710 research outputs found
Systematic Study of Two-Pion Production in NN Collisions -- from Single-Baryon to Di-Baryon Excitations
The two-pion production in nucleon-nucleon collisions has been studied by
exclusive and kinematically complete experiments from threshold up to =
1.36 GeV at CELSIUS-WASA. At near-threshold energies the total and differential
distributions for the and channels are dominated by
Roper excitation and its decay into and channels. At beam
energies 1.1 GeV the excitation governs the two-pion
production process. In the channel evidence is found for the
excitation of a higher-lying I=3/2 resonance, favorably the . The
isovector fusion processes leading to the deuteron and to quasi-stable He,
respectively, %with the production of an isovector pion-pair exhibit no or only
a modest ABC-effect, {\it i.e.} low-mass enhancement in the -invariant
mass spectrum, and can be described by conventional -channel
excitation. On the other hand, the isoscalar fusion process to the deuteron
%with the production of an isoscalar pion-pair exhibits a dramatic ABC-effect
correlated with a narrow resonance-like energy dependence in the total cross
section with a width of only 50 MeV and situated at a mass 90 MeV below the
mass.Comment: Proceedings HADRON0
Primakoff effect in eta-photoproduction off protons
We analyse data on forward eta-meson photoproduction off a proton target and
extract the eta to gamma gamma decay width utilizing the Primakoff effect. The
hadronic amplitude that enters into our analysis is strongly constrained
because it is fixed from a global fit to available gamma p to p eta data for
differential cross sections and polarizations. We compare our results with
present information on the two-photon eta-decay from the literature. We provide
predictions for future PrimEx experiments at Jefferson Laboratory in order to
motivate further studies.Comment: 5 pages, 6 figures, gamma-gamma*-eta form factor included, version to
appear in Eur. Phys. J. A
Radiative open charm decay of the Y(3940), Z(3930), X(4160) resonances
We determine the radiative decay amplitudes for decay into and , or and of some of the charmonium like
states classified as X,Y,Z resonances, plus some other hidden charm states
which are dynamically generated from the interaction of vector mesons with
charm. The mass distributions as a function of the or
invariant mass show a peculiar behavior as a consequence of
the nature of these states. The experimental search of these
magnitudes can shed light on the nature of these states.Comment: 18 pages, 9 figure
Exploration of hyperfine interaction between constituent quarks via eta productions
In this work, the different exchange freedom, one gluon, one pion or
Goldstone boson, in constituent quark model is investigated, which is
responsible to the hyperfine interaction between constituent quarks, via the
combined analysis of the eta production processes,
and . With the Goldstone-boson exchange, as well as
the one-gluon or one-pion exchange, both the spectrum and observables, such as,
the differential cross section and polarized beam asymmetry, are fitted to the
suggested values of Particle Data Group and the experimental data. The first
two types of exchange freedoms give acceptable description of the spectrum and
observables while the one pion exchange can not describe the observables and
spectrum simultaneously, so can be excluded. The experimental data for the two
processes considered here strongly support the mixing angles for two lowest S11
sates and D13 states as about -30 and 6 degree respectively.Comment: 7 pages, 4 figures, 4 table
The {\eta}'-carbon potential at low meson momenta
The production of mesons in coincidence with forward-going
protons has been studied in photon-induced reactions on C and on a
liquid hydrogen (LH) target for incoming photon energies of 1.3-2.6 GeV at
the electron accelerator ELSA. The mesons have been identified
via the decay
registered with the CBELSA/TAPS detector system. Coincident protons have been
identified in the MiniTAPS BaF array at polar angles of . Under these kinematic constraints the
mesons are produced with relatively low kinetic energy (
150 MeV) since the coincident protons take over most of the momentum of the
incident-photon beam. For the C-target this allows the determination of the
real part of the -carbon potential at low meson momenta by
comparing with collision model calculations of the kinetic energy
distribution and excitation function. Fitting the latter data for
mesons going backwards in the center-of-mass system yields a potential depth of
V = (44 16(stat)15(syst)) MeV, consistent with earlier
determinations of the potential depth in inclusive measurements for average
momenta of 1.1 GeV/. Within the experimental
uncertainties, there is no indication of a momentum dependence of the
-carbon potential. The LH data, taken as a reference to check
the data analysis and the model calculations, provide differential and integral
cross sections in good agreement with previous results for
photoproduction off the free proton.Comment: 9 pages, 13 figures. arXiv admin note: text overlap with
arXiv:1608.0607
Expanding contraceptive options for PMTCT clients: a mixed methods implementation study in Cape Town, South Africa
Abstract
Background
Clients of prevention of mother-to-child transmission (PMTCT) services in South Africa who use contraception following childbirth rely primarily on short-acting methods like condoms, pills, and injectables, even when they desire no future pregnancies. Evidence is needed on strategies for expanding contraceptive options for postpartum PMTCT clients to include long-acting and permanent methods.
