本文评述了近年来在氚β谱中寻找电子中微子质量绝对值$m(ν_e)$的实验。通过使用具有高接受度和分辨率的专用静电过滤器，可观察到的$m^2(ν_e)$的不确定性已被推低至约3 eV $^2$。新的质量上限为95% C. L时的$m(ν_e) < 2$ eV。鉴于早期的β衰变实验所得到的错误的和非物理的质量结果，特别注意系统效应。质量极限是在当前的中微子研究的背景下，在粒子和天体物理学进行了讨论。目前正在开发和建设的下一代β光谱实验的预览，他们的目标是降低$m^2(ν_e)$ -不确定性的另一个因素100，达到灵敏度极限$m(ν_e) < 0.2$ eV。
英文摘要：
The paper reviews recent experiments on tritium beta spectroscopy searching for the absolute value of the electron neutrino mass $m(ν_e)$. By use of dedicated electrostatic filters with high acceptance and resolution, the uncertainty on the observable $m^2(ν_e)$ has been pushed down to about 3 eV$^2$. The new upper limit of the mass is $m(ν_e) < 2$ eV at 95% C.L. In view of erroneous and unphysical mass results obtained by some earlier experiments in beta decay, particular attention is paid to systematic effects. The mass limit is discussed in the context of current neutrino research in particle- and astrophysics. A preview is given of the next generation of beta spectroscopy experiments currently under development and construction; they aim at lowering the $m^2(ν_e)$-uncertainty by another factor of 100, reaching a sensitivity limit $m(ν_e) < 0.2$ eV.
Following the successful observation of single conversion electrons from $^{83m}$Kr using Cyclotron Radiation Emission Spectroscopy (CRES), Project 8 is now advancing its focus toward a tritium beta decay spectrum. A tritium spectrum will be an important next step toward a direct measurement of the neutrino mass for Project 8. Here we discuss recent progress on the development and commissioning of a new gas cell for use with tritium, and outline the primary goals of the experiment for the near future.
We consider tritium beta decay with additional emission of light pseudoscalar or vector bosons coupling to electrons or neutrinos. The electron energy spectrum for all cases is evaluated and shown to be well estimated by approximated analytical expressions. We give the statistical sensitivity of KATRIN to the mass and coupling of the new bosons, both in the standard setup of the experiment as well as for future modifications in which the full energy spectrum of tritium decay is accessible.
Past and current direct neutrino mass experiments set limits on the so-called effective neutrino mass, which is an incoherent sum of neutrino masses and lepton mixing matrix elements. The electron energy spectrum which neglects the relativistic and nuclear recoil effects is often assumed. Alternative definitions of effective masses exist, and an exact relativistic spectrum is calculable. We quantitatively compare the validity of those different approximations as function of energy resolution and exposure in view of tritium beta decays in the KATRIN, Project 8 and PTOLEMY experiments. Furthermo…
We investigate the sensitivity of tritium $β$-decay experiments for keV-scale sterile neutrinos. Relic sterile neutrinos in the keV mass range can contribute both to the cold and warm dark matter content of the universe. This work shows that a large-scale tritium beta-decay experiment, similar to the KATRIN experiment that is under construction, can reach a statistical sensitivity of the active-sterile neutrino mixing of $\sin^2θ\sim 10^{-8}$. The effect of uncertainties in the known theoretical corrections to the tritium $β$-decay spectrum were investigated, and found not to affect the sensit…
The inverse tritium beta decay (ITBD) reaction, $ν_e + ^3$H $\to e^- + ^3$He, is a promising experimental tool for observing relic neutrinos created in the early Universe. This reaction has been selected by the PTOLEMY experiment for the search of relic neutrinos. Despite its potential, the ITBD reaction induced by any sources of neutrinos has yet to be observed. We show that an intense $^{51}$Cr radioactive neutrino source is suitable for observing the ITBD reaction for the first time. As the Sun is another source of intense electron neutrinos, we also examine the ITBD reaction rate from sola…
A description of the current state of the project for the study of coherent elastic neutrino-atom scattering using a tritium source and liquid helium detector is given. The project was proposed in our paper in 2019 and its main goal is to obtain a new record limit on the neutrino magnetic moment at a level below 10^{-12}μ_B using a tritium antineutrino source with an intensity of 10 MCi or even 40 MCi.
The Project 8 collaboration aims to measure the absolute neutrino mass scale using cyclotron radiation emission spectroscopy on the beta decay of tritium. The second phase of the project will measure a continuous spectrum of molecular tritium beta decays and extract the tritium endpoint value with an eV or sub-eV scale precision. Monoenergetic electrons emitted by gaseous $^{83\mathrm{m}}$Kr atoms are used to determine the relationship between cyclotron frequency and electron energy. This study allows us to optimize both the event reconstruction algorithm and the hardware configuration, in pre…
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.
