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Search Results: 1 - 10 of 200688 matches for " P. Achenbach "
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Associated Λ/Σ0 electroproduction with the Kaos spectrometer at MAMI
Achenbach P.
EPJ Web of Conferences , 2010, DOI: 10.1051/epjconf/20100307010
Abstract: An instrument of central importance for the strangeness photo- and electroproduction at the 1.5 GeV ¨ electron beam of the MAMI accelerator at the Institut fur Kernphysik in Mainz, Germany, is the newly installed magnetic spectrometer KAOS that is operated by the A1 collaboration in (e, e′ K ) reactions on the proton or light nuclei. Its compact design and its capability to detect negative and positive charged particles simultaneously complements the existing spectrometers. The strangeness program performed with Kaos in 2008–9 is addressing some important issues in the eld of elementary kaon photo- and electroproduction reactions. Although recent measurements have been performed at Je erson Lab, there are still a number of open problems in the interpretation of the data and the description of the elementary process using phenomenological models. With the identi cation of Λ and Σ0 hyperons in the missing mass spectra from kaon production o a liquid hydrogen target it is demonstrated that the extended facility at MAMI is capable to perform strangeness electroproduction spectroscopy at low momentum transfers Q2 < 0.5 (GeV/c)2 . The covered kinematics and systematic uncertainties in the cross-section extraction from the data are discussed.
Strangeness physics at MAMI: First results and perspectives
P. Achenbach
Physics , 2012,
Abstract: During the last two years several experimental approaches to strange systems have been realized at the spectrometer facility of the Mainz Microtron MAMI. An instrument of central importance for the strangeness electro-production program is the magnetic spectrometer Kaos that was installed during 2003-8 and is now operated by the A1 collaboration in (e,e'K) reactions on the proton or light nuclei. Since 2008 kaon production at low four-momentum transfers off a liquid hydrogen target was studied. The measurements were sensitive to details of the phenomenological models describing the reaction. Two very prominent isobar models, Kaon-Maid and Saclay-Lyon A, differ in the number of contributing nucleon resonances and their longitudinal couplings at the kinematics measured at MAMI. In order to use Kaos as a zero-degree double-arm spectrometer a magnetic chicane comprising two compensating sector magnets was constructed and a new electron-arm focal-plane detector system was built.
Active optical fibres in modern particle physics experiments
C. P. Achenbach
Physics , 2004,
Abstract: In modern particle physics experiments wavelength-shifting and scintillating fibres based on plastic polymers are used for tracking and calorimetry. In this review the role of photon trapping efficiencies, transmission functions and signal response times for common multimode active fibres is discussed. Numerical simulations involving three dimensional tracking of skew rays through curved fibres demonstrate the characteristics of trapped light. Of practical interest are the parametrisations of transmission functions and the minimum permissible radius of curvature. These are of great importance in today's experiments where high count rates and small numbers of photoelectrons are encountered. Special emphasis has been placed on the timing resolution of fibre detectors and its limitation due to variations in the path length of generated photons.
Characterisation of radiation damage in silicon photomultipliers with a Monte Carlo model
S. Sanchez Majos,P. Achenbach,J. Pochodzalla
Physics , 2008, DOI: 10.1016/j.nima.2008.06.021
Abstract: Measured response functions and low photon yield spectra of silicon photomultipliers (SiPM) were compared to multi-photoelectron pulse-height distributions generated by a Monte Carlo model. Characteristic parameters for SiPM were derived. The devices were irradiated with 14 MeV electrons at the Mainz microtron MAMI. It is shown that the first noticeable damage consists of an increase in the rate of dark pulses and the loss of uniformity in the pixel gains. Higher radiation doses reduced also the photon detection efficiency. The results are especially relevant for applications of SiPM in fibre detectors at high luminosity experiments.
Development of a compact scintillator hodoscope with wavelength-shifting fibre read-out
C. P. Achenbach,J. H. Cobb
Physics , 2004, DOI: 10.1016/j.nima.2004.10.018
Abstract: We report on the prototyping of a plastic scintillator hodoscope with wavelength-shifting fibre read-out by a multi-anode photomultiplier as part of the development of a detector for cosmic ray muons to be carried aboard an aircraft. Light yield and light attenuation measurements on single- and double-clad wavelength-shifting fibres were performed. Low power, low-threshold, discriminators were designed. A prototype 16-channel hodoscope with two planes was built and tested with cosmic rays. After correcting for geometrical factors a global intrinsic efficiency of $\epsilon > 98$ % was obtained in both planes. The overall performance of the hodoscope proved it to be well suited for the {\sc Adler} experiment to measure the high altitude muon flux.
