plugin to the PYTHIA8 event generator.
Date: February 1, 2011
Creator: Giele, W.T.; /Fermilab; Kosower, D.A.; /Saclay, SPhT; Skands, P.Z. & /CERN
Partner: UNT Libraries Government Documents Department