Ghost Particle Experiment Limits Neutrino Mass with Unprecedented Accuracy

A neutrino is lighter than 0.8 electron volts

New world record: KATRIN experiment limits neutrino mass with unprecedented accuracy.

The neutrino is perhaps the most fascinating elementary particle in our universe. In cosmology they play an important role in the formation of large-scale structures, while in particle physics their tiny but nonzero mass distinguishes them, pointing to new physical phenomena that go beyond our current theories. Without mass measurement neutrinosour understanding of the universe will remain incomplete.

Scientists often call neutrinos “ghost particles” because they almost never interact with other matter.

This is an international challenge KAрлсруэ THREEthis one NThe eutrino experiment (KATRIN) at the Karlsruhe Institute of Technology (KIT) with partners from six countries has become the most sensitive scale in the world for neutrinos. It uses the beta decay of tritium, an unstable isotope of hydrogen, to determine the mass of neutrinos through the energy distribution of electrons released during decay. This requires a serious technological effort: the 70-meter-long experiment contains the world’s most intense source of tritium, as well as a giant spectrometer to measure the decay energy of electrons with unprecedented accuracy.

KATRIN main spectrometer

Mounting the electrodes in the main spectrometer of the KATRIN experiment. Credit: Joachim Wolf / KIT

The high quality of data since the start of scientific measurements in 2019 has been steadily improving over the last two years. “KATRIN is an experiment with the highest technological requirements, and now it works like a perfect watch,” said Guido Drexlin (KIT), project manager and one of the two co-representatives of the experiment. Christian Weinheimer ([{” attribute=””>University of Münster), the other co-spokesperson, adds that “the increase of the signal rate and the reduction of background rate were decisive for the new result.”

Data analysis

The in-depth analysis of this data was demanding everything from the international analysis team led by its two coordinators, Susanne Mertens (Max Planck Institute for Physics and TU Munich) and Magnus Schlösser (KIT). Each and every effect, no matter how small, had to be investigated in detail. “Only by this laborious and intricate method we were able to exclude a systematic bias of our result due to distorting processes. We are particularly proud of our analysis team which successfully took up this huge challenge with great commitment,” the two analysis coordinators are pleased to report.

KATRIN Experiment Setup

The 70 meter long KATRIN experiment with its main components tritium source, main spectrometer and detector. Credit: Leonard Köllenberger/KATRIN Collaboration

The experimental data from the first year of measurements and the modeling based on a vanishingly small neutrino mass match perfectly: from this, a new upper limit on the neutrino mass of 0.8 eV can be determined (Nature Physics, July 2021). This is the first time that a direct neutrino mass experiment has entered the cosmologically and particle-physically important sub-eV mass range, where the fundamental mass scale of neutrinos is suspected to be. “The particle physics community is excited that the 1-eV-barrier has been broken by KATRIN,” comments neutrino expert John Wilkerson (University of North Carolina, Chair of the Executive Board).

Susanne Mertens explains the path to the new record: “Our team at the MPP in Munich has developed a new analysis method for KATRIN that is specially optimized for the requirements of this high-precision measurement. This strategy has been successfully used for past and current results. My group is highly motivated: We will continue to meet the future challenges of KATRIN analysis with new creative ideas and meticulous accuracy.”

Further measurements should improve sensitivity

KATRIN co-secretaries and coordinators are very optimistic about the future: “Further neutrino mass measurements will continue until the end of 2024. To realize the full potential of this unique experiment, we will not only steadily increase the statistics of signaling events, we are constantly developing and installing improvements to further reduce the background speed.

A special role in this is played by the development of a new detector system (TRISTAN), which allows KATRIN from 2025 to begin the search for “sterile” neutrinos with mass in the kiloelectronvolt range, a candidate for mysterious dark matter in space. which has already manifested itself in many astrophysical and cosmological observations, but whose physical nature is still unknown.

Reference: “Direct measurement of neutrino mass with sub-eV sensitivity” February 14, 2022, Physics of nature.
DOI: 10.1038 / s41567-021-01463-1 Ghost Particle Experiment Limits Neutrino Mass with Unprecedented Accuracy

Back to top button