51 research outputs found
Detection of K+ mesons in segmented electromagnetic calorimeters
The combination of the CrystalBall and TAPS electromagnetic calorimeters were installed in the MAMI A2 hall in 2003. Here they are able to detect the reaction products from photo-induced reactions in combination with the Glasgow photon tagger. In the last two years the MAMI facility was upgraded from 885 MeV to 1.5 GeV, the A2 photon tagger underwent a similar upgrade crossing the threshold for strangeness photoproduction. For the CrystalBall this created a new challenge, to identify K+ mesons above the large background from other charged hadrons, in a situation where the detector setup does not benefit from a magnetic field to help separate particle species. These proceedings outline a novel technique which uses the decay products of the K+ as a strangeness tag
X-ray emission from a crystal undulator—Experimental results at channeling of electrons
Experiments have been performed at the Mainz Microtron MAMI
to explore the radiation emission from a 4-period epitaxially grown strained layer Si1−xGex undulator with a period length λu = 9.9 μm. Electron energies of 270 and
855MeV have been chosen. In comparison with a flat silicon reference crystal, a broad excess yield around the theoretically expected photon energies of 0.069 and 0.637 MeV, respectively, has been observed for channeling at the undulating (110) planes. The results are discussed within the framework of the classical undulator theory
Usage of FTA (R) Classic Cards for Safe Storage, Shipment, and Detection of Arboviruses
Infections caused by arthropod-borne RNA viruses are overrepresented among emerging infectious diseases. Effective methods for collecting, storing, and transporting clinical or biological specimens are needed worldwide for disease surveillance. However, many tropical regions where these diseases are endemic lack analytical facilities and possibility of continuous cold chains, which presents challenges from both a biosafety and material preservation perspective. Whatman (R) FTA (R) Classic Cards may serve as an effective and safe option for transporting hazardous samples at room temperature, particularly for RNA viruses classified as biosafety level (BSL) 2 and 3 pathogens, from sampling sites to laboratories. In this study, we investigated the biosafety and perseverance of representative alpha-and flaviviruses stored on FTA (R) cards. To evaluate the virus inactivation capacity of FTA (R) cards, we used Sindbis virus (SINV), chikungunya virus (CHIKV), and Japanese encephalitis virus (JEV). We inoculated susceptible cells with dilution series of eluates from viral samples stored on the FTA (R) cards and observed for cytopathic effect to evaluate the ability of the cards to inactivate viruses. All tested viruses were inactivated after storage on FTA (R) cards. In addition, we quantified viral RNA of JEV, SINV, and tick-borne encephalitis virus (TBEV) stored on FTA (R) cards at 4 degrees C, 25 degrees C, and 37 degrees C for 30 days using two reverse transcriptase quantitative PCR assays. Viral RNA of SINV stored on FTA (R) cards was not reduced at either 4 degrees C or 25 degrees C over a 30-day period, but degraded rapidly at 37 degrees C. For JEV and TBEV, degradation was observed at all temperatures, with the most rapid degradation occurring at 37 degrees C. Therefore, the use of FTA (R) cards provides a safe and effective workflow for the collection, storage, and analysis of BSL 2- and 3-virus RNA samples, but there is a risk of false negative results if the cards are stored at higher temperatures for long periods of time. Conscious usage of the cards can be useful in disease surveillance and research, especially in tropical areas where transportation and cold chains are problematic
Future aspects of X-ray emission from crystal undulators at channeling of positrons
In connection with ideas to produce undulator-like radiation in the hundreds of keV up to the MeV region by means of positron and electron channeling, there is renewed interest to study various channeling phenomena also experimentally. With electrons experiments have been performed at the Mainz Microtron MAMI to explore channeling-radiation emission by a 4-period epitaxially grown strained
layer Si1−xGex undulator with a period length of λu = 9.9 μm. Unfortunately, high-quality positron beams of sufficient intensity are not easily accessible. The only serious candidate in Europe seems to be the Beam Test Facility (BTF) at INFN/LNF, Frascati, Italy. Some requirements to extent BTF in a facility which is also well suited for positron channeling-radiation experiments will be outlined
Neutron skin of Pb from Coherent Pion Photoproduction
Information on the size and shape of the neutron skin on Pb has been
extracted from coherent pion photoproduction cross sections measured using the
Crystal Ball together with the Glasgow tagger at the MAMI electron beam
facility. On exploitation of an interpolated fit of a theoretical model to the
measured cross sections the half-height radius and diffuseness of the neutron
distribution are found to be 6.70 fm and 0.55 fm respectively, corresponding to a neutron
skin thickness =0.15 fm.
