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  4. Measurement of the two-photon exchange contribution to lepton-proton scattering with OLYMPUS
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Measurement of the two-photon exchange contribution to lepton-proton scattering with OLYMPUS

Full metadata

Description

The OLYMPUS experiment measured the two-photon exchange contribution to elastic electron-proton scattering, over a range of four-momentum transfer from \(0.6 < Q^2 < 2.2\) \((\mathrm{GeV/c})^2\). The motivation for the experiment stemmed from measurements of the electric-to-magnetic form factor ratio of the proton \(\mu G_E/G_M\) extracted from polarization observables in polarized electron-proton scattering. Polarized electron-proton scattering experiments have revealed a significant decrease in \(\mu G_E/G_M\) at large \(Q^2\), in contrast to previous measurements from unpolarized electron-proton scattering. The commonly accepted hypothesis is that the discrepancy in the form factor ratio is due to neglected higher-order terms in the elastic electron-proton scattering cross section, in particular the two-photon exchange amplitude.

The goal of OLYMPUS was to measure the two-photon exchange contribution by measuring the positron-proton to electron-proton elastic scattering cross section ratio, \(\sigma_{e^+p}/\sigma_{e^-p}\). The two-photon exchange contribution is correlated to the deviation of the cross section ratio from unity.

In 2012, the OLYMPUS experiment collected over 4 fb\(^{-1}\) of \(e^+p\) and \(e^-p\) scattering data using electron and positron beams incident on a hydrogen gas target. The scattered leptons and protons were measured exclusively with a large acceptance spectrometer. OLYMPUS observed a slight rise in \(\sigma_{e^+p}/\sigma_{e^-p}\) of at most 1-2\% over a \(Q^2\) range of \(0.6 < Q^2 < 2.2\) \((\mathrm{GeV/c})^2\). This work discusses the motivations, experiment, analysis method, and the preliminary results for the cross section ratio as measured by OLYMPUS.

Date Created
2016
Contributors
  • Ice, Lauren (Author)
  • Alarcon, Ricardo O (Thesis advisor)
  • Dugger, Michael (Committee member)
  • Lebed, Richard (Committee member)
  • Ritchie, Barry (Committee member)
  • Arizona State University (Publisher)
Topical Subject
  • Physics
  • elastic electron scattering
  • elastic positron scattering
  • proton form factor ratio
  • two-photon exchange
  • Elastic scattering
  • Electrons--Scattering.
  • Protons--Scattering.
Resource Type
Text
Genre
Doctoral Dissertation
Academic theses
Extent
xi, 147 pages : illustrations (some color)
Language
eng
Copyright Statement
In Copyright
Reuse Permissions
All Rights Reserved
Primary Member of
ASU Electronic Theses and Dissertations
Peer-reviewed
No
Open Access
No
Handle
https://hdl.handle.net/2286/R.I.40823
Statement of Responsibility
by Lauren Ice
Description Source
Retrieved on May 30, 2017
Level of coding
full
Note
Partial requirement for: Ph.D., Arizona State University, 2016
Note type
thesis
Includes bibliographical references (pages 138-145)
Note type
bibliography
Field of study: Physics
System Created
  • 2016-12-01 07:10:30
System Modified
  • 2021-08-30 01:20:18
  •     
  • 1 year 5 months ago
Additional Formats
  • OAI Dublin Core
  • MODS XML

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