211 research outputs found
NLO Scale Dependence of Semi-Inclusive Processes
We discuss the order \alpha_s^2 gluon initiated QCD corrections to one
particle inclusive deep inelastic processes. We focus in the NLO evolution
kernels relevant for the non homogeneous QCD scale dependence of these cross
sections and factorization.Comment: Poster presentation at the XXIII Physics in Collision Conference
(PIC03), Zeuthen, Germany, June 2003, 3 pages, LaTeX, 4 eps figures, PSN
FRAP1
O(alpha_s^2) QCD corrections to the electroproduction of hadrons with high transverse momentum
We compute the order alpha_s^2 corrections to the one particle inclusive
electroproduction cross section of hadrons with non vanishing transverse
momentum. We perform the full calculation analytically, and obtain the
expression of the factorized (finite) cross section at this order. We compare
our results with H1 data on forward production of pi^0, and discuss the
phenomenological implications of the rather large higher order contributions
obtained in that case. Specifically, we analyze the cross section sensitivity
to the factorization and renormalization scales, and to the input fragmentation
functions, over the kinematical region covered by data. We conclude that the
data is well described by the O(alpha_s^2) predictions within the theoretical
uncertainties and without the inclusion of any physics content beyond the DGLAP
approach.Comment: 11 pages, LaTeX, 7 figure
On the dbar/ubar Asymmetry and Parton Distributions
We discuss the impact of different measurements of the dbar/ubar asymmetry in
the extraction of parameterizations of parton distribution functions.Comment: Contributed paper to LP01, 13 pages, 4 figure
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
Evaluating multi-loop Feynman diagrams with infrared and threshold singularities numerically
We present a method to evaluate numerically Feynman diagrams directly from
their Feynman parameters representation. We first disentangle overlapping
singularities using sector decomposition. Threshold singularities are treated
with an appropriate contour deformation. We have validated our technique
comparing with recent analytic results for the gg->h two-loop amplitudes with
heavy quarks and scalar quarks.Comment: 8 pages, 3 figures; references added, version to appear in JHE
Z-prime Gauge Bosons at the Tevatron
We study the discovery potential of the Tevatron for a Z-prime gauge boson.
We introduce a parametrization of the Z-prime signal which provides a
convenient bridge between collider searches and specific Z-prime models. The
cross section for p pbar -> Z-prime X -> l^+ l^- X depends primarily on the
Z-prime mass and the Z-prime decay branching fraction into leptons times the
average square coupling to up and down quarks. If the quark and lepton masses
are generated as in the standard model, then the Z-prime bosons accessible at
the Tevatron must couple to fermions proportionally to a linear combination of
baryon and lepton numbers in order to avoid the limits on Z--Z-prime mixing.
More generally, we present several families of U(1) extensions of the standard
model that include as special cases many of the Z-prime models discussed in the
literature. Typically, the CDF and D0 experiments are expected to probe
Z-prime-fermion couplings down to 0.1 for Z-prime masses in the 500--800 GeV
range, which in various models would substantially improve the limits set by
the LEP experiments.Comment: 34 pages, 13 figure
Semi-Inclusive Deep Inelastic Scattering processes from small to large P_T
We consider the azimuthal and dependence of hadrons produced in
unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes, within
the factorized QCD parton model. It is shown that at small values, P_T
\lsim 1 GeV/c, lowest order contributions, coupled to unintegrated (Transverse
Momentum Dependent) quark distribution and fragmentation functions, describe
all data. At larger values, P_T \gsim 1 GeV/c, the usual pQCD higher
order collinear contributions dominate. Having explained the full range
of available data, we give new detailed predictions concerning the azimuthal
and dependence of hadrons which could be measured in ongoing or planned
experiments by HERMES, COMPASS and JLab collaborations.Comment: 14 pages, 17 figures, uses revtex
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