Annihilation of low energy antiprotons in silicon

The goal of the AE$\mathrm{\bar{g}}$IS experiment at the Antiproton Decelerator (AD) at CERN, is to measure directly the Earth's gravitational acceleration on antimatter. To achieve this goal, the AE$\mathrm{\bar{g}}$IS collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a velocity of a few 100 m/s and measure the magnitude of the vertical deflection of the beam from a straight path. The final position of the falling antihydrogen will be detected by a position sensitive detector. This detector will consist of an active silicon part, where the annihilations take place, followed by an emulsion part. Together, they allow to achieve 1$$ precision on the measurement of $\bar{g}$ with about 600 reconstructed and time tagged annihilations. We present here, to the best of our knowledge, the first direct measurement of antiproton annihilation in a segmented silicon sensor, the first step towards designing a position sensitive silicon detector for the AE$\mathrm{\bar{g}}$IS experiment. We also present a first comparison with Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table

Prospects for measuring the gravitational free-fall of antihydrogen with emulsion detectors

The main goal of the AEgIS experiment at CERN is to test the weak equivalence principle for antimatter. AEgIS will measure the free-fall of an antihydrogen beam traversing a moir\'e deflectometer. The goal is to determine the gravitational acceleration g for antihydrogen with an initial relative accuracy of 1% by using an emulsion detector combined with a silicon micro-strip detector to measure the time of flight. Nuclear emulsions can measure the annihilation vertex of antihydrogen atoms with a precision of about 1 - 2 microns r.m.s. We present here results for emulsion detectors operated in vacuum using low energy antiprotons from the CERN antiproton decelerator. We compare with Monte Carlo simulations, and discuss the impact on the AEgIS project.Comment: 20 pages, 16 figures, 3 table

A Moiré Deflectometer for Antimatter

The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics - the moirè deflectometer - for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter

AEgIS Experiment: Measuring the Acceleration g of the Earth's Gravitational Field on Antihydrogen Beam

The AEgIS experiment [1] aims at directly measuring the gravitational acceleration g on a beam of cold antihydrogen (H) to a precision of 1%, performing the first test with antimatter of the (WEP) Weak Equivalence Principle. The experimental apparatus is sited at the Antiproton Decelerator (AD) at CERN, Geneva, Switzerland. After production by mixing of antiprotons with Rydberg state positronium atoms (Ps), the atoms will be driven to fly horizontally with a velocity of a few 100 ms−1 for a path length of about 1 meter. The small deflection, few tens of μm, will be measured using two material gratings (of period ∼ 80 μm) coupled to a position-sensitive detector working as a moiré deflectometer similarly to what has been done with matter atoms [2]. The shadow pattern produced by the beam will then be detected by reconstructing the annihilation points with a spatial resolution (∼ 2 μm) of each antiatom at the end of the flight path by the sensitive-position detector. During 2012 the experimental apparatus has been commissioned with antiprotons and positrons. Since the AD will not be running during 2013,during the refurbishment of the CERN accelerators, the experiment is currently working with positrons, electrons and protons, in order to prepare the way for the antihydrogen production in late 2014

A Review of the Occurrence of Bats (Chiroptera) on Islands in the North East Atlantic and on North Sea Installations

The bats recorded from Iceland, the Faroe Islands, the Shetland Islands, the Orkney Islands, and North Sea installations are reviewed to the end of 2012. In total 12 species have been positively identified, while a considerable proportion of all records are sightings of unidentified bats. Eight of the species are European in origin and four originate from the New World. The largest number of species (8) has been recorded in Iceland, but the greatest number of individuals (180) has been found in Orkney. The bat invasion on the Faroe Islands in 2010 is without precedence, when 70 observations of a minimum of 45 individuals were noted. Most bat observations in the study area occurred in the autumn, with fewer in the spring. Most observations were of single animals, but there were also sightings of up to 12 individuals. There has been a marked increase in bat records in the past three decades. We discuss whether this is a real increase, or due to improved communications, increased public awareness, increased shipping, changes in weather patterns and/or the effects of climate change. All factors appear to be involved.© Museum and Institute of Zoology PAS. The attached document is the author(’s’) final accepted/submitted version of the journal article. You are advised to consult the publisher’s version if you wish to cite from it

