23,667 research outputs found
Gluon saturation and Feynman scaling in leading neutron production
In this paper we extend the color dipole formalism to the study of leading
neutron production in collisions at high energies
and estimate the related observables, which were measured at HERA and may be
analysed in future electron-proton () colliders. In particular, we
calculate the Feynman distribution of leading neutrons, which is
expressed in terms of the pion flux and the photon-pion total cross section. In
the color dipole formalism, the photon-pion cross section is described in terms
of the dipole-pion scattering amplitude, which contains information about the
QCD dynamics at high energies and gluon saturation effects. We consider
different models for the scattering amplitude, which have been used to describe
the inclusive and diffractive HERA data. Moreover, the model dependence of
our predictions with the description of the pion flux is analysed in detail. We
show that the recently released H1 leading neutron spectra can be reproduced
using the color dipole formalism and that these spectra could help us to
observe more clearly gluon saturation effects in future colliders.Comment: 10 pages, 5 figure
Tetraquark Production in Double Parton Scattering
We develop a model to study tetraquark production in hadronic collisions. We
focus on double parton scattering and formulate a version of the color
evaporation model for the production of the and of the
tetraquark, a state composed by the quarks. We find that
the production cross section grows rapidly with the collision energy
and make predictions for the forthcoming higher energy data of the LHC.Comment: 13 pages, 3 figures. Corrections in the text and reference
Double vector meson production in the International Linear Collider
In this paper we study double vector meson production in
interactions at high energies and, using the color dipole picture, estimate the
main observables which can be probed at the International Linear Collider
(ILC). The total
cross-sections for , , and are computed
and the energy and virtuality dependencies are studied in detail. Our results
demonstrate that the experimental analysis of this process is feasible at the
ILC and it can be useful to constrain the QCD dynamics at high energies.Comment: 11 pages, 8 figure
Gluon saturation and the Froissart bound: a simple approach
At very high energies we expect that the hadronic cross sections satisfy the
Froissart bound, which is a well-established property of the strong
interactions. In this energy regime we also expect the formation of the Color
Glass Condensate, characterized by gluon saturation and a typical momentum
scale: the saturation scale . In this paper we show that if a saturation
window exists between the nonperturbative and perturbative regimes of Quantum
Chromodynamics (QCD), the total cross sections satisfy the Froissart bound.
Furthermore, we show that our approach allows us to describe the high energy
experimental data on total cross sections.Comment: 6 pages, 5 figures. Includes additional figures, discussion and
reference
Processo agroindustrial: elaboração de chips de macaxeira.
bitstream/item/28108/1/com.tec.222.pdfDisponível também on-line
Fetuses with right aortic arch Multicentre cohort study and meta-analysis.
OBJECTIVES: Recent antenatal screening guidelines for cardiac abnormalities has increased fetal diagnosis of right aortic arch (RAA). We aimed to establish outcome of fetal RAA without intra-cardiac abnormalities (ICA) to guide postnatal management. METHODOLOGY: Retrospective cohort study. Outcome measures were rates of chromosomal abnormalities, 22q11.2 deletion, fetal extra-cardiac abnormalities (ECA), postnatal ICA and ECA, symptoms and surgery for vascular ring. A systematic review and meta-analysis (reference: CRD42015016097) was performed; results are reported as proportions. Kaplan Meier analysis of vascular ring cases with surgery as endpoint was performed. RESULTS: Our cohort included 86 cases; 41 had a vascular ring. Rates of chromosomal abnormalities, 22q11.2 deletion, and fetal ECA were 14.1%, 6.4% and 17.4% respectively. Sixteen studies including our cohort (312 fetuses) were included in the systematic review. Overall chromosomal abnormalities and 22q11.2 deletion rates were 9.0% (95% CI 6.0-12.5) and 6.1% (95% CI 3.6-9.3) whilst rates for cases with no ECA were 4.6% (95% CI 2.3-7.8) and 5.1% (95% CI 2.4-8.6). ECA were seen in 14.6% (95% CI 10.6-19.0) prenatally and 4.0% (95%CI 1.5-7.6) after birth. Postnatal ICA were identified in 5.0% (95% CI 2.7-7.9). Rate of symptoms (follow up ≥24 months) was 25.2% (95% CI 16.6-35.0) while 17.1% (95% CI 9.9-25.7) had surgery. Two-year freedom from surgery was 83.0% (95% CI 74.3-90.1) CONCLUSIONS: Fetal RAA without ICA is more frequently associated with ECA than chromosomal abnormalities. Most cases however, are isolated. Vascular ring symptoms occur in about 25% of cases. Postnatal surveillance is required mainly in the first 2 years of life
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