Direct neutrino-mass measurement with sub-electronvolt sensitivity
M. Aker, A. Beglarian, J. Behrens, A. Berlev, U. Besserer, B. Bieringer, F. Block, S. Bobien, M. Böttcher, B. Bornschein, L. Bornschein, T. Brunst, T. S. Caldwell, R. M. D. Carney, L. La Cascio, S. Chilingaryan, W. Choi, K. Debowski, M. Deffert, M. Descher, D. Díaz Barrero, P. J. Doe, O. Dragoun, G. Drexlin, K. Eitel, E. Ellinger, R. Engel, Seishi Enomoto, A. Felden, J. A. Formaggio, F. M. Fränkle, G. Franklin, F. Friedel, A. Fulst, K. Gauda, W. Gil, F. Glück, Robin Größle, R. Gumbsheimer, V. Gupta, T. Höhn, V. Hannen, N. Haußmann, K. Helbing, S. Hickford, R. Hiller, D. Hillesheimer, D. Hinz, T. Houdy, A. Huber, A. Jansen, C. Karl, F. Kellerer, J. Kellerer, M. Kleifges, M. Klein, C. Köhler, L. Köllenberger, A. Kopmann, M. Korzeczek, A. Kovalík, B. Krasch, H. Krause, Bruno L. Lago, T. Lasserre, T. L. Le, O. Lebeda, B. Lehnert, A. Lokhov, M. Machatschek, E. Malcherek, Martin Mark, A. Marsteller, E. L. Martín, C. Melzer, A. Menshikov, S. Mertens, J. Mostafa, K. Müller, H. Neumann, S. Niemes, P. Oelpmann, D. S. Parno, A. W. P. Poon, J.M.L. Poyato, F. Priester, S. Ramachandran, R. G. H. Robertson, Werner Rodejohann, M. Röllig, C. Röttele, C. Rodenbeck, M. Ryšavý, R. Sack, Alejandro Sáenz, P. Schäfer, A. Pollithy, L. Schimpf, K. Schlösser, Magnus Schlösser
Abstract
Abstract Since the discovery of neutrino oscillations, we know that neutrinos have non-zero mass. However, the absolute neutrino-mass scale remains unknown. Here we report the upper limits on effective electron anti-neutrino mass, m ν , from the second physics run of the Karlsruhe Tritium Neutrino experiment. In this experiment, m ν is probed via a high-precision measurement of the tritium β -decay spectrum close to its endpoint. This method is independent of any cosmological model and does not rely on assumptions whether the neutrino is a Dirac or Majorana particle. By increasing the source activity and reducing the background with respect to the first physics campaign, we reached a sensitivity on m ν of 0.7 eV c –2 at a 90% confidence level (CL). The best fit to the spectral data yields $${{\mbox{}}}{m}_{\nu }^{2}{{\mbox{}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mstyle> <mml:mspace/> </mml:mstyle> <mml:msubsup> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mstyle> <mml:mspace/> </mml:mstyle> </mml:mrow> </mml:math> = (0.26 ± 0.34) eV 2 c –4 , resulting in an upper limit of m ν < 0.9 eV c –2 at 90% CL. By combining this result with the first neutrino-mass campaign, we find an upper limit of m ν < 0.8 eV c –2 at 90% CL.