59 research outputs found
Fragmentations Functions in Nuclear Media
We perform a detailed phenomenological analysis of how well hadronization in
nuclear environments can be described in terms of effective fragmentation
functions. The medium modified fragmentation functions are assumed to factorize
from the partonic scattering cross sections and evolve in the hard scale in the
same way as the standard or vacuum fragmentation functions. Based on precise
data on semi-inclusive deep-inelastic scattering off nuclei and hadron
production in deuteron-gold collisions, we extract sets of effective
fragmentation functions for pions and kaons at NLO accuracy. The obtained sets
provide a rather accurate description of the kinematical dependence of the
analyzed cross sections and are found to differ significantly from standard
fragmentation functions both in shape and magnitude. Our results support the
notion of factorization and universality in the studied nuclear environments,
at least in an effective way and within the precision of the available data.Comment: 17 pages, 11 figure
Global Analysis of Fragmentation Functions for Protons and Charged Hadrons
We present new sets of fragmentation functions for protons and inclusive
charged hadrons obtained in combined NLO QCD analyses of single-inclusive
hadron production in electron-positron annihilation, proton-proton collisions,
and deep-inelastic lepton-proton scattering. These analyses complement previous
results for pion and kaon fragmentation functions with charge and flavor
discrimination. The Lagrange multiplier technique is used to assess the
uncertainties in the extraction of the new sets of fragmentation functions.Comment: 14 pages, 14 figure
Heavy quark mass effects in parton-to-kaon hadronization probabilities
We examine the relevance of the heavy quarks masses in the perturbative QCD description of hard interactions where charged kaons are produced in the final state. We extract a set of parton-to-kaon hadronization probabilities from a next to leading order QCD global analysis where a general mass variable flavor number scheme accounting for mass effects is implemented. We compare the results with those obtained in the massless approximation and also with those found in the case of final state pions. At variance with the very significant improvement found for the much more precise pion fragmentation phenomenology, the heavy quark mass dependent scheme improves mildly the overall description of current kaon production data. Nevertheless, we find a noticeable reduction in the charm-to-kaon hadronization probability.Fil: Epele, Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: García Canal, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Sassot, Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin
Uncertainties in pion and kaon fragmentation functions
We present a detailed assessment of uncertainties in parton-to-pion and
parton-to-kaon fragmentation functions obtained in recent global QCD analyses
of single-inclusive hadron production data at next-to-leading order accuracy.
We use the robust Lagrange multiplier approach for determining uncertainties to
validate the applicability of the simpler but approximate Hessian method.
Extensive comparisons of the results obtained within both methods are presented
for the individual parton-to-pion and kaon fragmentation functions. We provide
Hessian eigenvector sets of pion and kaon fragmentation functions that allow
one to easily propagate their uncertainties to any observable. Various
applications of these sets are presented for pion and kaon production in
electron-positron annihilation, lepton-nucleon scattering, and proton-proton
collisions.Comment: 12 pages, 11 figure
Evidence for polarization of gluons in the proton
We discuss the impact of recent high-statistics RHIC data on the
determination of the gluon polarization in the proton in the context of a
global QCD analysis of polarized parton distributions. We find clear evidence
for a non-vanishing polarization of gluons in the region of momentum fraction
and at the scales mostly probed by the data. Although information from low
momentum fractions is presently lacking, this finding is suggestive of a
significant contribution of gluon spin to the proton spin, thereby limiting the
amount of orbital angular momentum required to balance the proton spin budget.Comment: 5 pages, 5 eps figure
Proton helicity structure function g_1^p from a holographic Pomeron
We present a detailed analysis of the polarized and the unpolarized deep
inelastic scattering structure functions of the proton, g_1^p and F_2^p
respectively, in the context of a holographic dual description based on type
IIB superstring theory. We compare this description with experimental data and
Quantum Chromodynamics estimates computed at leading, next-to-leading and
next-to-next-to-leading order in perturbation. We confront the predictions of a
holographic dual model and those of perturbative QCD for g_1^p at the
kinematics that will be probed by the forthcoming Electron-Ion Collider. We
find that the extrapolation of g_1^p to very small values the Bjorken variable
computed with a Holographic Pomeron model based on actual data at higher
momentum fractions is always positive and differs significantly with standard
projections based on perturbative QCD.Comment: 34 pages, 3 figure
Helicity Parton Distributions at a Future Electron-Ion Collider: A Quantitative Appraisal
We present a quantitative assessment of the impact a future electron-ion
collider will have on determinations of helicity quark and gluon densities and
their contributions to the proton spin. Our results are obtained by performing
a series of global QCD analyses at next-to-leading order accuracy based on
realistic sets of pseudo-data for the inclusive and semi-inclusive
deep-inelastic scattering of longitudinally polarized electrons and protons at
different, conceivable center-of-mass system energies.Comment: 11 pages, 8 figure
Uncertainties in pion and kaon fragmentation functions
We present a detailed assessment of uncertainties in parton-to-pion and parton-to-kaon fragmentation functions obtained in recent global QCD analyses of single-inclusive hadron production data at next-to-leading order accuracy. We use the robust Lagrange multiplier approach for determining uncertainties to validate the applicability of the simpler but approximate Hessian method. Extensive comparisons of the results obtained within both methods are presented for the individual parton-to-pion and kaon fragmentation functions. We provide Hessian eigenvector sets of pion and kaon fragmentation functions that allow one to easily propagate their uncertainties to any observable. Various applications of these sets are presented for pion and kaon production in electron-positron annihilation, lepton-nucleon scattering, and proton-proton collisions.Instituto de Física La Plat
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