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University of Nebraska - Lincoln

2001

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Full-Text Articles in Physics

Search For Gluinos And Squarks Using Like-Sign Dileptons In Pp̅ Collisions At √S= 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2001

Search For Gluinos And Squarks Using Like-Sign Dileptons In Pp̅ Collisions At √S= 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present results of the first search for like-sign dilepton (e±e±, e± μ±, μ± μ±) events associated with multijets and large missing energy using 106 pb-1 of data in pp̅ collisions at √s= 1.8 TeV collected during 1992–1995 by the CDF experiment. Finding no events that pass our selection, we examine pair production of gluinos () and squarks () in a constrained framework of the minimal supersymmetric standard model. At tanβ =2 and μ = -800 GeV/c2, we set 95% confidence level limits of M > 221 GeV/c2 for M –̴ Mq ...


Ratio Of Isolated Photon Cross Sections In Pp̅ Collisions At √S = 630 And 1800 Gev, V. M. Abazov, Gregory R. Snow, D0 Collaboration Dec 2001

Ratio Of Isolated Photon Cross Sections In Pp̅ Collisions At √S = 630 And 1800 Gev, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

The inclusive cross section for production of isolated photons has been measured in pp̅ collisions at √s = 630 GeV with the D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy (ET) range from 7–49 GeV and have pseudorapidity∣η∣ < 2.5. This measurement is combined with the previous D0 result at √s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the ET range.


Dilution-Induced Enhancement Of The Blocking Temperature In Exchange-Bias Heterosystems, Xi Chen, Christian Binek, A. Hochstrat, Wolfgang Kleemann Dec 2001

Dilution-Induced Enhancement Of The Blocking Temperature In Exchange-Bias Heterosystems, Xi Chen, Christian Binek, A. Hochstrat, Wolfgang Kleemann

Christian Binek Publications

The temperature dependence of the exchange bias field is investigated by superconducting quantum interference device magnetometry in Fe1-xZnxF2(110)/Fe14 nm/Ag35 nm, x=0.4. Its blocking temperature exhibits a significant enhancement with respect to the global ordering temperature TN=46.9 K, of the bulk antiferromagnet Fe0.6Zn0.4F2. The enhancement is attributed to fluctuations of the diamagnetic dilution which creates clusters on all length scales having a Zn dilution of 0<~x<~1. While the infinite clusters give rise to the well-known Griffiths phase, finite clusters also provoke a local enhancement of the exchange bias. The temperature dependence of the integral exchange bias effect is modeled by averaging all local contributions of the antiferromagnetic surface magnetization which exhibit a surface critical behavior.


Observation Of Diffractive J/Ψ Production At The Fermilab Tevatron, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2001

Observation Of Diffractive J/Ψ Production At The Fermilab Tevatron, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report the first observation of diffractive J/ψ(→μ+μ-) production in p̅p collisions at √s= 1.8 TeV. Diffractive events are identified by their rapidity gap signature. In a sample of events with two muons of transverse momentum pT,/sub> μ> 2 GeV/c within the pseudorapidity region |η| J/ψ production rates is found to be RJ=[1.45 ± 0.25]%. The ratio RJ(x) is presented as a function of x-Bjorken. By combining it with our previously measured corresponding ratio Rjj(x) for diffractive dijet production, we extract a ...


Search For New Physics Using Quaero: A General Interface To D0 Event Data, V. M. Abazov, Gregory R. Snow, D0 Collaboration Dec 2001

Search For New Physics Using Quaero: A General Interface To D0 Event Data, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We describe QUAERO, a method that (i) enables the automatic optimization of searches for physics beyond the standard model, and (ii) provides a mechanism for making high energy collider data generally available. We apply QUAERO to searches for standard model WW, ZZ , and tt̅ production, to searches for these objects produced through a new heavy resonance, and to the first direct search for W′→ WZ. Through this interface, we make three data sets collected by the D0 experiment at √s =1.8 TeV publicly available.


