2,208 research outputs found
Probing double parton scattering via associated open charm and bottom production in ultraperipheral collisions
In this article, we propose a novel channel for phenomenological studies of
the double-parton scattering (DPS) based upon associated production of charm
and bottom quark pairs in well-separated rapidity
intervals in ultra-peripheral high-energy proton-nucleus collisions. This
process provides a direct access to the double-gluon distribution in the proton
at small- and enables one to test the factorised DPS pocket formula. We have
made the corresponding theoretical predictions for the DPS contribution to this
process at typical LHC energies and beyond and we compute the
energy-independent (but photon momentum fraction dependent) effective cross
section.Comment: 15 pages, 7 figs., 1 table. One fig. added. Version accepted for
publication at EPJ
Exclusive heavy quark-pair production in ultraperipheral collisions
In this article, we study the fully differential observables of exclusive
production of heavy (charm and bottom) quark pairs in high-energy
ultraperipheral and collisions. In these processes, the nucleus
serves as an efficient source of the photon flux, while the QCD interaction of
the produced heavy-quark pair with the target ( or ) proceeds via an
exchange of gluons in a color singlet state, described by the gluon Wigner
distribution. The corresponding predictions for differential cross sections
were obtained by using the dipole -matrix in the McLerran--Venugopalan
saturation model with impact parameter dependence for the nucleus target, and
its recent generalization, for the proton target. Prospects of experimental
constraints on the gluon Wigner distribution in this class of reactions are
discussed.Comment: 21 pages, 18 figures, improved conclusio
Exclusive photoproduction of excited quarkonia in ultraperipheral collisions
In this paper, we discuss the exclusive photoproduction of ground and excited
states of and in ultraperipheral collisions
(UPCs). Using the potential model in order to obtain the vector meson wave
function, we find a good agreement of our calculations with data from the LHC
and HERA colliders for and in
collisions. We extend the calculations to the nuclear target case applying them
to UPCs with the use of the shadowing and finite coherence length effects
fitted to the data. Our results are compared to the recent LHC data, in both
incoherent ( at 2.76 TeV) and coherent ( at 2.76 and
5.02 TeV) processes. We also show the corresponding predictions for the excited
states, in the hope that future measurements could provide more detailed
information about the vector meson wave functions and nuclear effects.Comment: 21 pages, 7 figs, revised versio
Exclusive photo- and electroproduction of excited light vector mesons via holographic model
In this paper, we study total and differential observables of electro- and
photoproduction of light , and mesons as functions of the
center-of-mass energy of the collision and momentum transfer squared
. The corresponding vector mesons wave functions have been computed in the
framework of relativistic AdS/QCD holographic approach. A satisfactory
description of all available data on ground-state , and
mesons production cross sections has been achieved in the color
dipole picture. Finally, the key observables of excited ,
and states production in collisions
have been presented here using a common wave function formalism. This study
reveals a large theoretical uncertainty coming from the modeling of the partial
dipole amplitude in the nonperturbative kinematical domain. Hence, the latter
could benefit from future measurements of photoproduction of the excited
states
Luminosity indicators in dusty photoionized environments
The luminosity of the central source in ionizing radiation is an essential
parameter in a photoionized environment, and one of the most fundamental
physical quantities one can measure. We outline a method of determining
luminosity for any emission-line region using only infrared data. In dusty
environments, grains compete with hydrogen in absorbing continuum radiation.
Grains produce infrared emission, and hydrogen produces recombination lines. We
have computed a very large variety of photoionization models, using ranges of
abundances, grain mixtures, ionizing continua, densities, and ionization
parameters. The conditions were appropriate for such diverse objects as H II
regions, planetary nebulae, starburst galaxies, and the narrow and broad line
regions of active nuclei. The ratio of the total thermal grain emission
relative to H (IR/H) is the primary indicator of whether the
cloud behaves as a classical Str\"{o}mgren sphere (a hydrogen-bounded nebula)
or whether grains absorb most of the incident continuum (a dust-bounded
nebula). We find two global limits: when infrared recombination
lines determine the source luminosity in ionizing photons; when
the grains act as a bolometer to measure the luminosity.Comment: 12 pages 3 figures. Accepted ASP Sept.9
White light and multicolor emission tuning in triply doped Yb3+/Tm3+/Er3+ novel fluoro-phosphate transparent glass-ceramics
New Yb3+, Er3+ and Tm3+ doped fluoro-phosphate glasses belonging to the system NaPO3-YF3-BaF2-CaF2 and containing up to 10 wt% of rare-earth ion fluorides were prepared and characterized by differential scanning calorimetry, absorption spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and homogeneous glass-ceramics have been reproducibly obtained with a view to manage the red, green and blue emission bands and generate white light. X-ray diffraction as well as electron microscopy techniques have confirmed the formation of fluorite-type cubic nanocrystals at the beginning of the crystallization process while complex nanocrystalline phases are formed after a longer heat-treatment. The prepared glass-ceramics exhibit high optical transparency even after 170 h of thermal treatment. An improvement of up-conversion emission intensity - from 10 to 160 times larger - was measured in the glass-ceramics when compared to the parent glass, suggesting an important incorporation of the rare-earth ions into the crystalline phase(s). The involved mechanisms and lifetime were described in detail as a function of heat-treatment time. Finally, a large range of designable color rendering (from orange to turquoise through white) can be observed in these materials by controlling the laser excitation power and the crystallization rate.Canadian Excellence Research Chair program (CERC) on Enabling Photonic Innovations for Information and CommunicationFAPESPCNPqINCT - INOF/CePOFANR (CrystOG ANR-12-JS08-0002-01
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