3,710 research outputs found
Proton Polarization in the Reaction and the Measurement of Quadrupole Components in the N to Transition
The recoil proton polarization in the production off the proton with
longitudinally polarized electron beam has been studied as a means to measure
quadrupole components in the N to transition. On top of the
resonance a high sensitivity to a possible Coulomb quadrupole excitation is
found in parallel kinematics. The ratio of multipole amplitudes
can be determined from the ratio of the two in-scattering-plane recoil proton
polarization components. Avoiding the absolute measurement of the
polarizations, such a ratio allows small experimental uncertainties.
Furthermore, the electron helicity independent proton polarization component
enables the characterization of resonant and non-resonant pieces.Comment: 14 pages, 2 figures, LateX. Submitted to Z.Phys.
Polarization degrees of freedom in near-threshold photoproduction of omega mesons in the pi^0 gamma decay channel
We study polarization variables in the photoproduction of omega-mesons with
subsequent omega to gamma pi^0 decay. Single and double polarization
observables are calculated as a function of different final-state angles.
Reaction models include pomeron (natural parity) and pi^0 (unnatural parity)
exchange in the t-channel. In addition, the contribution of s-channel
resonances is considered. The sensitivity of the polarization observables to
the reaction dynamics is discussed.Comment: 10 pages, 10 figures, explicit reference to sign of decay asymmetry
adde
Double polarization experiments at intermediate energy
At modern electron accelerators with highly polarized, intense, high duty
factor beams double polarization coincidence experiments became feasible with
good statistical accuracy. The strong potential towards the precise
determination of small nucleon structure quantities is illustrated by two
recent examples from MAMI. The measurement of in the quasifree reaction
lead to a new parametrization of which is
significantly above the previously preferred one from elastic scattering.
A experiment at the energy of the resonance
yields preliminary results for the longitudinal quadrupole mixing. Both
experimental errors and model uncertainties are complementary to unpolarized
measurements.Comment: 8 pages, 6 figures, plenary talk given at PANIC'9
decays to from new data on
Data on the reaction with ,
taken with unpolarized or polarized beams in combination with an unpolarized or
polarized proton-target, were analyzed within the Bonn-Gatchina (BnGa) partial
wave analysis. Differential cross sections, several spin density matrix
elements, the beam asymmetry , the normalized helicity difference ,
and the correlation between linear photon and longitudinal target
polarization were included in a large data base on pion and photo-induced
reactions. The data on photoproduction are used to determine twelve
branching ratios; most of these are determined for the first
time.Comment: 6 pages, 4 figures, 2 table
Measuring longitudinal amplitudes for electroproduction of pseudoscalar mesons using recoil polarization in parallel kinematics
We propose a new method for measuring longitudinal amplitudes for
electroproduction of pseudoscalar mesons that exploits a symmetry relation for
polarization observables in parallel kinematics. This polarization technique
does not require variation of electron scattering kinematics and avoids the
major sources of systematic errors in Rosenbluth separation.Comment: intended for Phys. Rev. C as a Brief Repor
Measurement of the recoil polarization in the p (\vec e, e' \vec p) pi^0 reaction at the \Delta(1232) resonance
The recoil proton polarization has been measured in the p (\vec e,e'\vec p)
pi^0 reaction in parallel kinematics around W = 1232 MeV, Q^2 = 0.121 (GeV/c)^2
and epsilon = 0.718 using the polarized c.w. electron beam of the Mainz
Microtron. Due to the spin precession in a magnetic spectrometer, all three
proton polarization components P_x/P_e = (-11.4 \pm 1.3 \pm 1.4) %, P_y =
(-43.1 \pm 1.3 \pm 2.2) %, and P_z/P_e = (56.2 \pm 1.5 \pm 2.6) % could be
measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio CMR =
(-6.4\pm 0.7_{stat}\pm 0.8_{syst}) % was determined from P_x in the framework
of the Mainz Unitary Isobar Model. The consistency among the reduced
polarizations and the extraction of the ratio of longitudinal to transverse
response is discussed.Comment: 5 pages LaTeX, 1 table, 2 eps figure
Evidence for a negative-parity spin-doublet of nucleon resonances at 1.88\,GeV
Evidence is reported for two nucleon resonances with spin-parity
and at a mass just below 1.9\,GeV. The evidence is derived from a
coupled-channel analysis of a large number of pion and photo-produced
reactions. The two resonances are nearly degenerate in mass with two resonances
of the same spin but positive parity. Such parity doublets are predicted in
models claiming restoration of chiral symmetry in high-mass excitations of the
nucleon. Further examples of spin parity doublets are found in addition.
Alternatively, the spin doublet can be interpreted as member of the 56-plet
expected in the third excitation band of the nucleon. Implications for the
problem of the {\it missing resonances} are discussed.Comment: 10 pages, 3 figures, 4 tables, minor revisio
Final State Interaction Effects in pol 3He(pol e,e'p)
Asymmetries in quasi-elastic pol 3He(pol e,e'p) have been measured at a
momentum transfer of 0.67 (GeV/c)^2 and are compared to a calculation which
takes into account relativistic kinematics in the final state and a
relativistic one-body current operator. With an exact solution of the Faddeev
equation for the 3He-ground state and an approximate treatment of final state
interactions in the continuum good agreement is found with the experimental
data.Comment: 11 pages, 6 figures, submitted to Phys. Lett. B, revised version,
sensitivity study to relativity and NN-potential adde
Tests of the fundamental symmetries in eta meson decays
Patterns of chiral symmetry violation and tests of the conservation of the
fundamental C, P and CP symmetries are key physics issues in studies of the
pi0, eta and eta' meson decays. These tests include searches for rare or
forbidden decays and searches for asymmetries among the decay products in the
not-so-rare decays. Some examples for the rare decays are eta-->2pi, eta-->4pi0
(CP tests), decays into an odd number of photons (e.g., eta-->3g) and the decay
eta-->pi0e+e- (C tests). The experimental studies of the pi0, eta and eta'
meson decays are carried out at four European accelerator research facilities:
KLOE/KLOE-2 at DAFNE (Frascati), Crystal Ball at MAMI (Mainz), WASA at COSY
(J\"ulich), Crystal Barrel at ELSA (Bonn).Comment: 9 pages, 2 figures, proceedings of Symposium on Prospects in the
Physics of Discrete Symmetries, DISCRETE 2010, 6 - 11 December, Rome; v2:
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