76 research outputs found

    Pseudoscalar Higgs boson production at hadron colliders in NNLO QCD

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    We compute the total cross-section for direct production of the pseudoscalar Higgs boson in hadron collisions at next-to-next-to-leading order (NNLO) in perturbative QCD. The O(alpha_s^2) QCD corrections increase the NLO production cross-section by approximately 20-30 per cent.Comment: 5 pages, revtex

    Heavy flavour mass corrections to the longitudinal and transverse cross sections in e^+e^- - collisions

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    The sentence, 7th line below Eq. (28), starting with "Further we exclude all interference terms ...." is wrong and has been corrected. Eq. (33) : f_k^{l,(i)} -> h_k^{l,(i)} i=0,1 Second line below Eq. (33) m_bar(m)=m is replaced by m_bar(\mu_0)=\mu_0 with \mu_0=4.10 GeV and \mu_0=166.1 GeV for bottom and top respectively. The numbers in the third column of tables 1 and 2 are a little bit changed.Comment: 8 pages Latex, all compressed by uufile

    Bottom quark electroproduction in variable flavor number schemes

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    Two variable flavor number schemes are used to describe bottom quark production in deep inelastic electron-proton scattering. In these schemes the coefficient functions are derived from mass factorization of the heavy quark coefficient functions presented in a fixed flavor number scheme. Also one has to construct a parton density set with five light flavors (u,d,s,c,b) out of a set which only contains four light flavors (u,d,s,c). In order αs2\alpha_s^2 the two sets are discontinuous at μ=mb\mu=m_b which follows from mass factorization of the heavy quark coefficient functions when it is carried out in the MSˉ{\bar {\rm MS}}-scheme. Both variable flavor number schemes give almost identical predictions for the bottom structure functions F2,bF_{2,b} and FL,bF_{L,b}. Also they both agree well with the corresponding results based on fixed order four-flavor perturbation theory over a wide range in xx and Q2Q^2.Comment: Latex with seventeen PostScript figure

    Theoretical Uncertainties in the QCD Evolution of Structure Functions and their Impact on αs(MZ2)\alpha_s(M_Z^2)

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    The differences are discussed between various next-to-leading order prescriptions for the QCD evolution of parton densities and structure functions. Their quantitative impact is understood to an accuracy of 0.02\%. The uncertainties due to the freedom to choose the renormalization and factorization scales are studied. The quantitative consequences of the different uncertainties on the extraction of the strong coupling constant αs\alpha_s from scaling violations in deep--inelastic scattering are estimated for the kinematic regime accessible at HERA.Comment: 10 pages Latex, including 3 eps-figures, and a style file. To appear in: Proc. of the International Workshop: QCD and QED in Higher Orders, Rheinsberg, April, 1996, Nucl. Phys. {\bf B} (Proc. Suppl); The lay-out of the paper has been changed, one figure sent separately before has been bound i

    NNLO Corrections to the Polarized Drell-Yan Coefficient Function

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    We present the full next-to-next-to-leading order (NNLO) corrections to the coefficient function for the polarized cross section dΔσ/dQd \Delta\sigma/d Q of the Drell-Yan process. We study the effect of these corrections on the process p+pl+l+Xp+p\to l^+l^-+`X' at an C.M. energy S=200GeV\sqrt{S}=200 GeV. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for a lepton pair invariant mass Q<50GeVQ<50 GeV. For this reaction the dominant subprocess is given by q+qˉγ+Xq+\bar q\to \gamma^*+`X' and its higher order corrections so that it provides us with an excellent tool to measure the polarized sea-quark densities.Comment: 5 pages, 5 figures, 7th DESY Workshop on Elementary Particle Theory, Loops and Legs in Quantum Field Theory, Zinnowitz, Germany, April 25-30, 200

    Second order QCD corrections to the forward-backward asymmetry in e^+e^- - collisions

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    The sentence, 11th line below Eq. (30), starting with "Further in [14] one has included all interference terms ...." is wrong and has been corrected. Second line below Eq. (40) m_bar(m)=m is replaced by m_bar(\mu_0)=\mu_0 with \mu_0=4.10 GeV, \mu_0=1.30 GeV and \mu_0=166.1 GeV for bottom, charm and top respectively. The numbers in the second and third column of table 3 are a little bit changed. In the acknowledgement the funding agency is mentioned and one reference i.e. [20] is added.Comment: 11 pages Late

    NLO corrections to the polarized Drell-Yan cross section in proton-proton collisions

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    We present the full next-to-leading order (NLO) corrected inclusive cross section for massive lepton pair production in longitudinally polarized proton-proton collisions. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for Q<50GeVQ<50 {\rm GeV}. Like in unpolarized proton-proton scattering the dominant subprocess is given by the q(qˉ)gq(\bar q)g-channel so that massive lepton pair production provides us with an excellent method to measure the spin density of the gluon. Using our calculations we give predictions for the longitudinal spin asymmetry measurements at the RHIC.Comment: 4 pages, LaTeX, 2 Postscript figures. Talk presented at the 6th International Symposium on Radiative Corrections "RADCOR 2002" and 6th Zeuthen Workshop on Elementary Particle Theory. Kloster Banz, Germany, September 8-13, 200

    Non-singlet structure functions beyond the next-to-next-to leading order

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    We study the evolution of the flavour non-singlet deep-inelastic structure functions F_{2,NS} and F_3 at the next-to-next-to-next-to-leading order (N^3LO) of massless perturbative QCD. The present information on the corresponding three-loop coefficient functions is used to derive approximate expressions of these quantities which prove completely sufficient for values x > 10^{-2} of the Bjorken variable. The inclusion of the N^3LO corrections reduces the theoretical uncertainty of alpha_s determinations from non-singlet scaling violations arising from the truncation of the perturbation series to less than 1%. We also study the predictions of the soft-gluon resummation, of renormalization-scheme optimizations by the principle of minimal sensitivity (PMS) and the effective charge (ECH) method, and of the Pade' summation for the structure-function evolution kernels. The PMS, ECH and Pade' approaches are found to facilitate a reliable estimate of the corrections beyond N^3LO.Comment: 29 pages, LaTeX, 12 eps-figure

    Comparison between variable flavor number schemes for charm quark electroproduction

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    Where appropriate, the abbreviation 'VFNS' is replaced by 'CSN' to indicate the scheme using massive heavy quark coefficient functions proposed in this paper. The text below Eq. (2.13) and between Eqs. (2.33) and (2.36) has been considerably changed.Comment: 64 pages, LaTeX, 16 Postscript figure

    Top Quark Production Cross Section

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    The production rate for top quarks at the Fermilab Tevatron is presented using the exact order αs3\alpha_s^3 corrected cross section and the resummation of the leading soft gluon corrections in all orders of perturbation theory.Comment: preprint FERMILAB-Pub-93/270-T, ITP-SB-93-55, THU-93/23, Latex 9 pages, 8 postscript figures, uuencoded and appended at end of fil
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