651 Matching Results

Search Results

Advanced search parameters have been applied.

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

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

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

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

Impact ionization in GaAs: A screened exchange density-functional approach

Description: Results are presented of a fully ab initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave method. The calculated impact ionization rates show a marked orientation dependence in k space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab initio calculations of pair production rates in new and more complex materials.
Date: August 13, 2001
Creator: Picozzi, S., Asahi, R., Geller, C.B., Continenza, A., and Freeman, A.J.
Partner: UNT Libraries Government Documents Department

Search for the lightest scalar top quark in events with two leptons in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: Data collected by the D0 detector at a p{bar p} center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider have been used to search for pair production of the lightest supersymmetric partner of the top quark decaying into b{ell}{bar {nu}}. The search is performed in the {ell}{ell}{prime} = e{mu} and {mu}{mu} final states. No evidence for this process has been found in data samples of approximately 400 pb{sup -1}. The domain in the [M({bar t}{sub 1}),M({bar {nu}})] plane excluded at the 95% C.L. is substantially extended by this search.
Date: July 1, 2007
Creator: Abazov, V.M.; Abbott, B.; Abolins, M.; Acharya, B.S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Pair Creation at Large Inherent Angles

Description: In the next-generation linear colliders, the low-energy e{sup +}e{sup -} pairs created during the collision of high-energy e{sup +}e{sup -} beams would cause potential deleterious background problems to the detectors. At low collider energies, the pairs are made essentially by the incoherent process, where the pair is created by the interaction of beamstrahlung photons on the individual particles in the oncoming beam. This problem was first identified by Zolotarev, et al[1]. At energies where the beamstrahlung parameter {Upsilon} lies approximately in the range 0.6 {approx}&lt; {Upsilon} {approx}&lt; 100, pair creation from the beamstrahlung photons is dominated by a coherent process, first noted by Chen[2]. The seriousness of this pair creation problem lies in the transverse momenta that the pair particles carry when leaving the interaction point (IP) with large angles. One source of transverse momentum is from the kick by the field of the oncoming beam which results in an outcoming angle {theta} {proportional_to} 1/{radical}x, where x is the fractional energy of the particle relative to the initial beam particle energy[2,3]. As was shown in Ref. 131, there in fact exists an energy threshold for the coherent pairs, where x{sub th} {approx}&gt; 1/2{Upsilon}. Thus within a tolerable exiting angle, there exists an upper limit for {Upsilon} where all coherent pairs would leave the detector through the exhaust port[4]. A somewhat different analysis has been done by Schroeder[5]. In the next generation of linear colliders, as it occurs, the coherent pairs can be exponentially suppressed[2] by properly choosing the {Upsilon}({approx}&lt; 0.6). When this is achieved, the incoherent pairs becomes dominant. Since the central issue is the transverse momentum for particles with large angles, we notice that there is another source for it. Namely, when the pair particles are created at low energies, the intrinsic angles of these pairs when produced may ...
Date: April 25, 2007
Creator: Chen, P.; Tauchi, T.; Schroeder, D.V. & /SLAC
Partner: UNT Libraries Government Documents Department

Search for doubly-charged Higgs Boson production in the decay H++ H-- ---> mu+ mu+ mu- mu - with the D0 detector at s**(1/2) = 1.96-TeV

Description: This work presents a search for the pair production of doubly-charged Higgs Bosons in the process p{bar p} {yields} H{sup ++}H{sup --} {yields} {mu}{sup +}{mu}{sup +}{mu}{sup -}{mu}{sup -} using inclusive dimuon events. These data correspond to an integrated luminosity of about 113 pb 1 and were recorded by the D0 experiment between August 2002 and June 2003. In the absence of a signal, 95% confidence level mass limits of M(H{sub L}{sup {+-}{+-}}) &gt; 118.6 GeV/c{sup 2} and M(H{sub R}{sup {+-}{+-}}) &gt; 98.1 GeV/c{sup 2} are set for left-handed and right-handed doubly-charged Higgs boson, assuming 100% branching into muons and hypercharge |Y| = 2 and Yukawa coupling h{sub {mu}{mu}} &gt; 10{sup -7}. This is the first search for doubly-charged Higgs bosons at hadron colliders. It significantly extends the previous mass limit of 100.5 GeV/c{sup 2} for a left-handed doubly-charged Higgs boson measured in the muon final states by the OPAL collaboration.
Date: January 1, 2004
Creator: Zdrazil, Marian & /SUNY, Stony Brook
Partner: UNT Libraries Government Documents Department

