51 research outputs found
NLO Corrections to Deeply-Virtual Compton Scattering
We have calculated the NLO corrections to the twist-2 part of the
deeply-virtual Compton scattering amplitude. Our results for the transverse and
antisymmetric parts agree with recent calculations by Ji and Osborne and by
Belitsky and M\"uller. In addition we present NLO results for the longitudinal
part of the amplitude.Comment: 8 pages, Latex. Error in polarised gluonic coefficient in Eq.(8)
correcte
Color-Octet Contributions to Photoproduction
We have calculated the leading color-octet contributions to the production of
particles in photon-proton collisions. Using the values for the
color-octet matrix elements extracted from fits to prompt data at the
Tevatron, we demonstrate that distinctive color-octet signatures should be
visible in photoproduction. However, these predictions appear at
variance with recent experimental data obtained at HERA, indicating that the
phenomenological importance of the color-octet contributions is smaller than
expected from theoretical considerations and suggested by the Tevatron fits.Comment: 10 pages, LaTeX, epsfig, 4 figure
Color-Octet Production at Low
We study contributions from color-octet quarkonium formation mechanisms to
-integrated production cross sections in pion-nucleon
reactions. The observed polarization of the is not reproduced by the
lowest-order leading-twist color-singlet and color-octet mechanisms. This
suggests that there are important quarkonium production mechanisms beyond
leading twist.Comment: 9 page
Double-Spin Asymmetry of J/psi Production in Polarized pp Collisions at HERA-
We calculated the color-octet contribution to the double spin asymmetry of
hadroproduction with nonzero transverse momenta at fixed target
energies GeV. It is shown that the color-octet contribution
is dominant in the asymmetries. The expected asymmetries and statistical errors
in a future option of HERA with longitudinally polarized protons at HERA- should allow one to distinguish between different parametrizations for the
polarized gluon distribution in the proton.Comment: 14 pages with 6 figures (epsfig), LaTeX; Some figures are changed and
misprint is correcte
Hard Processes with Spin-Dependent Parton Distributions
To test a possible color-octet contribution of heavy quarkonium productions,
we propose '-productions for small- regions, where the color-singlet
' state cannot be produced by the gluon-gluon fusion owing to charge
conjugation. We also point out that these processes are very useful to deduce
informations of spin-dependent gluon distributions .Comment: 4 pages + 3 Postscript figures(2 PS files), LaTeX, Talk presented at
International Workshop HELION97, Kobe, Japan, 20-24 Jan. 199
Color-Octet Production at Low
We study contributions from color-octet quarkonium formation mechanisms to
hadroproduction at low . We include transitions of
color-octet states into ``direct'' and into
which decay radiatively into a . Together with earlier work, this
calculation constitutes a complete analysis of -integrated
production at leading twist. We find that the leading-twist contribution is not
sufficient to reproduce the observed production rates and polarization of the
and . Hence there must exist other important quarkonium
production mechanisms at low .Comment: REVTEX, 18 pages, 4 figures include
The Pro12Ala polymorphism of the PPAR gamma 2 gene is associated with hepatic glucose uptake during hyperinsulinemia in subjects with type 2 diabetes mellitus
The Relationship between Regular Sports Participation and Vigilance in Male and Female Adolescents
The present study investigated the relationship between regular sport participation (soccer) and vigilance performance. Two groups of male and female adolescents differentiated in terms of their sport participation (athletes, n = 39, and non-athletes, n = 36) took part in the study. In one session, participants performed the Leger Multi-stage fitness test to estimate their aerobic fitness level. In the other session, participants completed the Psychomotor Vigilance Task (PVT) to evaluate their vigilance performance. Perceived arousal prior to the task and motivation toward the task were also measured in the PVT session. The results revealed that athletes had better cardiovascular fitness and showed better performance in the PVT. However, correlation analyses did not show any significant relationship between cardiovascular fitness and performance in the PVT. Athletes showed larger scores in motivation and perceived arousal measures with respect to non-athletes, although, once again, these variables were not correlated with PVT performance. Gender differences were observed only in the Leger test, with males showing greater fitness level than females. The major outcome of this research points to a positive relationship between regular sport participation and vigilance during adolescence. This relationship did not seem to be influenced by gender, perceived arousal, motivation toward the task or cardiovascular fitness. We discuss our results in terms of the different hypotheses put forward in the literature to explain the relationship between physical activity and cognitive functioning.This research was supported by a Spanish
Ministerio de EducaciĂłn y Cultura (https://sede. educacion.gob.es) predoctoral grant (FPU13-05605) to the first author, and project research grants: Junta de Andalucia Proyecto de Excelencia SEJ-6414
(http://www.juntadeandalucia.es) and Ministerio de EconomĂa y Competitividad PSI2013-46385 (http://www.mineco.gob.es) to DS and FH
Hadroproduction and Polarization of Charmonium
In the limit of heavy quark mass, the production cross section and
polarization of quarkonia can be calculated in perturbative QCD. We study the
-averaged production of charmonium states in collisions at
fixed target energies. The data on the relative production rates of \jp and
is found to disagree with leading twist QCD. The polarization of the
\jp indicates that the discrepancy is not due to poorly known parton
distributions nor to the size of higher order effects (-factors). Rather,
the disagreement suggests important higher twist corrections, as has been
surmised earlier from the nuclear target -dependence of the production cross
section.Comment: 19 page
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