Adverse respiratory patterns in near-term spontaneously breathing newborn lambs with elevated airway liquid volumes at birth

Introduction

Recent evidence indicates that respiratory distress (RD) in near-term infants is caused by elevated airway liquid (EL) volume at the beginning of air-breathing after birth. While the adverse effects EL volumes on newborn lung function are known, the effects on respiratory control and breathing patterns shortly after birth (<4 h) are unknown. We investigated the effects of EL volumes on cardiorespiratory function and breathing patterns in spontaneously breathing near-term newborn lambs in the first hours after birth.

Methods

At 137-8 days gestation (2-3 days prior to delivery; term ∼147 days), sterile surgery was performed on fetal sheep (n = 17) to implant catheters and blood flow probes. At 140 days, lambs were delivered via caesarean section under spinal anaesthesia. Airway liquid volumes were adjusted to mimic the level expected following vaginal delivery (∼10 ml/kg; Controls; n = 7), or elective caesarean section (∼30 ml/kg; elevated airway liquid group; EL; n = 10). Spontaneous breathing and cardiorespiratory parameters were recorded over four hours after birth. Non-invasive respiratory support with supplemental oxygen was provided if required.

Results

EL lambs required higher inspired oxygen levels (p = 0.0002), were less active (p = 0.026), fed less (p = 0.008) and had higher respiratory morbidity scores than Controls (p < 0.0001). EL lambs also displayed higher rates of breathing patterns associated with RD, such as expiratory braking and tachypnoea. These patterns were particularly evident in male EL lambs who displayed higher levels of severe respiratory morbidity (e.g., expiratory braking) than female EL lambs.

Conclusion

The study demonstrates that EL volumes at birth trigger respiratory behaviour and breathing patterns that resemble clinically recognised features of RD in term infants.

Constant-pH Simulations with the Polarizable Atomic Multipole AMOEBA Force Field

Accurately predicting protein behavior across diverse pH environments remains a significant challenge in biomolecular simulations. Existing constant-pH molecular dynamics (CpHMD) algorithms are limited to fixed-charge force fields, hindering their application to biomolecular systems described by permanent atomic multipoles or induced dipoles. This work overcomes these limitations by introducing the first polarizable CpHMD algorithm in the context of the Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field. Additionally, our implementation in the open-source Force Field X (FFX) software has the unique ability to handle titration state changes for crystalline systems including flexible support for all 230 space groups. The evaluation of constant-pH molecular dynamics (CpHMD) with the AMOEBA force field was performed on 11 crystalline peptide systems that span the titrating amino acids (Asp, Glu, His, Lys, and Cys). Titration states were correctly predicted for 15 out of the 16 amino acids present in the 11 systems, including for the coordination of Zn2+ by cysteines. The lone exception was for a HIS-ALA peptide where CpHMD predicted both neutral histidine tautomers to be equally populated, whereas the experimental model did not consider multiple conformers and diffraction data are unavailable for rerefinement. This work demonstrates the promise polarizable CpHMD simulations for pKa predictions, the study of biochemical mechanisms such as the catalytic triad of proteases, and for improved protein-ligand binding affinity accuracy in the context of pharmaceutical lead optimization.

First Measurement Using Elliptically Polarized Photons of the Double-Polarization Observable E for γp→pπ^{0} and γp→nπ^{+}

We report the measurement of the helicity asymmetry E for the pπ^{0} and nπ^{+} final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G) and circularly polarized photons (e.g., E) and a longitudinally polarized target. The new data cover a photon energy range 270-1400 MeV for the pπ^{0} final state (230-842 MeV for the nπ^{+} final state) and the full range of pion polar angles, θ, providing the most precise measurement of the observable E. A moment analysis gives a clear observation of the pη cusp in the pπ^{0} final state.

Measurement of polarization observables T, P, and H in π0 and η photoproduction off quasi-free nucleons

The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive π 0 and η photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the γ p → π 0 p and γ p → η p reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the η n system at W = 1.68 GeV . A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the S 11 ( 1535 ) and S 11 ( 1650 ) resonances within the S 11 -partial wave.

Respiratory patterns in spontaneously breathing near-term lambs delivered by caesarean section under spinal anaesthesia

Introduction

The transition to newborn life has typically been studied in intubated and mechanically ventilated newborn lambs delivered via caesarean section (CS) under general anaesthesia. As a result, little is known of the spontaneous breathing patterns in lambs at birth, particularly those at risk of developing respiratory distress (RD). We have developed a method for delivering spontaneously breathing near-term lambs to characterise their breathing patterns in the immediate newborn period.

