196 research outputs found
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
T and F asymmetries in π0 photoproduction on the proton
The γp→π0p reaction was studied at laboratory photon energies from 425 to 1445 MeV with a transversely polarized target and a longitudinally polarized beam. The beam-target asymmetry F was measured for the first time and new high precision data for the target asymmetry T were obtained. The experiment was performed at the photon tagging facility of the Mainz Microtron (MAMI) using the Crystal Ball and TAPS photon spectrometers. The polarized cross sections were expanded in terms of associated Legendre functions and compared to recent predictions from several partial-wave analyses. The impact of the new data on our understanding of the underlying partial-wave amplitudes and baryon resonance contributions is discussed
Measurement of the transverse target and beam-target asymmetries in meson photoproduction at MAMI
We present new data for the transverse target asymmetry T and the very first
data for the beam-target asymmetry F in the
reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained
with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility
of the Mainz Microtron MAMI. All existing model predictions fail to reproduce
the new data indicating a significant impact on our understanding of the
underlying dynamics of meson photoproduction. The peculiar nodal
structure observed in existing T data close to threshold is not confirmed.Comment: 5 pages, 3 figures, accepted for publication in PR
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
Photoproduction of -pairs off protons and off neutrons
Total cross sections, angular distributions, and invariant-mass distributions
have been measured for the photoproduction of pairs off free
protons and off nucleons bound in the deuteron. The experiments were performed
at the MAMI accelerator facility in Mainz using the Glasgow photon tagging
spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered
electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin
radiator foils. The tagged photon beam covered energies up to 1400~MeV. The
data from the free proton target are in good agreement with previous
measurements and were only used to test the analysis procedures. The results
for differential cross sections (angular distributions and invariant-mass
distributions) for free and quasi-free protons are almost identical in shape,
but differ in absolute magnitude up to 15\%. Thus, moderate final-state
interaction effects are present. The data for quasi-free neutrons are similar
to the proton data in the second resonance region (final state invariant masses
up to 1550~MeV), where both reactions are dominated by the
decay. At higher energies,
angular and invariant-mass distributions are different. A simple analysis of
the shapes of the invariant-mass distributions in the third resonance region is
consistent with strong contributions of an decay
for the proton, while the reaction is dominated by a sequential decay via a
intermediate state for the neutron. The data are compared to
predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel
analysis.Comment: accepted for publication in Eur. Phys. J.
Photoproduction of π0-pairs off protons and off neutrons
Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of π0π0 pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to ≈1550 MeV), where both reactions are dominated by the N(1520)3/2−→Δ(1232)3/2+π decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an N⋆→Nσ decay for the proton, while the reaction is dominated by a sequential decay via a Δπ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis
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
Measurements of double-polarized compton scattering asymmetries and extraction of the proton spin polarizabilities
The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to extract the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the Δ(1232) region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields γE1E1=−3.5±1.2, γM1M1=3.16±0.85, γE1M2=−0.7±1.2, and γM1E2=1.99±0.29, in units of 10−4 fm4
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
Groundwater resources assessment using integrated geophysical techniques in the southwestern region of Peninsular Malaysia.
Combined geophysical techniques such as multi-electrode resistivity, induced polarization, and borehole geophysical techniques were carried out on volcano-sedimentary rocks in the north of Gemas as part of the groundwater resource’s investigations. The result identifies four resistivity units: the tuffaceous mudstone, tuffaceous sandstone, the tuff bed, and the shale layer. Two types of aquifer systems in terms of storage were identified within the area: one within a fracture system (tuff), which is the leaky area through which vertical flow of groundwater occurs, and an intergranular property of the sandy material of the aquifer which includes sandstone and tuffaceous sandstone. The result also reveals that the aquifer occupies a surface area of about 3,250,555 m2 with a mean depth of 43.71 m and a net volume of 9.798 × 107 m3. From the approximate volume of the porous zone (28 %) and the total aquifer volume, a usable capacity of (274.339 ± 30.177) × 107 m3 of water in the study area can be deduced. This study provides useful information that can be used to develop a much broader understanding of the nature of groundwater potential in the area and their relationship with the local geology
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