Diffractive photoproduction of heavy quarks in hadronic collisions

In this letter we study the diffractive photoproduction of heavy quarks in hadronic (pp/pA/AA) interactions for Tevatron and LHC energies. The integrated cross section and rapidity distribution for the process h_1 h_2 --> h_1 h_2 QQBAR (h_i = p,A and Q = c,b) are estimated using the Color Glass Condensate (CGC) formalism. Our results indicate that this production channel has larger cross sections than the competing reactions of double diffractive production and coherent AA reactions initiated by two-photon collisions.Comment: 4 pages, 2 figures, 1 table. Version to be published in Physical Review

Longitudinal profiles of Extensive Air Showers with inclusion of charm and bottom particles

Charm and bottom particles are rare in Extensive Air Showers but the effect of its presence can be radical in the development of the Extensive Air Showers (EAS). If such particles arise with a large fraction of the primary energy, they can reach large atmospheric depths, depositing its energy in deeper layers of the atmosphere. As a consequence, the EAS observables ($X_{max}$, $RMS$ and $N_{max}$) will be modified, as well as the shape of the longitudinal profile of the energy deposited in the atmosphere. In this paper, we will modify the CORSIKA Monte Carlo by the inclusion of charm and bottom production in the first interaction of the primary cosmic ray. Results for different selections of the typical $x_F$ values of the heavy particles and distinct production models will be presented.Comment: Replacement of tex file by the correct versio

The AGL Equation from the Dipole Picture

The AGL equation includes all multiple pomeron exchanges in the double logarithmic approximation (DLA) limit, leading to an unitarized gluon distribution in the small x regime. This equation was originally obtained using the Glauber-Mueller approach. We demonstrate in this paper that the AGL equation and, consequently, the GLR equation, can also be obtained from the dipole picture in the double logarithmic limit, using an evolution equation, recently proposed, which includes all multiple pomeron exchanges in the leading logarithmic approximation. Our conclusion is that the AGL equation is a good candidate for an unitarized evolution equation at small x in the DLA limit.Comment: 16 pages, 2 figures. Accepted for publication in Nuc. Phys.

New geochemical and isotopic constraints on the genesis of the Oliveira Azeméis granitoid melts (Porto-Tomar Shear Zone, Iberian Variscan Chain, Central-Western Portugal).

