Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 31 - 60 of 114

Full-Text Articles in Physics

Transient Spin Structures At The Antifero-To-Paramagnetic Phase Boundary Of Febr2, Christian Binek Aug 2000

Transient Spin Structures At The Antifero-To-Paramagnetic Phase Boundary Of Febr2, Christian Binek

Christian Binek Publications

Excess magnetization and anomalous susceptibility loss is observed on antiferromagnetic FeBr2 in an axial field H below and above its H-T-phase boundary between the multicritical temperature (Tm = 4.6 K) and the Néel temperature (TN = 14.1 K). These and other unusual properties of FeBr2 are attributed to frustration-induced intraplanar non-critical spin fluctuations, which can be simulated within the framework of a triaxial version of the 2D-ANNNI model.


Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek Aug 2000

Crossover From Transient Spin Structures Ot The Field-Induced Griffiths Phase Of Febr2, Christian Binek

Christian Binek Publications

In the presence of an applied axial magnetic field Ha the uniaxial antiferromagnets FeCl2 and FeBr2 show fluctuating domain-like antiferromagnetic correlations above the phase boundary Tc(Ha). They are detected by SQUID measurements of the low frequency out-of-phase susceptibility gc″ and indicate a field-induced Griffiths phase at temperatures Tc(Ha) < T < TN. In contrast to FeCl2, important additional frustration-induced intraplanar non-critical contributions to χ″ vs. T are found in FeBr2. For external fields above the Tc(Ha) line, Ha > 2.6 MA/m, they are shown to superimpose linearly on the Griffiths contributions. These dominate at Ha = 2.67 MA/m and are unequivocally modeled within the Landau theory of fluctuations near phase transitions by introducing a Lorentzian Tc distribution.


Search For Antiproton Decay At The Fermilab Antiproton Accumulator, S. Geer, J. Marriner, M. Martins, R. E. Ray, J. Streets, W. Wester Aug 2000

Search For Antiproton Decay At The Fermilab Antiproton Accumulator, S. Geer, J. Marriner, M. Martins, R. E. Ray, J. Streets, W. Wester

Gregory Snow Publications

A search for antiproton decay has been made at the Fermilab Antiproton Accumulator. Limits are placed on 13 antiproton decay modes. The results include the first explicit experimental limits on the muonic decay modes of the antiproton, and the first limits on the decay modes ℯ-γγ and ℯ-ω. The most stringent limit is for the decay mode→ ℯ-γ. At 90% C.L. we find that τ¯ / B (→ ℯ-γ)>7x105 yr. The most stringent limit for decay modes with a muon in the final state is for the decay → μ-γ . At ...


Magnetic Localization In Transition-Metal Nanowires, Ralph Skomski, H. Zeng, M. Zheng, David J. Sellmyer Aug 2000

Magnetic Localization In Transition-Metal Nanowires, Ralph Skomski, H. Zeng, M. Zheng, David J. Sellmyer

David Sellmyer Publications

Magnetization reversal in transition-metal nanowires is investigated. Model calculations explain why magnetization reversal is localized, as opposed to the sometimes assumed delocalized coherent-rotation and curling modes. The localization is a quite general phenomenon caused by morphological inhomogenities and occurring in both polycrystalline and single-crystalline wires. In the polycrystalline limit, the competition between interatomic exchange and anisotropy gives rise to a variety of random-anisotropy effects, whereas nearly single-crystalline wires exhibit a weak localization of the nucleation mode. Model predictions are used to explain the coercive and magnetic-viscosity behavior of Co (and Ni) nanowires electrodeposited in self-assembled alumina pores.


Limits On Anomalous Ww Γ And Wwz Couplings From Ww/WzEνjj Production, B. Abbott, Gregory Snow, D0 Collaboration Aug 2000

Limits On Anomalous Ww Γ And Wwz Couplings From Ww/Wz→Eνjj Production, B. Abbott, Gregory Snow, D0 Collaboration

Gregory Snow Publications

Limits on anomalous WW γ and WWZ couplings are presented from a study of WW/WZeνjj events produced in pp̅ collisions at √s = 1.8 TeV. Results from the analysis of data collected using the DØ detector during the 1993–1995 Tevatron collider run at Fermilab are combined with those of an earlier study from the 1992–1993 run. A fit to the transverse momentum spectrum of the W boson yields direct limits on anomalous WW γ and WWZ couplings. With the assumption that the WW γ and WWZ couplings are equal, we obtain -0.34 < λ < 0.36 (with Δk=0) and ...


