First measurement of the helicity asymmetry E in η photoproduction on the proton

© 2016 Results are presented for the first measurement of the double-polarization helicity asymmetry E for the η photoproduction reaction γp→ηp. Data were obtained using the FROzen Spin Target (FROST) with the CLAS spectrometer in Hall B at Jefferson Lab, covering a range of center-of-mass energy W from threshold to 2.15 GeV and a large range in center-of-mass polar angle. As an initial application of these data, the results have been incorporated into the Jülich–Bonn model to examine the case for the existence of a narrow N⁎ resonance between 1.66 and 1.70 GeV. The addition of these data to the world database results in marked changes in the predictions for the E observable from that model. Further comparison with several theoretical approaches indicates these data will significantly enhance our understanding of nucleon resonances

‘When helpers hurt’: women’s and midwives’ stories of obstetric violence in state health institutions, Colombo district, Sri Lanka

BACKGROUND: The paper explores how age, social position or class, and linguistic and cultural background intersect and place women in varying positions of control and vulnerability to obstetric violence in state health institutions in Colombo district, Sri Lanka. Obstetric violence occurs during pregnancy, childbirth and the immediate postpartum period; hence, it is violence that directly affects women. The authors aim to break the traditional culture of silence around obstetric violence and bring attention to the resulting implications for quality of care and patient trust in obstetric care facilities or providers.METHODS: Five focus group discussions were held with 28 public health midwives who had prior experience working in labor rooms. Six focus group discussions were held with 38 pregnant women with previous childbirth experience. Additionally, 10 of the 38 women, whom felt they had experienced excessive pain, fear, humiliation, and/or loss of dignity as patients in labor, participated in individual in-depth interviews. An intersectional framework was used to group the qualitative data into categories and themes for analysis.RESULTS: Obstetric violence appears to intersect with systems of power and oppression linked to structural gender, social, linguistic and cultural inequities in Sri Lanka. In our dataset, younger women, poorer women, and women who did not speak Sinhala seemed to experience more obstetric violence than those with relevant social connections and better economic positions. The women in our study rarely reported obstetric violence to legal or institutional authorities, nor within their informal social support networks. Instead, they sought obstetric care, particularly for childbirth, in other state hospitals in subsequent pregnancies.CONCLUSIONS: The quality of obstetric care in Sri Lanka needs improvement. Amongst other initiatives, policies and practices are required to sensitize health providers about the existence of obstetric violence, and repercussions are required for abusive or discriminatory practices. The ethics of care should be further reinforced in the professional training of obstetric health providers.</p

Measurement of two-photon exchange effect by comparing elastic e±p cross sections

Background: The electromagnetic form factors of the proton measured by unpolarized and polarized electron scattering experiments show a significant disagreement that grows with the squared four-momentum transfer (Q2). Calculations have shown that the two measurements can be largely reconciled by accounting for the contributions of two-photon exchange (TPE). TPE effects are not typically included in the standard set of radiative corrections since theoretical calculations of the TPE effects are highly model dependent, and, until recently, no direct evidence of significant TPE effects has been observed. Purpose: We measured the ratio of positron-proton to electron-proton elastic-scattering cross sections in order to determine the TPE contribution to elastic electron-proton scattering and thereby resolve the proton electric form factor discrepancy. Methods: We produced a mixed simultaneous electron-positron beam in Jefferson Lab's Hall B by passing the 5.6-GeV primary electron beam through a radiator to produce a bremsstrahlung photon beam and then passing the photon beam through a convertor to produce electron-positron pairs. The mixed electron-positron (lepton) beam with useful energies from approximately 0.85 to 3.5 GeV then struck a 30-cm-long liquid hydrogen (LH2) target located within the CEBAF Large Acceptance Spectrometer (CLAS). By detecting both the scattered leptons and the recoiling protons, we identified and reconstructed elastic scattering events and determined the incident lepton energy. A detailed description of the experiment is presented. Results: We present previously unpublished results for the quantity R2γ, the TPE correction to the elastic-scattering cross section, at Q2≈0.85 and 1.45 GeV2 over a large range of virtual photon polarization ?. Conclusions: Our results, along with recently published results from VEPP-3, demonstrate a nonzero contribution from TPE effects and are in excellent agreement with the calculations that include TPE effects and largely reconcile the form-factor discrepancy up to Q2≈2GeV2. These data are consistent with an increase in R2γ with decreasing ? at Q2≈0.85 and 1.45 GeV2. There are indications of a slight increase in R2γ with Q2

First measurement of the polarization observable E in the p→(γ→,π⁺)n reaction up to 2.25 GeV

© 2015 The Authors. First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction γ→p→→π+n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-. L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn-Gatchina, Jülich-Bonn, and SAID groups

φ -meson photoproduction on hydrogen in the neutral decay mode

We report the first measurement of the photoproduction cross section of the phi meson in its neutral decay mode in the reaction gamma p -> p phi(KSKL). The experiment was performed with a tagged photon beam of energy 1.6 pK(S)X to be K-L. The presented results significantly enlarge the existing data on phi photoproduction. These data, combined with the data from the charged decay mode, will help to constrain different mechanisms of phi photoproduction