404 research outputs found
A fresh look at factorization breaking in diffractive photoproduction of dijets at HERA at next-to-leading order QCD
We calculate the cross section of diffractive dijet photoproduction in
scattering at next-to-leading order (NLO) of perturbative QCD (pQCD), which we
supplement by a model of factorization breaking for the resolved-photon
contribution. In this model, the suppression depends on the flavor and momentum
fraction of the partons in the photon. We show that within experimental and
theoretical uncertainties, the resulting approach provides a good description
of the available HERA data in most of the bins. Hence, taken together with the
observation that NLO pQCD explains well the data on diffractive photoproduction
of open charm in scattering, our model of factorization breaking presents
a viable alternative to the scheme based on the global suppression factor.Comment: 9 pages, 4 figures. Final published versio
Rapidity and momentum transfer distributions of coherent photoproduction in ultraperipheral pPb collisions at the LHC
Based on accurate calculations of the flux of equivalent photons of the
proton and heavy nuclei and the pQCD framework for the gluon distribution in
the proton and nuclei, we analyze the rapidity and momentum transfer
distributions of coherent photoproduction in ultraperipheral proton-Pb
collisions at the LHC. We demonstrate that unlike the case of proton-proton
UPCs marred by certain theoretical uncertainties and experimental limitations,
after a cut excluding the region of small momentum transfers, ultraperipheral
proton-Pb collisions offer a clean way to study the gluon distribution in the
proton down to . Our analysis of the momentum transfer
distributions shows that an interplay of production by low-energy
photons on the nucleus and by high-energy photons on the proton in proton-Pb
UPCs can result in some excess of events at small in a definite region of
the rapidity y.Comment: 18 pages, 8 figures. The final published versio
Mixing and decays of the antidecuplet in the context of approximate SU(3) symmetry
We consider mixing of the antidecuplet with three J^P=1/2^+ octets (the
ground-state octet, the octet containing N(1440), \Lambda(1600), \Sigma(1660)
and \Xi(1690) and the octet containing N(1710), \Lambda(1800), \Sigma(1880) and
\Xi(1950)) in the framework of approximate flavor SU(3) symmetry. We give
general expressions for the partial decay widths of all members of the
antidecuplet as functions of the two mixing angles. Identifying N_{anti-10}
with the N(1670) observed by the GRAAL experiment, we show that the considered
mixing scenario can accommodate all present experimental and phenomenological
information on the \Theta^+ and N_{anti-10} decays: \Theta^+ could be as narrow
as 1 MeV; the N_{anti-10} -> N + \eta decay is sizable, while the N_{anti-10}
->N + \pi decay is suppressed and the N_{anti-10} ->\Lambda + K decay is
possibly suppressed. Constraining the mixing angles by the N_{anti-10} decays,
we make definite predictions for the \Sigma_{anti-10} decays. We point out that
\Sigma_{anti-10} with mass near 1770 MeV could be searched for in the available
data on K_S p invariant mass spectrum, which already revealed the \Theta^+
peak. It is important to experimentally verify the decay properties of
\Sigma(1770) because its mass and J^P=1/2^+ make it an attractive candidate for
\Sigma_{anti-10}.Comment: 57 pages, 31 figures, 4 table
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