Design criteria for multi-layered scintillating fibre arrays with inclined columns
P. Achenbach,L. Nungesser,J. Pochodzalla
Physics , 2008, DOI: 10.1016/j.nima.2008.02.097
Abstract: Multi-layered scintillating fibre arrays read-out are commonly used as high resolution charged particle hodoscopes. Fibres of a column along the geometrical trajectory of incident particles are typically grouped to one pixel of a multi-channel read-out device. In some applications the incident particles will cross the detection plane with large angles w.r.t. the normal to the layers. Then, the packing of the fibres needs to be adapted to the incident particles and the columns need to be inclined. In this paper possible fibre array geometries are shown, relevant design criteria for detectors are discussed, and the effect of diverging particles incident on fibre arrays was studied using a Monte Carlo simulation.
A new airborne detector for atmospheric muons
C. P. Achenbach,J. H. Cobb
Physics , 2001,
Abstract: The University of Oxford has started the design and development of the new experiment ADLER (Airborne Detector for Low Energy Rays). This apparatus will measure the cosmic-ray muon flux at an altitude of 10 - 13km. The detector should be flown by aircrafts on transatlantic routes crossing the magnetic equator to investigate the flux at different geomagnetic latitudes. The goal of the experiment is to obtain better constraints on the low energy atmospheric neutrino flux and the results will be of importance to the atmospheric neutrino anomaly.
Monitoring the Short-Term Response to Salt Exposure of Two Genetically Distinct Phragmites australis Clones with Different Salinity Tolerance Levels  [PDF]
Luciana Achenbach, Hans Brix
American Journal of Plant Sciences (AJPS) , 2014, DOI: 10.4236/ajps.2014.58122

Aims: Two genetically distinct clones of Phragmites australis were used to investigate the immediate response induced by osmotic stress. The study aimed at elucidating if the response time, the inhibition rate and the recovery from salinity stress vary between these two genotypes. The experimental work was conducted at the laboratory of the Institute of Bioscience, Aarhus University, Denmark. Methods: The light-saturated photosynthetic rate (Pmax), stomata conductance (gs) and transpiration rate (E) were measured over different periods of salt exposure (15, 70 and 240 minutes) and at different salt concentrations (20 and 40 parts per thousand salinity). Important findings: The osmotic stress induced stomata closure and reduction of Pmax and E for both clones. The clone-specific responses as measured through physiological parameters were negatively

The frontiers of the virtual photons program at MAMI
Sfienti C.,Achenbach P.,Ayerbe Gayoso C.,B?hm R.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20123701015
Abstract: The most recent results and the future physics program of the high precision electron-scattering experiment at MAMI are briefly outlined. The A1 high-resolution spectrometers facility allows for a unique quality of virtual photon experiments. High precision form factor measurements, few-baryon systems highresolution structure studies and the innovative way in the search of dark photons illustrate the interplay between such diverse fields as precision atomic physics, nuclear astrophysics and astroparticle physics, where hadron physics plays a central and connecting role.
Unpolarized and polarized elementary kaon electroproduction cross sections measured at MAMI
Achenbach P.,Ayerbe Gayoso C.,B?hm R.,Borodina O.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20123706004
Abstract: Present and future research into the electroproduction of kaons plays an important role at Mainz Microtron MAMI. With the Kaos spectrometer employed for kaon detection in the multi-spectrometer facility, cross section measurements of the exclusive p(e, e′K+)Λ, ∑0 reactions at low momentum transfers have been performed. Isobar and Regge-plus-resonance models were compared with the data. These measurements have clearly discriminated between effective Lagrangian models for photo- and electroproduction of strangeness. New experiments with polarized beam at low four-momentum transfer are addressing the imaginary part of the longitudinal-transverse response in this process, that can be separated by flipping the beam electron helicity. These studies are important for the understanding of basic coupling constants in the isobar models and the electromagnetic form factors of the hadrons and their resonances involved in the process.
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