We report on the measurement of the γp → J/ψp cross section from Eγ = 11.8 GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find 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).

We report measurements of the photon beam asymmetry Σ for the reactions γp → pπ 0 and γp → pη from the GLUEX experiment using a 9 GeV linearly-polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous π 0 measurements and are the first η measurements in this energy regime. The results are compared with theoretical predictions based on t-channel, quasi-particle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.

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We study the electronic structure of (n,0) zigzag carbon nanotubes by means of two complementary numerical methods. Using the semiempirical PM3 method, we carry out quantum-chemical calculations for tube fragments of different symmetry and size, which represent these tubes. Using the tight-binding method, we proceed in parallel to determine the band structure of these tubes. The effect of cluster size on the structure of frontier orbitals and on the cluster stability is investigated for the (6,0) tube. We show that the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of the (n,0) tube fragments are localized on the edge atoms. The comparison between the band structure of the (6,0) tube and the molecular orbitals of the (6,0) tube fragment with 13 carbon hexagons along the tube axis indicates that the spatial structure of the HOMO′s and the LUMO′s directly corresponds to that of the Bloch wave functions of occupied and unoccupied π bands near the Fermi level.