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 $\alpha_s$ QCD amplitude for exclusive neutrino and antineutrino production of a $D$ 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 $O(m_c)$ terms in the coefficient functions and $O(M_D)$ 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 $\alpha_s$ 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 $\pi$ and $\rho_L$ 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