Research to Continue at the Pierre Auger Observatory

For nearly 20 years, physicists from Siegen have been part of the international team studying cosmic rays at Argentina's Pierre Auger Observatory. The international collaboration has now been extended, with a new agreement formally signed at a ceremony.

Since the early 2000s, researchers have been studying cosmic rays at the Pierre Auger Observatory in the Argentinian pampas, using 1,660 water tanks and 27 telescopes. The Pierre Auger Observatory now serves as the leading global experiment for the measurement of the highest-energy charged particles, which constantly bombard the earth’s atmosphere from space. The origin of these cosmic ray particles, and the mechanism that gives them such high energy, are still unknown. To find answers, over 400 researchers from 17 countries work together at the Pierre Auger Observatory. Physicists from the University of Siegen have been part of the project almost from the very start. The international collaboration has now been extended by an additional ten years, with a delegation from Siegen traveling to Argentina to attend the ceremonial signing of the extension agreement.

“I was deeply impressed by my visit to this huge experiment, which is truly one-of-a-kind. Beyond the technology itself, I was especially fascinated with the excellent collaboration between international researchers, many of whom have been involved since the observatory’s inception. During the ceremony, representatives from the worlds of politics and research made impassioned arguments for the importance of this large-scale research project,” said University Kanzler Ulf Richter, who accompanied the Siegen researchers to the observatory.

Beyond the signing ceremony for the extension of the research agreement, the visitors also attended a tour of the detectors and telescope. The Siegen delegation also took part in a parade through the Argentinian town of Malargue, which is home to the observatory. The ceremony itself was preceded by the annual gathering of the researchers. Two different University of Siegen working groups are involved in the project, one under Dr. Markus Cristinziani and another under Dr. Markus Risse, both professors of physics.

“We are thrilled that the experiment is moving forward, allowing us to continue our research until the end of 2035. The detectors have now been technically upgraded and improved, so we are expecting even better measurement data over the course of this second phase of the Pierre Auger Observatory,” says Professor Cristinziani. “As part of the Pierre Auger collaboration, we have been working very successfully with colleagues from around the world for many years. Particularly in today's climate, this type of international collaboration sets a strong example,” says Professor Markus Risse, who has been involved with the project since 2000.

As part of the observatory’s expansion, the water tanks—used to measure the 'air showers' caused by cosmic rays—have been equipped with additional scintillation detectors. These react especially sensitively to electrons, while the water tanks are capable of recognizing muons, the heavier siblings to electrons. By combining the efforts of both types of detector, the researchers hope to determine the ratio of electrons and muons, which in turn will provide insights into the composition of cosmic rays. Beyond that upgrade, the detectors have also been outfitted with antenna capable of measuring radio signals emitted during the air showers. The electronics have now also been retrofitted to allow for study of not just cosmic rays but also atmospheric flashes.

Siegen physicists helped design and build the hardware for the detectors and radio signal measurements. They have also analyzed and interpreted the measurement data collected in Argentina. Their expertise in this area lies in particular in the search for tiny light particles, known as ultra-high energy photons — a field in which Siegen is a global leader. It’s been physically proven at this point that these kinds of photons play a role in cosmic processes. In practice, however, no one actually successfully measured this kind of photon at its highest energy levels. The upgrade might well increase the chances of such a discovery during phase II of the experiment.

Background: The detectors at the Pierre Auger Observatory measure cosmic rays indirectly, through the air showers triggered by the rays. These are the smallest particles, falling to the earth’s surface like raindrops. When electrons and muons from this kind of shower cross through the water tank, they create brief flashes of light that are picked up by the sensitive detectors. At the same time, telescopes monitor the skies above the experiment for fluorescent light triggered by the showers. The researchers then apply that data to determining the direction of arrival, energy, and type of cosmic ray. Since 2005, Siegen scientists have been working at the observatory in the “Astroparticle Physics” collaborative research group from the Ministry of Education and Research (BMBF).

Contact:
Professor Markus Cristinziani (Project Director) T
Tel.: +49 271 740-3629
Email: Markus.Cristinziani@uni-siegen.de

Professor Markus Risse
Tel.: +49 271 740-3789
Email: Risse@physik.uni-siegen.de

Professor Markus Cristinziani, Kanzler Ulf Richter and Professor Markus Risse (left to right) on the grounds of the Pierre Auger facility.