Methods
We examined the process of expanding contraceptive options in five health centers in Cape Town providing services to HIV-positive women. Maternal/child health service providers received training and coaching to strengthen contraceptive counseling for postpartum women, including PMTCT clients. Training and supplies were introduced to strengthen intrauterine device (IUD) services, and referral mechanisms for female sterilization were reinforced. We conducted interviews with separate samples of postpartum PMTCT clients (265 pre-intervention and 266 post-intervention) to assess knowledge and behaviors regarding postpartum contraception. The process of implementing the intervention was evaluated through systematic documentation and interpretation using an intervention tracking tool. In-depth interviews with providers who participated in study-sponsored training were conducted to assess their attitudes toward and experiences with promoting voluntary contraceptive services to HIV-positive clients.
Results
Following the intervention, 6% of interviewed PMTCT clients had the desired knowledge about the IUD and 23% had the desired knowledge about female sterilization. At both pre- and post-intervention, 7% of clients were sterilized and IUD use was negligible; by comparison, 75% of clients used injectables. Intervention tracking and in-depth interviews with providers revealed intervention shortcomings and health system constraints explaining the failure to produce intended effects.
Conclusions
The intervention failed to improve PMTCT clients’ knowledge about the IUD and sterilization or to increase use of those methods. To address the family planning needs of postpartum PMTCT clients in a way that is consistent with their fertility desires, services must expand the range of contraceptive options to include long-acting and permanent methods. In turn, to ensure consistent access to high quality family planning services that are effectively linked to HIV services, attention must also be focused on resolving underlying health system constraints weakening health service delivery more generally
Experimental constraints on the -nucleus real potential
In a search for mesic states, the production of -mesons in
coincidence with forward going protons has been studied in photon induced
reactions on C for incident photon energies of 1250 - 3100 MeV. The
pairs from decays of bound or quasi-free -mesons have
been measured with the CBELSA/TAPS detector system in coincidence with protons
registered in the MiniTAPS forward array. Structures in the total energy
distribution of the pairs, which would indicate the population
and decay of bound B states, are not observed. The
cross section of 0.3 nb/MeV/sr observed in the bound state energy regime
between -100 and 0 MeV may be accounted for by yield leaking into the bound
state regime because of the large in-medium width of the -meson. A
comparison of the measured total energy distribution with calculations suggests
the real part of the B potential to be small and only
weakly attractive with 35(stat) 20(syst) MeV
in contrast to some theoretical predictions of attractive potentials with a
depth of 100 - 150 MeV.Comment: 13 pages, 8 figure
Photoproduction of pi0 omega off protons for E(gamma) < 3 GeV
Differential and total cross-sections for photoproduction of gamma proton to
proton pi0 omega and gamma proton to Delta+ omega were determined from
measurements of the CB-ELSA experiment, performed at the electron accelerator
ELSA in Bonn. The measurements covered the photon energy range from the
production threshold up to 3GeV.Comment: 8 pages, 13 figure
Measurement of polarisation observables in photoproduction off the proton
The reaction is studied in the
photon energy range from threshold. Linearly polarised photon beams from
coherent bremsstrahlung enabled the first measurement of photon beam
asymmetries in this reaction up to MeV. In addition, the
recoil hyperon polarisation was determined through the asymmetry in the weak
decay up to MeV. The data are
compared to partial wave analyses, and the possible impact on the
interpretation of a recently observed cusp-like structure near the
thresholds is discussed.Comment: 6 pages, 5 figures. References [8,9,10,11] which were not on the
original submission are now include
Photoproduction of {\omega} Mesons off the Proton
The differential cross sections and unpolarized spin-density matrix elements
for the reaction were measured using the CBELSA/TAPS
experiment for initial photon energies ranging from the reaction threshold to
2.5 GeV. These observables were measured from the radiative decay of the
meson, . The cross sections cover the full
angular range and show the full extent of the -channel forward rise. The
overall shape of the angular distributions in the differential cross sections
and unpolarized spin-density matrix elements are in fair agreement with
previous data. In addition, for the first time, a beam of linearly-polarized
tagged photons in the energy range from 1150 MeV to 1650 MeV was used to
extract polarized spin-density matrix elements.
These data were included in the Bonn-Gatchina partial wave analysis (PWA).
The dominant contribution to photoproduction near threshold was found
to be the partial wave, which is primarily due to the sub-threshold
resonance. At higher energies, pomeron-exchange was found to
dominate whereas -exchange remained small. These -channel contributions
as well as further contributions from nucleon resonances were necessary to
describe the entire dataset: the , , and partial waves
were also found to contribute significantly.Comment: 8 pages, 5 figures, accepted for publication in Physics Letters
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