464 research outputs found

    Transverse Momentum Distributions in B-Decays

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    We consider transverse momentum distributions in B-decays. The O(alpha_S) coefficients for soft and collinear logarithms are computed to next-to-leading accuracy. Resummation of large logarithmic contributions is performed in impact parameter space within the general formalism for transverese momentum distributions. It is shown that the shape-function approach as used for the threshold distribution case cannot be extended to the transverse momentum one.Comment: LaTex file, 8 pages, 1 postscript figur

    Optimal Design of Elastic Circular Plane Arches

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    Arches represent a structural system adopted in construction practice for thousand years, and they are still widely adopted if large spans have to be covered. The structural efficiency of arches principally depends on the minimization of the eccentricity of the pressure curve, which allow us to reduce their structural weight. Despite the millenarian use and a very abundant literature, there is still scope for design optimization of arches. This study is framed within this context and is focused on plane circular arches under uniformly distributed vertical load and self-weight. The arches are elastically clamped at both end sections. A semianalytical approach is developed to minimize the volume, with the aim of determining the fundamental mechanical parameters governing the optimal design. Finally, the results are charted to allow their use in a design process

    An NLO calculation of the electroproduction of large-E_\bot hadrons

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    We present a Next-to-Leading Order calculation of the cross section for the leptoproduction of large-E⊄E_{\bot} hadrons and we compare our predictions with H1 data on the forward production of π0\pi^0. We find large higher order corrections and an important sensitivity to the renormalization and factorization scales. These large corrections are shown to arise in part from BFKL-like diagrams at the lowest order.Comment: 24 pages, plain LaTeX2e, 10 figure

    Factorization in Semi-Inclusive Polarized Deep Inelastic Scattering

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    We calculate and analize the O(αs){\cal{O}}(\alpha_s) one-particle inclusive cross section in polarized deep inelastic lepton-hadron scattering, using dimensional regularization and the HVBM prescription for Îł5\gamma_5. We discuss the factorization of all the collinear singularities related to the process, particularly those which are absorbed in the redefinition of the spin dependent analogue of the recently introduced fracture functions. This is done in the usual MS‟\overline{MS} scheme and in another one, called MSp‟\overline{MS_p}, which factorizes soft contributions and guarantees the axial current (non)conservation properties.Comment: 16 pages, figures included using FEYNMAN macr

    Next to Leading Order Semi-inclusive Spin Asymmetries

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    We have computed semi-inclusive spin asymmetries for proton and deuteron targets including next to leading order (NLO) QCD corrections and contributions coming from the target fragmentation region. These corrections have been estimated using NLO fragmentation functions, parton distributions and also a model for spin dependent fracture functions which is proposed here. We have found that NLO corrections are small but non-negligible in a scheme where gluons are polarised and that our estimate for target fragmentation effects does not modify significantly charged asymmetries but affects the so called difference asymmetries.Comment: Latex, 14 pages, 6 figures in 4 Postcript file

    Next to leading order evolution of SIDIS processes in the forward region

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    We compute the order αs2\alpha_s^2 quark initiated corrections to semi-inclusive deep inelastic scattering extending the approach developed recently for the gluon contributions. With these corrections we complete the order αs2\alpha_s^2 QCD description of these processes, verifying explicitly the factorization of collinear singularities. We also obtain the corresponding NLO evolution kernels, relevant for the scale dependence of fracture functions. We compare the non-homogeneous evolution effects driven by these kernels with those obtained at leading order accuracy and discuss their phenomenological implications.Comment: 18 pages, 4 ps figures, uses revtex4 and feynmf. Accepted for publication in Nuclear Physics

    Order-alpha_s^2 corrections to one-particle inclusive processes in DIS

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    We analyze the order-αs2\alpha_s^2 QCD corrections to semi-inclusive deep inelastic scattering and present results for processes initiated by a gluon. We focus in the most singular pieces of these corrections in order to obtain the hitherto unknown NLO evolution kernels relevant for the non homogeneous QCD scale dependence of these cross sections, and to check explicitly factorization at this order. In so doing we discuss the prescription of overlapping singularities in more than one variable.Comment: 16 pages, 9 eps figures. Uses revtex4 and feynm

    Leptonic ÎŒ \mu - and τ \tau -decays: mass effects, polarization effects and O(α) O(\alpha) radiative corrections

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    We calculate the radiative corrections to the unpolarized and the four polarized spectrum and rate functions in the leptonic decay of a polarized ÎŒ \mu into a polarized electron. The new feature of our calculation is that we keep the mass of the final state electron finite which is mandatory if one wants to investigate the threshold region of the decay. Analytical results are given for the energy spectrum and the polar angle distribution of the final state electron whose longitudinal and transverse polarization is calculated. We also provide analytical results on the integrated spectrum functions. We analyze the me→0 m_e \to 0 limit of our general results and investigate the quality of the me→0 m_e \to 0 approximation. In the me→0 m_e \to 0 case we discuss in some detail the role of the O(α) O(\alpha) anomalous helicity flip contribution of the final electron which survives the me→0 m_e \to 0 limit. The results presented in this 0203048 also apply to the leptonic decays of polarized τ \tau -leptons for which we provide numerical results.Comment: 39 pages, 11 postscript figures added. Updated version. Four references added. A few text improvements. Final version to appear in Phys.Rev.

    Diffractive Photoproduction in the Framework of Fracture Functions

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    Recent data on diffractive photoproduction of dijets are analyzed within the framework of fracture functions and paying special attention to the consequences of the use of different rapidity gap definitions in order to identify diffractive events. Although these effects are found to be significant, it is shown that once they are properly taken into account, a very precise agreement between diffractive DIS and diffractive dijet photoproduction emerges without any significant hint of hard factorization breaking.Comment: 13 pages, 4 figures. To appear in Phys.Rev.

    Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data

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    We present a combined next-to-leading order QCD analysis to data on both inclusive and semi-inclusive polarized deep inelastic scattering asymmetries. Performing NLO QCD global fits with different sets of observables, we evaluate the impact of the very recent semi-inclusive results presented by SMC in the extraction of NLO polarized parton distributions.Comment: 22 pages, 4 figures include
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