420 research outputs found
Ethical issues in the use of in-depth interviews: literature review and discussion
This paper reports a literature review on the topic of ethical issues in in-depth interviews. The review returned three
types of article: general discussion, issues in particular studies, and studies of interview-based research ethics. Whilst
many of the issues discussed in these articles are generic to research ethics, such as confidentiality, they often had particular
manifestations in this type of research. For example, privacy was a significant problem as interviews sometimes
probe unexpected areas. For similar reasons, it is difficult to give full information of the nature of a particular interview
at the outset, hence informed consent is problematic. Where a pair is interviewed (such as carer and cared-for) there are
major difficulties in maintaining confidentiality and protecting privacy. The potential for interviews to harm participants
emotionally is noted in some papers, although this is often set against potential therapeutic benefit. As well as
these generic issues, there are some ethical issues fairly specific to in-depth interviews. The problem of dual role is noted
in many papers. It can take many forms: an interviewer might be nurse and researcher, scientist and counsellor, or
reporter and evangelist. There are other specific issues such as taking sides in an interview, and protecting vulnerable
groups. Little specific study of the ethics of in-depth interviews has taken place. However, that which has shows some
important findings. For example, one study shows participants are not averse to discussing painful issues provided they
feel the study is worthwhile. Some papers make recommendations for researchers. One such is that they should consider
using a model of continuous (or process) consent rather than viewing consent as occurring once, at signature, prior
to the interview. However, there is a need for further study of this area, both philosophical and empirical
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
and photoproduction with fine center-of-mass energy resolution
Measurements of and cross-sections have been obtained with the photon
tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement
uses a novel meson identification technique in which the weak decay
products are characterized using the energy and timing characteristics of the
energy deposit in the calorimeter, a method that has the potential to be
applied at many other facilities. The fine center-of-mass energy ()
resolution and statistical accuracy of the new data results in a significant
impact on partial wave analyses aiming to better establish the excitation
spectrum of the nucleon. The new analyses disfavor a strong role for
quark-diquark dynamics in the nucleon.Comment: 7 pages, 8 figure
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
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
Quasi-free photoproduction of η-mesons off 3He nuclei
Quasi-free photoproduction of η-mesons has been measured off nucleons bound in 3He nuclei for incident photon energies from the threshold region up to 1.4 GeV. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with an almost 4π covering electromagnetic calorimeter, combining the TAPS and Crystal Ball detectors. The η-mesons were detected in coincidence with the recoil nucleons. This allowed a comparison of the production cross section off quasi-free protons and quasi-free neutrons and a full kinematic reconstruction of the final state, eliminating effects from nuclear Fermi motion. In the S11(1535) resonance peak, the data agree with the neutron/proton cross section ratio extracted from measurements with deuteron targets. More importantly, the prominent structure observed in photoproduction off quasi-free neutrons bound in the deuteron is also clearly observed. Its parameters (width, strength) are consistent with the expectations from the deuteron results. On an absolute scale the cross sections for both quasi-free protons and neutrons are suppressed with respect to the deuteron target pointing to significant nuclear final-state interaction effects
Measurement of the beam-helicity asymmetry in the photoproduction of -pairs off protons and off neutrons
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz
for the photoproduction of mixed-charge pion pairs in the reactions
off free protons and
and
off quasi-free nucleons bound
in the deuteron for incident photon energies up to 1.4 GeV. Circularly
polarized photons were produced from bremsstrahlung of longitudinally polarized
electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The charged
pions, recoil protons, recoil neutrons, and decay photons from mesons
were detected in the 4 electromagnetic calorimeter composed of the Crystal
Ball and TAPS detectors. Using a complete kinematic reconstruction of the final
state, excellent agreement was found between the results for free and
quasi-free protons, suggesting that the quasi-free neutron results are also a
close approximation of the free-neutron asymmetries. A comparison of the
results to the predictions of the Two-Pion-MAID reaction model shows that the
reaction mechanisms are still not well understood, in particular at low
incident photon energies in the second nucleon-resonance region.Comment: accepted for publication in Eur. phys. J.
The isospin structure of photoproduction of pi-eta pairs from the nucleon in the threshold region
Photoproduction of -pairs from nucleons has been investigated from
threshold up to incident photon energies of ~1.4~GeV. The quasi-free
reactions , ,
, and were for
the first time measured from nucleons bound in the deuteron. The corresponding
reactions from a free-proton target were also studied to investigate
final-state interaction effects (for neutral pions the free-proton results
could be compared to previous measurements; the reaction was measured for the first time). For the
final state coherent production via the
reaction was also investigated. The experiments were performed at the tagged
photon beam of the Mainz MAMI accelerator using an almost coverage
electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors.
The total cross sections for the four different final states obey the relation
as expected for a
dominant contribution from a
reaction chain,
which is also supported by the shapes of the invariant-mass distributions of
nucleon-meson and - pairs. The experimental results are compared to
the predictions from an isobar reaction model.Comment: accepted for publication in Phys. Lett.
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
- …