Next-to-Leading Order Calculation of the Single Transverse Spin Asymmetry in the Drell-Yan Process

Description: We calculate the next-to-leading order perturbative QCD corrections to the transverse momentum weighted single transverse spin asymmetry in Drell-Yan lepton pair production in hadronic collisions. We identify the splitting function relevant for the scale evolution of the twist-three quark-gluon correlation function. We comment on the consequences of our results for phenomenology.
Date: March 30, 2009
Creator: Vogelsang, Werner & Yuan, Feng
Partner: UNT Libraries Government Documents Department

Transverse momentum dependent quark distributions and polarized Drell-Yan processes

Description: We study the spin-dependent quark distributions at large transverse momentum. We derive their transverse momentum behaviors in the collinear factorization approach in this region. We further calculate the angular distribution of the Drell-Yan lepton pair production with polarized beams and present the results in terms of the collinear twist-three quark-gluon correlation functions. In the intermediate transverse momentum region, we find that the two pproaches: the collinear factorization and the transverse momentum dependent factorization approaches are consistent in the description of the lepton pair angular distributions.
Date: September 11, 2009
Creator: Zhou, J.; Yuan, F. & Liang, Z.-T.
Partner: UNT Libraries Government Documents Department

THRESHOLD RESUMMATION EFFECTS IN THE POLARIZED DRELL-YAN MECHANISM.

Description: We present theoretical predictions for the cross sections and spin asymmetries in dilepton pair production in transversely polarized pp and {bar p}p collisions. We use the available fixed-order corrections as well as the all-order resummation of threshold logarithms for the pair mass and rapidity distributions. Numerical results for pp collisions at {radical}s = 10 GeV at J-PARC and for {bar p}p collisions at {radical}s = 14.5 GeV at GSI-PAX are given.
Date: October 2, 2006
Creator: YOKOYA, H. & VOGELSANG, W.
Partner: UNT Libraries Government Documents Department

Search for pair production of second generation scalar leptoquarks in p anti-p collisions at s**(1/2) = 1.96-TeV

Description: The authors report on a search for the pair production of second generation scalar leptoquarks (LQ{sub 2}) in p{bar p} collisions at the center-of-mass energy {radical}s = 1.96 TeV, using data corresponding to an integrated luminosity of 294 {+-} 19 pb{sup -1} recorded with the D0 detector. No evidence for a leptoquark signal in the LQ{sub 2} {ovr LQ}{sub 2} {yields} {mu}q{mu}q channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of m{sub LQ{sub 2}} &gt; 247 GeV for {beta} = {Beta}(LQ{sub 2} {yields} {mu}q) = 1 and m{sub LQ{sub 2}} &gt; 182 GeV for {beta} = 1/2. Combining these limits with previous D0 results, the lower limits on the mass of a second generation scalar leptoquark are m{sub LQ{sub 2}} &gt; 251 GeV and m{sub LQ{sub 2}} &gt; 204 GeV for {beta} = 1 and {beta} = 1/2, respectively.
Date: January 1, 2006
Creator: Abazov, V. M.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adams, M.; Adams, T. et al.
Partner: UNT Libraries Government Documents Department

Electron and Photon Interactions in the Regime of Strong LPM Suppression

Description: Most searches for ultra-high energy (UHE) astrophysical neutrinos look for radio emission from the electromagnetic and hadronic showers produced in their interactions. The radio frequency spectrum and angular distribution depend on the shower development, so are sensitive to the interaction cross sections. At energies above about 1016 eV (in ice), the Landau-Pomeranchuk-Migdal (LPM) effect significantly reduces the cross sections for the two dominant electromagnetic interactions: bremsstrahlung and pair production. At higher energies, above about 1020 eV, the photonuclear cross section becomes larger than that for pair production, and direct pair production and electronuclear interactions become dominant over bremsstrahlung. The electron interaction length reaches a maximum around 1021 eV, and then decreases slowly as the electron energy increases further. In this regime, the growth in the photon cross section and electron energy loss moderates the rise in nu e shower length, which rises from ~;;5 m at 1016 eV to ~;;40 m at 1019 eV and ~;;100 m at 1020 eV, but only to ~;;300 m at 1024 eV. In contrast, without photonuclear and electronuclear interactions, the shower length would be over 10 km at 1024 eV.
Date: June 10, 2010
Creator: Gerhardt, L. & Klein, S.
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