Search For Quark-Lepton Compositeness And A Heavy W′ Boson Using The Eν Channel In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Dec 2001

Search For Quark-Lepton Compositeness And A Heavy W′ Boson Using The Eν Channel In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present searches for quark-lepton compositeness and a heavy W′ boson at high electron-neutrino transverse mass. We use ~110 pb-1 of data collected in pp̅ collisions at √s= 1.8 TeV by the CDF Collaboration during 1992–1995. The data are consistent with standard model expectations. Limits are set on the quark-lepton compositeness scale Λ, the ratio of partial cross sections σ (W′ → eν)/ σ (W → eν), and the mass of a W′ boson with standard model couplings. We exclude Λ< 2.81 TeV and a W′ boson with mass below 754 GeV/c2 at the 95% confidence level. Combining with our previously ...


Atomic And Electronic Structure Of Co/Srtio3/Co Tunnel Junctions, Ivan I. Oleinik, Evgeny Y. Tsymbal, David G. Pettifor Dec 2001

Atomic And Electronic Structure Of Co/Srtio3/Co Tunnel Junctions, Ivan I. Oleinik, Evgeny Y. Tsymbal, David G. Pettifor

Evgeny Tsymbal Publications

First-principles density-functional calculations of the atomic and electronic structure of Co/SrTiO3 /Co (001) magnetic tunnel junctions (MTJ’s) are performed. Different interface terminations are considered and the most stable structure with the TiO2 termination is identified based on energetics of adhesion. The calculated electronic structure of the TiO2-terminated MTJ shows an exchange coupling between the interface Co and Ti atoms mediated by oxygen. This coupling induces a magnetic moment of 0.25 µB on the interface Ti atom, which is aligned antiparallel to the magnetic moment of the Co layer. We argue that this ...


Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben Dec 2001

Electronic-Structure Modifications Induced By Surface Segregation In La0.65Pb0.35Mno3 Thin Films, C.N. Borca, B. Xu, T. Komesu, H.-K. Jeong, M.T. Liu, Sy_Hwang Liou, Shane Stadler, Y. Idzerda, Peter A. Dowben

Si-Hwang Liou Publications

Using spin-polarized inverse photoemission and X-ray absorption spectroscopy techniques, we show that the electronic structure of La0.65Pb0.35MnO3 thin films depends on the composition at the surface. With a gentle annealing procedure, the surface provides a maximum of 80% spin asymmetry at 0.5 eV above the Fermi level in spite of extensive Pb segregation. A heavily annealed (restructured) surface exhibits a reduced surface "ordering" temperature of 240 K (compared to the approximately 335 K bulk value) as well as a reduced spin asymmetry value of 40% at 0.5 eV above Fermi energy.


Interactions Of Ultrashort, Ultrahigh Intensity Laser Pulses With Underdense Plasmas, Xiaofang Wang, Wei Yu, Sterling Backus, Margaret Murnane, Henry Kapteyn, Donald P. Umstadter Nov 2001

Interactions Of Ultrashort, Ultrahigh Intensity Laser Pulses With Underdense Plasmas, Xiaofang Wang, Wei Yu, Sterling Backus, Margaret Murnane, Henry Kapteyn, Donald P. Umstadter

Donald Umstadter Publications

The interactions of ultraintense laser pulses with underdense plasmas are studied in a new regime in which the longitudinal spatial extent of the pulse duration is close to both the laser focal spot size and the plasma wavelength.


Status Of The Lilac Experiment, N. Saleh, P. Han, C. Keppel, P. Gueye, V Yanovsky, Donald P. Umstadter Nov 2001

Status Of The Lilac Experiment, N. Saleh, P. Han, C. Keppel, P. Gueye, V Yanovsky, Donald P. Umstadter

Donald Umstadter Publications

We present the status of the LILAC experiment [1], including results on the propagation of 30-fs duration laser pulses in plasmas of the requisite density, and measurements of the dark current [2]. We also discuss the status of a laser upgrade, an electron beam line and plans for the future.