Molecular-Dynamics Study Of Phase Transitions In Alkali Thiocyanates, M. M. Ossowski, John R. Hardy, R. W. Smith Aug 2000

Molecular-Dynamics Study Of Phase Transitions In Alkali Thiocyanates, M. M. Ossowski, John R. Hardy, R. W. Smith

John R. Hardy Papers

An account is presented of our studies of the order-disorder phase transitions in KSCN, RbSCN, and CsSCN. These are based on parameter-free interionic potentials based on the Gordon-Kim modified electron gas formalism extended to molecular ions. We performed static structural relaxations and supercell molecular dynamics and predicted with reasonable accuracy the temperatures for the onset of the transitions. In particular, we address the question of how the SCN- ions disorder to yield subsequent structural transformations. We found high-temperature phases of average Fm3m symmetry for both KSCN and RbSCN. We argue that in reality the full appearance of these ...


Effect Of Disorder On Perpendicular Magnetotransport In Co/Cu Multilayers, Evgeny Y. Tsymbal Aug 2000

Effect Of Disorder On Perpendicular Magnetotransport In Co/Cu Multilayers, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

We investigate the spin-dependent conductance of the Co/Cu multilayers in the current-perpendicular-tothe- plane (CPP) geometry. Using a realistic tight-binding model for the electronic band structure of the multilayer, and introducing disorder in the on-site atomic energies we calculate the conductance and giant magnetoresistance (GMR) within the quantum-mechanical linear response theory by performing averaging over random disorder configurations. By varying the thickness and the number of individual layers and the degree of disorder in the multilayers, we analyze factors influencing the CPP GMR. In particular, we show the importance of the thickness-dependent interface resistance, which depends on the mean free ...


Theory Of Magnetostatic Coupling In Thin-Film Rectangular Magnetic Elements, Evgeny Y. Tsymbal Aug 2000

Theory Of Magnetostatic Coupling In Thin-Film Rectangular Magnetic Elements, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

A theory of magnetostatic coupling in thin-film uniformly magnetized arrays of rectangular magnetic elements is presented. Analytic expressions for the magnetostatic energy and the dipolar fields are derived. The influence of the aspect ratio and the spacing between the elements on the magnetostatic coupling is investigated. It is found that increasing the aspect ratio reduces the critical distance between the elements, above which the magnetostatic inter-element coupling can be neglected.


Static-Electric-Field-Induced Polarization Effects In Harmonic Generation, Bogdan Borca, A.V. Flegel, M.V. Frolov, N. L. Manakov, Dejan B. Milosevic, Anthony F. Starace Jul 2000

Static-Electric-Field-Induced Polarization Effects In Harmonic Generation, Bogdan Borca, A.V. Flegel, M.V. Frolov, N. L. Manakov, Dejan B. Milosevic, Anthony F. Starace

Anthony F. Starace Publications

Two static-electric-field-induced effects on harmonic generation are demonstrated analytically and numerically: elliptic dichroism (in which the harmonic yield is different for right and left elliptically polarized laser fields) and elliptical polarization of harmonics produced by linearly polarized driving laser fields. Both effects stem from interference of real and imaginary parts of the nonlinear atomic susceptibilities. Possibilities for experimentally measuring these effects are discussed.


