172 research outputs found
Deuteron form factor measurements at low momentum transfers
A precise measurement of the elastic electron-deuteron scattering cross section at four-momentum transfers of 0.24 fm(-1) \u3c = Q \u3c = 2.7 fm(-1) has been performed at the Mainz Microtron. In this paper we describe the utilized experimental setup and the necessary analysis procedure to precisely determine the deuteron charge form factor from these data. Finally, the deuteron charge radius r(d) can be extracted from an extrapolation of that form factor to Q(2) = 0
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
A Large-Scale FPGA-Based Trigger and Dead-Time Free DAQ System for the Kaos Spectrometer at MAMI
The Kaos spectrometer is maintained by the A1 collaboration at the Mainz
Microtron MAMI with a focus on the study of (e,e'K^+) coincidence reactions.
For its electron-arm two vertical planes of fiber arrays, each comprising
approximately 10 000 fibers, are operated close to zero degree scattering angle
and in close proximity to the electron beam. A nearly dead-time free DAQ system
to acquire timing and tracking information has been installed for this
spectrometer arm. The signals of 144 multi-anode photomultipliers are collected
by 96-channel front-end boards, digitized by double-threshold discriminators
and the signal time is picked up by state-of-the-art F1 time-to-digital
converter chips. In order to minimize background rates a sophisticated trigger
logic was implemented in newly developed Vuprom modules. The trigger performs
noise suppression, signal cluster finding, particle tracking, and coincidence
timing, and can be expanded for kinematical matching (e'K^+) coincidences. The
full system was designed to process more than 4 000 read-out channels and to
cope with the high electron flux in the spectrometer and the high count rate
requirement of the detectors. It was successfully in-beam tested at MAMI in
2009.Comment: Contributed to 17th IEEE Real Time Conference (RT10), Lisbon, 24-28
May 201
Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence
We measured the ratio of the transverse to longitudinal
components of polarization transferred from electrons to bound protons in
by the process at the
Mainz Microtron (MAMI). We observed consistent deviations from unity of this
ratio normalized to the free-proton ratio,
, for both -
and -shell knocked out protons, even though they are embedded in averaged
local densities that differ by about a factor of two. The dependence of the
double ratio on proton virtuality is similar to the one for knocked out protons
from and , suggesting a universal behavior.
It further implies no dependence on average local nuclear density
Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering off Si and Zr
We report on a new measurement of the beam-normal single spin asymmetry
in the elastic scattering of 570 MeV transversely polarized
electrons off Si and Zr at . The
studied kinematics allow for a comprehensive comparison with former results on
C. No significant mass dependence of the beam-normal single spin
asymmetry is observed in the mass regime from C to Zr.Comment: Submitted for publication to Physics Letters
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
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