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arXiv · 2310.12634

Improved treatment of the $T_2$ molecular final-states uncertainties for the KATRIN neutrino-mass measurement

S. Schneidewind·J. Schürmann·A. Lokhov·C. Weinheimer·A. Saenz
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Abstract

The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to determine the effective mass of the electron antineutrino via a high-precision measurement of the tritium beta-decay spectrum in its end-point region. The target neutrino-mass sensitivity of 0.2 eV / c^2 at 90% C.L. can only be achieved in the case of high statistics and a good control of the systematic uncertainties. One key systematic effect originates from the calculation of the molecular final states of T_2 beta decay. In the first neutrino-mass analyses of KATRIN the contribution of the uncertainty of the molecular final-states distribution (FSD) was estimated via a conservative phenomenological approach to be 0.02 eV^2 / c^4. In this paper a new procedure is presented for estimating the FSD-related uncertainties by considering the details of the final-states calculation, i.e. the uncertainties of constants, parameters, and functions used in the calculation as well as its convergence itself as a function of the basis-set size used in expanding the molecular wave functions. The calculated uncertainties are directly propagated into the experimental observable, the squared neutrino mass m_nu^2. With the new procedure the FSD-related uncertainty is constrained to 0.0013 eV^2 / c^4, for the experimental conditions of the first KATRIN measurement campaign.

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S. Schneidewind, J. Schürmann, A. Lokhov, C. Weinheimer, A. Saenz. 2023-10-19. Improved treatment of the $T_2$ molecular final-states uncertainties for the KATRIN neutrino-mass measurement. https://arxiv.org/abs/2310.12634

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