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Search for leptoquarks at d-Zero

Description: We present in this paper the current status of searches for leptoquarks at D0. These results include the use of next leading order theoretical predictions for the cross section for pair production of leptoquarks at hadron colliders. We also present a new optimized analysis for first generation leptoquarks with significant increase in sensitivity relative to earlier searches using DO data. The mass limits derived from this first generation leptoquark search are relevant to the recently reported high mass events at HERA.
Date: June 1, 1997
Creator: Norman, D.M.
Partner: UNT Libraries Government Documents Department

Boson pair production and triple gauge couplings

Description: The D0 and CDF Collaborations measure boson pair production including W{gamma}, WW, WZ, ZZ and Z{gamma} production in p{anti p} collisions at {radical}s = 1800 GeV. New results, from direct measurements, are described including W{gamma}, WW, and Z{gamma} production cross sections and limits on non-Standard Model triple gauge boson couplings. The limits on anomalous WW{gamma}, WWZ, Z{gamma}{gamma} and ZZ{gamma} couplings are the most restrictive available. Prospects for Run II are discussed.
Date: June 1, 1997
Creator: Diehl, H.T. & Collaborations, D0 and CDF
Partner: UNT Libraries Government Documents Department

Supersymmetric Higgs Boson Pair Production: Discovery Prospects at Hadron Colliders

Description: We study the potential of hadron colliders in the search for the pair production of neutral Higgs bosons in the framework of the Minimal Supersymmetric Standard Model. We perform a detailed signal and background analysis, working out efficient kinematical cuts for the extraction of the signal. The important role of squark loop contributions to the signal is re-emphasized. If the signal is sufficiently enhanced by these contributions, it could even be observable at the next run of the upgraded Tevatron collider in the near future. At the LHC the pair production of light and heavy Higgs bosons might be detectable simultaneously.
Date: September 15, 1999
Creator: Mizukoahi, Jose K.
Partner: UNT Libraries Government Documents Department

Why e{superscript +}e{superscript -} {yields} t tbar is Different

Description: Unlike other examples of fermion pair production in e{sup +}e{sup -} collisions, we show that top-quark pairs are produced in an essentially unique spin configuration in polarized e{sup +}e{sup -} colliders at all energies. Since the directions of the electroweak decay products of polarized top-quarks are strongly correlated to the top-quark spin axis, this unique spin configuration leads to a distinctive topology for top-quark pair events which can be used to constrain anomalous couplings to the top-quark. A significant interference effect between the longitudinal and transverse W-bosons in the decay of polarized top-quarks is also discussed.
Date: February 18, 1999
Creator: Parke, Stephen
Partner: UNT Libraries Government Documents Department

Vector boson pair production and trilinear gauge boson couplings - Results from the Tevatron

Description: Direct measurements of vector boson pair production processes and trilinear gauge boson couplings have been conducted by the CDF and D0 Collaborations. Preliminary results from searches for anomalous WW/WZ {yields} {mu}{nu} jet jet and WZ {yields} eee{nu} production are presented. 95% CL anomalous coupling limits from previously published D0 results are -0.20< {lambda} < 0.20 ({Delta}{kappa} = 0) and -3.0<{Delta}{kappa} < 0:43 ({lambda} = 0) for {Lambda} = 2000 GeV where the WW{gamma} couplings are assumed to equal the WWZ couplings. Combined D0 + LEP experiment anomalous coupling limits are presented for the #12;rst time. 95% CL limits are -0.16 < {lambda}{sub {gamma}} < 0:10 ({Delta}{kappa} = 0) and -0.15< {Delta}{kappa}{sub {gamma}}#20; < 0:41 ({lambda} = 0) under the assumption that the couplings are related by the \HISZ" constraints. 95% CL anomalous ZZ{gamma} and Z{gamma}{gamma} coupling limits from D0 are jh{sup Z}{sub 30} j < 0:36 (h{sup Z}{sub 40 = 0) and jh{sup Z}{sub 40} j < 0:05 (h{sup Z}{sub 30} = 0) for {Lambda} = 750 GeV. CDF reports the first observation of a ZZ event. Prospects for Run II are discussed.
Date: October 1, 1998
Creator: Diehl, H. T.
Partner: UNT Libraries Government Documents Department

