The Measurement of the TL' Asymmetry in n0 Electroproduction Near Threshold

Shabestari, Mitra H., Department of Physics, University of Virginia
Liyanage, Nilanga, Department of Physics, University of Virginia
Crabb, Donald, Department of Physics, University of Virginia
Higinbotham, Douglas
Liuti, Simonetta, Department of Physics, University of Virginia

The experimental data onπ 0 electroproduction over the past few years have indicated troublesome discrepancies with the predictions of chiral perturbation theory. The differences have been observed in low Q 2 and near threshold (low∆W) for unpolarized cross section σ 0 =σ T +ǫ L σ L and asymmetry A TL ′. That is, while phenomenological models show better agreement withσ 0 data in this region, the inconsistency of chiral perturbation theory with experimental data in this region is particularly serious. The failure seems to come from a combination of multipoles that is already fixed byπ 0 photoproduction, so that, it cannot be varied. The current experimental data, however, are not spanned over a fine grid of Q 2 and ∆W and have somewhat large statistical and systematic errors. To confirm or refute these discrepancies, experiment E04-007 at Hall A of Jefferson Lab was intended to provide data on π 0 electroproduction, H ( e, e ′ p ) π 0 , that extend the data in Q 2 and∆W. The use of Hall A BigBite spectrometer, with its large solid angle and momentum acceptance, allows the collection of data with higher precision. Systematic error is minimized since the BigBite spectrometer can measure the entire proton's angular distribution within three kinematic settings. The data were collected in near threshold: the region that is specified by 0.056 (GeV/c) 2  Q 2  0.45 (GeV/c) 2 , and 0 MeV∆W45 MeV. Polarized electrons at energies of 1193 MeV and 2322 MeV were scattered off a cryogenic hydrogen target. The pion was identified by detecting the scattered electron in the left high-resolution spectrometer in coincidence with the recoiled proton, detected in BigBite spectrometer. In this work, the data on TL ′ asymmetry function is presented. To my husband and best friend, Mehrdad.

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PHD (Doctor of Philosophy)
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