Studies of charmed baryons at LHCb

We report a search for the doubly charmed baryon $\Xi_{cc}^{+}$ through the decay $\Xi_{cc}^{+} \to \Lambda_{c}^{+} K^{-} \pi^{+}$, using a data sample corresponding to an integrated luminosity of $0.65~\mathrm{pb^{-1}}$ of $pp$ collisions at $\mathrm{\sqrt{s}} = 7~\mathrm{TeV}$. In the mass range 3300-3800$~\mathrm{MeV}/c^{2}$ no significant signal is observed. Upper limits at $95\%$ confidence level are set on $R$, the ratio of the production cross section of the $\Xi_{cc}^{+}$ times the relevant branching fraction over the $\Lambda_{c}^{+}$ cross section, as a function of the $\Xi_{cc}^{+}$ mass and lifetime. The largest upper limits on $R$ over the investigated mass range are $R<1.5\times10^{-2}$ for a lifetime of $100~\mathrm{fs}$ and $R<3.9\times10^{-4}$ for a lifetime of $400~\mathrm{fs}$.Comment: Article to appear in the proceedings of The 6th International Workshop on Charm Physics (CHARM 2013

Charmed baryons from LHCb

The vast amount of $c\overline{c}$ production that can be recorded by the LHCb detector makes it an ideal environment to study the hadronic production of charmed baryons, along with the properties of their decays. We briefly describe the LHCb experiment and the triggering mechanisms it uses for recording charm production. Previous charmed baryon results from LHCb are detailed, with a description of the future plans for the charmed baryon programme.Comment: 12 pages, 6 figures. To be published in the proceedings of CHARM-2015, Detroit, MI, 18-22 May 201

Array optimisation for multichannel electrical resistivity tomography instruments

In recent years there has been considerable research into the selection of near-optimal arrays of electrode configurations that enhance the resolution of electrical resistivity tomography (ERT) images. Several algorithms have been developed that select resistivity measurements based on their contribution to the cumulative sensitivity of the array (Furman et al., 2004; Hennig and Weller, 2005) or its model resolution matrix (Stummer et al. , 2004; Wilkinson et al., 2006a; 2006b). Homogeneous subsurface resistivity distributions were assumed for these studies, although better results can be obtained using the same algorithms if the resistivity distribution is known a priori (Anthansiou, 2006). When compared to standard arrays, such as dipole-dipole or Wenner- Schlumberger, optimised arrays can substantially improve the resolution of the ERT image for the same number of measurements (Wilkinson et al., 2006b). The driver for researching array optimisation techniques has been the development of computer controlled ERT systems that can address arbitrary combinations of current and potential electrodes. Unfortunately all the published optimisation algorithms share a problem that is likely to impede their wider use: the arrays that they produce are inherently ‘single channel’ (SC). Since they do not take advantage of the multichannel (MC) capability of modern ERT instruments, the optimised arrays that they produce are rather inefficient to use compared to many standard arrays that are well suited to MC operation. However, we have developed a simple extension that constrains our previous algorithm to choose near-optimal configurations that also fit well into a MC measurement scheme. This extension could easily be adapted to work with the other optimisation schemes cited above

Geophysical and geochemical investigations over the Long Rake, Haddon Fields, Derbyshire

Geophysical and geochemical investigations were undertaken over the Long Rake at Haddon Fields, Derbyshire in order to establish methods, or combinations of methods, showing the best response to the mineralisation. The mineralised structure carries high concentrations of fluorite with associated lead and zinc minerals and the gangue minerals baryte and calcite. The ground examined was relatively undisturbed with good geological control from drill hole data. Gravity and magnetic anomalies such as those obtained over the Long Rake could have limited applications for the indirect location of veins the approximate position of which is known. Induced polarisation, resistivity and electro-magnetic measurements failed to produce anomalies which could be directly attributed to the mineralisation or its host structure. However, reconnaissance mapping with very low frequency electro-magnetic (VLF-EM) and Radiohm methods showed that, over a large section of the survey area, the fluorspar vein could be mapped by its association with the subdrift shale/limestone contact. The determination of a wide range of elements in soils and tills showed that the more mobile elements such as F and Zn are particularly useful in detecting mineralisation over broad areas. Less mobile elements tend to exhibit localised disperson patterns which have applications in precisely locating an orebody. Elements enriched in soil above the Long Rake, in areas of thin overburden, include Pb, Ba, Sr, Ca, Zn, Rb and Th. Thickening cover towards the west tends to mask anomalies of many elements above the Rake, only Ba, Sr and Pb maintaining significant contrast. The collection of basal till samples was made difficult by the occurrence of large limestone boulders. However, results indicated that the method has no advantage over soil geochemistry in this environment, as geochemical contrast is not improved. Levels of Ba and Ca were highly variable and the concentration of Ba appeared to be directly related to the sampling depth

Can strikes really improve the condition of the masses?