Surface Electronic Phase Transition In Colossal Magnetoresistive Manganese Perovskites: La0.65Sr0.35Mno3, Hani Dulli, E. Ward Plummer, Peter A. Dowben, Jaewu Choi, Sy_Hwang Liou Jul 2000

Surface Electronic Phase Transition In Colossal Magnetoresistive Manganese Perovskites: La0.65Sr0.35Mno3, Hani Dulli, E. Ward Plummer, Peter A. Dowben, Jaewu Choi, Sy_Hwang Liou

Peter Dowben Publications

We have observed a distinct surface phase transition for an important class of giant magnetoresistance materials [La1-x Srx MnO3 (x = 0.35)]. The surface phase transition occurs at 240 K compared to 370 K for the bulk and is fundamentally different. In the bulk, a ferromagnetic metal to paramagnetic bad-metal transition occurs, while the lower-temperature surface transition is from an insulator to a semimetal. The surface of this manganese perovskite is electronically and compositionally quite different from the bulk with important implications for the behavior of artificially grown layered transition-metal oxides and for the use of surface ...


Freezing Field Dependance Of The Exchange Bias In Uniaxial Fef2-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek Jul 2000

Freezing Field Dependance Of The Exchange Bias In Uniaxial Fef2-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek

Christian Binek Publications

The exchange bias effect is measured for the first time in FeF2–CoPt heterosystems with perpendicular anisotropy. The exchange previous field exhibits a strong dependence on the axial previous freezing field. This behavior is explained in terms of the microscopic spin structure at the interface, which is established on cooling to below TN. We calculate the dependence of the spin structure on the previous freezing field within the framework of an Ising model. It takes into account the Zeeman energy as well as an antiferromagnetic exchange coupling between the adjacent layers at the interface.


Effective Surface Debye Temperature For Nimnsb.100. Epitaxial Films, C.N. Borca, Takashi Komesu, Hae-Kyung Jeong, Peter A. Dowben, D. Ristoiu, Ch. Hordequin, J. Pierre, J. P. Nozie`Res Jul 2000

Effective Surface Debye Temperature For Nimnsb.100. Epitaxial Films, C.N. Borca, Takashi Komesu, Hae-Kyung Jeong, Peter A. Dowben, D. Ristoiu, Ch. Hordequin, J. Pierre, J. P. Nozie`Res

Peter Dowben Publications

The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145613 K. This is far smaller than the bulk Debye temperature of 31265 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface. © 2000 American Institute of Physics. [S0003-6951(00)05127-5]


Search For The Charged Higgs Boson In The Decays Of Top Quark Pairs In The EΤ And Μτ Channels At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Jul 2000

Search For The Charged Higgs Boson In The Decays Of Top Quark Pairs In The EΤ And Μτ Channels At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

Top quark production offers the unique opportunity to search for a charged Higgs boson (H±), as the contribution from tH+b τ + νb can be large in extensions of the standard model. We use results from a search for top quark pair production by the Collider Detector at Fermilab (CDF) in the e τ +ET+jets and μ τ+ET+jets signatures to set an upper limit on the branching ratio of Ɓ (tH+b) in 106 pb-1 of data. The upper limit is in the range 0.5 to 0.6 at 95 ...


Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben Jul 2000

Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben

Peter Dowben Publications

We present evidence for a change in electron – phonon coupling across a bulk ph=e transition. Below the lattice stiffening transition at around 160 K, there is a change in the diffracted peak width observed by neutron and X-ray scattering techniques. Also, the electronic band structure of the copolymer is shifting in binding energy below 160 K, decreasing the density of states near the Fermi level. The value of the effective Debye temperature above the transition temperature is approximately 50 K, while below 160 K, the value of the Debye parameter is 245 K. We postulate that the coupling between ...


Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben Jun 2000

Changes In Electron-Phonon Coupling Across A Bulk Phase Transition In Copolymer Films Of Vinylidene Fluoride (70%) With Trifluoroethylene (30%), C. N. Borca, Shireen Adenwalla, Jaewu Choi, Lee Robertson, H. You, V. M. Fridkin, S. P. Palto, N. Petukhova, Stephen Ducharme, Peter A. Dowben

Peter Dowben Publications

We present evidence for a change in electron - phonon coupling across a bulk phase transition. Below the lattice stiffening transition at around 160 K, there is a change in the diffracted peak width observed by neutron and X-ray scattering techniques. Also, the electronic band structure of the copolymer is shifting in binding energy below 160 K, decreasing the density of states near the Fermi level. The value of the effective Debye temperature above the transition temperature is approximately 50 K, while below 160 K, the value of the Debye parameter is 245 K. We postulate that the coupling between electrons ...


