An improved upper limit on the neutrino mass from a direct kinematic method by KATRIN (1909.06048v1)

Abstract: We report on the neutrino mass measurement result from the first four-week science run of the Karlsruhe Tritium Neutrino experiment KATRIN in spring 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are energy analyzed by a high-resolution MAC-E filter. A fit of the integrated electron spectrum over a narrow interval around the kinematic endpoint at 18.57 keV gives an effective neutrino mass square value of $(-1.0^{+0.9}_{-1.1})$ eV$^2$. From this we derive an upper limit of 1.1 eV (90$\%$ confidence level) on the absolute mass scale of neutrinos. This value coincides with the KATRIN sensitivity. It improves upon previous mass limits from kinematic measurements by almost a factor of two and provides model-independent input to cosmological studies of structure formation.

• The paper demonstrates an improved upper limit on neutrino mass of 1.1 eV using a direct kinematic method.
• The study employs a high-purity gaseous tritium source and a MAC-E filter spectrometer to enhance measurement precision.
• These findings refine neutrino mass models and offer vital inputs for cosmological predictions and future neutrino research.

An Improved Upper Limit on Neutrino Mass from the KATRIN Experiment

The paper "An Improved Upper Limit on the Neutrino Mass from a Direct Kinematic Method by KATRIN" presents significant advancements in the field of neutrino physics, particularly in the measurement of neutrino mass. This research is conducted by the Karlsruhe Tritium Neutrino (KATRIN) experiment and elaborates on the results from their initial science run in 2019, which substantially improves constraints on the neutrino mass scale.

Overview and Methodology

The KATRIN experiment employs a direct kinematic method to measure the mass of neutrinos using a high-purity gaseous molecular tritium source. The experiment is designed to determine the mass via the analysis of beta-decay electrons, leveraging the advanced Magnetic Adiabatic Collimation with Electrostatic Filtering (MAC-E filter) spectrometer. This spectrometer facilitates the high-precision energy measurement necessary to detect the subtle changes in the endpoint spectrum of the beta decay from tritium. The goal of KATRIN is to achieve a sensitivity of 0.2 eV on the neutrino mass after completing its full campaign.

The paper reports on the results from a four-week data collection period, indicating a derived upper limit on the absolute mass scale of neutrinos of 1.1 eV at 90% confidence level. This represents nearly a two-fold improvement over previous kinematic measurements, placing stronger constraints on models predicting quasi-degenerate neutrino masses.

Key Findings

• Neutrino Mass Measurement: The KATRIN experiment provides an effective neutrino mass square value of $(-1.0~ ^{+~ 0.9}_ {-~ 1.1})$~eV$^2$, resulting in an upper limit on the neutrino mass of 1.1 eV at 90% confidence.
• Enhanced Sensitivity: This new limit denotes a significant enhancement in sensitivity and improves upon previous indirect and direct measurements, illustrating the efficacy of the KATRIN setup.
• Technical Innovations: The setup includes a windowless gaseous tritium source and an electrostatic spectrometer optimized for high-precision measurement, minimizing systematic uncertainty through a sophisticated design involving large-volume air coils and advanced vacuum technologies.

Implications

The improved constraints on the neutrino mass have substantial implications for both theoretical and practical aspects in physics. Theoretically, these results support the narrowing of viable models regarding neutrino masses, thereby providing vital inputs for cosmological models. This mass scale input helps refine our understanding of the role of neutrinos in the formation of large-scale structures in the universe, which is crucial for models such as ΛCDM in cosmology.

Future Prospects

KATRIN's ongoing mission aims to reach even lower neutrino mass limits by extending data collection to about 1000 days, thus achieving greater statistical significance and further reducing systematic uncertainties. Moreover, the methodology and results of KATRIN lay the groundwork for future experiments and analyses in neutrino science, including searching for signatures of physics beyond the Standard Model such as sterile neutrinos.

This work provides a robust framework for future studies aimed at probing the fundamental nature of neutrinos while pushing the boundaries of existing technologies in high-precision particle physics experiments.