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SANE's Measurement of the Proton's Virtual Photon Spin Asymmetry, A^p_1, at Large Bjorken x (open access)

SANE's Measurement of the Proton's Virtual Photon Spin Asymmetry, A^p_1, at Large Bjorken x

The experiment SANE (Spin Asymmetries of the Nucleon Experiment) measured inclusive double polarization electron asymmetries on a proton target at the Continuous Electron Beam Accelerator Facility at the Thomas Jefferson National Laboratory in Newport News Virgina. Polarized electrons were scattered from a solid {sup 14}NH{sub 3} polarized target provided by the University of Virginia target group. Measurements were taken with the target polarization oriented at 80 degrees and 180 degrees relative to the beam direction, and beam energies of 4.7 and 5.9 GeV were used. Scattered electrons were detected by a multi-component novel non-magnetic detector package constructed for this experiment. Asymmetries measured at the two target orientations allow for the extraction of the virtual Compton asymmetries A{sub 1}{sup p} and A{sub 2}{sup p} as well as the spin structure functions g{sub 1}{sup p} and g{sub 2}{sup p}. This work addresses the extraction of the virtual Compton asymmetry A{sub 1}{sup p} in the deep inelastic regime. The analysis uses data in the kinematic range from Bjorken x of 0.30 to 0.55, separated into four Q{sup 2} bins from 1.9 to 4.7 GeV{sup 2}.
Date: May 1, 2012
Creator: Mulholland, Jonathan
System: The UNT Digital Library
Precision Measurement of Electroproduction of pi{sup 0} near Threshold (open access)

Precision Measurement of Electroproduction of pi{sup 0} near Threshold

Electromagnetic production of neutral pions near threshold is the most basic, lowest energy reaction in which a new hadron is created. The electromagnetic interaction is well understood so measurements of this reaction can yield direct insight into the hadronic production mechanism. During the past three decades there have been many developments in both the measurement and theory of threshold pion production, starting with measurements of photo-production at Saclay in 1986 and at Mainz in 1990. These measurements indicated a surprising discrepancy with so-called Low Energy Theorems (LETs) which are based on quite fundamental symmetries and considerations. Chiral Perturbation Theory (ChPT) is an e#11;ective #12;eld theoretic description of the nuclear force which contains the underlying symmetries of the force but deals with nucleons and pions rather than quarks and gluons. It has the advantage of being applicable at low energies but requires tuning some parameters to experimental data. Once these parameters have been determined ChPT predicts how the reaction should behave as a function of the kinematic variable. When applied to the reaction, p({gamma},{pi}{sup 0})p, near threshold it explained the discrepancy with the LETs and made predictions for electroproduction, p(e,e'p){pi}#25;{sup 0}. Electroproduction measurements at Mainz in the 1990's showed a clear …
Date: May 1, 2012
Creator: Chirapatpimol, Khem
System: The UNT Digital Library