The question—the very serious and practical question raised in Mr. Johnston's late interesting paper is this—Can the toiling masses really improve their condition by these incessant and unhappy Strikes, or are they only beating their hands against the iron bars of inexorable Economic Law? For instance, the question is not whether if all nominal incomes were raised real incomes would be raised too, and that if everybody had twice as many shillings, other things being unaltered, everybody would be twice as well off. Briefly summarised, the proposition placed before us in Mr. Johnston's paper is that strikes, if carried out on any extended scale, must fail, because a mere increase of nominal wages, unaccompanied by any increase in production, cannot really improve the condition of the masses. The aim of this paper is to show that it can. In all industries increased wages will signify increased price of goods. But these goods again are of two kinds, those which the masses consume, and those which they do not. The question before us is simply whether strikes when they are successful can really improve the labourer's position. I have tried to show that they can. It is for the present company to decide for themselves Whether I have succeeded

Monitoring hydraulic processes with automated time-lapse electrical resistivity tomography (ALERT)

Hydraulic processes in porous media can be monitored in a minimally invasive fashion by time-lapse electrical resistivity tomography (ERT). The permanent installation of specifically designed ERT instrumentation, telemetry and information technology (IT) infrastructure enables automation of data collection, transfer, processing, management and interpretation. Such an approach gives rise to a dramatic increase in temporal resolution, thus providing new insight into rapidly occurring subsurface processes. In this paper, we discuss a practical implementation of automated time-lapse ERT. We present the results of a recent study in which we used controlled hydraulic experiments in two test cells at reduced field scale to explore the limiting conditions for process monitoring with cross-borehole ERT measurements. The first experiment used three adjacent boreholes to monitor rapidly rising and falling water levels. For the second experiment we injected a saline tracer into a homogeneous flow field in freshwater-saturated sand; the dynamics of the plume were then monitored with 2D measurements across a 9-borehole fence and 3D measurements across a 3x3 grid of boreholes. We investigated different strategies for practical data acquisition and show that simple re-ordering of ERT measurement schemes can help harmonise data collection with the nature of the monitored process. The methodology of automated time-lapse ERT was found to perform well in different monitoring scenarios (2D/3D plus time) at time scales associated with realistic subsurface processes. The limiting factor is the finite amount of time needed for the acquisition of sufficiently comprehensive datasets. We found that, given the complexity of our monitoring scenarios, typical frame rates of at least 1.5–3 images per hour were possible without compromising image quality

Gravitational quantum states of neutrons in a rough waveguide

A theory of gravitational quantum states of ultracold neutrons in waveguides with absorbing/scattering walls is presented. The theory covers recent experiments in which the ultracold neutrons were beamed between a mirror and a rough scatterer/absorber. The analysis is based on a recently developed theory of quantum transport along random rough walls which is modified in order to include leaky (absorbing) interfaces and, more importantly, the low-amplitude high-aperture roughness. The calculations are focused on a regime when the direct transitions into the continuous spectrum above the absorption threshold dominate the depletion of neutrons from the gravitational states and are more efficient than the processes involving the intermediate states. The theoretical results for the neutron count are sensitive to the correlation radius (lateral size) of surface inhomogeneities and to the ratio of the particle energy to the absorption threshold in a weak roughness limit. The main impediment for observation of the higher gravitational states is the "overhang" of the particle wave functions which can be overcome only by use scatterers with strong roughness. In general, the strong roughness with high amplitude is preferable if one wants just to detect the individual gravitational states, while the strong roughness experiments with small amplitude and high aperture are preferable for the quantitative analysis of the data. We also discuss the ways to further improve the accuracy of calculations and to optimize the experimental regime.Comment: 48 pages, 14 figure

The detection and tracking of mine-water pollution from abandoned mines using electrical tomography

Increasing emphasis is being placed on the environmental and societal impact of mining, particularly in the EU, where the environmental impacts of abandoned mine sites (spoil heaps and tailings) are now subject to the legally binding Water Framework and Mine Waste Directives. Traditional sampling to monitor the impact of mining on surface waters and groundwater is laborious, expensive and often unrepresentative. In particular, sparse and infrequent borehole sampling may fail to capture the dynamic behaviour associated with important events such as flash flooding, mine-water break-out, and subsurface acid mine drainage. Current monitoring practice is therefore failing to provide the information needed to assess the socio-economic and environmental impact of mining on vulnerable eco-systems, or to give adequate early warning to allow preventative maintenance or containment. BGS has developed a tomographic imaging system known as ALERT ( Automated time-Lapse Electrical Resistivity Tomography) which allows the near real-time measurement of geoelectric properties "on demand", thereby giving early warning of potential threats to vulnerable water systems. Permanent in-situ geoelectric measurements are used to provide surrogate indicators of hydrochemical and hydrogeological properties. The ALERT survey concept uses electrode arrays, permanently buried in shallow trenches at the surface but these arrays could equally be deployed in mine entries or shafts or underground workings. This sensor network is then interrogated from the office by wireless telemetry (e.g: GSM, low-power radio, internet, and satellite) to provide volumetric images of the subsurface at regular intervals. Once installed, no manual intervention is required; data is transmitted automatically according to a pre-programmed schedule and for specific survey parameters, both of which may be varied remotely as conditions change (i.e: an adaptive sampling approach). The entire process from data capture to visualisation on the web-portal is seamless, with no manual intervention. Examples are given where ALERT has been installed and used to remotely monitor (i) seawater intrusion in a coastal aquifer (ii) domestic landfills and contaminated land and (iii) vulnerable earth embankments. The full potential of the ALERT concept for monitoring mine-waste has yet to be demonstrated. However we have used manual electrical tomography surveys to characterise mine-waste pollution at an abandoned metalliferous mine in the Central Wales orefield in the UK. Hydrogeochemical sampling confirms that electrical tomography can provide a reliable surrogate for the mapping and long-term monitoring of mine-water pollution

Estimation of gloss from rough surface parameters

Gloss is a quantity used in the optical industry to quantify and categorize materials according to how well they scatter light specularly. With the aid of phase perturbation theory, we derive an approximate expression for this quantity for a one-dimensional randomly rough surface. It is demonstrated that gloss depends in an exponential way on two dimensionless quantities that are associated with the surface randomness: the root-mean-square roughness times the perpendicular momentum transfer for the specular direction, and a correlation function dependent factor times a lateral momentum variable associated with the collection angle. Rigorous Monte Carlo simulations are used to access the quality of this approximation, and good agreement is observed over large regions of parameter space.Comment: 5 page