Photon and di-photon results from CDF and D0

Description: Measurements by the Fermilab D0 and CDF collaborations of prompt photon events in p{anti p} collisions at {radical}s = 1.8 TeV are reported. The measured isolated photon cross sections are compared to current parton distribution functions and NLO QCD predictions. The cross section ratio of forward to central {eta} bins and {eta} distributions are presented and compared with theoretical predictions. {gamma}+2jet events yield insight into final state radiation. A new measurement of {gamma}+{mu} events is presented which probes the charm content of the proton. Finally, di-photon results are presented as a probe of initial state radiation; these results are compared to NLO QCD, Pythia parton showers, and resummation models.
Date: May 11, 1999
Creator: Hanlet, Pierrick
Partner: UNT Libraries Government Documents Department

Drell-Yan Lepton Pair Azimuthal Asymmetry in Hadronic Processes

Description: We study the azimuthal asymmetry in the Drell-Yan lepton pair production in hadronic scattering processes at moderate transverse momentum region, taking into account the contributions from the twist-three quark-gluon correlations from the unpolarized hadrons. The contributions are found to dominate the asymmetry, and are not power suppressed by qt/Q at small qt where qt and Q are the transverse momentum and invariant mass of the lepton pair. Accordingly, the Lam-Tung relation will be violated at this momentum region, and its violation depends on the twist-three functions. However, at large transverse momentum qt~;;Q, the Lam-Tung relation still holds because all corrections are power suppressed by Lambda2/qt2 ~;; Lambda2/Q2 where Lambda is the typical nonperturbative scale.
Date: January 22, 2009
Creator: Zhou, Jian; Yuan, Feng & Liang, Zuo-Tang
Partner: UNT Libraries Government Documents Department

First observations of beam losses due to bound-free pairproduction in a heavy-ion collider

Description: We report the first observations of beam losses due tobound-free pair production at the interaction point of a heavy-ioncollider. This process is expected to be a major luminosity limit for theLarge Hadron Collider (LHC) when it operates with 208Pb82+ ions becausethe localized energy deposition by the lost ions may quenchsuperconducting magnet coils. Measurements were performed at theRelativistic Heavy Ion Collider (RHIC) during operation with 100GeV/nucleon 63Cu29+ ions. At RHIC, the rate, energy and magnetic fieldare low enough so that magnet quenching is not an issue. The hadronicshowers produced when the single-electron ions struck the RHIC beampipewere observed using an array of photodiodes. The measurement confirms theorder of magnitude of the theoretical cross section previously calculatedby others.
Date: June 15, 2007
Creator: Bruce, R.; Jowett, J.M.; Gilardoni, S.; Drees, A.; Fischer, W.; Tepikian, S. et al.
Partner: UNT Libraries Government Documents Department

Test of structure functions using lepton pairs: W-charge asymmetry and Drell-Yan production at CDF

Description: The charge asymmetry of leptons from W-bosons and the Drell-Yan cross section of massive charged lepton pairs from {gamma}*/Z-bosons produced in p{anti p} collisions are measured using 110 pb{sup -1} of collisions taken by the Collider Detector at Fermilab (CDF) during 1992-95. The W-asymmetry measurement provides a precise constraint of the slope of the quark distribution ratio, d(x)/u(x), over the x range of 0.006 to 0.34. The Drell-Yan measurement spans the mass range of 11 to 500 GeV/c{sup 2}, and QCD calculations using recent parton distribution functions are in good agreement with it.
Date: October 1, 1998
Creator: Sakumoto, W.
Partner: UNT Libraries Government Documents Department

EPDL97: the evaluated photo data library `97 version

Description: The Evaluated Photon Data Library, 1997 version (EPLD97), is designed for use in photon transport calculations at Lawrence Livermore National Laboratory. This library includes photon interaction data for all elements with atomic number between Z = 1 (hydrogne) and 100 (fermium), including: photoionization, photoexcitation, coherent and incoherent scattering, and pair and triplet porduction cross sections. For use in applications data is provided for all elements over the energy range 1 eV to 100 GeV. This report documents the sources and treatment of the data included inthis library. EPDL97 completely supersedes the earlier 1989 version of EPDL and it is highly recommended that useres only use the most recent version of this library.
Date: September 19, 1997
Creator: Cullen, D.E.; Hubbell, J.H. & Kissel, L.
Partner: UNT Libraries Government Documents Department

Multiphoton processes in the field of two-frequency circularly polarized plane electromagnetic waves

