Unveiling neutrino masses through precise experiments

Unveiling neutrino masses through precise experiments
by Robert Schreiber
Berlin, Germany (SPX) Apr 22, 2024

The existence of neutrinos, elusive particles suggested to account for missing energy and momentum in radioactive beta decay, was hypothesized in the 1930s and confirmed experimentally in 1956. These particles are known for only interacting through weak interaction, allowing trillions to pass through us harmlessly every second from cosmic sources like the sun. This interaction was pivotal in understanding that neutrinos could oscillate between three known types, challenging previous assumptions in particle physics that neutrinos, like photons, had no rest mass.

These oscillations imply neutrinos have mass, a notion contradicting the standard model of particle physics but critical for new physics theories. Determining the exact mass of neutrinos opens a door to these new theories, though measuring this requires complex experiments due to neutrinos' elusive nature.

Christoph Schweiger, a doctoral student at the Max Planck Institute for Nuclear Physics, highlights two experimental approaches to "weigh" neutrinos. The first method involves the beta decay of tritium, observed in the KATRIN experiment at Karlsruhe Institute of Technology, which monitors the decay of a neutron into a proton. The second method is through the electron capture of holmium-163, which is part of the ECHo collaboration's work, aiming to measure decay processes with extreme precision as mass and energy are equivalent under Einstein's theory.

Schweiger discusses a third approach, the Heidelberg pentatrap experiment, involving Penning traps that measure mass by the frequency of ion movement. This technique is described as so sensitive that it could detect a single water drop on an Airbus A-380. His work involves comparing the masses of holmium-163 and dysprosium-163 ions to calculate the neutrino's mass.

From these experiments, the Heidelberg team managed to enhance the precision of previous measurements fiftyfold, a testament to both their technical skills and the collaborative efforts across three theory groups. This improved precision helps reduce systematic uncertainties, a key in confirming the findings.

The KATRIN experiment has since set a significant upper limit on neutrino mass at an almost imperceptible 0.8 electron volts per speed of light squared, roughly equivalent to comparing the weight of four raisins to the sun. Additional cosmological analyses suggest even lower upper limits, highlighting the complexities and dependencies of such measurements on theoretical models.

Understanding neutrino masses remains a daunting challenge at the frontier of modern physics, with the Heidelberg results marking a significant step toward unraveling this longstanding mystery.

Research Report:Direct high-precision Penning-trap measurement of the Q-value of the electron capture in 163Ho for the determination of the electron neutrino mass