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Edmond L. Berger

Publications and source records attributed to Edmond L. Berger.

At least 91 records · Page 5Linked to original sources

Threshold Resummation of Soft Gluons in Hadronic Reactions -- An Introduction

I discuss the motivation for resummation of the effects of initial-state soft gluon radiation, to all orders in the strong coupling strength, for processes in which the near-threshold region in the partonic subenergy is important. I summarize the method of "perturbative resummation" and its application to the calculation of the total cross section for top quark production at hadron colliders. Comments are included on the differences between the treatment of subleading logarithmic terms in this method and in other approaches.

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Isolated Prompt Photon Production

We show that the conventionally defined partonic cross section for the production of isolated prompt photons is not an infrared safe quantity. We work out the case of $e^+e^- \to γ+ X$ in detail, and we discuss implications for hadron reactions such as $p \bar{p} \to γ+ X$.

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Threshold Resummation and the Total Cross Section for Top Quark Production

We discuss the motivation for resummation of the effects of initial-state soft-gluon radiation, to all orders in the strong coupling strength, for processes in which the near-threshold region in the partonic subenergy is important. We summarize our calculation of the total cross section for top quark production at hadron colliders. Comments are included on the differences between our treatment of subleading logarithmic terms and other methods.

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Threshold Resummation of the Total Cross Section for Heavy Quark Production in Hadronic Collisions

We discuss calculations of the inclusive total cross section for heavy quark production at hadron collider energies within the context of perturbative quantum chromodynamics, including resummation of the effects of initial-state soft gluon radiation to all orders in the strong coupling strength. We resum the universal leading-logarithm contributions, and we restrict our integrations to the region of phase space that is demonstrably perturbative. We include a detailed comparison of the differences between ours and other methods. We provide predictions of the physical cross section as a function of the heavy quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV, and we discuss estimated uncertainties.

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Isolated Prompt Photon Cross Sections

We show that the conventionally defined partonic cross section for the production of isolated prompt photons is not an infrared safe quantity. We work out the case of $e^+e^-\toγ+ X$, and discuss implications for hadron reactions.

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Inclusive Production of $t\bar{t}$ Pairs in Hadronic Collisions

We summarize our calculation of the total cross section for top quark production at hadron colliders within the context of perturbative quantum chromodynamics, including resummation of the effects of initial-state soft gluon radiation to all orders in the strong coupling strength.

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Calculation of the Cross Section for Top Quark Production

We summarize calculations of the cross section for top quark production at hadron colliders within the context of perturbative quantum chromodynamics, including resummation of the effects of initial-state soft gluon radiation to all orders in the strong coupling strength. In our approach we resum the universal leading-logarithm contributions, and we restrict the calculation to the region of phase space that is demonstrably perturbative. We compare our approach with other methods. We present predictions of the physical cross section as a function of the top quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV, and we discuss estimated uncertainties.

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Isolated Prompt Photon Production in Hadronic Final States of $e^+e^-$ Annihilation

We provide complete analytic expressions for the isolated prompt photon production cross section in $e^+e^-$ annihilation reactions through one-loop order in quantum chromodynamics (QCD) perturbation theory. Functional dependences on the isolation cone size $δ$ and isolation energy parameter $ε$ are derived. The energy dependence as well as the full angular dependence of the cross section on $θ_γ$ are displayed, where $θ_γ$ specifies the direction of the photon with respect to the $e^+e^-$ collision axis. We point out that conventional perturbative QCD factorization breaks down for isolated photon production in $e^+e^-$ annihilation reactions in a specific region of phase space. We discuss the implications of this breakdown for the extraction of fragmentation functions from $e^+e^-$ annihilation data and for computations of prompt photon production in hadron-hadron reactions.

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The Perturbative Resummed Series for Top Production

Our calculation of the total cross section for inclusive production of $t\bar{t}$ pairs in hadron collisions is summarized. The principal ingredient of this calculation is resummation of the universal leading-logarithm effects of gluon radiation to all orders in the quantum chromodynamics coupling strength, restricted to the region of phase space that is manifestly perturbative. We present predictions of the physical cross section as a function of top quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV.

