Exclusive Backward-Angle Omega Meson Electroproduction

Thesis/Dissertation · Sun Oct 01 00:00:00 EDT 2017

DOI:https://doi.org/10.2172/1408890· OSTI ID:1408890

Wenliang, Li ^[1]

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1. Univ. of Regina, Regina, SK (Canada)

Exclusive meson electroproduction at different squared four-momenta of the exchanged virtual photon, Q² , and at different four-momentum transfers, t and u, can be used to probe QCD's transition from hadronic degrees of freedom at the long distance scale to quark-gluon degrees of freedom at the short distance scale. Backward-angle meson electroproduction was previously ignored, but is anticipated to offer complimentary information to conventional forward-angle meson electroproduction studies on nucleon structure. This work is a pioneering study of backward-angle ω cross sections through the exclusive ¹H(e, e'p)ω reaction using the missing mass reconstruction technique. The extracted cross sections are separated into the transverse (T), longitudinal (L), and LT, TT interference terms. The analyzed data were part of experiment E01-004 (Fπ-2), which used 2.6-5.2 GeV electron beams and HMS+SOS spectrometers in Jefferson Lab Hall C. The primary objective was to detect coincidence π in the forward-angle, where the backward-angle omega events were fortuitously detected. The experiment has central Q² values of 1.60 and 2.45 GeV² , at W = 2.21 GeV. There was significant coverage in phi and epsilon, which allowed separation of σ_T,L,LT,TT . The data set has a unique u coverage of -u ~ 0, which corresponds to -t > 4 GeV² . The separated σ_T result suggest a flat ~ 1/Q^1.33±1.21 dependence, whereas sigma_L seems to hold a stronger 1/Q^9.43±6.28 dependence. The σL/σ_T ratio indicate σ_T dominance at Q² = 2.45 GeV² at the ~90% confidence level. After translating the results into the -t space of the published CLAS data, our data show evidence of a backward-angle omega electroproduction peak at both Q² settings. Previously, this phenomenon showing both forward and backward-angle peaks was only observed in the meson photoproduction data. Through comparison of our σ_T data with the prediction of the Transition Distribution Amplitude (TDA) model, and signs of σ_T dominance, promising indications of the applicability of the TDA factorization are demonstrated at a much lower Q² value than its preferred range of Q² > 10 GeV². These studies have opened a new means to study the transition of the nucleon wavefunction through backward-angle experimental observables.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1408890
• Report Number(s): JLAB-PHY-17-2599; DOE/OR/23177-4262
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS