Photoproduction of the ω\omega meson on the proton at large momentum transfer

The differential cross section, $d\sigma/dt$ for $\omega$ meson exclusive photoproduction on the proton above the resonance region ($2.6<W<2.9$ GeV) was measured up to a momentum transfer $-t = 5$ GeV$^2$ using the CLAS detector at Jefferson Laboratory. The $\omega$ channel was identified by detecting a proton and $\pi^+$ in the final state and using the missing mass technique. While the low momentum transfer region shows the typical diffractive pattern expected from Pomeron and Reggeon exchange, at large $-t$ the differential cross section has a flat behavior. This feature can be explained by introducing quark interchange processes in addition to the QCD-inspired two-gluon exchange.Comment: 5 pages, 5 figure

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Deuteron Magnetic Dipole Disintegration by 180° Electron Scattering

The magnetic dipole disintegration of the deuteron has been measured for excitation energies up to 16 MeV in the presence of relatively small electric multipole contributions by using a method of inelastic electron scattering at 180°. Electrons of initial energy 41.5 MeV were magnetically deflected before and after scattering so that those scattered at 180° entered a magnetic spectrometer set at 160° with respect to the incident beam. The experimental cross sections measured relative to elastic scattering from the proton are higher than predicted by the electrodisintegration theory of Jankus. The discrepancy may be an indication of mesonic exchange currents which are not included in the Jankus theory

Electron scattering from 10B

Electron scattering measurements have been made in order to determine the longitudinal and transverse form factors of low-lying level in 10B. With the exception of the broad 5.18 MeV level, results were obtained for all known levels up to 6.7 MeV. The measurements span the momentum transfer range q=0.48–2.58 fm-1. The primary objective of this work was to improve the data on the pure isovector M3 form factor of the 1.740 MeV excitation, the transform of which yields the 1p3/2 single-nucleon wave function. A Woods-Saxon potential was found to provide a much better representation of the data than the harmonic oscillator model, and the rms size of this orbit was determined to be 2.79±0.11 fm in the relative core-particle coordinate frame. Nevertheless, confidence in the quantitative details of this interpretation is hindered by conflicting evidence regarding the contribution of core polarization. Our analysis of the Coulomb elastic form factor gave an rms radius for the ground-state charge distribution equal to 2.58±0.05±0.05 fm, slightly larger than values previously published. Longitudinal and transverse form factors deduced for inelastic transitions were compared with theoretical results of conventional 1p-shell models, models with 1ħω and 2ħω configurations involving the 1s, 2s1d, and 2p1f shells, and finally, a model that included core polarization. Although restricted 1p-shell models were found to provide good predictions for the 10B natural-parity level spectrum and transverse form factors, they were less successful for C2 form factors: not only is there a considerable dependence on the 1p-shell interaction, but these models give just 45% of the total observed C2 transition strength. Only a 10% improvement was realized by expanding the shell model space to include 2ħω configurations. The inclusion of even higher-excited configurations by means of core polarization calculations was essential to remove the remaining shortfall

Investigation of the 10B(γ,p) reaction using tagged photons

The reaction 10B(γ,p) has been studied using tagged photons of mean energies Eγ=57.6 and 72.9 MeV. Angular distributions and derived single-particle momentum distributions for protons leading to the ground state of 9Be and higher excited states are compared to various calculations made using model parameters constrained by 10B(e,e′p)9Be and 9Be(p,p′)9Be measurements. The effects of varying final-state interactions (including channel couplings) and meson exchange currents are considered. A sizable discrepancy between direct-knockout calculations and the experimental results is observed. If meson exchange currents are included in an approximate fashion, a good description of the 10B(γ,p0)9Be data is found

Measurements of the electric and magnetic form factors of the proton from Q2=1.75 to 8.83 (GeV/c)2

The proton elastic form factors GEp(Q2) and GMp(Q2) have been extracted for Q2=1.75 to 8.83 (GeV/c)2 via a Rosenbluth separation to ep elastic cross section measurements in the angular range 13°≤θ≤90°. The Q2 range covered more than doubles that of the existing data. For Q2\u3c4 \u3e(GeV/c)2, where the data overlap with previous measurements, the total uncertainties have been reduced to \u3c 14% in GEp and \u3c 1.5% in GMp. Results for GEp(Q2) are consistent with the dipole fit GD(Q2)=(1+Q2/0.71)-2, while those for GMp(Q2)/μpGD(Q2) decrease smoothly from 1.05 to 0.92. Deviations from form factor scaling are observed up to 20%. The ratio Q2F2/F1 is observed to approach a constant value for Q2\u3e3 (GeV/c)2. Comparisons are made to vector meson dominance, dimensional scaling, QCD sum rule, diquark, and constituent quark models, none of which fully characterize all the new data

Radial Dependence of the Nucleon Effective Mass in 10B

The dynamic properties of the atomic nucleus depend strongly on correlations between the nucleons. We present a combined analysis of inelastic electron-scattering data and electron-induced proton knockout measurements in an effort to obtain phenomenological information on nucleon-nucleon correlations. Our results indicate that the ratio of radial wave functions extracted from precise 10B(e,e′) and 10B(e,e′p) measurements evolve from an interior depression for small Em, characteristic of short-range correlations, to a surface-peaked enhancement for larger Em, characteristic of long-range correlations. This observation can be interpreted in terms of the nucleon effective mass

Relativistic Effects and Two-Body Currents in 2H(e⃗,e′p)n Using Out-of-Plane Detection

Measurements of the 2H(e⃗,e′p)n reaction were performed with the out-of-plane magnetic spectrometers (OOPS) at the MIT-Bates Linear Accelerator. The longitudinal-transverse, fLT and fLT′, and the transverse-transverse, fTT, interference responses at a missing momentum of 210MeV/c were simultaneously extracted in the dip region at Q2 = 0.15 (GeV/c)2. In comparison to models of deuteron electrodisintegration, the data clearly reveal strong effects of relativity and final-state interactions and the importance of two-body meson-exchange currents and isobar configurations. We demonstrate that such effects can be disentangled by extracting these responses using the novel out-of-plane technique