BEGIN:VCALENDAR
VERSION:2.0
PRODID:Data::ICal 0.22
BEGIN:VEVENT
DESCRIPTION:Larry Weinstein\, ODU\n\nThis talk will describe how to make in
tense identical positron and electron beams at Jefferson Lab and use them
to measure two-photon exchange contributions to elastic electron-proton s
cattering. It will cover the results of a recent test run in CLAS where w
e produced about 10 pA each of electrons and positrons.\n\nThe proton elec
tric form factor describes the charge distribution of the proton. This ha
s been measured extensively with electron scattering using Rosenbluth sepa
rations and polarization measurements. These measurements of the proton e
lectric form factor disagree by a factor of three at Q 2 = 6
GeV 2 . Since alpha\, the fine structure constant\, is less
than 1%\, electron-proton scattering should be almost exclusively one-pho
ton exchange. However\, a two-photon exchange contribution of about 5% co
uld explain the discrepancy between the measurements. We will determine th
e two-photon exchange contribution by measuring the ratio of the electron-
proton and positron-proton elastic scattering cross sections to 1%.
DTSTART:20061031T203000Z
LOCATION:Physics Building\, Room 204
SUMMARY:Positron-proton scattering and the proton charge distribution
END:VEVENT
END:VCALENDAR