Description: The authors solve Dirac`s equation for an electron in the field of a two-frequency plane electromagnetic wave, deriving general formulae for the probabilities of radiation of a photon by the electron, and for the probabilities for pair production by a photon when the two-frequency wave is circularly polarized. In contrast to the case of a monochromatic-plane electromagnetic wave, when an electron is in the field of a two-frequency circularly polarized wave, besides the absorption of multiphotons and emission of simple harmonics of the individual waves, stimulated multiphoton emission processes and various composite harmonic-photon emission processes are occurred: when a high-energy photon is in a such a field, multiphoton processes also follow the pair production processes.
Date: July 1, 1997
Creator: Yu, An & Takahashi, H.
Partner: UNT Libraries Government Documents Department

Gamma ray burst model

Description: We present a model for gamma ray bursts based on the compression of neutron stars in close binary systems. Our general relativistic hydrodynamiccomputer simulations of close neutron star binaries have found that as the orbit shrinks the density of the neutron stars rises. This compressional effect has been estimated to produce thermal energies in the neutron stars of the order of magnitude 10{sup 52}to 10{sup 53} ergs on a timescale of a few seconds.This is a possible source of energy for gamma-ray bursts. The hot neutron stars will emit neutrino pairs which will partially recombine to form an electron positron pair plasma. The pair plasma will recombine after expansion to produce photons which closely mimic the characteristics of gamma-raybursts.
Date: February 17, 1998
Creator: Wilson, J. R.; Salmonson, J. D. & Mathews, G. J.
Partner: UNT Libraries Government Documents Department

Search for squarks and gluinos using dileptons

Description: Gluinos and squarks can be produced in {ital p{anti p}} collisions at {radical}s = 1.8 TeV and decay via charginos and neutralinos to final states containing two (or more) leptons. There is no charge correlation between the leptons of charginos from gluino decays as gluinos are Majorana particles. The strategy of this analysis is to search for an excess of events containing two like-sign isolated leptons, missing energy, and jets. The analysis is based on 81 pb{sup -1} of 1994-5 data recorded at CDF.
Date: October 1, 1996
Creator: Done, J. P.
Partner: UNT Libraries Government Documents Department

Recent top quark physics results at the Tevatron

Description: The evidence of top quark pair production in pp collisions has been firmly established by both the CDF and the D{O} collaborations at Fermilab. In this paper the latest top quark physics results from both experiments at the Tevatron Collider are presented. The experimental analyses have concentrated in improving the accuracy of top quark production and decay measurements like cross sections, mass and, branching fractions. The results shown correspond to the final data set collected with both detectors during the complete Tevatron Run L. This represents a total recorded integrated luminosity of {approximately}110 pb{sup -1} for CDF and {approximately}100 pb{sup -1} for D{O}.
Date: July 1, 1996
Creator: Valls, J.A.
Partner: UNT Libraries Government Documents Department

Searches with taus at the Tevatron

Description: We discuss tau identification techniques at hadron colliders, and present the measurements and the searches performed so far. We report on top quark pair production in the decay channel containing at least one tau lepton. Also, we present results dedicated to searches for new particles, with taus in the final state. We present a search for the charged Higgs boson in the tau decay channel, as well as for the leptoquark family containing tau leptons. Finally, we indicate the capabilities of detecting and triggering on tau leptons in the future collider run.
Date: April 29, 1999
Creator: Gallinaro, M.
Partner: UNT Libraries Government Documents Department

Top pair production in e+e- and {gamma}{gamma} processes

Description: We analyze spin correlations between top quark and anti-top quark produced at polarized e{sup +} e{sup -} and {gamma}{gamma} colliders. We consider a generic spin basis to find a strong spin correlation. Optimal spin decompositions for top quark pair are presented for e{sup +}e{sup -} and {gamma}{gamma} colliders. We show the cross- section in these bases and discuss the characteristics of results.
Date: February 1, 1998
Creator: Hori, M.; Kiyo, Y.; Kodaira, J.; Nasuno, T. & Parke, S.
Partner: UNT Libraries Government Documents Department

Spin-dependent Drell-Yan and double prompt photon production to NLO QCD

Description: The authors present the complete O({alpha}{sub s}{sup 2}) radiative corrections to the (non singlet) polarized Drell Yan cross section for the production of a lepton pair with a nonzero q{sub T}. The helicity of the incoming states is arbitrary. In the case of double photon, results for the longitudinal asymmetries and on the p{sub T} behavior of the cross section are also given (to O({alpha}{sub em}{sup 2}{alpha}{sub s})) in the central rapidity region of the tagged photon.
Date: July 1, 1997
Creator: Chang, S.; Coriano, C.; Field, R.D. & Gordon, L.E
Partner: UNT Libraries Government Documents Department