Rare-Earth Boride Thin Film System, Peter A. Dowben, Zenchen Zhong, David J. Sellmyer Jun 2000

Rare-Earth Boride Thin Film System, Peter A. Dowben, Zenchen Zhong, David J. Sellmyer

Peter Dowben Publications

Disclosed is a system made by a method for depositing rare-earth boride onto the surface of a substrate which is submerged in an organic solution of borane and a rare-earth halide. Application of electromagnetic radiation, preferably in the visible wavelength range, through a mask near the surface of the submerged substrate, drives the formation and deposition of rare-earth boride onto a substrate in desired patterns.


Search For Scalar Top And Scalar Bottom Quarks In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Jun 2000

Search For Scalar Top And Scalar Bottom Quarks In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have searched for direct pair production of scalar top and scalar bottom quarks in 88 pb-1 of pp̅ collisions at √s =1.8 TeV with the CDF detector. We looked for events with a pair of heavy flavor jets and missing energy, consistent with scalar top (bottom) quark decays to a charm (bottom) quark and a neutralino. The numbers of events that pass our selections show no significant deviation from standard model expectations. We compare our results to the next-to-leading order scalar quark production cross sections to exclude regions in scalar quark-neutralino mass parameter space.


Search For A W′ Boson Via The Decay Mode W′→Μν Μ In 1.8 Tev Pp̅ Collisions, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Jun 2000

Search For A W′ Boson Via The Decay Mode W′→Μν Μ In 1.8 Tev Pp̅ Collisions, F. Abe, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report the results of a search for a W′ boson produced in pp̅ collisions at a center-of-mass energy of 1.8 TeV using a 107 pb-1 data sample recorded by the Collider Detector at Fermilab. We consider the decay channel W′→ μνμ and search for anomalous production of high transverse mass μνμ lepton pairs. We observe no excess of events above background and set limits on the rate of W′ boson production and decay relative to standard model W boson production and decay using a fit of the transverse mass distribution observed. If we assume standard ...


Observation Of Phase-Matched Relativistic Harmonic Generation, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter Jun 2000

Observation Of Phase-Matched Relativistic Harmonic Generation, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter

Donald Umstadter Publications

Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Third-harmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse.


Electron Acceleration And The Propagation Of Ultrashort High-Intensity Laser Pulses In Plasmas, Xiaofang Wang, Mohan Krishnan, Ned Saleh, Haiwen Wang, Donald P. Umstadter Jun 2000

Electron Acceleration And The Propagation Of Ultrashort High-Intensity Laser Pulses In Plasmas, Xiaofang Wang, Mohan Krishnan, Ned Saleh, Haiwen Wang, Donald P. Umstadter

Donald Umstadter Publications

Reported are interactions of high-intensity laser pulses ( λ = 810 nm and l≤3×1018 W/cm2) with plasmas in a new parameter regime, in which the pulse duration ( τ = 29 fs) corresponds to 0.6–2.6 plasma periods. Relativistic filamentation is observed to cause laser-beam breakup and scattering of the beam out of the vacuum propagation angle. A beam of megaelectronvolt electrons with divergence angle as small as 1° is generated in the forward direction, which is correlated to the growth of the relativistic filamentation. Raman scattering, however, is found to be much less than previous long-pulse ...


Search For Scalar Top Quark Production In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Jun 2000

Search For Scalar Top Quark Production In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have searched for direct production of scalar top quarks at the Collider Detector at Fermilab in 88 pb-1 of pp collisions at √s =1.8 TeV. We assume the scalar top quark decays into either a bottom quark and a chargino or a bottom quark, a lepton, and a scalar neutrino. The event signature for both decay scenarios is a lepton, missing transverse energy, and at least two b-quark jets. For a chargino mass of 90 GeV/c2 and scalar neutrino masses of at least 40 GeV/c2, we find no evidence for scalar top ...


