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Beam Physics Seminar

Thursday, April 27, 2006, 3:30 PM
ARC, 231/233

Parity-violating Electron Scattering on Hydrogen and Helium
and Strangeness in the Nucleon

Kent Paschke
Parity violation in elastic electron scattering is sensitive to possible strange quark contributions to 
the vector structure of the nucleon, and thus provides an opportunity to isolate effects of the q-qbar sea.
The small parity-violating asymmetry in the cross section for the scattering of polarized electrons, which
arises from an interference of the electromagnetic and weak neutral-current interactions, when combined
with the known electromagnetic form factors, provides access to strange quark matrix elements. The
HAPPEX collaboration in Hall A at Jefferson Lab has measured the parity-violating asymmetry in the
scattering of longitudinally-polarized 3 GeV electrons from both hydrogen and 4He cryogenic targets, at a
small scattering angle (6 degrees) and low four-momentum transfer (Q2 ~ 0.1 GeV2). The asymmetry for
hydrogen is a function of a linear combination of GsE and GsM, the strange quark contributions to the
electric and magnetic form factors of the nucleon respectively, and that for 4He is a function solely of GsE.
The combination of the two measurements therefore allows GsM and GsE to be separately determined.
Preliminary results will be presented from the complete data set, obtained in runs in 2004 and 2005, yielding
results of unprecedented precision.

Talk Slides: (Slides)

For more information, please contact Dr. Alex Bogacz, Chair of CASA Seminar Committee