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<font color="#cc0000"><b>Physics Seminar<br>
Friday, July 19th<br>
CEBAF Center AUD.<br>
11:00AM<br>
Cookies and coffee at 10:45AM</b></font><br>
<font color="#3333ff"><b><br>
"The Olympus Experiment"</b></font><br>
<br>
<b><font color="#3333ff">Roberto Perez Benito<br>
Helmholtz Institute Mainz</font></b><br>
<br>
Recent determinations of the proton electric to magnetic form factor
ratio<br>
indicate an unexpected discrepancy between the ratio obtained using
polar-<br>
ization transfer measurements and the ratio from the Rosenbluth
separation<br>
technique in unpolarized cross section measurements. This
discrepancy has<br>
been explained as the e ect of two-photon exchange.<br>
<br>
The OLYMPUS experiment at DESY has been carried out to measure<br>
the ratio of positron-proton and electron-proton elastic scattering
cross sec-<br>
tions. The experiment utilized intense beams of electrons and
positrons in<br>
the DORIS ring at 2.0 GeV, an unpolarized internal hydrogen gas
target,<br>
and the former BLAST detector from the MIT-Bates Linear Accelerator<br>
Center with modest upgrades. In order to reduce the systematic error
due<br>
to relative luminosity, redundant measurements of the luminosity
were made.<br>
<br>
The symmetric M ller/Bhabha luminosity monitor built in Mainz con-<br>
sisted of two symmetric arrays of lead uoride (PbF2) crystals.
Results on<br>
the performance of the symmetric M ller/Bhabha luminosity monitor
will be<br>
presented in this contribution together with the physics case for
OLYMPUS<br>
and the current status of the project.<br>
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