The results give the first successful extraction of a neutron skin with an
electromagnetic probe and indicate the skin of Pb has a halo character.
The measurement provides valuable new constraints on both the structure of
nuclei and the equation of state for neutron-rich matter.Comment: 4 figures 5 pages. Version submitted to journal. Includes additional
studies of systematic effects in the extracted diffuseness, which led to a
small increase in the quoted systematic error. These additional studies are
discussed in the revised manuscript. Also includes minor editorial
improvements to the tex
Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B
A precise measurement of the Dalitz plot parameter, alpha, for the eta->3pi^0
decay is presented. The experiment was performed with the Crystal Ball and TAPS
large acceptance photon detectors at the tagged photon beam facility of the
MAMI-B electron accelerator in Mainz. High statistics of 1.8*10^6 eta->3pi^0
events were obtained, giving the result alpha = -0.032 +/- 0.002(stat) +/-
0.002(syst).Comment: 9 pages, 6 figures, published in the online-first section of EPJ A,
included changes referees asked for, added DO
Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis
Masses, widths and photocouplings of baryon resonances are determined in a
coupled-channel partial wave analysis of a large variety of data. The
Bonn-Gatchina partial wave formalism is extended to include a decomposition of
t- and u-exchange amplitudes into individual partial waves. The multipole
transition amplitudes for and are
given and compared to results from other analyses.Comment: 18 pages, 14 figure
Photoproduction of mesons off nuclei
Recent results for the photoproduction of mesons off nuclei are reviewed.
These experiments have been performed for two major lines of research related
to the properties of the strong interaction. The investigation of nucleon
resonances requires light nuclei as targets for the extraction of the isospin
composition of the electromagnetic excitations. This is done with quasi-free
meson photoproduction off the bound neutron and supplemented with the
measurement of coherent photoproduction reactions, serving as spin and/or
isospin filters. Furthermore, photoproduction from light and heavy nuclei is a
very efficient tool for the study of the interactions of mesons with nuclear
matter and the in-medium properties of hadrons. Experiments are currently
rapidly developing due to the combination of high quality tagged (and
polarized) photon beams with state-of-the-art 4pi detectors and polarized
targets
Evaluation of the polarization observables I^S and I^C in the reaction gamma p --> pi^0 eta p
We evaluate the polarization observables I^S and I^C for the reaction gamma p
--> pi^0 eta p, using a chiral unitary framework developed earlier. The I^S and
I^C observables have been recently measured for the first time by the
CBELSA/TAPS collaboration. The theoretical predictions of I^S and I^C, given
for altogether 18 angle dependent functions, are in good agreement with the
measurements. Also, the asymmetry dSigma/dcos(theta) evaluated here agrees with
the data. We show the importance of the Delta(1700)D33 resonance and its S-wave
decay into eta Delta(1232). The result can be considered as a further
confirmation of the dynamical nature of this resonance. At the highest
energies, deviations of the predictions from the data start to become
noticeable, which leaves room for additional processes and resonances such as a
Delta(1940)D33. We also point out how to further improve the calculation.Comment: Version accepted for publication by the European Physical Journal A,
9 pages, 7 figure
Coherent photoproduction of π0- and η-mesons off 7Li
Abstract.: Coherent photoproduction of π0-mesons from threshold (E th ≈ 136 MeV) throughout the Δ-resonance region and of η-mesons close to the production threshold (E th ≈ 570 MeV for η has been measured for 7Li nuclei. The experiment was performed using the tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4π solid-angle electromagnetic calorimeter. The reactions were identified by a combined invariant-mass and missing-energy analysis. A comparison of the pion data to plane-wave impulse modelling tests the nuclear mass form factor. So far coherent η production had been only identified for the lightest nuclear systems (2H and 3He . For 3He a large enhancement of the cross section above plane-wave approximations had been reported, indicating the formation of a quasi-bound state. The present Li data for η production agree with a plane-wave approximation. Contrary to 3He , neither a threshold enhancement of the total cross section nor a deviation of the angular distributions from the expected form factor dependence were observe
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