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

Abstract

We performed a search for any sign of an additional neutrino mass state in β-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 .Throughout the last couple decades it has become clear that the Standard Model (SM) of elementary particles cannot explain some of the observed phenomena in particle physics, astrophysics and cosmology. These are baryon asymmetry, dark matter, neutrino oscillations and others. Neutrino oscillations from short baseline experiments favor the existence of an additional neutrino mass state to the three active neutrinos in the SM. Astrophysical observations and cosmology also point to the fact that the effective number of neutrinos is greater than 3 [1]. This can be interpreted as a possible existence of at least one sterile neutrino. Sterile neutrino is a natural consequence of the non-zero neutrino mass and appears in many theories beyond the SM. From this point of view, addition of a. Would a sterile neutrino be found it will be the first particle beyond the Standard Model. While there is a number of the results which disfavor or even are in contradiction with the hypothesis of sterile neutrino, many experiments are undergoing or are planning to search for them. For details we refer to the "Light sterile neutrinos: a white paper" [2].It becomes important to check all possible experimental data to prove, disprove or set an upper limit for the sterile neutrino hypothesis. Results of the reanalysis of our data on the direct electron antineutrino mass measurements in Tritium β-decay in the Troitsk nu-mass experiment [4] are presented in this paper. The group led by V. M. Lobashev was obtaining these data in the period of 1997-2004. We used the same file set and analysis framework as for the electron antineutrino mass. We performed a search for any sign of an additional neutrino mass state in the β-electron spectrum. Such a state with a finite mass would exhibit itself as a kink in the spectrum. Recently a similar analysis was published based on the Mainz data [3].The Troitsk experiment has two major parts: an integrating electrostatic spectrometer with adiabatic magnetic collimation and a windowless gaseous tritium source as a volume for β-decays. The spectrometer resolution was about 4 eV. We measured an integrated electron spectrum at the region of the last 200-300 eV from the spectrum endpoint (18575 eV) by varying the electrostatic potential V on the spectrometer electrode. All details on experimental setup, data taking, analysis, corrections and estimation of systematic error are published in Ref. [4]. For electron antineutrino mass squared we published the value m 2 ν = −0.67 ± 2.53 eV 2 . In accordance with Ref.[4], the spectrum of electrons ...

Light sterile neutrinos

“…The expression (53) of the Kurie function shows that a heavy nonstandard neutrino mass m k with k ≥ 4 can be measured by observing a kink of the kinetic energy spectrum of the emitted electron at Q − m k below the end point [104,222,[241][242][243][244][245][246][247]. Recently, the Mainz [219] and Troitsk [220,221] collaborations reanalyzed the measured spectra which led to the limits (55) and (56) searching for the effect of a heavy neutrino mass m 4 . The negative results led to the upper bounds for the mixing factor |U e4 | 2 shown in Fig.…”

“…The existence of massive neutrinos at the eV scale can be probed in β-decay experiments [219][220][221][222][223][224][225] and in neutrinoless double-β decay experiments [13,106,176,[226][227][228][229][230][231][232][233][234].…”

Thresholde−p⟶ nνescattering and the electron neutrino mass

“…If the neutrino were massive, the threshold energy would be shifted towards higher values by m ν and one would observe a depletion of counts compared to the massless case, as shown in the figure. The measurement would have to involve a beam energy scan, covering a region from below to above the threshold and the possible neutrino mass could be determined by fitting the functional dependence (1).…”

“…A finite neutrino mass would manifest as a depletion of counts, compared to the case of the massless neutrino, in the electron kinetic energy distribution near the endpoint. The latest results for the limit on the electron neutrino mass have been derived over a decade ago from data collected in two eV-precision experiments: at Troitsk (Russia) [1][2][3][4] (m ν < 2.05 eV at 95% c.l.) and Mainz (Germany) [5,6], [7] (m 2 µ = −0.6 ± 2.2(stat) ± 2.1(syst) eV 2 or m ν < 2.3 eV at 95% c.l.).…”

The electron capture in 163Ho experiment – ECHo

“…as derived by a global fit of short-baseline neutrino oscillation data [168]. By restricting the analysis to the data of ν e andν e disappearance experiments [171,172] and taking into account the Mainz [173] and Troitsk [174,175] bounds, the constrains on the sterile neutrino parameters are less stringent and are indicated by the region within the gray curves which enclose the 95.45% C.L. allowed regions.…”