Results 1 - 10 of 12337
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[en] A new formulation is given for the predictions of QCD in deep inelastic scattering. Its main element is the conversion from ordinary moments to so-called localized moments. This makes it possible to avoid a number of theoretical uncertainties present in traditional formulations. The usual method of removing such uncertainties is to resort to models. The sensitivity to the model assumptions has been analyzed both for the traditional formulation and for the new formulation. In the first case it turned out to be very important, and in the second case not very important. In this connection the experimental status of QCD and the value of the parameter Λ are discussed
[en] We compute the two-loop enhancement factors for our earlier one-loop calculations of leading ($1/Q$) power corrections to the mean values of some event shape variables in deep inelastic lepton scattering. The enhancement is found to be equal to the universal ''Milan factor'' for those shape variables considered, provided the one-loop calculation is performed in a particular way. As a result, the phenomenology of power corrections to DIS event shapes remains largely unaffected. (author)
[en] A way to detect experimentally the existence of triple gluon coupling and the Adler-Bell-Jackiw anomaly is to measure the Q2-dependence of polarized deep inelastic scattering. These effects lead to a ln ln Q2 term which we calculate by introducing a new gluon operator in the Wilson expansion
[en] The work discussed here is an extension of work previously funded by U.S. Department of Energy Grant DE-FG02-97ER41025. Measurements of charged pion photoproduction from deuterium using the Laser Electron Gamma Source (LEGS) at the Brookhaven National Laboratory previously made by us, as members of the LEGS Collaboration, resulted in the most interesting result of two decades of work. By measuring the production of a charged pion (π+) in coincidence with an emitted photon we observed structures in the residual two-nucleon system. These indicated the existence of rare, long-lived states not explicable by standard nuclear theory; they suggested a set of configurations not explicable in terms of a nucleon-nucleon pair. The existence of such “exotic” structures has formed the foundation for most of the work that has ensued. Several measurements at various laboratories have supported, but not proved, the existence of these exotic states. The rarity of these states made their existence undetectable in most previous measurements. Only by observing characteristic signatures of such states (i.e., decay photons), by using very specific kinematics which isolate certain reaction products, or by measuring polarization-dependent observables. During the period of this grant we pursued and made progress on the development of experiments to be performed at the High Intensity Gamma Source (HIGS) of the Tri Universities Nuclear Laboratory (TUNL). Our understanding of photon- and electron-induced nuclear reactions depends on understanding of the basic electron and photon interaction. Recently, the issue of two-photon contributions has arisen in the context of deeply inelastic electron scattering. One way to address this is to measure asymmetries in the Bethe-Heitler ee process. We also made progress in developing the detectors required to measure these asymmetries at HIGS. During the last several years the apparent discrepancy between the size of the proton as measured using electrons and that as measured using muons has received a great deal of attention. Working with colleagues at the Jefferson Laboratory (JLAB) we showed that the apparent discrepancy was almost surely the result of mistakes in the statistical analysis of electron scattering data, that there is almost surely no discrepancy.
[en] New data on the Sivers azimuthal asymmetry measured in semi-inclusive deep-inelastic scattering processes have recently been released by the COMPASS Collaboration at CERN. Their increased precision and their particular binning, in terms of as well as , motivates a new extraction of the Sivers function, within the framework of a simple and transparent parametrization. Signals of TMD effects visible in the Sivers asymmetries are critically assessed. A thorough study of the uncertainties affecting the extracted Sivers function is presented, including the low- and large- regions.
[en] Preliminary results on the spin transfer to the Λ and hyperons measured by the HERMES Collaboration are presented. Longitudinal spin transfer directed along the virtual-photon momentum in the Λ rest frame is found to be DΛ LL = 0.19 ± 0.04stat ± 0.02syst, the transverse component being compatible with zero. For both longitudinal and transverse components are compatible with zero within statistical errors of ±0.1.