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  1. Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive π0 production

    Aghasyan, M. ; Avakian, H. ; Rossi, P. ; ... - Physics Letters. B
    We present studies of single-spin asymmetries for neutral pion electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV polarized electrons from an unpolarized hydrogen target, using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. A substantial sin Φh amplitude has been measured in the distribution of the cross section asymmetry as a function of the azimuthal angle Φh of the produced neutral pion. The dependence of this amplitude on Bjorken x and on the pion transverse momentum is extracted with significantly higher precision than previous data and is compared to model calculations.

  2. X-Ray Diffraction Microscopy of Magnetic Structures

    Turner, Joshua J. ; Huang, Xiaojing ; Krupin, Oleg ; ... - Physical Review Letters

  3. On the extraction of P11 resonances from πN data

    Nakamura, Satoshi X. ; Lee, Tsung -Shung ; Sato, Toru - Physical Review C, Nuclear Physics
    With the accuracy of the available P11 amplitudes of πΔ scattering, we show that two resonance poles near the pi Delta threshold, obtained in several analyses, are stable against large variations of parameters within a dynamical coupled-channels analysis. The number of poles in the 1.5 GeV < W < 2 GeV region could be more than one, depending on how the structure of the single-energy solution of SAID is fitted. Lastly, our results indicate the need of more accurate πN scattering data in the W > 1.6 GeV region for high precision resonance extractions.

  4. Primakoff effect in η-photoproduction off protons

    Haidenbauer, J. ; Krewald, S. ; MeiBner, U. -G. - European Physical Journal. A
    In this paper, we analyse data on forward η -meson photoproduction off a proton target and extract the η → γγ decay width utilizing the Primakoff effect. The hadronic amplitude that enters into our analysis is strongly constrained because it is fixed from a global fit to available γp → pη data for differential cross-sections and polarizations. Finally, we compare our results with present information on the two-photon η-decay from the literature. We provide predictions for future PrimEx experiments at Jefferson Laboratory in order to motivate further studies.

  5. High-energy amplitudes in N = 4 SYM in the next-to-leading order

    Chirilli, Giovanni ; Balitsky, Ian - Physics Letters. B
    In this study, the high-energy behavior of the N = 4 SYM amplitudes in the Regge limit can be calculated order by order in perturbation theory using the high-energy operator expansion in Wilson lines. At large $$N_c$$, a typical four-point amplitude is determined by a single BFKL pomeron. The conformal structure of the four-point amplitude is fixed in terms of two functions: pomeron intercept and the coefficient function in front of the pomeron (the product of two residues). The pomeron intercept is universal while the coefficient function depends on the correlator in question. The intercept is known in the firstmore » two orders in coupling constant: BFKL intercept and NLO BFKL intercept calculated in Ref. 1. As an example of using the Wilson-line OPE, we calculate the coefficient function in front of the pomeron for the correlator of four $Z^2$ currents in the first two orders in perturbation theory.« less

  6. Partial wave analysis of the reaction γ p → p ω and the search for nucleon resonances

    Williams, M. ; Applegate, D. ; Bellis, M. ; ... - Physical Review C, Nuclear Physics
    We performed an event-based partial wave analysis (PWA) of the reaction γ p -> p ω on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> π+ π - π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as wellmore » as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2+ state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive.« less

  7. Double and single pion photoproduction within a dynamical coupled-channels model

    Julia-Diaz, Bruno ; Lee, T. -S. H. ; Matsuyama, Akihiko ; ... - Physical Review C, Nuclear Physics
    Within a dynamical coupled-channels model which has already been fixed from analyzing the data of the πN → πN and γN → πN reactions, we present the predicted double pion photoproduction cross sections up to the second resonance region, W < 1.7 GeV. The roles played by the different mechanisms within our model in determining both the single and double pion photoproduction reactions are analyzed, focusing on the effects due to the direct γN → ππN mechanism, the interplay between the resonant and non-resonant amplitudes, and the coupled-channels effects. As a result, the model parameters which can be determined mostmore » effectively in the combined studies of both the single and double pion photoproduction data are identified for future studies.« less

  8. NLO evolution of color dipoles in N=4 SYM

    Chirilli, Giovanni A. ; Balitsky, Ian - Nuclear Physics. B
    Here, high-energy behavior of amplitudes in a gauge theory can be reformulated in terms of the evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the conformally invariant BK equation for the evolution of color dipoles. In QCD, the next-to-leading order BK equation has both conformal and non-conformal parts, the latter providing the running of the coupling constant. To separate the conformally invariant effects from the running-coupling effects, we calculate the NLO evolution of the color dipoles in the conformal $${\cal N}$$=4 SYM theory. We define the "composite dipole operator" with the rapidity cutoff preserving conformalmore » invariance.« less
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