Methods

At 137-8 days gestation (2-3 days prior to delivery; term ∼147 days), fetal lambs (n = 7) were partially exteriorised for instrumentation (insertion of catheters and flow probes) before they were returned to the uterus. At 140 days, lambs were delivered via CS under light maternal sedation and spinal anaesthesia. Lambs were physically stimulated and when continuous breathing was established, the umbilical cord was clamped. Breathing patterns were assessed by measuring intrapleural and upper-tracheal pressures during the first four hours after birth.

Results

Newborn lambs display significant heterogeneity in respiratory patterns in the immediate newborn period that change with time after birth. Seven distinct breathing patterns were identified including: (i) quiet (tidal) breathing, (ii) breathing during active periods, (iii) breathing during oral feeding, (iv) tachypnoea, (v) expiratory braking manoeuvres, (vi) expiratory pauses or holding, and (vii) step changes in ventilation.

Conclusions

We have described normal respiratory behaviour in newborn lambs, in order to identify respiratory behaviours that are indicative of RD in term newborn infants.

Triangle Singularity as the Origin of the a_{1}(1420)

The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the a_{1}(1420), decaying to f_{0}(980)π. With a mass too close to and a width smaller than the axial-vector ground state a_{1}(1260), it was immediately interpreted as a new light exotic meson, similar to the X, Y, Z states in the hidden-charm sector. We show that a resonancelike signal fully matching the experimental data is produced by the decay of the a_{1}(1260) resonance into K^{*}(→Kπ)K[over ¯] and subsequent rescattering through a triangle singularity into the coupled f_{0}(980)π channel. The amplitude for this process is calculated using a new approach based on dispersion relations. The triangle-singularity model is fitted to the partial-wave data of the COMPASS experiment. Despite having fewer parameters, this fit shows a slightly better quality than the one using a resonance hypothesis and thus eliminates the need for an additional resonance in order to describe the data. We thereby demonstrate for the first time in the light-meson sector that a resonancelike structure in the experimental data can be described by rescattering through a triangle singularity, providing evidence for a genuine three-body effect.

BaSAlt - A mixed-methods study protocol on setting-based physical activity promotion and counseling in nursing homes

Introduction

Physical activity (PA) is a major contributor to healthy aging. However, physical inactivity is prevalent among the elderly in Germany, particularly in institutionalized settings such as nursing homes. This paper aims to describe the study objectives, design, methods, assessment types, collection schedules and considerations for analyzing the data within the BaSAlt study on facilitators and barriers for PA promotion in nursing homes.

Methods

We designed the BaSAlt study as a participatory intervention study with multiple measurement points in six to eight nursing homes with a total of approx. 200 residents using four main modules: (1) setting-level analysis of physical activity patterns, physical activity-related climate and physical activity-related interaction with ‘significant others,’ and organizational facilitators and barriers to physical activity, (2) physical-activity related individual-level analysis of objective and self-reported physical activity and sedentary behavior, a geriatric assessment with established procedures, assessment of people's activity and health biographies (biographical mapping) as well as their motivational, subjective well-being and distress status, and (3) a counseling module that integrates counseling at the setting level as well as individual physical activity counseling for residents. In module (4) evaluation, the effects of integrated counseling with regard to the implementation of PA promotion strategies are analyzed.

Discussion

This study will extend our knowledge of physical activity promotion in German nursing homes. Its findings will inform governmental authorities, care professionals, and academics on how to reach a particular group, characterized by inactivity, multimorbidity, and a high prevalence of dementia, residing in nursing homes, a setting that will gain further relevance in the future.

Single π 0 production off neutrons bound in deuteron with linearly polarized photons

The quasifree γ → d → π 0 n ( p ) photon beam asymmetry, Σ , has been measured at photon energies, E γ , from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 ∘ to 148 ∘ . In this kinematic region, polarization observables are sensitive to contributions from the Δ ( 1232 ) and N(1440) resonances. The extracted values of Σ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID and Bonn-Gatchina analyses; while a revised SAID fit, including the new Σ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict π 0 n photoproduction observables, based on fits to published data in the channels π 0 p , π + n and π - p .