Search for high mass photon pairs in p{anti p}{yields}{gamma}{gamma}jj events at {radical}s = 1.8 TeV

Description: A search for new physics in the channel p{anti p} {yields} {gamma}{gamma}jj has been studied. In some extended Higgs models, a light neutral scalar Higgs boson is produced with suppressed couplings to fermions and standard model(SM) strength couplings to vector bosons(bosonic Higgs), thus enhancing the H {yields} {gamma}{gamma} channel. We required one photon in the event with E{sup {gamma}}{sub T} > 20 GeV, {vert_bar}{eta}{sup {gamma}}{vert_bar} < 1.1 or 1.5 < {vert_bar}{eta}{sup {gamma}}{vert_bar} < 2.0 and a second photon with E{sup {gamma}}{sub T} > 15 GeV, {vert_bar}{eta}{sup {gamma}}{vert_bar} < 1.1 or 1.5 < {vert_bar}{eta}{sup {gamma}}{vert_bar} < 2.25. Additionally, we required one hadronic jet in the event with E{sup jet}{sub T} > 20 GeV, {vert_bar}{eta}{sup jet}{vert_bar} < 2.0 and a second hadronic jet with E{sup jet}{sub T} > 15 GeV, {vert_bar}{eta}{sup jet}{vert_bar} < 2.25. The photons are required to have a {summation}{rvec E}{sub T}({gamma}) {>=} 10 GeV, and likewise the jets are required to have a {summation}{rvec E}{sub T}(jet) {>=} 10 GeV. The final M{sub {gamma}{gamma}} distribution is consistent with background and no resonance is observed. A 90(95)% C.L. upper limit cross section vs M{sub {gamma}{gamma}} is calculated, which ranges from 0.6(0.7) pb{sup -1} for M{sub {gamma}{gamma}} = 60 GeV/c{sup 2} to 0.3(0.4) pb{sup -1} for M{sub {gamma}{gamma}} = 130 GeV/c{sup 2}. With standard model coupling strengths between the bosonic Higgs and vector bosons, a 90(95)% C.L. bosonic Higgs lower mass limit is set at 86(81) GeV/c{sup 2}.
Date: October 1, 1997
Creator: Abbott, B.
Partner: UNT Libraries Government Documents Department

Top quark physics and searches for new phenomena at the Tevatron

Description: The CDF and D0 collaborations each have collected over 110 pb{sup -1} from top quark physics and searches for first generation leptoquarks (LQ), using the entire statistics of these large data sets. After careful selection, both collaborations have collected top quark data samples consisting of several dozen events each. From these events both experiments have measured the top quark mass and pair production cross section in a variety of decay channels, including the so-called dilepton, lepton plus jets, and all jets channels. The combined top quark mass from both experiments in the lepton plus jets channels is m{sub t} = 175.6{+-}5.5 GeV/c{sup 2}. CDF and D0 have also performed optimized searches for the pair production of first generation leptoquarks. No candidate events were found. Combining the results from the ee+jets, e{nu}+jets, and {nu}{nu}+jets channels both experiments set 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of {beta}, the branching fraction to a charged lepton.
Date: January 1, 1998
Creator: Hall, R.E.
Partner: UNT Libraries Government Documents Department

Top Quark Physics at a Polarized Muon Collider

Description: Top quark pair production is presented at a polarized Muon Collider above the threshold region. The off-diagonal spin basis is the natural basis for this discussion as the top quark pairs are produced in an essentially unique spin configuration for 100% polarization. Modest polarization, say 30%, can lead to 90% of all top quark pair events being in one spin configuration. This will lead to sensitive tests on anomalous top quark couplings.
Date: February 1, 1998
Creator: Parke, S.
Partner: UNT Libraries Government Documents Department

Spin-dependent Drell-Yan and double prompt photon production to NLO QCD

Description: We present the complete O({alpha}{sub s}{sup 2}) radiative corrections to the (non singlet) polarized Drell Yan cross section for the production of a lepton pair with a nonzero qT. The helicity of the incoming states is arbitrary. In the case of double photon, results for the longitudinal asymmetries and on the pT behavior of the cross section are also given (to O({alpha}{sub em}{sup 2}{alpha}{sub s})) in the central rapidity region of the tagged photon.
Date: September 1, 1997
Creator: Chang, Sanghyeon; Coriano, C.; Field, R.D. & Gordon, L.E.
Partner: UNT Libraries Government Documents Department