Search for high-mass resonances decaying to dilepton final states in pp collisions at s√=7 TeV with the ATLAS detector

The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to an electron-positron pair or a muon-antimuon pair. The search is sensitive to heavy neutral Z′ gauge bosons, Randall-Sundrum gravitons, Z * bosons, techni-mesons, Kaluza-Klein Z/γ bosons, and bosons predicted by Torsion models. Results are presented based on an analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.9 fb−1 in the e + e − channel and 5.0 fb−1 in the μ + μ −channel. A Z ′ boson with Standard Model-like couplings is excluded at 95 % confidence level for masses below 2.22 TeV. A Randall-Sundrum graviton with coupling k/MPl=0.1 is excluded at 95 % confidence level for masses below 2.16 TeV. Limits on the other models are also presented, including Technicolor and Minimal Z′ Models

Raman and XANES spectroscopy of permanently densified vitreous silica

Vitreous SiO2 was permanently densified at pressures ranging up to 8 GPa at 700 °C, where its density reached a value of 2.58 g/cm3. The series of glasses formed were analyzed by Raman spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy at both the oxygen and silicon K-edges. Changes in the Raman spectra are most evident in the Si–O–Si bending and rocking region near 500 cm-1, as the broad band becomes narrower and shifts to higher frequency, indicating a narrower distribution of Si–O–Si bond angles in the compacted glasses. A pronounced shift to lower frequency of the weak high-frequency bands associated with Si–O stretching motions is also observed, indicating a lengthening of Si–O bonds with increasing densification. More subtle changes are observed in both the Si and O K-edge spectra, with the O K-edge appearing more sensitive to short-range structural modifications such as narrowing of the intertetrahedral angle. In contrast to the structure of permanently densified v-SiO2 formed at room temperature, in which medium-range order is mostly affected, densification at higher temperatures is accomplished at shorter range, although at the pressures of this study, the glass remains principally a fully polymerized tetrahedral framework glass

The combined effects of water and fluorine on the viscosity of silicic magmas

The Newtonian viscosity of water-plus-fluorine-bearing silicate melt of haplogranitic composition (HPG8) has been determined. Viscosities of HPG8 melt with addition of 3.11 and 4.25 wt.% of F and up to 3 wt.% H2O have been obtained using a micropenetration technique in the interval 109.74 to 1011.84 Pa s and temperatures varying from 370 to 700°C, at ambient pressure. Determination of the temperature dependence of viscosity from this and previous studies permits the parameterization of the viscosity of melts containing water and fluorine, having similar composition, within a 0.3 log units standard error. The viscosity of water-bearing, F-rich haplogranitic samples is represented by a modified Vogel-Fulcher-Tammann (VFT) equation which provides a non-Arrhenian description of the temperature dependence of the viscosity. The results of this study indicate that, taken individually or together, both H2O and F- have a strong and similar effect on the viscosity of SiO2-rich compositions. This similarity between F2O-1 and H2O greatly simplifies the task of predicting viscosity for volatile-rich, highly silicic magmas. The low viscosities of hydrous fluorine-bearing granitic melts favour efficient crystallization-fractionaction paths for these liquids, controlling degassing paths and consequently the eruptive behaviour. Numerical simulations of eruptive events normally do not take into account the contribution of fluorine; this may introduce a significant error in the description of the fluid-dynamic properties of magma and, therefore, in the accurate prediction of eruptive scenarios, as well as in hazard assessment studies. Fluorine, unlike water, remains dissolved in the melt at high concentrations and low confining pressures. The incorporation of fluorine data and the modelling of fluorine-bearing viscosity data are therefore of fundamental importance for simulations of magma dynamics and prediction of eruptive scenarios

Electrical conductivity of a phonotephrite from Mt Vesuvius: The importance of chemical composition on the electrical conductivity of silicate melts

The bulk electrical conductivity of the phonotephritic lava from the 1944 eruption of Mt Vesuvius was measured using complex impedance spectroscopy in a multianvil apparatus at 1 GPa and temperatures up to 700 °C. Melting experiments prior to the electrical measurements were also performed on this sample in a piston cylinder apparatus in order to gauge how bulk conductivity varies as a function of its melt fraction. Unlike the behaviour found in basaltic rocks in which conductivity increases with increasing melt fraction, we observe a conductivity decrease of the order of a factor of ten for samples at 700 °C ranging in melt fraction from 32 vol.% to completely molten.We attribute this anomalous behaviour to the progressive loss of highly conductive leucite upon melting. The addition of potassium to the melt phase, however, does not result in an increase of the total alkali concentration due to the melting of other mineral components. We also present an empirical model to predict the electrical conductivity of fully molten silicate liquids as a function of temperature and chemical composition, based on conductivity data for natural silicate liquids found in the literature. The inclusion of compositional terms reduces the error by more than a factor of four with respect to a composition independent, temperature-only parameterization

