89 research outputs found
Light Meson Dynamics Workshop. Mini proceedings
The mini-proceedings of the Light Meson Dynamics Workshop held in Mainz from
February 10th to 12th, 2014, are presented. The web page of the conference,
which contains all talks, can be found at
https://indico.cern.ch/event/287442/overview .Comment: 46 pages, 17 contributions. Editors: W. Gradl, P. Masjuan, M.
Ostrick, and S. Schere
A new measurement of the neutron detection efficiency for the NaI Crystal Ball detector
We report on a measurement of the neutron detection efficiency in NaI
crystals in the Crystal Ball detector obtained from a study of single p0
photoproduction on deuterium using the tagged photon beam at the Mainz
Microtron. The results were obtained up to a neutron energy of 400 MeV. They
are compared to previous measurements made more than 15 years ago at the pion
beam at the BNL AGS
Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons
Precise helicity-dependent cross sections and the double-polarization observable E were measured for η
photoproduction from quasifree protons and neutrons bound in the deuteron. The η → 2γ and η → 3π0 → 6γ
decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The
measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz.
A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon
beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with
the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results
show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off
the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions
with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The
behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them with Legendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which
uses an interference of P11 and S11 partial waves to explain the narrow structure
Measurement of pi^0 photoproduction on the proton at MAMI C
Differential cross sections for the gamma p -> pi^0 p reaction have been
measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C,
up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a
fine energy and angular binning, increase the existing quantity of pi^0
photoproduction data by ~47%. Owing to the unprecedented statistical accuracy
and the full angular coverage, the results are sensitive to high partial-wave
amplitudes. This is demonstrated by the decomposition of the differential cross
sections in terms of Legendre polynomials and by further comparison to model
predictions. A new solution of the SAID partial-wave analysis obtained after
adding the new data into the fit is presented.Comment: 13 pages, 12 figures, 1 tabl
Determination of the scalar polarizabilities of the proton using beam asymmetry in Compton scattering
The scalar dipole polarizabilities, and , are
fundamental properties related to the internal dynamics of the nucleon. The
currently accepted values of the proton polarizabilities were determined by
fitting to unpolarized proton Compton scattering cross section data. The
measurement of the beam asymmetry in a certain kinematical range
provides an alternative approach to the extraction of the scalar
polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured
for Compton scattering below pion photoproduction threshold for the first time.
The results are compared with model calculations and the influence of the
experimental data on the extraction of the scalar polarizabilities is
determined.Comment: 6 pages, 5 figure
A Precise Multi-Channel QDC FEE utilizing FPGAs as Discriminators and Delay Elements Based on the TRB3 as TDC and Readout Platform
First measurement of polarisation transfer in deuteron photodisintegration
A first measurement of the polarisation transfer from a circularly-polarised
photon to the final state neutron () in deuterium photodisintegration
has been carried out. This quantity is determined over the photon energy range
370~--~700~MeV and for neutron centre-of-mass breakup angles
. The polarisation of the final state neutrons was
determined by an ancillary large-acceptance nucleon polarimeter, surrounding a
cryogenic liquid deuterium target within the Crystal Ball detector at MAMI. The
polarimeter characterised charge exchange of the ejected neutrons to
determine their polarisation. The new data are also compared to a
theoretical model based on nucleonic and nucleon resonance degrees of freedom
constrained by the current world-database of deuterium photodisintegration
measurements. Structures in observed in the region of the
could not be explained by conventional models of deuteron
photodisintegration
Spin polarizabilities of the proton by measurement of Compton double-polarization observables
The Compton double-polarization observable has been measured
for the first time in the resonance region using a circularly
polarized photon beam incident on a longitudinally polarized target at the
Mainz Microtron. This paper reports these results, together with the
model-dependent extraction of four proton spin polarizabilities from fits to
additional asymmetry data using dispersion relation and chiral perturbation
theory calculations, with the former resulting in: , , and
, in units of .Comment: 7 pages, 5 figures, 2 tables, accepted for publication in PR
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