62,013 research outputs found
Lepton-pair production in ultraperipheral collisions at AFTER@LHC
We investigate the potentialities offered by the study of lepton-pair
production in ultraperipheral collisions at a fixed-target experiment using the
proton and ion LHC beams. In these collisions, exclusive or semi-exclusive
lepton-pair production can be used as luminosity monitor as well as a check of
the equivalent-photon approximation, via the measurement of the Bethe-Heitler
cross section. It can also serve as a probe of the inner hadron structure via
the measurement of the lepton-pair azimuthal asymmetry which is sensitive to
the timelike virtual Compton scattering. We also briefly discuss the
possibility offered by the study of eta(c) production. Finally, we outline the
possibilities for lepton-pair production by Pomeron-Odderon fusion in exclusive
pp and pA collisions.Comment: 21 pages, 19 figures, uses jheppub.sty (included
Transition metal oxides using quantum Monte Carlo
The transition metal-oxygen bond appears prominently throughout chemistry and
solid-state physics. Many materials, from biomolecules to ferroelectrics to the
components of supernova remnants contain this bond in some form. Many of these
materials' properties strongly depend on fine details of the TM-O bond and
intricate correlation effects, which make accurate calculations of their
properties very challenging. We present quantum Monte Carlo, an explicitly
correlated class of methods, to improve the accuracy of electronic structure
calculations over more traditional methods like density functional theory. We
find that unlike s-p type bonding, the amount of hybridization of the d-p bond
in TM-O materials is strongly dependant on electronic correlation.Comment: 20 pages, 4 figures, to appear as a topical review in J. Physics:
Condensed Matte
Exclusive neutrino-production of a charmed meson
We calculate the leading order in QCD amplitude for exclusive
neutrino and antineutrino production of a pseudoscalar charmed meson on an
unpolarized nucleon. We work in the framework of the collinear QCD approach
where generalized parton distributions (GPDs) factorize from perturbatively
calculable coefficient functions. We include both terms in the
coefficient functions and mass term contributions in the heavy meson
distribution amplitudes. We emphasize the sensitivity of specific observables
on the transversity quark GPDs.Comment: 17 pages,16 figures. Version 2, to be published in Phys Rev D,
misprint corrected in unnumbered equation after eq.43, plots corrected after
numerical bug repaire
Hard exclusive neutrino production of a light meson
We update the leading order in QCD amplitude for deep exclusive
neutrino and antineutrino production of a light meson on an unpolarized
nucleon. The factorization theorems of the collinear QCD approach allow us to
write the amplitude as the convolution of generalized parton distributions
(GPDs) and perturbatively calculable coefficient functions. We study both the
pseudoscalar meson and longitudinally polarized vector meson cases. It turns
out that, contrarily to the electroproduction case, the leading twist
scattering amplitudes for and productions are proportional to
one another, which may serve as an interesting new test of the leading twist
dominance of exclusive processes at medium scale. The dominance of the gluonic
contribution to most cross sections is stressed.Comment: 9 pages, 8 figures. second version (to be published in Phys Rev D):
misprint in name of second author corrected; one added reference; minor
misprints corrected. arXiv admin note: text overlap with arXiv:1702.0031
On timelike and spacelike hard exclusive reactions
We show to next-to-leading order accuracy in the strong coupling alpha_s how
the collinear factorization properties of QCD in the generalized Bjorken regime
relate exclusive amplitudes for spacelike and timelike hadronic processes. This
yields simple space--to--timelike relations linking the amplitudes for
electroproduction of a photon or meson to those for photo- or meso-production
of a lepton pair. These relations constitute a new test of the relevance of
leading twist analyzes of experimental data.Comment: v2: major text revision; results, references, and author added; v3:
matches the published version Phys. Rev. D86, rapid communication
Probing GPDs in photoproduction processes at hadron colliders
Generalized parton distributions (GPDs) enter QCD factorization theorems for
hard exclusive reactions. They encode rich information about hadron partonic
structure. We explore a possibility to constrain GPDs in experiments at LHC
considering two different exclusive processes: the timelike Compton scattering
and the photoproduction of heavy vector mesons.Comment: 6 pages, 2 figures; presented at PHOTON 2015: International
Conference on the Structure and the Interactions of the Photon, Novosibirsk,
Russia, 15 - 19 June, 2015. arXiv admin note: text overlap with
arXiv:1411.375
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