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Search Results: 1 - 10 of 219586 matches for " C. Amsler "
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Search for WIMPs in liquid argon
C. Amsler
Physics , 2011,
Abstract: Our group from the University of Zurich is performing R&D work towards the design of a large liquid argon detector to detect Weakly Interacting Massive Particles (WIMPs). This project is developed within the DARWIN Collaboration funded by ASPERA to prepare a proposal for the next generation of WIMP searches using noble liquids. We are performing R&D to detect the VUV light from recoiling argon nuclei. Results obtained with one ton of liquid argon (ArDM prototype) and prospects using a monoenergetic neutron source are discussed.
Proton-Antiproton Annihilation and Meson Spectroscopy with the Crystal Barrel
Claude Amsler
Physics , 1997, DOI: 10.1103/RevModPhys.70.1293
Abstract: This report reviews the achievements of the Crystal Barrel experiment at the Low Energy Antiproton Ring (LEAR) at CERN. During seven years of operation Crystal Barrel has collected very large statistical samples in pbarp annihilation, especially at rest and with emphasis on final states with high neutral multiplicity. The measured rates for annihilation into various two-body channels and for electromagnetic processes have been used to test simple models for the annihilation mechanism based on the quark internal structure of hadrons. From three-body annihilations three scalar mesons, a0(1450), f0(1370) and f0(1500) have been established in various decay modes. One of them, f0(1500), may be identified with the expected ground state scalar glueball.
Luminescence quenching of the triplet excimer state by air traces in gaseous argon
C. Amsler,V. Boccone,A. Buchler,R. Chandrasekharan,C. Regenfus,J. Rochet
Physics , 2007, DOI: 10.1088/1748-0221/3/02/P02001
Abstract: While developing a liquid argon detector for dark matter searches we investigate the influence of air contamination on the VUV scintillation yield in gaseous argon at atmospheric pressure. We determine with a radioactive alpha-source the photon yield for various partial air pressures and different reflectors and wavelength shifters. We find for the fast scintillation component a time constant tau1= 11.3 +- 2.8 ns, independent of gas purity. However, the decay time of the slow component depends on gas purity and is a good indicator for the total VUV light yield. This dependence is attributed to impurities destroying the long-lived argon excimer states. The population ratio between the slowly and the fast decaying excimer states is determined for alpha-particles to be 5.5 +-0.6 in argon gas at 1100 mbar and room temperature. The measured mean life of the slow component is tau2 = 3.140 +- 0.067 microsec at a partial air pressure of 2 x 10-6 mbar.
Study of nuclear recoils in liquid argon with monoenergetic neutrons
C. Regenfus,Y. Allkofer,C. Amsler,W. Creus,A. Ferella,J. Rochet,M. Walter
Physics , 2012, DOI: 10.1088/1742-6596/375/1/012019
Abstract: For the development of liquid argon dark matter detectors we assembled a setup in the laboratory to scatter neutrons on a small liquid argon target. The neutrons are produced mono-energetically (E_kin=2.45 MeV) by nuclear fusion in a deuterium plasma and are collimated onto a 3" liquid argon cell operating in single-phase mode (zero electric field). Organic liquid scintillators are used to tag scattered neutrons and to provide a time-of-flight measurement. The setup is designed to study light pulse shapes and scintillation yields from nuclear and electronic recoils as well as from {\alpha}-particles at working points relevant to dark matter searches. Liquid argon offers the possibility to scrutinise scintillation yields in noble liquids with respect to the populations of the two fundamental excimer states. Here we present experimental methods and first results from recent data towards such studies.
Mark Eugene Amsler
Macabéa : Revista Eletr?nica do Netlli , 2012,
Abstract: A critical pragmatics finds good grounding in Bakhtin and Voloshinov’s theory of the Utterance in Marxism and the Philosophy of Language (1929). In this essay I explore and extend the notion of ‘reaccenting’ with that of ‘retexting’ and call attention to the role of textualities in the performance and deformance of written language. Critical pragmatic moves beyond stylistics and proposes a more critical linguistic approach to literary texts. I use critical pragmatics informed by Bakhtin’s theory of the utterance to read Langston Hughes’s dialogic lyrics in Montage of a Dream Deferred (1951) and poetic retexting as a literate and critical practice.