Laser Acceleration Of Protons From Thin Film Targets, K. Flippo, Sudeep Banerjee, V. Yu. Bychenkov, S. Gu, Anatoly Maksimchuk, G. Mourou, K. Nemoto, Donald P. Umstadter Nov 2001

Laser Acceleration Of Protons From Thin Film Targets, K. Flippo, Sudeep Banerjee, V. Yu. Bychenkov, S. Gu, Anatoly Maksimchuk, G. Mourou, K. Nemoto, Donald P. Umstadter

Donald Umstadter Publications

A collimated beam of fast protons, with energies as high as 10 MeV and total number of 109, confined in a cone angle of 40°±10° has been observed when a 10 TW laser with frequencies either ω0 (corresponding to 1 μm) or 2ω0 was focused to an intensity of a few times 1018 W/cm2 on the surface of a thin film target. The protons, which originate from impurities on the front side of the target, are accelerated over a region extending into the target and exit out the backside in a direction normal ...


Charged-Particle Multiplicity Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Nov 2001

Charged-Particle Multiplicity Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on a measurement of the mean charged-particle multiplicity of jets in dijet events with dijet masses in the range 80-630 GeV/c2, produced at the Tevatron in pp̅ collisions with √s= 1.8 TeV and recorded by the Collider Detector at Fermilab. The data are fit to perturbative-QCD calculations carried out in the framework of the modified leading log approximation and the hypothesis of local parton-hadron duality. The fit yields values for two parameters in that framework: the ratio of parton multiplicities in gluon and quark jets, r=Ng-jet partons/Nq-jet partons =1.7 ± 0 ...


Ac Susceptibility Studies Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek Nov 2001

Ac Susceptibility Studies Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek

Christian Binek Publications

Discontinuous metal–insulator multilayers [Co80Fe20(t)/Al2O3(3 nm)]10 are prepared by ion-beam sputtering and investigated by SQUID magnetometry and previous AC susceptometry. For 1.0less-than-or-equals, slanttless-than-or-equals, slant1.6 nm, two coexisting subsystems of dipolar coupled nanoparticles are encountered. While a spin-glass-like freezing particulate fraction dominates at t=1.0 nm, a percolating dipolar ferromagnetic fraction becomes increasingly important at higher nominal thickness of t.


Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek Nov 2001

Exchange Bias In Fef20-Copt Heterosystems With Perpendicular Anisotropy, Christian Binek

Christian Binek Publications

The previous exchange bias effect is measured in heterosystems with perpendicular anisotropy consisting of Co/Pt multilayers on top of the (0 0 1) face of a previous FeF2 single crystal. The resulting previous exchange field HE exhibits a strong dependence on temperature and the axial freezing field, HF. Within the framework of an Ising-type model, the HE vs. T as well as the HE vs. HF data are explained in terms of the microscopic spin structure at the interface.


Characterization Of The Native Cr2O3 Oxide Surface Of Cro2, Ruihua Cheng, B. Xu, C.N. Borca, Andrei Sokolov, C.S. Yang, Lu Yuan, Sy_Hwang Liou, Bernard Doudin, Peter A. Dowben Nov 2001

Characterization Of The Native Cr2O3 Oxide Surface Of Cro2, Ruihua Cheng, B. Xu, C.N. Borca, Andrei Sokolov, C.S. Yang, Lu Yuan, Sy_Hwang Liou, Bernard Doudin, Peter A. Dowben

Peter Dowben Publications

Using photoemission and inverse photoemission, we have been able to characterize the Cr2O3 oxide surface of CrO2 thin films. The Cr2O3 surface oxide exhibits a band gap of about 3 eV, although the bulk CrO2 is conducting. The thickness of this insulating Cr2O3 layer is twice the photoelectron escape depth which is about 2 nm thick. The effective Cr2O3 surface layer Debye temperature, describing motion normal to the surface, is about 370 K. From a comparison of CrO2 films grown by different techniques, with different ...


Transverse Magnetism Of The Diluted Antiferromagnet Fe1-Xmgxbr2 (X=0.15), Christian Binek Nov 2001

Transverse Magnetism Of The Diluted Antiferromagnet Fe1-Xmgxbr2 (X=0.15), Christian Binek

Christian Binek Publications

Neutron diffraction and magnetization measurements of the diluted crystal Fe1−xMgxBr2 (xnot, vert, similar0.15) were performed. Successive phase transitions at zero applied field at TN1not, vert, similar12 K and TN2not, vert, similar10 K were found. A previous transverse term ferromagnetic moment was detected just below TN2.


