Abstract
The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c2, i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experiment’s windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritium—one of the key parameters required in the derivation of the electron neutrino mass. The concentrations cx for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10−3 or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, εT, is derived with precision of <10−3 and trueness of <3 × 10−3, being within and surpassing the actual requirements for KATRIN, respectively.
Highlights
The neutrino was postulated and theoretically described in the early 1930s to explain the conservation of energy, momentum, and angular momentum during β-decay [1,2]
The aforementioned tritium-related parameter values rely on Raman spectroscopy measurements, in which all hydrogen isotopologues circulating in the loop are monitored
“KNM1”), the gas composition inside the windowless gaseous tritium source (WGTS) was kept “tritium-lean”, meaning that it was extremely different from the conditions for standard Karlsruhe Tritium Neutrino (KATRIN) operation [13]
Summary
The (electron) neutrino was postulated and theoretically described in the early 1930s to explain the conservation of energy, momentum, and angular momentum (spin) during β-decay [1,2]. These were conducted independently and more or less in parallel during the 1990s up to the early 2000s, nearly contemporary to the aforementioned neutrino oscillation measurements In both experiments, molecular tritium (T2 ) sources were utilized, namely condensed and gaseous tritium sources, respectively; and in both, the analysis of the tritium β-decay spectrum near the endpoint E0 = 18.6 keV was performed using a so-called MAC-E energy filter [9]. It was already clear from cosmological observations and calculations, that the mass limit was expected to be quite a bit lower Already during the latter stages of the Mainz and Troitsk experiments, a collaborative follow-up experiment—the Karlsruhe Tritium Neutrino experiment, KATRIN, to be hosted at the Tritium Laboratory Karlsruhe (TLK)—was proposed, and initiated, that should exhibit substantially improved measurement sensitivity
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