[Jlab-seminars] Physics Seminar

[Luci Collins]

*Physics Seminar
Friday, July 19th
CEBAF Center AUD.
11:00AM
Cookies and coffee at 10:45AM*
*
"The Olympus Experiment"*

*Roberto Perez Benito
Helmholtz Institute Mainz*

Recent determinations of the proton electric to magnetic form factor ratio
indicate an unexpected discrepancy between the ratio obtained using polar-
ization transfer measurements and the ratio from the Rosenbluth separation
technique in unpolarized cross section measurements. This discrepancy has
been explained as the eect of two-photon exchange.

The OLYMPUS experiment at DESY has been carried out to measure
the ratio of positron-proton and electron-proton elastic scattering 
cross sec-
tions. The experiment utilized intense beams of electrons and positrons in
the DORIS ring at 2.0 GeV, an unpolarized internal hydrogen gas target,
and the former BLAST detector from the MIT-Bates Linear Accelerator
Center with modest upgrades. In order to reduce the systematic error due
to relative luminosity, redundant measurements of the luminosity were made.

The symmetric M
ller/Bhabha luminosity monitor built in Mainz con-
sisted of two symmetric arrays of lead uoride (PbF2) crystals. Results on
the performance of the symmetric M
ller/Bhabha luminosity monitor will be
presented in this contribution together with the physics case for OLYMPUS
and the current status of the project.
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