Measuring the gravitational free-fall of antihydrogen

Antihydrogen holds the promise to test, for the first time, the universality of free-fall with a system composed entirely of antiparticles. The AEgIS experiment at CERN's antiproton decelerator aims to measure the gravitational interaction between matter and antimatter by measuring the deflection of a beam of antihydrogen in the Earths gravitational field ( g ¯ $\overline {\textrm {g}}$ ). The principle of the experiment is as follows: cold antihydrogen atoms are synthesized in a Penning-Malberg trap and are Stark accelerated towards a moiré deflectometer, the classical counterpart of an atom interferometer, and annihilate on a position sensitive detector. Crucial to the success of the experiment is the spatial precision of the position sensitive detector. We propose a novel free-fall detector based on a hybrid of two technologies: emulsion detectors, which have an intrinsic spatial resolution of 50 nm but no temporal information, and a silicon strip / scintillating fiber tracker to provide timing and positional information. In 2012 we tested emulsion films in vacuum with antiprotons from CERN's antiproton decelerator. The annihilation vertices could be observed directly on the emulsion surface using the microscope facility available at the University of Bern. The annihilation vertices were successfully reconstructed with a resolution of 1-2 μmon the impact parameter. If such a precision can be realized in the final detector, Monte Carlo simulations suggest of order 500 antihydrogen annihilations will be sufficient to determine g ¯ $\overline {\textrm {g}}$ with a 1 % accuracy. This paper presents current research towards the development of this technology for use in the AEgIS apparatus and prospects for the realization of the final detector

Global Iwasawa-decomposition of SL(n,AQ)

We discuss the Iwasawa-decomposition of a general matrix in SL($n$, $\mathbb{Q}_p$) and SL($n$, $\mathbb{R}$). For SL($n$, $\mathbb{Q}_p$) we define an algorithm for computing a complete Iwasawa-decomposition and give a formula parameterizing the full family of decompositions. Furthermore, we prove that the $p$-adic norms of the coordinates on the Cartan torus are unique across all decompositions and give a closed formula for them which is proven using induction. For the case SL($n$, $\mathbb{R}$), the decomposition is unique and we give formulae for the complete decomposition which are also proven inductively. Lastly we outline a method for deriving the norms of the coordinates on the Cartan torus in the framework of representation theory. This yields a simple formula valid globally which expresses these norms in terms of the vector norms of generalized Pl\"ucker coordinates

Genetic diversity of a successful colonizer: isolated populations of Metrioptera roeselii regain variation at an unusually rapid rate

Newly founded isolated populations need to overcome detrimental effects of low genetic diversity. The establishment success of a population may therefore depend on various mechanisms such as assortative mating, purging of deleterious alleles, creation of new mutations and/or repeated inflow of new genotypes to reduce the effects of inbreeding and further loss of genetic variation. We compared the level of genetic variation in introduced populations of an insect species (Metrioptera roeselii) far beyond its natural distribution with levels found in their respective founder populations and coupled the data with timing since establishment. This allowed us to analyze if the introduced populations showed signs of temporal changes in genetic variation and have made it possible to evaluate underlying mechanisms. For this, we used neutral genetic markers, seven microsatellite loci and a 676-bp-long sequence of the mtDNA COI gene. All tested indices (allelic richness, unbiased expected heterozygosity, effective size, haplotype diversity, and nucleotide diversity) except inbreeding coefficient had significantly higher values in populations within the founding populations inside the continuous area of the species distribution compared with the introduced populations. A logarithmic model showed a significant correlation of both allelic richness and unbiased expected heterozygosity with age of the isolated populations. Considering the species' inferred colonization history and likely introduction pathways, we suggest that multiple introductions are the main mechanism behind the temporal pattern observed. However, we argue that influences of assortative mating, directional selection, and effects of an exceptional high intrapopulation mutation rate may have impacts. The ability to regain genetic diversity at this level may be one of the main reasons why M.roeselii successfully continue to colonize northern Europe

Relation between viral fitness and immune escape within the hepatitis C virus protease

BACKGROUND: The hepatitis C virus (HCV) mutates within human leucocyte antigen (HLA) class I restricted immunodominant epitopes of the non‐structural (NS) 3/4A protease to escape cytotoxic T lymphocyte (CTL) recognition and promote viral persistence. However, variability is not unlimited, and sometimes almost absent, and factors that restrict viral variability have not been defined experimentally. AIMS: We wished to explore whether the variability of the immunodominant CTL epitope at residues 1073–1081 of the NS3 protease was limited by viral fitness. PATIENTS: Venous blood was obtained from six patients (four HLA‐A2+) with chronic HCV infection and from one HLA‐A2+ patient with acute HCV infection. METHODS: NS3/4A genes were amplified from serum, cloned in a eukaryotic expression plasmid, sequenced, and expressed. CTL recognition of naturally occurring and artificially introduced escape mutations in HLA‐A2‐restricted NS3 epitopes were determined using CTLs from human blood and genetically immunised HLA‐A2‐transgenic mice. HCV replicons were used to test the effect of escape mutations on HCV protease activity and RNA replication. RESULTS: Sequence analysis of NS3/4A confirmed low genetic variability. The major viral species had functional proteases with 1073–1081 epitopes that were generally recognised by cross reactive human and murine HLA‐A2 restricted CTLs. Introduction of mutations at five positions of the 1073–1081 epitope prevented CTL recognition but three of these reduced protease activity and RNA replication. CONCLUSIONS: Viral fitness can indeed limit the variability of HCV within immunological epitopes. This helps to explain why certain immunological escape variants never appear as a major viral species in infected humans