Measurement of the Charge-Averaged Elastic Lepton-Proton Scattering Cross Section by the OLYMPUS Experiment

We report the first measurement of the average of the electron-proton and positron-proton elastic scattering cross sections. This lepton charge-averaged cross section is insensitive to the leading effects of hard two-photon exchange, giving more robust access to the proton's electromagnetic form factors. The cross section was extracted from data taken by the OLYMPUS experiment at DESY, in which alternating stored electron and positron beams were scattered from a windowless gaseous hydrogen target. Elastic scattering events were identified from the coincident detection of the scattered lepton and recoil proton in a large-acceptance toroidal spectrometer. The luminosity was determined from the rates of Møller, Bhabha, and elastic scattering in forward electromagnetic calorimeters. The data provide some selectivity between existing form factor global fits and will provide valuable constraints to future fits.

Measurement of the helicity asymmetry E for the reaction γ p → π 0 p : The CBELSA/TAPS Collaboration

A measurement of the double-polarization observable E for the reaction γ p → π 0 p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C4 H9 OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range fromE γ = 600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.

Observation of the pη^{'} Cusp in the New Precise Beam Asymmetry Σ Data for γp→pη

Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748  MeV to W=2045  MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447  MeV (W=1896  MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.

Helicity-Dependent Cross Sections for the Photoproduction of π^{0} Pairs from Nucleons

The double-polarization observable E and helicity-dependent cross sections σ_{1/2}, σ_{3/2} have been measured for the photoproduction of π^{0} pairs off quasifree protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost 4π covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the γN→Nπ^{0}π^{0} reaction. They are compared to predictions from reaction models in view of nucleon resonance contributions and also to a refit of one model that predicted results for the proton and for the neutron target. The comparison of the prediction and the refit demonstrates the large impact of the new data.

Signatures of the d^{*}(2380) Hexaquark in d(γ,pn[over →])

We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570  MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.

First Measurement of Near-Threshold J/ψ Exclusive Photoproduction off the Proton

We report on the measurement of the γp→J/ψp cross section from E_{γ}=11.8  GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find that the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section dσ/dt has an exponential slope of 1.67±0.39  GeV^{-2} at 10.7 GeV average energy. The LHCb pentaquark candidates P_{c}^{+} can be produced in the s channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions B(P_{c}^{+}→J/ψp) and cross sections σ(γp→P_{c}^{+})×B(P_{c}^{+}→J/ψp).

The Mutational Profile of Unicystic Ameloblastoma

BRAF V600E is the most common mutation in conventional ameloblastoma (AM) of the mandible. In contrast, maxillary AMs appear to harbor more frequently RAS, FGFR2, or SMO mutations. Unicystic ameloblastoma (UAM) is considered a less aggressive variant of ameloblastoma, amenable to more conservative treatment, and classified as a distinct entity. The aim of this study was to characterize the mutation profile of UAM ( n = 39) and to compare it to conventional AM ( n = 39). The associations between mutation status and recurrence probability were also analyzed. In the mandible, 94% of UAMs (29/31, including 8/8 luminal, 6/8 intraluminal, and 15/15 mural subtypes) and 74% of AMs (28/38) revealed BRAF V600E mutations. Among the BRAF wild-type cases, 1 UAM showed a missense SMO mutation (p.L412F), whereas 2 NRAS (p.Q61R), 2 HRAS (p.Q61R), and 2 FGFR2 (p.C383R) activating mutations were identified in AM. Of the 3 maxillary UAMs, only 1 revealed a BRAF V600E mutation. Taken together, our findings demonstrate high frequency of activating BRAF V600E mutations in both UAM and AM of the mandible. In maxillary UAMs, the BRAF V600E mutation prevalence appears to be lower as was shown for AM previously. It could therefore be argued that UAM and AM are part of the spectrum of the same disease. AMs without BRAF V600E mutations were associated with an increased rate of local recurrence ( P = 0.0003), which might indicate that routine mutation testing also has an impact on prognosis.

Realization of Security Concepts for DICOM-based Distributed Medical Services

Exploiting distributed hard- and software resources for tele-medicine requires a fast, secure, and platform-independent data exchange. Standards without inherent security mechanisms such as DICOM may ease non-authorized data access. Therefore, exemplary telemedical data streams were analyzed within the Berlin metropolitan area network using specialized magnetic resonance imaging techniques and distributed resources for data postprocessing. For secure DICOM communication both the Secure Socket Layer Protocol and a DICOM-conform partial encryption of patient-relevant data were implemented. Partial encryption exhibited the highest transfer rate and enabled a secure long-term storage. Different data streams between secured and unsecured networks were realized using partial encryption.

