Nobel Prize in Physics for Measurements on Neutrinos


This year, the Noble Prize in physics was awarded to the particle physicists Takaaki Kajita (56) from Japan and Arthur McDonald (72) from Canada for proving that neutrinos have mass. Neutrinos are subatomic particles that have the ability to pass through matter with negligible interaction. Only vast detectors are able to measure neutrinos. Aachen researchers headed by Dr. Stefan Roth from the Chair of Experimental Physics IIIB contribute to the development of new technologies for particle measurements using the ND280 near detector.

  Researchers working on the monitoring system in the Aachen lab © Peter Winandy Researchers working on the monitoring system in the Aachen lab

The detector is located in the J-PARC research center (Japanese Proton Accelerator Research Complex) in Japan. At J-PARC at the Japanese East coast, a high-intensity proton beam creates neutrinos that are sent on a 295 km journey through subterranean Japan, only to be detected by after the 295 km journey by Super Kamiokande, the world's largest underground neutrino detector, which is located in the Kamioka district in West Japan. Before the proton beam is sent on its journey, it is measured by the ND280 at J-PARC.

It is the Super Kamiokande detector that Takaaki Kajita used for the measurements that won him the 2015 Nobel Prize. He succeeded in proving that so-called neutrino oscillations take place, which demonstrate that neutrinos have mass.

Neutrino oscillation is a phenomenon which occurs when neutrinos travel long distances. It is extremely difficult to detect neutrinos, as they can penetrate ordinary matter almost without any trace or disturbance.

Iniitally, starting in 1996, the Super Kamiokande detector was used to measure naturally occuring neutrinos. A few years later, the investigations were complemented by the Tokai-to-Kamioka (T2K) experiment, which introduced the use of an artificially generated proton beam to further investigate neutrino oscillations.

Researchers from RWTH Aachen have been contributing to the T2K experiment, a truly international collaboration of about 500 scientists and particle physicists in Asia, Europe and North America. At J-PARC, the RWTH physicists participated in building the ND280 and today contribute to operating the detector.

At the heart of the detector, three so-called  time projection chambers provide complete track information on charged particles which travel through a gas volume contained in the chambers. RWTH researcher Dr. Stefan Roth and his team have developed a comprehensive system for monitoring and continous calibration of the chambers. Several units of the system are installed in Japan. They are operated from Aachen, where the data are analyzed and transferred back to a database in Japan. With the help of the system, the detector resolution can be optimized.

"The Nobel Prize for our colleague Takaaki Kajita shows that it was a good decision to participate in the Japanese neutrino program," states Dr. Roth. "We would like to congratulate Takaaki Kajita, and we are looking forward to new discoveries lying ahead of us."