Troitsk Nu-mass Experiment Research Articles

Detritiation of the Electrostatic Spectrometer of Troitsk Nu-mass Experiment

This paper describes the methods and presents the results of the “Troitsk Nu-mass” experiment spectrometer cleanup after the in\ er volume (40 m3) and surfaces (160 m2) were contaminated by 5.2 GBq of tritium. The Troitsk Nu-mass experiment of the Institute for Nuclear Research of the Russian Academy of Sciences (Moscow) is designed to measure the spectrum of electrons from tritium decays in order to search for hypothetical particles—sterile neutrinos. Due to some equipment failures, the spectrometer internal volume was contaminated with tritium. The contamination made measurements impossible, and the research program stopped. Different methods were used for cleanup: vacuum extraction, hydrogen soaks, and water vapor soaks. As a result of detritiation, the background level of the main detector of the Troitsk Nu-mass spectrometer was reduced approximately by more than ten times, which made it possible to resume work. The results are consistent with the literature data obtained earlier for normal conditions in the air and can be used for detritiation of similar installations.

Electron evaporation from magnetic trap in Troitsk nu-mass experiment

This paper is dedicated to the simulation of the so-called trapping-effect observed in the Troitsk nu-mass experiment. The effect is caused by the magnetic trapping of decay electrons in the windowless gaseous tritium source and the gradual evaporation of those electrons. As a result, alongside regular tritium beta-spectrum electrons, we see additional electrons that are initially trapped in the source and escape it with changed energy. The spectrum of evaporated electrons is quite peculiar (almost flat for monochromatic initial electrons) and could not be directly measured in the experiment. So one has to rely on simulations. Also, it is possible that the same effect could be observed in other cases of magnetic traps.

TRISTAN measurements at the Troitsk nu-mass experiment

The KATRIN (Karlsruhe Tritium Neutrino) experiment investigates the energetic endpoint of the tritium beta-decay spectrum to determine the effective mass of the electron anti-neutrino with a sensitivity of 200 meV (90 % C.L.) after an effective data taking time of three years. The TRISTAN (tritium beta-decay to search for sterile neutrinos) group aims at detecting a sterile neutrino signature by measuring the entire tritium beta-decay spectrum with an upgraded KATRIN system. One of the greatest challenges is to handle the high signal rates generated by the strong activity of the KATRIN tritium source. Therefore, a novel multipixel silicon drift detector is being designed which is able to handle rates up to 100 Mcps with an excellent energy resolution for electrons of 300 eV (FWHM) at 10 keV. First seven-pixel prototype detectors were successfully installed and operated at the Troitsk nu-mass experiment, one of KATRIN’s technological predecessors. In this work, we present the results of these measurement campaigns.

Measurements with a TRISTAN prototype detector system at the “Troitsk nu-mass” experiment in integral and differential mode

Sterile neutrinos emerge in minimal extensions of the Standard Model which can solve a number of open questions in astroparticle physics. For example, sterile neutrinos in the keV-mass range are viable dark matter candidates. Their existence would lead to a kink-like distortion in the tritium β-decay spectrum. In this work we report about the instrumentation of the Troitsk nu-mass experiment with a 7-pixel TRISTAN prototype detector and measurements in both differential and integral mode. The combination of the two modes is a key requirement for a precise sterile neutrino search, as both methods are prone to largely different systematic uncertainties. Thanks to the excellent performance of the TRISTAN detector at high rates, a sterile neutrino search up to masses of about 6 keV could be performed, which enlarges the previous accessible mass range by a factor of 3. Upper limits on the neutrino mixing amplitude in the mass range < 5.6 keV (differential) and < 6.6 keV (integral) are presented. These results demonstrate the feasibility of a sterile neutrino search as planned in the upgrade of the KATRIN experiment with the final TRISTAN detector and read-out system.

Shape-based event pileup separation in Troitsk nu-mass experiment

Nowadays continuous signal digitization becomes a standard procedure in experimental physics. Though, signal pileup separation at high count rate remains a problem. The article presents algorithms which could be used for detection and extraction of events based on the shape of a single pulse. We also explain how these algorithms were applied in data analysis for the “Troitsk nu-mass” experiment.

Processing of higher count rates in Troitsk nu-mass experiment

In this article we give a short outline of current status of search for sterile neutrinos with masses up to 4 keV in “Troitsk nu-mass experiment”. We also discuss major sources of systematic uncertainties and methods to lower them.

First measurements in search for keV sterile neutrino in tritium beta-decay in the Troitsk nu-mass experiment

We present the first measurements of tritium beta-decay spectrum in the electron energy range 16-18.6 keV. The goal is to find distortions which may correspond to the presence of a heavy sterile neutrinos. A possible contribution of this kind would manifest itself as a kink in the spectrum with a similar shape but with end point shifted by the value of a heavy neutrino mass. We set a new upper limits to the neutrino mixing matrix element U^2_{e4} which improve existing limits by a factor from 2 to 5 in the mass range 0.1-2 keV.

The search for an additional neutrino mass eigenstate in the 2–100 eV region from ‘Troitsk nu-mass’ data: a detailed analysis

In this paper we present the details of our previously published results for the search for an additional neutrino mass state in the β-electron spectrum from the Troitsk nu-mass experiment. Here we present the steps of the analysis and show a set of likelihood functions obtained for each additional heavy mass value. We demonstrate how systematic errors were estimated. We also compare our results with those published recently for a similar analysis for Mainz data and try to explain why there is a factor of 2–3 difference in the sensitivity for an additional heavy mass.

Upper limit on additional neutrino mass eigenstate in 2 to 100 eV region from “Troitsk nu-Mass” data

We performed a search for any sign of an additional neutrino mass state in beta-electron spectrum based on data reanalysis of direct electron antineutrino mass measurements in Tritium beta-decay in the Troitsk nu-mass experiment. The existing data set allows us to search for such a state in the mass range up to 100 eV. The lowest value at a 95% C.L. upper limit for the contribution of a heavy eigenstate into electron neutrino is around or less than 1% for masses above 20 eV.

Measurement of the electron antineutrino mass in tritium beta decay in the Troitsk nu-mass experiment

The results obtained in the Troitsk nu-mass experiment by measuring the electron-antineutrino mass in tritium beta decay are presented. The facility used consists of a gaseous windowless tritium source and an electrostatic electron spectrometer involving an adiabatic magnetic collimation. Runs in which measurement conditions were reliably established were thoroughly selected in analyzing data obtained from 1994 to 2004. All known systematic effects were taken into account. For the square of the electron-antineutrino mass, the treatment of measured spectra yielded the following result: m ν 2 = −0.67 ± 1.89stat. ± 1.68syst. eV2. The use of the Bayesian method and the Feldman-Cousins unified approach made it possible to obtain the following upper limits on the mass: m ν < 2.12 eV (at a 95% C.L.; Bayesian method) and m ν < 2.05 eV (at a 95% C.L., Feldman-Cousins method). At the same time, an estimation of the sensitivity limit without allowance for negative values of the square of the mass leads to m ν < 2.2 eV (at a 95% C.L.). Measured spectra were analyzed for the possible existence of an additional structure (step) in the electron spectrum near the boundary energy. The conclusion drawn from this analysis was that, within the existing statistical errors, there are no reasons for introducing such a feature.