Cyclotrimerization of phenylacetylene catalyzed by a cobalt half-sandwich complex embedded in an engineered variant of transmembrane protein FhuA

An (η⁵-cyclopentadienyl)cobalt(i) complex was covalently incorporated in an engineered variant of the β-barrel protein FhuA. The new biohydrid catalyst cyclotrimerized phenylacetylene to give regioisomeric triphenylbenzenes.

First Measurement of Transverse-Spin-Dependent Azimuthal Asymmetries in the Drell-Yan Process

The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190  GeV/c π^{-} beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3  GeV/c^{2} and 8.5  GeV/c^{2}. Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.

Study of η and η' Photoproduction at MAMI

The reactions γp→ηp and γp→η^{'}p are measured from their thresholds up to the center-of-mass energy W=1.96  GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η^{'} threshold, W=1896  MeV (E_{γ}=1447  MeV). Within the framework of a revised ηMAID isobar model, the cusp, in connection with a steep rise of the η^{'} total cross section from its threshold, can only be explained by a strong coupling of the poorly known N(1895)1/2^{-} state to both ηp and η^{'}p. Including the new high-accuracy results in the ηMAID fit to available η and η^{'} photoproduction data allows the determination of the N(1895)1/2^{-} properties.

Short communication: Repeatability of β-hydroxybutyrate measurements in capillary blood obtained from the external vulvar skin

The primary objective of this study was to evaluate the repeatability of measurements of β-hydroxybutyrate (BHB) concentrations in capillary blood obtained from minimal-invasive puncturing of different sites at the external vulva skin of dairy cows. A total of 240 multiparous cows sampled once within 21 d in milk were enrolled in the study. Capillary blood samples were obtained from the right and left labium of the external vulva skin and additionally from a site close to the first puncture. Samples were analyzed by using an electronic hand-held device [FreeStyle Precison Neo (FSP-Neo), Abbott GmbH & Co., Wiesbaden, Germany)]. Additionally, samples from a coccygeal vessel were analyzed as reference in a laboratory. Mean deviations (± standard deviation) between the 3 capillary sampling sites ranged from 0.01 ± 0.14 (left vs. right labium) to 0.02 ± 0.13 mmol/L (left or right labium vs. additional site). The BHB concentrations in capillary blood compared with the reference showed a mean deviation of 0.14 ± 0.18 mmol/L. The Spearman correlation coefficient between BHB concentrations in capillary blood and coccygeal blood was 85.4%. Mixed model analyses showed no significant effect of sampling site or squeezing the skin during sampling procedures on the differences toward the reference. Based on laboratory BHB concentrations of ≥1.2 and ≥1.4 mmol/L, respectively, the prevalence of hyperketonemia was 10.4 (n = 25) and 5.0% (n = 12). Thresholds to detect hyperketonemia with the FSP-Neo were optimized by receiver operating characteristic analyses. Based on a laboratory BHB concentration of ≥1.2 mmol/L thresholds were determined as 1.1 (left labium, 2nd puncture) and 1.0 mmol/L (right labium), with sensitivities between 94 and 99% and specificities between 89 and 97%. Based on a serum BHB concentration of 1.4 mmol/L, receiver operating characteristic analyses resulted in optimized cutoffs of 1.4 mmol/L for all sampling sites at the vulva, with sensitivities of 100% and specificities between 96 and 99%. In conclusion, vulvar capillary blood is suitable for accurate measuring of BHB concentrations by using the FSP-Neo. After adjusting the thresholds, the FSP-Neo provides very good test characteristics independent of the capillary sampling site or squeezing the skin and allows a practical and reliable screening tool for dairy cows.

Short communication: Repeatability of β-hydroxybutyrate measurements in capillary blood obtained from the external vulvar skin

