Search for Extra Space-Dimensions at the LHC

The introduction of extra space dimensions in the theory could be an elegant way tovsolve the hierarchy problem. There could even be one energy scale at which all interactions could unify. The limits coming from our knowledge of the gravitation at low distance allow this energy scale to be as low as few TeV. This situation is extremely interesting experimentally in the context of the LHC which will cover the range from 100 GeV to few TeV. This article describes the different analyses developed by the LHC experiments to study this new phenomenology.Comment: 7 pages, 6 figure

Ion-lithium collision dynamics studied with an in-ring MOTReMi

We present a novel experimental tool allowing for kinematically complete studies of break-up processes of laser-cooled atoms. This apparatus, the 'MOTReMi', is a combination of a magneto-optical trap (MOT) and a Reaction Microscope (ReMi). Operated in an ion-storage ring, the new setup enables to study the dynamics in swift ion-atom collisions on an unprecedented level of precision and detail. In first experiments on collisions with 1.5 MeV/amu O$^{8+}$-Li the pure ionization of the valence electron as well as ionization-excitation of the lithium target has been investigated

Phonon splitting and anomalous enhancement of infrared-active modes in BaFe2_2As2_2

We present a comprehensive infrared spectroscopic study of lattice dynamics in the pnictide parent compound BaFe$_2$As$_2$. In the tetragonal structural phase, we observe the two degenerate symmetry-allowed in-plane infrared active phonon modes. Following the structural transition from the tetragonal to orthorhombic phase, we observe splitting into four non-degenerate phonon modes and a significant phonon strength enhancement. These detailed data allow us to provide a physical explanation for the anomalous phonon strength enhancement as the result of anisotropic conductivity due to Hund's coupling.Comment: 5 pages, 3 figures, 1 tabl

Influence of normal and radial contributions of local current density on local electrochemical impedance spectroscopy.

A new tri-electrode probe is presented and applied to local electrochemical impedance spectroscopy (LEIS) measurements. As opposed to two-probe systems, the three-probe one allows measurement not only of normal, but also of radial contributions of local current densities to the local impedance values. The results concerning the cases of the blocking electrode and the electrode with faradaic reaction are discussed from the theoretical point of view for a disk electrode. Numerical simulations and experimental results are compared for the case of the ferri/ferrocyanide electrode reaction at the Pt working electrode disk. At the centre of the disk, the impedance taking into account both normal and radial contributions was in good agreement with the local impedance measured in terms of only the normal contribution. At the periphery of the electrode, the impedance taking into account both normal and radial contributions differed significantly from the local impedance measured in terms of only the normal contribution. The radial impedance results at the periphery of the electrode are in good agreement with the usual explanation that the associated larger current density is attributed to the geometry of the electrode, which exhibits a greater accessibility at the electrode edge

Polarization and Interference Effects in Ionization of Li by Ion Impact

We present initial-state selective fully differential cross sections for ionization of lithium by 24 MeV O8+ impact. The data for ionization from the 2s and 2p states look qualitatively different from each other and from 1s ionization of He. For ionization from the 2p state, to which in our study the mL=-1 substate predominantly contributes, we observe orientational dichroism and for 2s ionization pronounced interference which we trace back to the nodal structure of the initial-state wave function

Two-Stage Rotational Disordering of a Molecular Crystal Surface: C60

We propose a two-stage mechanism for the rotational surface disordering phase transition of a molecular crystal, as realized in C$_{60}$ fullerite. Our study, based on Monte Carlo simulations, uncovers the existence of a new intermediate regime, between a low temperature ordered $(2 \times 2)$ state, and a high temperature $(1 \times 1)$ disordered phase. In the intermediate regime there is partial disorder, strongest for a subset of particularly frustrated surface molecules. These concepts and calculations provide a coherent understanding of experimental observations, with possible extension to other molecular crystal surfaces.Comment: 4 pages, 2 figure

Matter-gravity interaction in a multiply warped braneworld,

The role of a bulk graviton in predicting the signature of extra dimensions through collider-based experiments is explored in the context of a multiply warped spacetime. In particular it is shown that in a doubly warped braneworld model, the presence of the sixth dimension, results in enhanced concentration of graviton Kaluza Klein (KK) modes compared to that obtained in the usual 5-dimensional Randall-Sundrum model. Also, the couplings of these massive graviton KK modes with the matter fields on the visible brane turn out to be appreciably larger than that in the corresponding 5- dimensional model. The significance of these results are discussed in the context of KK graviton search at the Large Hadron Collider (LHC).Comment: 13 pages, 2 table

Postcollision Effects in Target Ionization by Ion Impact at Large Momentum Transfer

We have measured and calculated fully differential cross sections for target ionization in 16-MeV O7++He and 24-MeV O8++Li collisions. As in previous studies, in the case of the He target we observe a pronounced forward shift in the angular distribution of the electrons relative to the direction of the momentum transfer q at small q (q \u3c 1 a.u.). An unexpected result is that we also find a strong forward shift at large q (q \u3e 2 a.u.), while at intermediate q this shift becomes very weak or even turns into a backward shift. For the Li target, in contrast, the forward shift monotonically increases with increasing q. These observations are qualitatively reproduced by our calculations. The comparison to theory suggests that at large q the forward shift is due to the postcollision interaction between the outgoing projectile and the ejected electron, but at small q it is mostly due to an interplay between the projectile-target core interaction and the electron-target core interaction

High energy pseudogap and its evolution with doping in Fe-based superconductors as revealed by optical spectroscopy

We report optical spectroscopic measurements on electron- and hole-doped BaFe2As2. We show that the compounds in the normal state are not simple metals. The optical conductivity spectra contain, in addition to the free carrier response at low frequency, a temperature-dependent gap-like suppression at rather high energy scale near 0.6 eV. This suppression evolves with the As-Fe-As bond angle induced by electron- or hole-doping. Furthermore, the feature becomes much weaker in the Fe-chalcogenide compounds. We elaborate that the feature is caused by the strong Hund's rule coupling effect between the itinerant electrons and localized electron moment arising from the multiple Fe 3d orbitals. Our experiments demonstrate the coexistence of itinerant and localized electrons in iron-based compounds, which would then lead to a more comprehensive picture about the metallic magnetism in the materials.Comment: 6 pages, 7 figure