67 research outputs found
Characterization of a CCD array for Bragg spectroscopy
The average pixel distance as well as the relative orientation of an array of
6 CCD detectors have been measured with accuracies of about 0.5 nm and 50
rad, respectively. Such a precision satisfies the needs of modern crystal
spectroscopy experiments in the field of exotic atoms and highly charged ions.
Two different measurements have been performed by illuminating masks in front
of the detector array by remote sources of radiation. In one case, an aluminum
mask was irradiated with X-rays and in a second attempt, a nanometric quartz
wafer was illuminated by a light bulb. Both methods gave consistent results
with a smaller error for the optical method. In addition, the thermal expansion
of the CCD detectors was characterized between -105 C and -40 C.Comment: Submitted to Review of Scientific Instrument
Measurement of the charged pion mass using X-ray spectroscopy of exotic atoms
The transitions in pionic nitrogen and muonic oxygen were measured
simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4\,bar. Due to
the precise knowledge of the muon mass the muonic line provides the energy
calibration for the pionic transition. A value of
(139.57077\,\,0.00018)\,MeV/c (\,1.3ppm) is derived for the
mass of the negatively charged pion, which is 4.2ppm larger than the present
world average
Hadronic shift in pionic hydrogen
The hadronic shift in pionic hydrogen has been redetermined to be
\,eV by X-ray
spectroscopy of ground state transitions applying various energy calibration
schemes. The experiment was performed at the high-intensity low-energy pion
beam of the Paul Scherrer Institut by using the cyclotron trap and an
ultimate-resolution Bragg spectrometer with bent crystals.Comment: 10 pages, 6 figure
Remarks on the pion-nucleon sigma-term
The pion-nucleon -term can be stringently constrained by the
combination of analyticity, unitarity, and crossing symmetry with
phenomenological information on the pion-nucleon scattering lengths. Recently,
lattice calculations at the physical point have been reported that find lower
values by about with respect to the phenomenological determination.
We point out that a lattice measurement of the pion-nucleon scattering lengths
could help resolve the situation by testing the values extracted from
spectroscopy measurements in pionic atoms.Comment: 5 pages, 2 figures; version published in PL
Roy-Steiner-equation analysis of pion-nucleon scattering
We review the structure of Roy-Steiner equations for pion-nucleon scattering,
the solution for the partial waves of the t-channel process , as well as the high-accuracy extraction of the pion-nucleon S-wave
scattering lengths from data on pionic hydrogen and deuterium. We then proceed
to construct solutions for the lowest partial waves of the s-channel process
and demonstrate that accurate solutions can be found if the
scattering lengths are imposed as constraints. Detailed error estimates of all
input quantities in the solution procedure are performed and explicit
parameterizations for the resulting low-energy phase shifts as well as results
for subthreshold parameters and higher threshold parameters are presented.
Furthermore, we discuss the extraction of the pion-nucleon -term via
the Cheng-Dashen low-energy theorem, including the role of isospin-breaking
corrections, to obtain a precision determination consistent with all
constraints from analyticity, unitarity, crossing symmetry, and pionic-atom
data. We perform the matching to chiral perturbation theory in the subthreshold
region and detail the consequences for the chiral convergence of the threshold
parameters and the nucleon mass.Comment: 101 pages, 28 figures; journal versio
Chiral dynamics with (non)strange quarks
We review the results and achievements of the project B.3. Topics addressed include pion photoproduction off the proton and off deuterium, three-flavor chiral perturbation theory studies, chiral symmetry tests in Goldstone boson decays, the development of unitarized chiral perturbation theory to next-to-leading order, the two-pole structure of the Λ(1405), the dynamical generation of the lowest S11 resonances, the theory of hadronic atoms and its application to various systems, precision studies in light-meson decays based on dispersion theory, the Roy–Steiner analysis of pion–nucleon scattering, a high-precision extraction of the elusive pion–nucleon σ-term, and aspects of chiral dynamics in few-nucleon systems
Threshold π<sup>0</sup> photoproduction on transverse polarised protons at MAMI
Polarisation-dependent differential cross sections σTσT associated with the target asymmetry T have been measured for the reaction View the MathML sourceγp→→pπ0 with transverse target polarisation from π0π0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σTσT have been used in combination with our previous measurements of the unpolarised cross section σ0σ0 and the beam asymmetry Σ for a model-independent determination of S- and P -wave multipoles in the π0π0 threshold region, which includes for the first time a direct determination of the imaginary part of the E0+E0+ multipole
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