The primary objective of this study was to evaluate the repeatability of measurements of β-hydroxybutyrate (BHB) concentrations in capillary blood obtained from minimal-invasive puncturing of different sites at the external vulva skin of dairy cows. A total of 240 multiparous cows sampled once within 21 d in milk were enrolled in the study. Capillary blood samples were obtained from the right and left labium of the external vulva skin and additionally from a site close to the first puncture. Samples were analyzed by using an electronic hand-held device [FreeStyle Precison Neo (FSP-Neo), Abbott GmbH & Co., Wiesbaden, Germany)]. Additionally, samples from a coccygeal vessel were analyzed as reference in a laboratory. Mean deviations (± standard deviation) between the 3 capillary sampling sites ranged from 0.01 ± 0.14 (left vs. right labium) to 0.02 ± 0.13 mmol/L (left or right labium vs. additional site). The BHB concentrations in capillary blood compared with the reference showed a mean deviation of 0.14 ± 0.18 mmol/L. The Spearman correlation coefficient between BHB concentrations in capillary blood and coccygeal blood was 85.4%. Mixed model analyses showed no significant effect of sampling site or squeezing the skin during sampling procedures on the differences toward the reference. Based on laboratory BHB concentrations of ≥1.2 and ≥1.4 mmol/L, respectively, the prevalence of hyperketonemia was 10.4 (n = 25) and 5.0% (n = 12). Thresholds to detect hyperketonemia with the FSP-Neo were optimized by receiver operating characteristic analyses. Based on a laboratory BHB concentration of ≥1.2 mmol/L thresholds were determined as 1.1 (left labium, 2nd puncture) and 1.0 mmol/L (right labium), with sensitivities between 94 and 99% and specificities between 89 and 97%. Based on a serum BHB concentration of 1.4 mmol/L, receiver operating characteristic analyses resulted in optimized cutoffs of 1.4 mmol/L for all sampling sites at the vulva, with sensitivities of 100% and specificities between 96 and 99%. In conclusion, vulvar capillary blood is suitable for accurate measuring of BHB concentrations by using the FSP-Neo. After adjusting the thresholds, the FSP-Neo provides very good test characteristics independent of the capillary sampling site or squeezing the skin and allows a practical and reliable screening tool for dairy cows.

Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment

The OLYMPUS Collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, R_{2γ}, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01 GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of ≈20° to 80°. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved gas electron multiplier and multiwire proportional chamber detectors at 12°, as well as symmetric Møller or Bhabha calorimeters at 1.29°. A total integrated luminosity of 4.5  fb^{-1} was collected. In the extraction of R_{2γ}, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of R_{2γ}, presented here for a wide range of virtual photon polarization 0.456<ε<0.978, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.

Insight into the Narrow Structure in η Photoproduction on the Neutron from Helicity-Dependent Cross Sections

The double polarization observable E and the helicity dependent cross sections σ_{1/2} and σ_{3/2} were measured for η photoproduction from quasifree protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost 4π detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from η→2γ and η→3π^{0}. The results show that the narrow structure previously observed in η photoproduction from the neutron is only apparent in σ_{1/2} and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in η production are only N 1/2^{-} (S_{11}) and N 1/2^{+} (P_{11}). Furthermore, the extracted Legendre coefficients of the angular distributions for σ_{1/2} are in good agreement with recent reaction model predictions assuming a narrow resonance in the P_{11} wave as the origin of this structure.

Three-body nature of N(*) and Δ(*) resonances from sequential decay chains

The Nπ^{0}π^{0} decays of positive-parity N^{*} and Δ^{*} resonances at about 2 GeV are studied at ELSA by photoproduction of two neutral pions off protons. The data reveal clear evidence for several intermediate resonances: Δ(1232), N(1520)3/2^{-}, and N(1680)5/2^{+}, with spin parities J^{P}=3/2^{+}, 3/2^{-}, and 5/2^{+}. The partial wave analysis (within the Bonn-Gatchina approach) identifies N(1440)1/2^{+} and the N(ππ)_{S wave} (abbreviated as Nσ here) as further isobars and assigns the final states to the formation of nucleon and Δ resonances and to nonresonant contributions. We observe the known Δ(1232)π decays of Δ(1910)1/2^{+}, Δ(1920)3/2^{+}, Δ(1905)5/2^{+}, Δ(1950)7/2^{+}, and of the corresponding spin-parity series in the nucleon sector, N(1880)1/2^{+}, N(1900)3/2^{+}, N(2000)5/2^{+}, and N(1990)7/2^{+}. For the nucleon resonances, these decay modes are reported here for the first time. Further new decay modes proceed via N(1440)1/2^{+}π, N(1520)3/2^{-}π, N(1680)5/2^{+}π, and Nσ. The latter decay modes are observed in the decay of N^{*} resonances and at most weakly in Δ^{*} decays. It is argued that these decay modes provide evidence for a 3-quark nature of N^{*} resonances rather than a quark-diquark structure.