Local Impurity-Assisted Conductance In Magnetic Tunnel Junctions, Evgeny Y. Tsymbal, David G. Pettifor Nov 2001

Local Impurity-Assisted Conductance In Magnetic Tunnel Junctions, Evgeny Y. Tsymbal, David G. Pettifor

Evgeny Tsymbal Publications

Using a simple tight-binding model and the Kubo formula we have calculated the lateral distribution of the tunneling conductance across a magnetic tunnel junction probed by STM. We find that the presence of an isolated impurity within the barrier layer can cause a spike in the conductance distribution, which is in agreement with recent experiments. We show that the local tunneling magnetoresistance (TMR) is very sensitive to the electronic state of the impurity and to the lateral position of the tip. The latter dramatic variation in TMR could be detected by STM.


Search For Narrow Diphoton Resonances And For Γγ+W/Z Signatures In Pp̅ Collisions At √S=1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Nov 2001

Search For Narrow Diphoton Resonances And For Γγ+W/Z Signatures In Pp̅ Collisions At √S=1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present results of searches for diphoton resonances produced both inclusively and also in association with a vector boson (W or Z) using 100 pb-1 of pp̅ collisions using the CDF detector. We set upper limits on the product of cross section times branching ratio for both pp̅→ γγ+X and pp̅→ γγ+ W/Z. Comparing the inclusive production to the expectations from heavy sgoldstinos we derive limits on the supersymmetrybreaking scale √F in the TeV range, depending on the sgoldstino mass and the choice of other parameters. Also, using a NLO prediction for the associated production of a ...


Multiwavelength Monitoring Of The Narrow-Line Seyfert 1 Galaxy Arakelian 564. Iii. Optical Observations And The Optical--Uv--X-Ray Connection, O. Shemmer, P. Romano, R. Bertram, W. Brinkmann, S. Collier, K. A. Crowley, E. Detsis, A. V. Filippenko, C. Martin Gaskell, T. A. George, M. Gliozzi, M. E. Hiller, T. L. Jewell, Shai Kaspi, Elizabeth S. Klimek, M. H. Lannon, W D. Li, P. Martini, Smita Mathur, H. Negoro, Hagai Netzer, Iossif Papadakis, Ioannis Papamastorakis, Bradley M. Peterson, Bradley W. Peterson, Richard William Pogge, V. I. Pronik, Kenneth S. Rumstay, S. G. Sergeev, G. M. Stirpe, C. J. Taylor, R. R. Treffers, T. J. Turner, P. Uttley, Marianne Vestergaard, Kaspar Von Braun, R. M. Wagner, Z. Zheng Nov 2001

Multiwavelength Monitoring Of The Narrow-Line Seyfert 1 Galaxy Arakelian 564. Iii. Optical Observations And The Optical--Uv--X-Ray Connection, O. Shemmer, P. Romano, R. Bertram, W. Brinkmann, S. Collier, K. A. Crowley, E. Detsis, A. V. Filippenko, C. Martin Gaskell, T. A. George, M. Gliozzi, M. E. Hiller, T. L. Jewell, Shai Kaspi, Elizabeth S. Klimek, M. H. Lannon, W D. Li, P. Martini, Smita Mathur, H. Negoro, Hagai Netzer, Iossif Papadakis, Ioannis Papamastorakis, Bradley M. Peterson, Bradley W. Peterson, Richard William Pogge, V. I. Pronik, Kenneth S. Rumstay, S. G. Sergeev, G. M. Stirpe, C. J. Taylor, R. R. Treffers, T. J. Turner, P. Uttley, Marianne Vestergaard, Kaspar Von Braun, R. M. Wagner, Z. Zheng

Faculty Publications, Department of Physics and Astronomy

We present the results of a 2 yr long optical monitoring program of the narrow-line Seyfert 1 galaxy Ark 564. The majority of this monitoring project was also covered by X-ray observations (RXT E), and for a period of ~50 days, we observed the galaxy in UV (HST) and X-rays (RXTE and ASCA) simultaneously with the ground-based observations. Rapid and large-amplitude variations seen in the X-ray band, on a daily and hourly timescale, were not detected at optical and UV wavelengths, which in turn exhibited much lower variability either on short (1 day) or long (several months) timescales. The only ...