A Cone Of Coherent Light, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter Jun 2000

A Cone Of Coherent Light, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter

Donald Umstadter Publications

Lasers come in infrared and visible varieties, but none yet in the x-ray band. A compact and powerful source of coherent x rays is the dream of many physicists, who see applications such as making atomic scale, three-dimensional movies of a melting crystal or an operating photosynthesis protein. In a step toward that goal, a research team has detected high frequency coherent light generated by a new process. As they report in the 12 June PRL, intense laser pulses can stimulate free electrons in a plasma to emit coherent light at triple the input frequency in a narrowly-directed cone. The ...


Photoionization And Photofragmentation Of Gaseous Toluene Using 80-Fs, 800-Nm Laser Pulses, A. M. Müller, Cornelis J. Uiterwaal, B. Witzel, J. Wanner, K.-L. Kompa Jun 2000

Photoionization And Photofragmentation Of Gaseous Toluene Using 80-Fs, 800-Nm Laser Pulses, A. M. Müller, Cornelis J. Uiterwaal, B. Witzel, J. Wanner, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

This paper presents ion yields resulting from multiphoton ionization and fragmentation of gaseous toluene (C7H8) in the focus of an 80 fs Ti:sapphire laser beam (λ = 800 nm) with a sufficiently small B-integral [Siegman, Lasers (University Science Books, Mill Valley, CA, 1986)]. The peak intensity was varied between 1.9x1013 and 2.8x1013Wcm-2, and both linear and circular polarization were used. Over the whole range of intensities studied, only the singly charged parent ion and its fragment, C7H7+, are found. Although the Keldysh adiabaticity parameter equals 0.86 ...


Pulse Radiolysis Of Liquid Water Using Picosecond Electron Pulses Produced By A Table-Top Terawatt Laser System, Ned Saleh, Kirk Flippo, Koshichi Nemoto, Donald P. Umstadter, Robert A. Crowell, Charles D. Jonah, Alexander D. Trifunac Jun 2000

Pulse Radiolysis Of Liquid Water Using Picosecond Electron Pulses Produced By A Table-Top Terawatt Laser System, Ned Saleh, Kirk Flippo, Koshichi Nemoto, Donald P. Umstadter, Robert A. Crowell, Charles D. Jonah, Alexander D. Trifunac

Donald Umstadter Publications

A laser based electron generator is shown, for the first time, to produce sufficient charge to conduct time resolved investigations of radiation induced chemical events. Electron pulses generated by focussing terawatt laser pulses into a supersonic helium gas jet are used to ionize liquid water. The decay of the hydrated electrons produced by the ionizing electron pulses is monitored with 0.3 µs time resolution. Hydrated electron concentrations as high as 22 µM were generated. The results show that terawatt lasers offer both an alternative to linear accelerators and a means to achieve subpicosecond time resolution for pulse radiolysis studies.


System Architecture And Hardware Design Of The Cdf Xft Online Track Processor, S. Holm, J.R. Dittman, J. Freeman, R. Klein, J.D. Lewis, T.M. Shaw, T. Wesson, C. Ciobanu, J. Gerstenslager, J. Hoftiezer, R. Hughes, M. Johnson, P. Koehn, C. Neu, C. Sanchez, B.L. Winer, Kenneth A. Bloom, D. Gerdes, J.W. Dawson, W.N. Haberichter Jun 2000

System Architecture And Hardware Design Of The Cdf Xft Online Track Processor, S. Holm, J.R. Dittman, J. Freeman, R. Klein, J.D. Lewis, T.M. Shaw, T. Wesson, C. Ciobanu, J. Gerstenslager, J. Hoftiezer, R. Hughes, M. Johnson, P. Koehn, C. Neu, C. Sanchez, B.L. Winer, Kenneth A. Bloom, D. Gerdes, J.W. Dawson, W.N. Haberichter

Kenneth Bloom Publications

A trigger track processor is being designed for CDF Run 2. This processor identifies high momentum (PT > 1.5 GeV/c) charged tracks in the new central outer tracking chamber for the CDF I1 detector. The design of the track processor, called the extremely Fast Trackcr (XFT), is highly parallel and handle an input rate of 183 Gbitslsec and output rate of 44 Gbitdsec. The XFT is pipclined and reports the results for a new event every 132ns. The XFT uses threc stages, hit classification, segment finding, and segment linking. The pattem recognition algorithm for the three stages are ...


