139 research outputs found
Design criteria for multi-layered scintillating fibre arrays with inclined columns
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.Comment: submitted to Nucl. Instrum. Meth.
Future non-linear stability for reflection symmetric solutions of the Einstein-Vlasov system of Bianchi types II and VI
Using the methods developed for the Bianchi I case we have shown that a
boostrap argument is also suitable to treat the future non-linear stability for
reflection symmetric solutions of the Einstein-Vlasov system of Bianchi types
II and VI. These solutions are asymptotic to the Collins-Stewart solution
with dust and the Ellis-MacCallum solution respectively. We have thus
generalized the results obtained by Rendall and Uggla in the case of locally
rotationally symmetric Bianchi II spacetimes to the reflection symmetric case.
However we needed to assume small data. For Bianchi VI there is no
analogous previous result.Comment: 30 page
Recoil polarization and beam-recoil double polarization measurement of \eta electroproduction on the proton in the region of the S_{11}(1535) resonance
The beam-recoil double polarization P_{x'}^h and P_{z'}^h and the recoil
polarization P_{y'} were measured for the first time for the
p(\vec{e},e'\vec{p})\eta reaction at a four-momentum transfer of Q^2=0.1
GeV^2/c^2 and a center of mass production angle of \theta = 120^\circ at MAMI
C. With a center of mass energy range of 1500 MeV < W < 1550 MeV the region of
the S_{11}(1535) and D_{13}(1520) resonance was covered. The results are
discussed in the framework of a phenomenological isobar model (Eta-MAID). While
P_{x'}^h and P_{z'}^h are in good agreement with the model, P_{y'} shows a
significant deviation, consistent with existing photoproduction data on the
polarized-target asymmetry.Comment: 4 pages, 1 figur
Search for Light Gauge Bosons of the Dark Sector at the Mainz Microtron
A new exclusion limit for the electromagnetic production of a light U(1)
gauge boson {\gamma}' decaying to e^+e^- was determined by the A1 Collaboration
at the Mainz Microtron. Such light gauge bosons appear in several extensions of
the standard model and are also discussed as candidates for the interaction of
dark matter with standard model matter. In electron scattering from a heavy
nucleus, the existing limits for a narrow state coupling to e^+e^- were reduced
by nearly an order of magnitude in the range of the lepton pair mass of 210
MeV/c^2 < m_e^+e^- < 300 MeV/c^2. This experiment demonstrates the potential of
high current and high resolution fixed target experiments for the search for
physics beyond the standard model.Comment: 4 pages, 7 figure
Reply to Comment on "High-Precision Determination of the Electric and Magnetic Form Factors of the Proton"
In arXiv:1108.3058v1 [nucl-ex], Arrington criticizes the Coulomb corrections
we applied in the analysis of high precision form factor data (see
Phys.Rev.Lett.105:242001, 2010, arXiv:1007.5076v3 [nucl-ex]). We show, by
comparing different calculations cited in the Comment, that the criticism of
the Comment neglects the large uncertainty of "more modern" TPE corrections.
This uncertainty has also been seen in recent polarized measurements. We rerun
our analysis using one of these calculations. The results show that the Comment
exaggerates the quantitative effect at small Q^2.Comment: 1 page, 2 figure, To appear as a Reply Comment in Physical Review
Letter
High-precision determination of the electric and magnetic form factors of the proton
New precise results of a measurement of the elastic electron-proton
scattering cross section performed at the Mainz Microtron MAMI are presented.
About 1400 cross sections were measured with negative four-momentum transfers
squared up to Q^2=1 (GeV/c)^2 with statistical errors below 0.2%. The electric
and magnetic form factors of the proton were extracted by fits of a large
variety of form factor models directly to the cross sections. The form factors
show some features at the scale of the pion cloud. The charge and magnetic
radii are determined to be r_E=0.879(5)(stat.)(4)(syst.)(2)(model)(4)(group) fm
and r_M=0.777(13)(stat.)(9)(syst.)(5)(model)(2)(group) fm.Comment: 5 pages, 2 figures, published in Phys. Rev. Lett. v3: added
references, updated text, color figure
The electric and magnetic form factors of the proton
The paper describes a precise measurement of electron scattering off the
proton at momentum transfers of \ GeV. The
average point-to-point error of the cross sections in this experiment is
0.37%. These data are used for a coherent new analysis together with all world
data of unpolarized and polarized electron scattering from the very smallest to
the highest momentum transfers so far measured. The extracted electric and
magnetic form factors provide new insight into their exact shape, deviating
from the classical dipole form, and of structure on top of this gross shape.
The data reaching very low values are used for a new determination of the
electric and magnetic radii. An empirical determination of the
Two-Photon-Exchange (TPE) correction is presented. The implications of this
correction on the radii and the question of a directly visible signal of the
pion cloud are addressed.Comment: 38 pages, 20 figures. Updated data files. PRC versio
Particle tracking in kaon electroproduction with cathode-charge sampling in multi-wire proportional chambers
Wire chambers are routinely operated as tracking detectors in magnetic
spectrometers at high-intensity continuous electron beams. Especially in
experiments studying reactions with small cross-sections the reaction yield is
limited by the background rate in the chambers. One way to determine the track
of a charged particle through a multi-wire proportional chamber (MWPC) is the
measurement of the charge distribution induced on its cathodes. In practical
applications of this read-out method, the algorithm to relate the measured
charge distribution to the avalanche position is an important factor for the
achievable position resolution and for the track reconstruction efficiency. An
algorithm was developed for operating two large-sized MWPCs in a strong
background environment with multiple-particle tracks. Resulting efficiencies
were determined as a function of the electron beam current and on the signal
amplitudes. Because of the different energy-losses of pions, kaons, and protons
in the momentum range of the spectrometer the efficiencies depend also on the
particle species
Evidence for and Subcellular Localization of a Ca-Stimulated Phospholipase D from Maize Roots
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