Probing Few-Body Nuclear Dynamics via ^{3}H and ^{3}He (e,e^{'}p)pn Cross-Section Measurements

We report the first measurement of the (e,e^{'}p) three-body breakup reaction cross sections in helium-3 (^{3}He) and tritium (^{3}H) at large momentum transfer [⟨Q^{2}⟩≈1.9  (GeV/c)^{2}] and x_{B}>1 kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta 40≤p_{miss}≤500  MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab initio calculations. Overall good agreement, within ±20%, is observed between data and calculations for the full p_{miss} range for ^{3}H and for 100≤p_{miss}≤350  MeV/c for ^{3}He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at p_{miss}>250  MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of ^{3}He plus ^{3}H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire p_{miss} range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of 500  MeV/c.

The species composition of naked amoeba in epiphytic mosses of Zhytomyr region

From epiphytic habitats of Zhytomyr region we identified 16 species of naked amoebae. This species: Vahlkampfia sp. (1), Saccamoeba stagnicola (Page, 1974), Saccamoeba sp. (1), Cashia limacoides (Page, 1974), Korotnevella sp. (1), Vexillifera sp., Ripella platypodia (Smirnov, Nassonova, Chao et Cavalier-Smith, 2007), Ripella sp., Cochliopodium sp. (1), Mayorella cantabrigiensis (Page, 1983), Mayorella sp., Thecamoeba striata Penard, 1890, Thecamoeba sp., Stenamoeba stenopodia (Page, 1969; Smirnov et al., 2007), Acanthamoeba sp. (1), Stygamoeba polymorpha (Sawyer, 1975). The most common were the amoebae Cochliopodium sp., Acanthamoeba sp. (1), S. stenopodia, Vexillifera sp., the least common – T. striata, R. platypodia, Mayorella sp., S. stagnicola, Saccamoeba sp. (1), S. polymorpha. On the species composition of the naked amoebae in epiphytic habitats Zhytomyr region is affected by the humidity of the substrate: a decrease in humidity reduced the species richness of amoebae. The connection of the species composition of amoebae with height above the ground with increasing height above the ground decreases the species composition of amoebae. At the levels of 0–1,5 m, the most common amoeba occur (S. stenopodia, Cochliopodium sp. (1), M. cantabrigiensis, Acanthamoeba sp. (1)), at a height of 1–1,5 m, most amoeba disappear and the least appears common view of Thecamoeba sp. In wet mosses dominating species Vahlkampfia sp. (1), Vahlkampfia sp. (2), R. platypodia, S. stenopodia, Cochliopodium sp. (1), M. cantabrigiensis, Acanthamoeba sp. (1), dry epiphytes of the study area met C. limacoides, Korotnevella sp. (1), S. polymorpha. The most heterogeneous complexes of the wet habitats, while dry – fairly uniform. We identified all species can be considered everybody, meet as in mosses and aquatic and soil habitats.

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).

Direct Observation of Proton-Neutron Short-Range Correlation Dominance in Heavy Nuclei

We measured the triple coincidence A(e,e^{'}np) and A(e,e^{'}pp) reactions on carbon, aluminum, iron, and lead targets at Q^{2}>1.5  (GeV/c)^{2}, x_{B}>1.1 and missing momentum >400  MeV/c. This was the first direct measurement of both proton-proton (pp) and neutron-proton (np) short-range correlated (SRC) pair knockout from heavy asymmetric nuclei. For all measured nuclei, the average proton-proton (pp) to neutron-proton (np) reduced cross-section ratio is about 6%, in agreement with previous indirect measurements. Correcting for single-charge exchange effects decreased the SRC pairs ratio to ∼3%, which is lower than previous results. Comparisons to theoretical generalized contact formalism (GCF) cross-section calculations show good agreement using both phenomenological and chiral nucleon-nucleon potentials, favoring a lower pp to np pair ratio. The ability of the GCF calculation to describe the experimental data using either phenomenological or chiral potentials suggests possible reduction of scale and scheme dependence in cross-section ratios. Our results also support the high-resolution description of high-momentum states being predominantly due to nucleons in SRC pairs.