A Look At What Is (And Isn't) Known About Quasar Broad Line Regions And How Narrow-Line Seyfert 1s Fit In, C. Martin Gaskell Jun 2000

A Look At What Is (And Isn't) Known About Quasar Broad Line Regions And How Narrow-Line Seyfert 1s Fit In, C. Martin Gaskell

Faculty Publications, Department of Physics and Astronomy

The evidence is reviewed that the Broad Line Region (BLR) probably has two distinct components located at about the same distance from the central black hole. One component, BLR II, is optically-thick, low-ionization emission at least some of which arises from a disc and the other, BLR I, is probably optically-thin emission from a more spherically symmetric halo or atmosphere. The high Fe II/Hβ ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are not due to strong Fe II emission, as is commonly thought, but to unusually weak Balmer emission, probably caused by higher densities. NLS1s probably differ from ...


Diffractive Dijets With A Leading Antiproton In P̅P Collisions At √S = 1800 Gev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration May 2000

Diffractive Dijets With A Leading Antiproton In P̅P Collisions At √S = 1800 Gev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report results from a study of events with a leading antiproton of beam momentum fraction 0.905 <xF < 0.965 and 4-momentum transfer squared |t|< 3 GeV2 produced in p̅p collisions at √s =1800 GeV at the Fermilab Tevatron collider. Approximately 2% of the events contain two jets of transverse energy ETjet > 7 GeV. Using the dijet events, we evaluate the diffractive structure function of the antiproton and compare it with expectations based on results obtained in diffractive deep inelastic scattering experiments at the DESY ep collider HERA.


Measurement Of The Differential Dijet Mass Cross Section In Pp̅ Collisions At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration May 2000

Measurement Of The Differential Dijet Mass Cross Section In Pp̅ Collisions At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present a measurement of the cross section for production of two or more jets as a function of dijet mass, based on an integrated luminosity of 86 pb-1 collected with the Collider Detector at Fermilab. Our dijet mass spectrum is described within errors by next-to-leading order QCD predictions using CTEQ4HJ parton distributions, and is in good agreement with a similar measurement from the DØ experiment.


Nanostructure And Magnetic Properties Of Composite Copt:C Films, M. Yu, Yi Liu, David J. Sellmyer May 2000

Nanostructure And Magnetic Properties Of Composite Copt:C Films, M. Yu, Yi Liu, David J. Sellmyer

David Sellmyer Publications

The nanostructure and magnetic properties of composite CoPt:C films at room temperature were investigated as a function of annealing temperature, carbon concentration, and film thickness. CoPt:C films with a variety of carbon concentrations were fabricated by cosputtering Co, Pt, and C onto water-cooled Si(100) substrates followed by annealing. X-ray diffraction and transmission electron microscopy analyses indicate that nanocrystallites of face-centered-tetragonal (fct) CoPt phase, which has a uniaxial magnetocrystalline anisotropy constant of about 5×107 erg/cm3, can be formed in carbon matrix when the annealing temperature is higher than 600 °C. The grain sizes of ...


Temperature Dependence Of Magnetic Hysteresis Of RcoX:Co Nanocomposites (R=Pr And Sm), J. Ping Liu, Ralph Skomski, Yi Liu, David J. Sellmyer May 2000

Temperature Dependence Of Magnetic Hysteresis Of RcoX:Co Nanocomposites (R=Pr And Sm), J. Ping Liu, Ralph Skomski, Yi Liu, David J. Sellmyer

David Sellmyer Publications

The temperature dependence of magnetic hysteresis of RCox:Co (R=Pr and Sm) nanocomposite films is reported. These films are prepared by dc and rf sputtering and subsequent thermal processing. It is found that the squareness of the hysteresis loops deteriorates with decreasing temperature. This is attributed to the enhanced magnetic anisotropy of the hard phases at low temperatures. The analysis of the magnetic reversal process shows that the anisotropy enhancement leads to a transition from cooperated to independent behavior. This analysis agrees well with the experimental results.