Speaker
Description
The KATRIN experiment aims to measure or exclude the effective
electron neutrino mass $m_\nu$ down to 0.2 eV/$c^2$ (90 % C.L.) by measuring
the tritium beta spectrum near its endpoint $E_0$, and performing a fit
including the parameters $E_0$ and $m_\nu^2$. Since these are highly correlated,
a systematic shift influencing the obtained neutrino mass would be
visible in the endpoint and thus tritium $Q$ value. $Q$ has been derived from the mass difference of $^3$He$^+$ and $^3$H with 70 meV precision (cf. PRL. 114, 013003 (2015)).
This has not been applicable to KATRIN so far due to uncertainty of the measured plasma potential in the tritium source.
The KATRIN $Q$ value can also be determined by absolute calibration
with conversion electron lines from co-circulating $^\mathrm{83m}$Kr.
This is however limited by nuclear gamma transition
energy uncertainties of $^\mathrm{83m}$Kr to 0.5 eV accuracy. The excited
nucleus of $^\mathrm{83m}$Kr decays in a two-step cascade of 32.2 keV and 9.4 keV
highly converted gamma transitions.
In new measurements performed at KATRIN, a large set of conversion electron
lines, including a new line, was measured with a gaseous and a condensed
krypton source. Following the method described in EPJ C 82
(2022) 700, the $^\mathrm{83m}$Kr gamma transition energies can be determined,
which can allow for reduction of tritium $Q$ value uncertainty to
~0.1 eV. This poster presents the status of the analysis.
Supported by BMBF under contract number 05A20PMA.
| Submitted on behalf of a Collaboration? | Yes |
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