OLYMPUS experiment sheds light on structure of protons

A team of Researchers from MIT finally able to solve the mystery of structure of protons after seven- year long experiment, named OLYMPUS, in the Laboratory for Nuclear Science at the German Electron Synchrotron (DESY) in Hamburg.

They began the experiment in the early 2000s with the help of Polarized electron beams. It measure electron- proton elastic scattering using the spin of the protons and electrons. Furthermore, experiment demonstrate that the ratio of electric to magnetic charge distributions decreased dramatically with higher-energy interactions between the electrons and protons.

The result is published in the journal Physical Review Letters. It is revealed that during the process not one but two photons being exchanged during the interaction, which in turn cause the uneven charge distribution.

Speaking about the experiment Richard Milner, a professor of physics and member of the Laboratory for Nuclear Science’s Hadronic Physics Group said that analysis of OLYMPUS measurements shows that most of the time, one of the photons has high energy and other carries very little energy

“We saw little if no evidence for a hard two-photon exchange,” Milner says.

About Experiment:

Explaining the process Douglas Hasell, a principal research scientist in the Laboratory for Nuclear Science and the Hadronic Physics Group at MIT, and another of the paper’s authors said

In this experiment, they probe the structure by bombarding the protons with both positively charged positrons and negatively charged electrons and then examine the intensity of the scattered electrons at different angles. Moreover by doing this it could also be determined that how the proton’s electric charge and magnetization are distributed.

“If you see a difference (in the measurements), it would indicate that there is a two-photon effect that is significant.”

The collisions were run for three months, and the resulting data took a further three years to analyze, Hasell added.

The difference between the theoretical and experimental results means further experiments may need to be carried out in the future, at even higher energies where the two-photon exchange effect is expected to be larger, Hasell says.

It may prove difficult to achieve the same level of precision reached in the OLYMPUS experiment, however.

“We ran the experiment for three months and produced very precise measurements,” he says. “You would have to run for years to get the same level of precision, unless the performance (of the experiment) could be improved.”

In the immediate future, the researchers plan to see how the theoretical physics community responds to the data, before deciding on their next step, Hasell says.

“It may be that they can make a small adjustment to a detail within their theoretical models to bring it all into agreement, and explain the data at both higher and lower energies,” he says.

“Then it will be up to the experimentalists to check if that holds to be the case.”

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