43,436 research outputs found
Top Spin and Experimental Tests
We examine pair mass dependence near threshold as a means to measure the spin
of the top quark in hadron collisions, and we discuss the possibility that a
top squark signal could be hidden among the top events.Comment: 9 pages, RevTeX, 3 figures. Contribution to the Thinkshop on
Top-Quark Physics for the Tevatron Run II, Fermilab, October 16 - 18, 199
Analytic Calculation of Prompt Photon plus Associated Heavy Flavor at Next-to-Leading Order in QCD
Contributions through second order, , in perturbative quantum
chromodynamics are calculated analytically for inclusive associated production
of a prompt photon and a charm quark at large values of transverse momentum in
high energy hadron-hadron collisions. Seven partonic subprocesses contribute at
order . We find important corrections to the lowest order,
, subprocess . We demonstrate to what
extent data from may serve to measure
the charm quark density in the nucleon.Comment: 34 pages RevTex plus 9 figures submitted as uuencoded ps files;
figures replaced and text revised to include one additional referenc
Production of a Prompt Photon in Association with Charm at Next-to-Leading Order in QCD
A second order, , calculation in perturbative quantum
chromodynamics of the two particle inclusive cross section is presented for the
reaction for large values of the
transverse momentum of the prompt photon and charm quark. The combination of
analytic and Monte Carlo integration methods used here to perform phase-space
integrations facilitates imposition of photon isolation restrictions and other
selections of relevance in experiments. Differential distributions are provided
for various observables. Positive correlations in rapidity are predicted.Comment: 27 pages in RevTex plus 14 figures in one compressed PS fil
Predictions for associated production of gauginos and gluinos at NLO in SUSY-QCD
NLO SUSY-QCD contributions to associated production of gluinos and gauginos
are shown to enhance the cross sections by about 10% at the Tevatron and by as
much as a factor of two at the LHC. They shift the mass determinations or
discovery limits, soften the spectra, and stabilize the predictions
against variations of the renormalization and factorization scales.Comment: 4 pages, Latex (uses Moriond style file), 8 eps-figures. Talk
presented at the XXXVth Rencontres de Moriond, QCD and High Energy Hadronic
Interactions, Les Arcs, France, March 18-25, 200
Missing heavy flavor backgrounds to Higgs boson production
We investigate characteristics of the signal and backgrounds for Higgs boson
decay into WW at the Fermilab Tevatron and CERN Large Hadron Collider. In the
the lepton-pair-plus-missing-energy final state, we show that the background
receives an important contribution from semileptonic decays of heavy flavors.
Lepton isolation cuts provide too little suppression of these heavy flavor
contributions, and an additional 4 to 8 orders-of-magnitude suppression must
come from physics cuts. We demonstrate that an increase of the minimum
transverse momentum of nonleading leptons in multilepton events is one
effective way to achieve the needed suppression, without appreciable loss of
the Higgs boson signal. Such a cut would impact the efficiency of searches for
supersymmetry as well. We emphasize the importance of direct measurement of the
lepton background from heavy flavor production.Comment: 23 pgs., 10 figs, revtex4, 1 Ref. added, minor typos corrected, to
appear in Phys. Rev.
Next-to-leading Order SUSY-QCD Calculation of Associated Production of Gauginos and Gluinos
Results are presented of a next-to-leading order calculation in perturbative
QCD of the production of charginos and neutralinos in association with gluinos
at hadron colliders. Predictions for cross sections are shown at the energies
of the Fermilab Tevatron and CERN Large Hadron Collider for a typical
supergravity (SUGRA) model of the sparticle mass spectrum and for a light
gluino model.Comment: 3 pages, latex, 4 figures, paper presented by E. L. Berger at ICHEP
2000, the XXXth International Conference on High Energy Physics July 27 -
August 2, 2000, Osaka, Japa
Erratum: Next-to-leading order supersymmetric QCD predictions for associated production of gauginos and gluinos [Phys. Rev. D 62, 095014 (2000)]
Errors in the published version of the paper are corrected, and new figures
are provided.Comment: 3 pages, latex, 4 figure
Spitzer Observations of Gamma-Ray Burst Host Galaxies: A Unique Window into High Redshift Chemical Evolution and Star-formation
We present deep Spitzer 3.6 micron observations of three z~5 GRB host
galaxies. Our observations reveal that z~5 GRB hosts are a factor of 3 less
luminous than the median rest-frame V-band luminosity of spectroscopically
confirmed z~5 galaxies in the GOODS fields and the UDF. The strong connection
between GRBs and massive star formation implies that not all star-forming
galaxies at these redshifts are currently being accounted for in deep surveys
and GRBs provide a unique way to measure the contribution to the star-formation
rate density from galaxies at the faint end of the galaxy luminosity function.
By correlating the co-moving star-formation rate density with co-moving GRB
rates at lower redshifts, we estimate a lower limit to the star-formation rate
density of 0.12+/-0.09 and 0.09+/-0.05 M_sun/yr/Mpc^3 at z~4.5 and z~6,
respectively. Finally, we provide evidence that the average metallicity of
star-forming galaxies evolves as (stellar mass density)^(0.69+/-0.17) between
and , probably indicative of the loss of a significant
fraction of metals to the intergalactic medium, particularly in low-mass
galaxies.Comment: ApJ, in pres
Isolated Prompt Photon Production in Hadronic Final States of Annihilation
We provide complete analytic expressions for the isolated prompt photon
production cross section in annihilation reactions through one-loop
order in quantum chromodynamics (QCD) perturbation theory. Functional
dependences on the isolation cone size and isolation energy parameter
are derived. The energy dependence as well as the full angular
dependence of the cross section on are displayed, where
specifies the direction of the photon with respect to the
collision axis. We point out that conventional perturbative QCD
factorization breaks down for isolated photon production in
annihilation reactions in a specific region of phase space. We discuss the
implications of this breakdown for the extraction of fragmentation functions
from annihilation data and for computations of prompt photon
production in hadron-hadron reactions.Comment: 54 pages RevTeX plus 19 postscript figures submitted together in one
compressed fil
Next-to-Leading Order SUSY-QCD Predictions for Associated Production of Gauginos and Gluinos
We present complete results of a next-to-leading order calculation of the
production of gaugino-like charginos (\chargino) and neutralinos
(\neutralino) in association with gluinos (\gluino) at hadron colliders,
including the strong corrections from the exchange of colored particles and
sparticles. Adopting a variety of models for the sparticle mass spectrum,
including typical supergravity (SUGRA) models and a light gluino model, we
provide predictions for total and differential cross sections at the energies
of the Fermilab Tevatron and CERN Large Hadron Collider (LHC).Comment: 91 pages, Latex, including 26 figure
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