Magnetic States Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek Oct 2001

Magnetic States Of Discontinuous Co80fe20al2o3 Multilayers, Christian Binek

Christian Binek Publications

Discontinuous metal–insulator multilayers [Co80Fe20(t)/Al2O3(3 nm)]n were studied by SQUID magnetometry and AC susceptometry. CoFe forms ferromagnetic particles in the Al2O3 matrix. In this paper, we focus on the field dependence of the AC susceptibility of samples with t=1.3 nm. We find strong evidence for transitions from a superpara- to a superferromagnetic and, finally, to a reentrant superspin glass previous state.


Exchange Bias In Fe0.6zn0.4f2 Heterostructures, Christian Binek Oct 2001

Exchange Bias In Fe0.6zn0.4f2 Heterostructures, Christian Binek

Christian Binek Publications

The previous exchange bias field, He, is measured in Fe0.6Zn0.4F2/Fe heterosystems prepared from Fe layers of 14 and 5 nm thickness which are deposited on top of the compensated (1 1 0) surface of the antiferromagnet. Deviations from a linear dependence of He on the magnetization of the Fe layer are attributed to ferromagnetic domains. Moreover, piezomagnetism and its influence on He are evidenced.


Magnetic Nanodot Arrays Produced By Direct Laser Interference Lithography, M. Zheng, M. Yu, Yi Liu, Ralph Skomski, Sy_Hwang Liou, David J. Sellmyer, V.N. Petryakov, Yu K. Verevkin, N.I. Polushkin, N. N. Salashchenko Oct 2001

Magnetic Nanodot Arrays Produced By Direct Laser Interference Lithography, M. Zheng, M. Yu, Yi Liu, Ralph Skomski, Sy_Hwang Liou, David J. Sellmyer, V.N. Petryakov, Yu K. Verevkin, N.I. Polushkin, N. N. Salashchenko

Si-Hwang Liou Publications

Periodic magnetic nanodot arrays have been produced on an area as large as 1 cm×1 cm by direct nanolithography using interferometric laser radiation. The dots are formed by the local annealing of sputtered amorphous Co–C films in regions where the laser intensity is highest. At room temperature the dots exhibit ferromagnetic order and are embedded in a paramagnetic matrix. The onset of room-temperature ferromagnetism is caused by nanoscale chemical and morphological changes during dot formation and reflects the phase separation of magnetic Co-rich clusters. The present single-step nanolithography is potentially an efficient method for fabrication of patterned magnetic ...


Temporary Anion States Of Selected Amino Acids, Kayvan Aflatooni, B. Hitt, Gordon A. Gallup, Paul Burrow Oct 2001

Temporary Anion States Of Selected Amino Acids, Kayvan Aflatooni, B. Hitt, Gordon A. Gallup, Paul Burrow

Paul Burrow Publications

Vertical attachment energies for the formation of low-lying temporary anion states of glycine, alanine, phenylalanine, tryptophan, and proline in the gas phase are reported using electron transmission spectroscopy. Electron attachment into the empty π* orbital of the –COOH group was observed in all the compounds. Temporary anion states associated with the side groups in phenylalanine and tryptophan are found to be stabilized with respect to those in the reference compounds toluene and indole, respectively, by approximately 0.2 eV. We attribute this to electrostatic effects and explore, using simple theoretical models, the extent to which such anion states could be ...


Search For First-Generation Scalar And Vector Leptoquarks, V. M. Abazov, Gregory R. Snow, D0 Collaboration Oct 2001

Search For First-Generation Scalar And Vector Leptoquarks, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We describe a search for the pair production of first-generation scalar and vector leptoquarks in the ee j j and eν jj channels by the DO. Collaboration. The data are from the 1992–1996 pp̅ run at √s =1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the ee j j and eν jj channels are combined with those from a previous DO. analysis of the νν jj channel to obtain 95% confidence level (C.L.) upper limits on ...


