545 research outputs found
Transverse Momentum Distributions in B-Decays
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
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
Next to Leading Order QCD Corrections to Polarized Production in DIS
We calculate next to leading order QCD corrections to semi-inclusive
polarized deep inelastic scattering and annihilation cross sections
for processes where the polarization of the identified final-state hadron can
also be determined. Using dimensional regularization and the HVBM prescription
for the matrix, we compute corrections for different spin-dependent
observables, both in the and factorization
schemes, and analyse their structure. In addition to the well known corrections
to polarized parton distributions, we also present those for final-state
polarized fracture functions and polarized fragmentation functions, in a
consistent factorization scheme.Comment: final version with few corrections, to be published in Nuc. Phys.
Resistive Plate Chambers with Gd-coated electrodes as thermal neutron detectors
Abstract Resistive Plate Chambers (RPCs) are wide spread, cheap, easy-to-build and large size detectors, used mainly to reveal ionising particles in high-energy physics experiments. Here a technique, consisting in coating the inner surface of the bakelite electrodes with a mixture of linseed oil and Gd 2 O 3 is reported. This allows to make RPCs sensitive also to thermal neutrons, making them suitable to be employed for industrial, medical or de-mining applications. Thermal neutron-sensitive RPCs can be operated at atmospheric pressure, are lightweighted, have low Îł -ray sensitivity and are easy to handle even when large areas have to be covered. This paper reports the results of the first test of this detector, performed at the Geel Linear Accelerator (GELINA) in Belgium
An NLO calculation of the electroproduction of large-E_\bot hadrons
We present a Next-to-Leading Order calculation of the cross section for the
leptoproduction of large- hadrons and we compare our predictions with
H1 data on the forward production of . 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
We calculate and analize the one-particle inclusive
cross section in polarized deep inelastic lepton-hadron scattering, using
dimensional regularization and the HVBM prescription for . 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 scheme and in another one, called ,
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
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
We compute the order 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 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
We analyze the order- 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 - and -decays: mass effects, polarization effects and radiative corrections
We calculate the radiative corrections to the unpolarized and the four
polarized spectrum and rate functions in the leptonic decay of a polarized 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 limit of our general results and investigate the
quality of the approximation. In the case we
discuss in some detail the role of the anomalous helicity flip
contribution of the final electron which survives the limit. The
results presented in this 0203048 also apply to the leptonic decays of
polarized -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.
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