The rheology of peralkaline rhyolites from Pantelleria Island

The viscosity of pantelleritic melts from the Khaggiar lava flow (5.5 ka — Pantelleria Island) was investigated as a function of temperature and water content. High (1673–1323 K) and low (973–613 K) temperature dry and hydrous liquid viscosities were determined by a combination of concentric cylinder (102.44 to 104.56 Pa s) and micropenetration (108.67 to 1011.37) viscometric techniques. The effect of water, from 0.02 to 3.55 wt.% H2O, was explored in the temperature range of 973–613 K. Liquid viscosities have been parameterized by means of a modified Vogel–Fulcher–Tammann equation (VFT) which describes viscosities and derivative properties (glass transition temperature Tg, fragility m) of silicic liquids as a function of T–X (H2O). The results yield the expected strong decrease of viscosity with temperature and water content. Fragility, as a mea- sure of the deviation from Arrhenian behavior, increases with H2O content from m=23 to m=28. The peralkalinity (molar alkali excess over alumina), which characterizes the pantelleritic magmas, exerts a primary control over the rheological behavior of these melts. The excess of alkalies over alumina content is responsible for the peculiarly low viscosities of pantelleritic liquids compared to their metaluminous counterpart in the high temperature range, and leads to an even more dramatic decrease in the viscosities of these rhyolites in the low temperature range. Comparison with available models shows substantial differences between the measured and calculated vis- cosities. Based on our new viscosity results combined with existing literature data, we propose a new param- eterization based on a modified Vogel–Fulcher–Tammann equation, accounting for the effect of water and composition, which can be used to determine the viscosity of pantelleritic melts. The derived relationship reproduces the experimental data (58 in total) in the viscosity range from 102.44 to 1011.37 Pa s and in the temperature range from 613 to 1673 K within a root-mean-square-error (RMSE) of 0.12 log units. Application of this calculation model for high temperature low viscosity hydrous melt is limited by the lack of experimental data and needs verification by additional measurements. Volcanological implications for welding and rheomorphic processes as well as conduit dynamic modeling are also discussed in light of the results presented in this workThe viscosity of pantelleritic melts from the Khaggiar lava flow (5.5 ka — Pantelleria Island) was investigated as a function of temperature and water content. High (1673–1323 K) and low (973–613 K) temperature dry and hydrous liquid viscosities were determined by a combination of concentric cylinder (102.44 to 104.56 Pa s) and micropenetration (108.67 to 1011.37) viscometric techniques. The effect of water, from 0.02 to 3.55 wt.% H2O, was explored in the temperature range of 973–613 K. Liquid viscosities have been parameterized by means of a modified Vogel–Fulcher–Tammann equation (VFT) which describes viscosities and derivative properties (glass transition temperature Tg, fragility m) of silicic liquids as a function of T–X (H2O). The results yield the expected strong decrease of viscosity with temperature and water content. Fragility, as a measure of the deviation from Arrhenian behavior, increases with H2O content from m = 23 to m = 28. The peralkalinity (molar alkali excess over alumina), which characterizes the pantelleritic magmas, exerts a primary control over the rheological behavior of these melts. The excess of alkalies over alumina content is responsible for the peculiarly low viscosities of pantelleritic liquids compared to their metaluminous counterpart in the high temperature range, and leads to an even more dramatic decrease in the viscosities of these rhyolites in the low temperature range. Comparison with available models shows substantial differences between the measured and calculated viscosities. Based on our new viscosity results combined with existing literature data, we propose a new parameterization based on a modified Vogel–Fulcher–Tammann equation, accounting for the effect of water and composition, which can be used to determine the viscosity of pantelleritic melts. The derived relationship reproduces the experimental data (58 in total) in the viscosity range from 102.44 to 1011.37 Pa s and in the temperature range from 613 to 1673 K within a root-mean-square-error (RMSE) of 0.12 log units. Application of this calculation model for high temperature low viscosity hydrous melt is limited by the lack of experimental data and needs verification by additional measurements. Volcanological implications for welding and rheomorphic processes as well as conduit dynamic modeling are also discussed in light of the results presented in this work