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The Perturbative Resummed Series for Top Quark Production in Hadron Reactions

Our calculation of the total cross section for inclusive production of $t\bar{t}$ pairs in hadron collisions is presented. The principal ingredient of the calculation is resummation of the universal leading-logarithm effects of gluon radiation to all orders in the quantum chromodynamics coupling strength, restricted to the region of phase space that is demonstrably perturbative. We derive the perturbative regime of the resummed series, starting from the principal-value resummation approach, and we isolate the perturbative domain in both moment space and, upon inversion of the corresponding Mellin transform, in momentum space. We show that our perturbative result does not depend on the manner non-perturbative or infrared effects are handled in principal-value resummation. We treat both the quark-antiquark and gluon-gluon production channels consistently in the $\overline{\rm MS}$ factorization scheme. We compare our method and results with other resummation methods that rely on the choice of infrared cutoffs. We derive the renormalization/factorization scale dependence of our resummed cross section, and we discuss factorization scheme dependence and remaining theoretical uncertainties, including estimates of possible non-perturbative contributions. We include the full content of the exact next-to-leading order calculation in obtaining our final results. We present predictions of the physical cross section as a function of top quark mass in proton-antiproton reactions at center-of-mass energies of 1.8 and 2.0 TeV. We also provide the differential cross section as a function of the parton-parton subenergy.

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Production of a Prompt Photon in Association with Charm at Next-to-Leading Order in QCD

A second order, $O(α^2_s)$, calculation in perturbative quantum chromodynamics of the two particle inclusive cross section is presented for the reaction $p +\bar{p}\rightarrow γ+ c + X$ 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.

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Analytic Calculation of Prompt Photon plus Associated Heavy Flavor at Next-to-Leading Order in QCD

Contributions through second order, $O(α^2_s)$, 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 $α^2_s$. We find important corrections to the lowest order, $O(α_s)$, subprocess $c g \rightarrow γc$. We demonstrate to what extent data from $p +\bar{p}\rightarrow γ+ c + X$ may serve to measure the charm quark density in the nucleon.

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Top Quark Production Dynamics in QCD

A calculation of the total cross section for top quark production in hadron-hadron collisions is presented based on an all-orders perturbative resummation of initial-state gluon radiative contributions to the basic quantum chromodynamics subprocesses. Principal-value resummation is used to evaluate all relevant large threshold contributions. In this method there are no arbitrary infrared cutoffs, and the perturbative regime of applicability is well defined, two attributes that significantly reduce the estimated uncertainty of the results. For $p\bar{p}$ collisions at center-of-mass energy $\sqrt{s}=1.8$ TeV and a top mass of 175 GeV, we obtain $σ(t\bar{t})=5.52^{+0.07}_{-0.45} pb$, in agreement with experiment. Predicted cross sections are provided as a function of top mass in $p\bar{p}$ collisions at $\sqrt{s}=2.0$ TeV and in $p p$ collisions at CERN LHC energies.

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Inclusive Prompt Photon Production in Hadronic Final States of $e^+e^-$ Annihilation

We provide complete analytic expressions for the inclusive prompt photon production cross section in hadronic final states of $e^+e^-$ annihilation reactions through one-loop order in quantum chromodynamics perturbation theory. Computed explicitly are direct photon production through first order in the electromagnetic strength $α_{em}$ and the quark-to-photon and gluon-to-photon fragmentation contributions through first order in the strong coupling $α_s$. The full angular dependence of the cross sections is displayed, separated into transverse $(1 +\cos ^2θ_γ)$ and longitudinal $(\sin ^2θ_γ)$ components, where $θ_γ$ specifies the direction of the photon with respect to the $e^+e^-$ collision axis. We discuss extraction of fragmentation functions from $e^+e^-$ data.

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Perturbative Gluon Resummation of the Top Quark Production Cross Section

We present a calculation of the total cross section for top quark production based on a new perturbative resummation of gluon radiative corrections to the basic QCD subprocesses. We use Principal Value Resummation to calculate all relevant large threshold corrections. Advantages of this method include its independence from arbitrary infrared cutoffs and specification of the perturbative regime of applicability. For $p\bar{p}$ collisions at center-of-mass energy $\sqrt{s}=1.8$TeV and a top mass of 175 GeV, we compute $σ(t\bar{t})=5.52^{+0.07}_{-0.45}pb$.

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Transverse Momentum Distributions for Heavy Quark Pairs

We study the transverse momentum distribution for a $pair$ of heavy quarks produced in hadron-hadron interactions. Predictions for the large transverse momentum region are based on exact order $α_s^3$ QCD perturbation theory. For the small transverse momentum region, we use techniques for all orders resummation of leading logarithmic contributions associated with initial state soft gluon radiation. The combination provides the transverse momentum distribution of heavy quark pairs for all transverse momenta. Explicit results are presented for $b\bar b$ pair production at the Fermilab Tevatron collider and for $c\bar c$ pair production at fixed target energies.

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Bottom Quark Cross Sections at Collider and Fixed-Target Energies at the SSC and LHC

Calculations of inclusive cross sections for the production of bottom quarks in proton-proton collisions are presented as a function of energy, transverse momentum, and Feynman $x_F$ for values of $\sqrt{s}$ from $100~$GeV to $40~$TeV. In addition, we provide simple parametrizations of our theoretical results that should facilitate estimates of rates, acceptances, and efficiencies of proposed new detectors.

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