04.02.2013

OLYMPUS successfully concludes data taking

The nuclear physics experiment OLYMPUS at the DORIS accelerator successfully concluded its second data taking phase. In a two-month period until well into January, the scientists were able to collect four inverse femtobarns of electron-proton and positron-proton collisions. After definitely shutting down DORIS operation in January, the scientists used the detector for one month to take cosmic tracks to exactly determine the alignment of the detector components.

The OLYMPUS detector at the DORIS storage ring.

The international OLYMPUS collaboration consisting of 13 institutes aims at investigating the interaction of electrons and protons with high precision. With the operation of the OLYMPUS detector at DORIS, it will be clarified whether at the collisions there is only an exchange of one force particle called photon or sometimes also of two. In the latter case there should be differences when comparing the collisions of electrons and protons with those of anti-electrons, the so-called positrons, and protons.

For this aim, the team installed the OLYMPUS detector at the DORIS accelerator. In it, electrons and positrons from DORIS are alternately shot on hydrogen gas flowing through a target cell. Once a day, the team switches the kind of stored particles. After a first four-week measuring period in February 2012, the scientists now concluded the second data taking. They collected a total of four inverse femtobarns of data (an inverse femtobarn is the standard measure in particle physics indicating the number of particle collisions). “In the second measuring period, we had an increased hydrogen target flow and moreover an automatic top-up modus; this provided us with a very high data rate,” said OLYMPUS team member Uwe Schneekloth with satisfaction.

After the shutdown of the DORIS accelerator on 2 January, until today OLYMPUS continued to record tracks of cosmic muons which will be used to improve the accuracy of the evaluation. “With the help of the tracks, we will be able to calibrate our drift chambers and to reconstruct the particle tracks with more precision,” said Jürgen Diefenbach from Hampton University in Virginia (US). Following the measuring period, the detector is now being optically measured again and the inhomogeneous magnetic field is mapped. In their final analysis to be started now, the scientists will use these data to obtain results with an inaccuracy of one percent at most.