Five Years of AMS – Embarking on a New Era in Astroparticle Physics

AMS Copyright: © NASA

For five years now, the Alpha Magnetic Spectrometer (AMS) has been orbiting our planet aboard the International Space Station ISS, 400 kilometers above the Earth’s surface. The AMS took about 15 years to construct, weighs over 7 tons, and is valued at about 1.5 billion euros – thus, it is the largest basic research experiment on the ISS.

  Verhältnis von Wasserstoff- und Helium-Kernen in der kosmischen Strahlung Copyright: © AMS Kollaboration The relation between hydrogen nuclei (protons) and helium nuclei in cosmic rays depending on the impulse of the nuclei

In 2011, on its final mission, space shuttle Endeavour had carried this unique piece of equipment in its payload bay and delivered it to the International Space Station. Since its activation, the AMS has recorded 90 billion charged particles from cosmic rays before they were absorbed in the atmosphere. This unique dataset, which has been measured to an accuracy of about 1 percent, provides information on the highest-energy processes in our galaxy and thus will help answer some of the biggest open questions in modern physics.

On December 8, 2016, the spokesperson for the AMS project, Nobel Prize winner Samuel C. C. Ting from the Massachusetts Institute of Technology, provided a summary of the first five years of the AMS project at the European research center CERN. The German research institutions participating in the project are RWTH Aachen, the Karlsruhe Institute of Technology, and Forschungszentrum Jülich. Their activities, which receive funding from the German Aerospace Center DLR, are coordinated by RWTH professor Stefan Schael.

Forschungszentrum Jülich and RWTH Aachen collaborate on the project within the Jülich Aachen Research Alliance, JARA for short. The group’s activities are coordinated by Professor Henning Gast. The group from Karlsruhe is headed by Dr. Iris Gebauer.

The scientific results of AMS include several surprises for experts. They clearly show that our understanding of the origin, acceleration, and transport of cosmic radiation from its sources into our galaxy and to the AMS is incomplete. So far, researchers assumed that such particles were generated and accelerated in supernova explosions and by heavy stars within our galaxy. The high-precision data generated by the AMS however show that the existing models must be extended (see figure).

A tiny fraction of cosmic rays consists of antimatter particles. These can be seen as highly sensitive indicators for new and unexpected processes. At high energies, AMS observed both more positrons and antiprotons than expected. Both could be explained by interactions with dark matter particles in our galaxy. But such an interpretation requires independent confirmation, for example through evidence of the production of dark matter particles at the Large Hadron Collider at CERN in Geneva.

Following hydrogen, helium is the second most common element in the universe. Within the lase five years, AMS has recorded 3.7 billion helium events. One of the big open questions in physics is why we do not observe any antihelium in the universe. If the universe originated from nothing, at the beginning, there must have been matter and anti-matter in equal quantities. For this reason, AMS has also searched for antihelium nuclei in its data. The observation of a single antihelium nucleus would fundamentally change the dominant worldview in modern physics.

According to Samuel Ting, AMS observed a number of candidates for antihelium, whose mass is compatible with 3He. However, only with the help of comprehensive computer simulations AMS was only able to investigate whether these rare events could be attributed to another cause . Run on a worldwide network of large-scale computers, these simulations took more than 10 million hours of computation time. More than 50 percent of these calculations were performed at the Supercomputing Center of Forschungszentrum Jülich. These simulations did not deliver any explanation for the observed antihelium candidates. However, computer simulations only approximate real-world scenarios. For this reason, it is a key priority of the AMS collaboration to develop methods that make it possible to verify this result using the measurement data only.

The precision of the AMS data has yielded several important insights and thus introduced a new era in astroparticle physics. As always when research is breaking new ground in fundamental research, the results lead to important new questions that can only be posed on the basis of such new results.

AMS will continue to measure cosmic rays with unprecedented precision until the International Space Station will ends its service life.


Professor Dr. Stefan Schael, RWTH Aachen University

Dr. Iris Gebauer, Karlsruher Institut für Technologie,

Source: Press and Communication