Claude Amsler,Frank Close
Physics , 1995, DOI: 10.1016/0370-2693(95)00579-A
Abstract: We show that the newly discovered scalar meson $f_0(1500)$ at LEAR has properties compatible with the lightest scalar glueball predicted by lattice QCD and incompatible with a $\qqbar$ state. We suggest that decays of glueballs are into pairs of glueballs (including $\eta, \eta'$ or $(\pi\pi)_S$) or by mixing with nearby $Q\bar{Q}$ states. The partial widths of $f_0(1500)$ are in accord with this hypothesis, tests of which include characteristic radiative decays to $\gamma\phi,\gamma\omega, \gamma\rho$ and the prediction of a further scalar state, $f_0'(1500 - 1800)$ which couples strongly to $K\bar{K}$, $\eta\eta$ and $\eta\eta'$.
Is $f_0(1500)$ a Scalar Glueball?
Claude Amsler,Frank Close
Physics , 1995, DOI: 10.1103/PhysRevD.53.295
Abstract: Following the discovery of two new scalar mesons, $f_0(1370)$ and $f_0(1500)$ at the Low Energy Antiproton Ring at CERN, we argue that the observed properties of this pair are incompatible with them both being $\qqbar$ mesons. We show instead that $f_0(1500)$ is compatible with the ground state glueball expected around 1500 MeV mixed with the nearby states of the $0^{++}$ $Q\bar{Q}$ nonet. Tests of this hypothesis include the prediction of a further scalar state, $f_0'(1500 - 1800)$ which couples strongly to $K\bar{K}$, $\eta\eta$ and $\eta\eta'$. Signatures for a possible tensor glueball at $\sim $2 GeV are also considered.
Crystal structure prediction using the Minima Hopping method
Maximilian Amsler,Stefan Goedecker
Physics , 2010, DOI: 10.1063/1.3512900
Abstract: A structure prediction method is presented based on the Minima Hopping method. Optimized moves on the configurational enthalpy surface are performed to escape local minima using variable cell shape molecular dynamics by aligning the initial atomic and cell velocities to low curvature directions of the current minimum. The method is applied to both silicon crystals and binary Lennard-Jones mixtures and the results are compared to previous investigations. It is shown that a high success rate is achieved and a reliable prediction of unknown ground state structures is possible.
Scintillation efficiency of liquid argon in low energy neutron-argon scattering
W. Creus,Y. Allkofer,C. Amsler,A. D. Ferella,J. Rochet,L. Scotto-Lavina,M. Walter
Physics , 2015, DOI: 10.1088/1748-0221/10/08/P08002
Abstract: Experiments searching for weak interacting massive particles with noble gases such as liquid argon require very low detection thresholds for nuclear recoils. A determination of the scintillation efficiency is crucial to quantify the response of the detector at low energy. We report the results obtained with a small liquid argon cell using a monoenergetic neutron beam produced by a deuterium-deuterium fusion source. The light yield relative to electrons was measured for six argon recoil energies between 11 and 120 keV at zero electric drift field.
A new application of emulsions to measure the gravitational force on antihydrogen
C. Amsler,A. Ariga,T. Ariga,S. Braccini,C. Canali,A. Ereditato,J. Kawada,M. Kimura,I. Kreslo,C. Pistillo,P. Scampoli,J. W. Storey
Physics , 2012, DOI: 10.1088/1748-0221/8/02/P02015
Abstract: We propose to build and operate a detector based on the emulsion film technology for the measurement of the gravitational acceleration on antimatter, to be performed by the AEgIS experiment (AD6) at CERN. The goal of AEgIS is to test the weak equivalence principle with a precision of 1% on the gravitational acceleration g by measuring the vertical position of the anni- hilation vertex of antihydrogen atoms after their free fall in a horizontal vacuum pipe. With the emulsion technology developed at the University of Bern we propose to improve the performance of AEgIS by exploiting the superior position resolution of emulsion films over other particle de- tectors. The idea is to use a new type of emulsion films, especially developed for applications in vacuum, to yield a spatial resolution of the order of one micron in the measurement of the sag of the antihydrogen atoms in the gravitational field. This is an order of magnitude better than what was planned in the original AEgIS proposal.
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