The Porto-Tomar Shear Zone (PTSZ) is a very important tectonic structure that separates, in central-western Portugal, two of the major tectonic units of the Iberian Variscan Chain: the Ossa-Morena Zone, to the west, and the Central Iberian Zone, to the east. The Oliveira de Azeméis area lies in the northern sector of the PTZC and it is characterized by the occurrence of strongly deformed granitoids. Country rocks are dominantly pelitic metasediments which, according to recent geological mapping (Pereira et al., 2007), belong to the Precambrian Lourosa Formation and the Ordovician São João de Ver Formation. Using Rb-Sr whole-rock isotopic data, Pinto (1979) proposed an age of 379 12 Ma for the Oliveira de Azeméis granitoids. In this work, new results were obtained on these granitoids in the area between the villages of Travanca and Curval, especially in the Sacramento quarry. In this critical outcrop, strongly deformed two-mica granite (displaying S-C structures, with dextral NNW-SSE shear planes) pass into diatexites and metatexites with garnet, cordierite and sillimanite-bearing melanosomes. Leucosomes seem to have mainly granitic s.s. compositions, but cm-thick bands of leucotonalite were also found. Major element geochemistry of granite samples shows the following ranges: 71.4% SiO2 74.2%; 0.74% Fe2O3t 2.48%; 0.35% MgO 0.60%; 0.49% CaO 1.32%; 2.90% Na2O 3.11%; 4.70% K2O 5.47%; 1.17 ASI 1.36. Trace element data reveal a strong fractionation between highly incompatible LILE and less incompatible HFSE (248 PM normalized Rb/Y 671) and between LREE and HREE (18.6 PM normalized La/Lu 54.7). These features, in particular the peraluminous composition, the high K contents and the distinct rare-earth fractionation suggest that the Oliveira de Azeméis granites are mostly the result of partial melting of metasediments with a large pelitic component and that garnet is a likely residual phase. Isotope geochemistry data show that the previously reported isochron should not correspond to a true age since the 87Sr/86Sr(380Ma) obtained in the granite samples analysed in the present work are very low, varying from 0.6978 to 0.7063, with an average value of 0.7023, which are unrealistic in S-type granitic melts. Probably, the 380 Ma date is the consequence of mixing of different melt source components in the samples used in its calculation. Using the granite whole-rock samples collected in this work, a 328 28 Ma errorchron (MSWD=4.0; initial 87Sr/86Sr=0,7106 0.0045) is now obtained. Assuming a typical syn-tectonic Variscan age of 320 Ma for the studied granites, 87Sr/86Sr and "Nd range from 0.7100 to 0.7133 and from -6.5 to -7.9, respectively. A micaschist sample collected in this area displays 87Sr/86Sr(320Ma) = 0.7146 and "Nd(320Ma) = -9.2. Therefore, the Sr and Nd isotope composition agrees with the clearly dominance of a melt component derived by anatexis of a metapelitic source. Two samples of a garnet-bearing (and comparatively zircon-rich) diatexite show 87Sr/86Sr(320Ma) values (0.7120 and 0.7102) similar to those found in granites, but have higher "Nd(320Ma): -2.0 and -1.6. This may be explained by either (a) the involvement of a different source in the genesis of this diatexite or (b) the occurrence of Nd isotope disequilibrium during the melting process, with the preservation of high 143Nd/144Nd ratios in refractory phases such as garnet and/or zircon. A Rb-Sr wr-feldspar-biotite-muscovite isochron of 301.2 5.6 Ma (MSWD=0.42; initial 87Sr/86Sr=0,71516 0.00074) in a granite sample is interpreted as recording the final stage of the operation of the shear zone, which was accompanied by mica recrystallization. Funding: projects Petrochron (PTDC/CTE-GIX/112561/2009) and Geobiotec (PEst-C/CTE/UI4035/2011). References Pereira E. et allia (2007) – Carta Geológica 1/50000 de Oliveira de Azeméis. INETI, Lisboa. Pinto M.S. (1979) – PhD Thesis. Univ. Leed

Gluon saturation and the Froissart bound: a simple approach

At very high energies we expect that the hadronic cross sections satisfy the Froissart bound, which is a well-established property of the strong interactions. In this energy regime we also expect the formation of the Color Glass Condensate, characterized by gluon saturation and a typical momentum scale: the saturation scale $Q_s$. In this paper we show that if a saturation window exists between the nonperturbative and perturbative regimes of Quantum Chromodynamics (QCD), the total cross sections satisfy the Froissart bound. Furthermore, we show that our approach allows us to describe the high energy experimental data on $pp/p\bar{p}$ total cross sections.Comment: 6 pages, 5 figures. Includes additional figures, discussion and reference

Plasmon-exciton polaritons in 2D semiconductor/metal interfaces

The realization and control of polaritons is of paramount importance in the prospect of novel photonic devices. Here, we investigate the emergence of plasmon-exciton polaritons in hybrid structures consisting of a two-dimensional (2D) transition metal dichalcogenide (TMDC) deposited onto a metal substrate or coating a metallic thin-film. We determine the polaritonic spectrum and show that, in the former case, the addition of a top dielectric layer, and, in the latter, the thickness of the metal film,can be used to tune and promote plasmon-exciton interactions well within the strong coupling regime. Our results demonstrate that Rabi splittings exceeding 100 meV can be readily achieved in planar dielectric/TMDC/metal structures under ambient conditions. We thus believe that this work provides a simple and intuitive picture to tailor strong coupling in plexcitonics, with potential applications for engineering compact photonic devices with tunable optical properties.Comment: 6 pages, including 5 figures and reference