[Jlab-seminars] Physics Seminar: January 26, 2018: Andrew Puckett; Polarization transfer observables in elastic electron-proton scattering at Q2 = 2.5, 5.2, 6.8 and 8.5 GeV2

[Stephanie Tysor]

Physics Seminar 

Andrew Puckett 

University of Connecticut 



Polarization transfer observables in elastic electron-proton 

scattering at Q 2 = 2.5, 5.2, 6.8 and 8.5 GeV 2 







Abstract: 





Electromagnetic form factors (EMFF) are among the most fundamental measurable properties of nucleon structure. The study of nucleon EMFFs at large momentum transfer Q 2 is currently a unique worldwide capability of CEBAF. The precise polarization transfer (PT) measurements of the proton's electromagnetic form factor ratio G p E /G p M from Halls A and C, covering a wide range of Q 2 , are among the most cited results from Jefferson Lab, owing to the surprising discovery of the rapid decrease of the proton form factor ratio G p E /G p M for Q 2 ̰> 1 GeV 2 . These results strongly contradicted existing cross section data suggesting that G p E /G p M was approximately constant up to Q 2 ≈ 7 GeV 2 . The third and final set of experiments of the 6 GeV era dedicated to measuring polarization transfer in high-Q 2 elastic ep scattering was carried out in Hall C during fall-spring of 2007-2008. The GEp-III experiment (E04-108) extended the knowledge of the proton's electromagnetic form factor ratio to Q 2 = 8.5 GeV 2 . The companion GEp-2γ experiment (E04-019) produced precise (̰< 1% total uncertainty) measurements of the angular dependence of the PT observables at Q 2 = 2.5 GeV 2 , to search for or constrain effects beyond the Born approximation thought to be responsible for the disagreement between values of G p E extracted from cross section and polarization data. The GEp-III/GEp-2γ collaboration has recently published the final results of both experiments, including the previously unpublished full-acceptance data from the GEp-2γ experiment, resulting in an approximate tripling of the statistics for two of the three production kinematics. In this seminar, I will review the common apparatus, the data analysis, and the final results of both experiments, and discuss the implications of the data for our understanding of the proton's structure, as well as lessons applicable to future experiments. I will then conclude with a brief overview of the high-Q 2 nucleon form factor program planned for the 12 GeV era of CEBAF. 





Friday, January 26, 2018 

11:00am 

CEBAF Auditorium 

-- 
Stephanie Tysor 
Hall A Administrative Assistant 
Thomas Jefferson National Accelerator Facility 
(office)757-269-6005 (fax)757-269-5235 
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