QCD Corrections to Semi-inclusive Hadron Production in Electron Positron Annihilation at Two Loops PDF Download
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Author: Alexander Mitov
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Languages : en
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Author: Alexander Mitov
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Languages : en
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Author: S. Brodsky
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Languages : en
Pages : 20
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I survey a number of interesting tests of quantum chromodynamics at the amplitude level which can be carried out in electron-positron annihilation and in photon-photon collisions at low energy. Some of the tests require e{sup +}e{sup -} center of mass energy as small as {radical}s = 2 GeV. Other tests which involve a spectrum of energies can be carried out advantageously at high energy facilities using the radiative return method. These include measurements of fundamental processes such as timelike form factors and transition amplitudes, timelike Compton scattering, timelike photon to meson transition amplitudes, and two-photon exclusive processes. Many of these reactions test basic principles of QCD such as hadronization at the amplitude level, factorization, and hadron helicity conservation, tools also used in the analysis of exclusive B and D decays. Measurements of the final-state polarization in hadron pair production determine the relative phase of the timelike form factors and thus strongly discriminate between analytic forms of models which fit the form factors in the spacelike region. The role of two-photon exchange amplitudes can be tested using the charge asymmetry of the e{sup +}e{sup -} {yields} B{bar B} processes. These tests can help resolve the discrepancy between the Jefferson laboratory measurements of the ratio of G{sub E} and G{sub M} proton form factors using the polarization transfer method versus measurements using the traditional Rosenbluth method. Precision measurements of the electron-positron annihilation cross section can test the generalized Crewther relation and determine whether the effective couplings defined from physical measurements show infrared fixed-point and near conformal behavior. I also discuss a number of tests of novel QCD phenomena accessible in e{sup +}e{sup -} annihilation, including near-threshold reactions, the production of baryonium, gluonium states, and pentaquarks.
Author: Andrea A. Almasy
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Languages : en
Pages : 0
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Author: Yuri Dokshitzer
Publisher: Atlantica Séguier Frontières
ISBN: 9782863321010
Category : Perturbation (Quantum dynamics).
Languages : en
Pages : 286
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Author:
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Category : Physics
Languages : en
Pages : 1454
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![Results on [alpha]{sub S} and QCD from (and Above) the Z° PDF](https://books.google.com/books/content/images/frontcover/8PRdAQAACAAJ?fife=w80-h100)
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Languages : en
Pages : 28
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In electron-positron annihilation hadronic activity is, by construction, limited to the final state, making the study of hadronic events cleaner and simpler relative to lepton-hadron and hadron-hadron collisions, from both the experimental and theoretical points-of-view. To be specific, samples of hadronic events can be selected by experiments at the Z° resonance with efficiency and purity of better than 99%. Jet and event-shape observables have been calculated at next-to-leading order, O([alpha]{sub s}2), and some inclusive observables have been calculated at O([alpha]{sub s}3). Non-perturbative calculations, in the form of power corrections to perturbatively-evaluated observables, have been performed, and there are well-understood models of hadronization that have been carefully tuned to the data collected over the past 20 years. Electron-positron annihilation thus provides an ideal environment for precise tests of QCD, and has yielded spectacular results. Here, measurements of [alpha]{sub s} from ee− annihilation experiments are reviewed and compared with measurements from other processes. Highlights are presented of recent QCD studies in ee− annihilation at the Z° resonance.
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Languages : en
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We compute the next-to-leading-order QCD corrections to the production of two Z-bosons in the annihilation of two gluons at the LHC. Being enhanced by a large gluon flux, these corrections provide a distinct and, potentially, the dominant part of the N3LO QCD contributions to Z-pair production in proton collisions. The gg → ZZ annihilation is a loop-induced process that receives the dominant contribution from loops of five light quarks, that are included in our computation in the massless approximation. We find that QCD corrections increase the gg → ZZ production cross section by O(50%-100%) depending on the values of the renormalization and factorization scales used in the leading-order computation and the collider energy. As a result, the large corrections to the gg → ZZ channel increase the pp → ZZ cross section by about 6% to 8%, exceeding the estimated theoretical uncertainty of the recent next-to-next-to-leading-order QCD calculation.
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Languages : en
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Using a model calculation of dihadron fragmentation functions, we fit the spin asymmetry recently extracted by HERMES for the semi-inclusive pion pair production in deep-inelastic scattering on a transversely polarized proton target. By evolving the obtained dihadron fragmentation functions, we make predictions for the correlation of the angular distributions of two pion pairs produced in electron-positron annihilations at BELLE kinematics. Our study shows that the combination of two-hadron inclusive deep-inelastic scattering and electron-positron annihilation measurements can provide a valid alternative to Collins effect for the extraction of the quark transversity distribution in the nucleon.
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Languages : en
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We discuss hadron mass corrections and threshold resummation for deep-inelastic scattering lN-->l'X and semi-inclusive annihilation e+e- → hX processes, and provide a prescription how to consistently combine these two corrections respecting all kinematic thresholds. We find an interesting interplay between threshold resummation and target mass corrections for deep-inelastic scattering at large values of Bjorken xB. In semi-inclusive annihilation, on the contrary, the two considered corrections are relevant in different kinematic regions and do not affect each other. A detailed analysis is nonetheless of interest in the light of recent high precision data from BaBar and Belle on pion and kaon production, with which we compare our calculations. For both deep inelastic scattering and single inclusive annihilation, the size of the combined corrections compared to the precision of world data is shown to be large. Therefore, we conclude that these theoretical corrections are relevant for global QCD fits in order to extract precise parton distributions at large Bjorken xB, and fragmentation functions over the whole kinematic range.
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Languages : en
Pages : 13
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Here, we compute the next-to-leading order virtual QCD corrections to Higgs-pair production via gluon fusion. We also present analytic results for the two-loop contributions to the spin-0 and spin-2 form factors in the amplitude. The reducible contributions, given by the double-triangle diagrams, are evaluated exactly while the two-loop irreducible diagrams are evaluated by an asymptotic expansion in heavy top-quark mass up to and including terms of O(1/m$8\atop{t}$). We estimate that mass effects can reduce the hadronic cross section by at most 10 %, assuming that the finite top-quark mass effects are of similar size in the entire range of partonic energies.
