Frankfurt 2014 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 2: Hadronenstruktur und -spektroskopie

HK 2.3: Talk

Monday, March 17, 2014, 15:00–15:15, HZ 3

Symmetric Møller/Bhabha luminosity monitor for the OLYMPUS experiment — •Perez Benito Roberto for the OLYMPUS collaboration — Helmholtz-Institut Mainz, Germany

The OLYMPUS experiment ran on the DORIS storage ring at DESY, Hamburg to measure the elastic cross sections for both positron and electron scattering from hydrogen to quantify the two-photon contribution to elastic ep scattering. Two-photon exchange is widely considered to be responsible for the the discrepancy in the proton form factor ratio determined using the Rosenbluth technique and polarization transfer. The experiment alternated daily between positron and electron beams at 2.01 GeV incident on an unpolarized, internal, hydrogen gas target. The luminosity delivered to the experiment was monitored by a redundant set of detectors: a high precision, symmetric Møller / Bhabha calorimeter and a tracking telescope at 12 degrees. The symmetric Møller/Bhabha calorimeter was built at Mainz and consisted of two symmetric arrays of lead fluoride crystals. Results on the performance of the SYMB luminosity monitor will be presented together with an overview of the OLYMPUS experiment.