Determination of the Leptonic Mixing Angle Theta-13 with the Double Chooz Experiment

• Applicant: Professor Dr. Christopher Wiebusch
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2007
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 39031316

The main goal of the Double Chooz experiment is the measurement of flavor oscillations of anti-electron neutrinos. The experimental setup consists of two nearly identical detectors that measure the flux of anti-electron neutrinos at different distances from the two reactor cores at the Chooz nuclear power plant in France. The experiment is optimized for measuring the disappearance of reactor neutrinos related to the leptonic mixing angle Theta-13 but it is also sensitive to additional oscillation modes related to hypothetical sterile neutrinos. The Double Chooz collaboration has successfully pioneered the experimental concept of using identical near and far detectors minimizing systematic uncertainties. Upon start of the project in 2006, it was unclear, if the effect existed and could be measured. Meanwhile Theta-13 is the neutrino mixing angle that has been measured with the smallest relative error, also because of results from Double Chooz. With one far detector, Double Chooz started operation in 2011, The second, near, detector of Double Chooz has been commissioned early 2015 and the experiment operated in its full configuration until 2018. Our group at RWTH Aachen has been funded by the DFG since 2007. We have significantly contributed to the construction and operation of Double Chooz, and to the data analysis, particularly the previous measurements of Theta-13. We have provided about 15% of the photomultipliers of both inner detectors and have developed the trigger system and additional components of the data acquisition system, which has been working very reliably at essentially 100% efficiency during all phases of detector operation. The analysis of the experimental data is still ongoing. Goal of this proposal is the production of a final result for the measurement of Theta-13, and additionally a final result for the search for sterile neutrinos. The determination of Theta-13 will be ultimately limited by systematic uncertainties and thus we are aiming for minimizing these errors for the final result. The Double Chooz experiment has several unique advantages in this direction: The two detectors are positioned such that the relative flux contribution from the two reactors is similar for both detectors. Furthermore, during phases when reactors are stopped, backgrounds can be precisely measured. Therefore, we expect that the result of Double Chooz will significantly contribute to the global knowledge of the value Theta-13 for many years. The uncertainty of Theta-13 is of critical importance to the field of neutrino oscillations, because it is an input to other measurements such as the measurement of the neutrino mass hierarchy, CP violation in the lepton sector and tests of the unitarity of the PMNS matrix.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Achim Stahl