Observation Of Orbitally Excited B Mesons In Pp̅ Collisions At √S =1.8  Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Oct 2001

Observation Of Orbitally Excited B Mesons In Pp̅ Collisions At √S =1.8  Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We measure the relative rate of production of orbitally excited (L=1) states of B mesons (B**) by observing their decays into B π ±. We reconstruct B mesons through semileptonic decay channels using data collected in pp̅ collisions at √s =1.8 TeV. The fraction of light B mesons that are produced as L=1B** states is measured to be 0.28±0.06(stat) ±0.03(syst). We also measure the collective mass of the B** states, and quantify the result by quoting the (model-dependent) mass of the lowest B** state to be m (B1)=5.71 ...


Monte Carlo Studies Of Mott Scattering Asymmetries From Gold Foils, M. A. Khakoo, D. Roundy, C. Hicks, N. Margolis, E. Yeung, A. W. Ross, Timothy J. Gay Oct 2001

Monte Carlo Studies Of Mott Scattering Asymmetries From Gold Foils, M. A. Khakoo, D. Roundy, C. Hicks, N. Margolis, E. Yeung, A. W. Ross, Timothy J. Gay

Timothy J. Gay Publications

We present the results of a series of model Monte Carlo calculations of the scattering of spin-polarized electrons from gold foil targets. Our calculations examine the behavior of the left-right scattering asymmetry A as a function of various parameters conventionally used in extrapolation of the left-right asymmetry to single atom and/or elastic scattering conditions. These parameters include target thickness, scattered count rate, and the maximum energy that an electron can have lost in the target and still be detected. Data are obtained at incident electron energies of 10–120 keV, with detector-subtended half-cone angles of 5°, 10°, and 20 ...


Double Diffraction Dissociation At The Fermilab Tevatron Collider, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Oct 2001

Double Diffraction Dissociation At The Fermilab Tevatron Collider, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We present results from a measurement of double diffraction dissociation in p̅p collisions at the Fermilab Tevatron collider. The production cross section for events with a central pseudorapidity gap of width Δη0 > 3 (overlapping η=0) is found to be 4.43±0.02(stat) ± 1.18(syst) mb [3.42 ± 0.01(stat) ± 1.09(syst) mb] at √s=1800[630] GeV. Our results are compared with previous measurements and with predictions based on Regge theory and factorization.


Domain State Susceptibility In Fecl2/Copt-Heterostructures, Christian Binek Sep 2001

Domain State Susceptibility In Fecl2/Copt-Heterostructures, Christian Binek

Christian Binek Publications

Magnetic heterostructures with perpendicular anisotropy consisting of antiferromagnetic (111)-oriented FeCl2 single crystals and thin ferromagnetic CoPt-multilayers are investigated by ac-susceptometry after cooling in various axial magnetic fields to below the Néel temperature. The freezing process drives the system into a metastable antiferromagnetic domain state which gives rise to a huge excess contribution to the complex parallel susceptibility on heating in zero magnetic field. Its glow curve-like temperature dependence is modeled within the framework of a simple analytical approach. It involves the susceptibility of thermally activated clusters originating from antiferromagnetic stacking faults as well as the contribution of pairs of ...


Threshold Effects On Angular Distributions For Multiphoton Detachment By Intense Elliptically Polarized Light, Bogdan Borca, M.V. Frolov, N. L. Manakov, Anthony F. Starace Sep 2001

Threshold Effects On Angular Distributions For Multiphoton Detachment By Intense Elliptically Polarized Light, Bogdan Borca, M.V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

Unusual threshold effects are found theoretically in the frequency and intensity dependence of angular distributions produced by an elliptically polarized laser as well as in the elliptic dichroism parameter, which measures the asymmetry of the angular distribution.


Measurement Of DΣ/Dm And Forward-Backward Charge Asymmetry For High-Mass Drell-Yan E+E- Pairs From Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Sep 2001

Measurement Of DΣ/Dm And Forward-Backward Charge Asymmetry For High-Mass Drell-Yan E+E- Pairs From Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on a measurement of the mass dependence of the forward-backward charge asymmetry, AFB, and production cross section dσ /dM for e+e- pairs with mass Mee> 40 GeV/c2. The data sample consists of 108 pb-1 of pp̅ collisions at √s= 1.8 TeV taken by the Collider Detector at Fermilab during 1992–1995. The measured asymmetry and dσ/dM are compared with the predictions of the standard model and a model with an extra Z′ gauge boson.