Pushing the Frontier in Measuring the Mass of the Lightest Lepton: Results from the Karlsruhe Tritium Neutrino Experiment

The determination of the neutrino mass is one of the major challenges in particle physics today. Experiments, based solely on the kinematics of β-decay, provide a largely model-independent probe to the neutrino mass scale. The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to directly measure the effective electron antineutrino mass with a sensitivity of 0.2 eV (90% CL). It employs a cryogenic, highly pure, molecular tritium source providing a high luminosity of signal electrons. It is coupled to a high-resolution, integrating spectrometer for energy analysis. In this talk we present the principle of the measurement as well as how it was technically realised in a 70-m long beamline. Subsequent to a sequence of commissioning measurements, in 2019 the first neutrino mass run took place which will be discussed in detail. Our blind analyses allowed us to set an upper limit of 1.1 eV on the neutrino-mass scale at a 90% confidence level. This first result, based on a few weeks of running at a reduced source intensity and dominated by statistical uncertainty, improved on prior limits by nearly a factor of two. Finally, the talk will conclude with an outlook on future neutrino mass campaigns and on studies aiming to probe new physics theories (like sterile neutrinos) from the recorded high-resolution tritium β-spectra

Accurate calibration of the Raman system for the Karlsruhe Tritium Neutrino Experiment

The KATRIN experiment aims to measure the neutrino mass with a sensitivity of m=0.2 eV/c² (90% C.L.). One parameter, the isotopic composition of the tritium gas source, is measured inline by Raman spectroscopy. The required measurement trueness of the composition is <10%. Thus, accurate calibration of the Raman system is required. This is successfully obtained by two independent calibration methods: a gas sampling technique and an approach via theoretical intensities plus spectral sensitivity

Probing the Neutrino-Mass Scale with the KATRIN Experiment

The absolute mass scale of neutrinos is an intriguing open question in contemporary physics. The as-yet-unknown mass of the lightest and, at the same time, most abundant massive elementary particle species bears fundamental relevance to theoretical particle physics, astrophysics, and cosmology. The most model-independent experimental approach consists of precision measurements of the kinematics of weak decays, notably tritium β decay. With the KATRIN experiment, this direct neutrino-mass measurement has entered the sub-eV domain, recently pushing the upper limit on the electron-based neutrino mass down to 0.8 eV (90% CL) on the basis of first-year data out of ongoing, multiyear operations. Here, we review the experimental apparatus of KATRIN, the progress of data taking, and initial results. While KATRIN is heading toward the target sensitivity of 0.2 eV, other scientific goals are pursued. We discuss the search for light sterile neutrinos and an outlook on future keV-scale sterile-neutrino searches as well as further physics opportunities beyond the Standard Model

Versatile Confocal Raman Imaging Microscope Built from Off-the-Shelf Opto-Mechanical Components

Confocal Raman microscopic (CRM) imaging has evolved to become a key tool for spatially resolved, compositional analysis and imaging, down to the μm-scale, and nowadays one may choose between numerous commercial instruments. That notwithstanding, situations may arise which exclude the use of a commercial instrument, e.g., if the analysis involves toxic or radioactive samples/environments; one may not wish to render an expensive instrument unusable for other uses, due to contamination. Therefore, custom-designed CRM instrumentation—being adaptable to hazardous conditions and providing operational flexibility—may be beneficial. Here, we describe a CRM setup, which is constructed nearly in its entirety from off-the-shelf optomechanical and optical components. The original aim was to develop a CRM suitable for the investigation of samples exposed to tritium. For increased flexibility, the CRM system incorporates optical fiber coupling to both the Raman excitation laser and the spectrometer. Lateral raster scans and axial profiling of samples are facilitated by the use of a motorized xyz-translation assembly. Besides the description of the construction and alignment of the CRM system, we also provide (i) the experimental evaluation of system performance (such as, e.g., spatial resolution) and (ii) examples of Raman raster maps and axial profiles of selected thin-film samples (such as, e.g., graphene sheets)

The Generation and Analysis of Tritium-substituted Methane

An unavoidable category of molecular species in large-scale tritium applications, such as nuclear fusion, are tritium-substituted hydrocarbons; these form by radiochemical reactions in the presence of (circulating) tritium and carbon (mainly from the steel of vessels and tubing). Tritiumsubstituted methane species, CQ$_4$ (with Q = H , D , T), are often the precursor for higher-order reaction chains, and thus are of particular interest. Here we describe the controlled production of CQ$_4$ carried out in the CAPER facility of the Tritium Laboratory Karlsruhe (TLK), exploiting catalytic reactions and species-enrichment via the CAPER-integral permeator. CQ4 was generated in substantial quantity (>1000 cm$^3$ at ~850 mbar, with CQ$_4$ - content of up to ~20 %). These samples were analyzed using laser Raman and mass spectrometry, to determine the relative isotopologue composition and to trace the generation of tritiated chain-hydrocarbons.Comment: 10 pages, 4 figures. This article has been accepted for publication in Fusion Science and Technology, published by Taylor & Franci

First observation of tritium adsorption on graphene

In this work, we report on the first-ever studies of graphene exposed to tritium gas in a controlled environment. The single layer graphene on $\textrm{SiO}_2$/Si substrate was exposed to 400 mbar of $\textrm{T}_2$ for a total time of ~55 h. The resistivity of the graphene sample was measured in-situ during tritium exposure using the Van der Pauw method. After the exposure, the samples were scanned with a confocal Raman microscope to study the effect of tritium on the graphene structure as well as the homogeneity of spectral modifications. We found that the sheet resistance increases by three orders of magnitude during the exposure. By Raman microscopy, we demonstrate that the graphene film can withstand the bombardment from the beta-decay of tritium, and primary and secondary ions. Additionally, the Raman spectra after tritium exposure are comparable with previously observed results in hydrogen-loading experiments carried out by other groups. By thermal annealing we could demonstrate, using Raman spectral analysis, that the structural changes were partially reversible. Considering all observations, we conclude that the graphene film was at least partially tritiated during the tritium exposure.Comment: Submitted to Nanoscale Advances (RSC), 14 pages, 4 figure

Custom-built light-pipe cell for high-resolution infrared absorption spectroscopy of tritiated water vapor and other hazardous gases

We present a new custom-built cell for high-resolution absorption spectroscopy of hazardous gases. The use of an aluminum light-pipe enables sensitive detection due to the small tube diameter and an increased particle density in the interaction volume for a limited analyte amount in the cell, while avoiding additional surfaces such as mirrors. To demonstrate this, we have used the cell to measure tritiated water isotopologues (HTO and traces of T2O) for which spectroscopic data is scarce, due to the challenge of performing spectroscopy of these highly radio-chemical aggressive substances. For this purpose, the new cell also features the efficient inline-production of tritiated water. In this paper we present the concept of the light-pipe cell and demonstrate its performance with a high-resolution absorption spectrum of gaseous HTO generated inside of this cell