Bound-state beta decay of tritium: Path to first observation and novel approach to direct neutrino mass measurement
Max-Planck-Institut für Kernphysik（马克斯·普朗克核物理研究所）；Institute for Astroparticle Physics, Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院天体粒子物理研究所）；AG Moderne Optik, Institut für Physik, Humboldt-Universität zu Berlin（柏林洪堡大学物理学院现代光学研究组）
Project 8 is a tritium endpoint neutrino mass experiment utilizing a phased program to achieve sensitivity to the range of neutrino masses allowed by the inverted mass hierarchy. The Cyclotron Radiation Emission Spectroscopy (CRES) technique is employed to measure the differential energy spectrum of decay electrons with high precision. We present an overview of the Project 8 experimental program, from first demonstration of the CRES technique to ultimate sensitivity with an atomic tritium source. We highlight recent advances in preparation for the first measurement of the continuous tritium sp…
The Karlsruhe Tritium Neutrino (KATRIN) experiment will provide a measurement of the effective electron-neutrino mass, $m(ν_e)$, based on a precision measurement of the tritium beta decay spectrum near its endpoint. The effective mass is an average of the neutrino mass eigenvalues $m_i$ weighted by the flavor-mass mixing parameters $U_{ei}$ according to the relation $m^2(ν_e)= \sum_{i=1}^3 |U_{ei} |^2 m_i^2$. The KATRIN apparatus uses a windowless gaseous tritium source (WGTS) and a spectrometer based on the MAC-E filter concept to measure the beta energy spectrum. The KATRIN program is design…
Sterile neutrinos in the mass range of a few keV are candidates for both cold and warm dark matter. An ad-mixture of a heavy neutrino mass eigenstate to the electron neutrino would result in a minuscule distortion - a 'kink' - in a $β$-decay spectrum. In this paper we show that a wavelet transform is a very powerful shape analysis method to detect this signature. For a tritium source strength, similar to what is expected from the KATRIN experiment, a statistical sensitivity to active-to-sterile neutrino mixing down to $\sin^2 θ= 10^{-6}$ ($90\%$ CL) can be obtained after 3 years of measurement…
Measurement of the inhomogeneity of the KATRIN tritium source electric potential by high-resolution spectroscopy of conversion electrons from $^{83m}$Kr
The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to search for the effective electron antineutrino mass with a sensitivity of 0.2 eV (90 % C.L.). In order to achieve this goal, KATRIN measurement phases focusing on the neutrino mass search are alternated with phases of investigations of systematic effects. During these phases, metastable $^{83\mathrm{m}}$Kr is used as a calibration source. The monoenergetic conversion electrons emitted accompanying the decay of $^{83\mathrm{m}}$Kr allow a direct access to the starting conditions of $β$-electrons produced inside the windowless gaseous tr…
Sensitivity of Neutrino Mass Experiments to the Cosmic Neutrino Background
KATRIN中微子实验是下一代氚β衰变实验，旨在测量90% C. L时电子中微子的质量优于200 meV。由于其强烈的氚源，KATRIN也可以作为中微子捕获过程的可能目标，νe +3 H \to 3 He + + e-。后一个过程没有能量阈值，对宇宙中微子背景（CνB）很敏感。本文探讨了KATRIN实验对残余中微子密度的潜在敏感性。KATRIN实验对CνB超密度比为2.0 × 10^9（超过标准一致性模型预测值（在90% C. L.））的情况很敏感，探讨某些推测性宇宙学模型的有效性
The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the effective electron anti-neutrino mass with an unprecedented sensitivity of 0.2 eV/c$^2$, using beta-electrons from tritium decay. Super-conducting magnets will guide the electrons through a vacuum beam-line from the windowless gaseous tritium source through differential and cryogenic pumping sections to a high resolution spectrometer. At the same time tritium gas has to be prevented from entering the spectrometer. Therefore, the pumping sections have to reduce the tritium flow by at least 14 orders of magnitude. This paper …
The most sensitive direct method to establish the absolute neutrino mass is observation of the endpoint of the tritium beta-decay spectrum. Cyclotron Radiation Emission Spectroscopy (CRES) is a precision spectrographic technique that can probe much of the unexplored neutrino mass range with $\mathcal{O}({\rm eV})$ resolution. A lower bound of $m(ν_e) \gtrsim 9(0.1)\, {\rm meV}$ is set by observations of neutrino oscillations, while the KATRIN Experiment - the current-generation tritium beta-decay experiment that is based on Magnetic Adiabatic Collimation with an Electrostatic (MAC-E) filter - …
The determination of the neutrino mass is one of the major challenges in astroparticle physics today. Direct neutrino mass experiments, based solely on the kinematics of beta-decay, provide a largely model-independent probe to the neutrino mass scale. The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to directly measure the effective electron antineutrino mass with a sensitivity of 0.2 eV 90% CL. In this work we report on the first operation of KATRIN with tritium which took place in 2018. During this commissioning phase of the tritium circulation system, excellent agreement of th…
We propose an experimental setup to observe coherent elastic neutrino-atom scattering (CE$ν$AS) using electron antineutrinos from tritium decay and a liquid helium target. In this scattering process with the whole atom, that has not beeen observed so far, the electrons tend to screen the weak charge of the nucleus as seen by the electron antineutrino probe. The interference between the nucleus and the electron cloud produces a sharp dip in the recoil spectrum at atomic recoil energies of about 9 meV, reducing sizeably the number of expected events with respect to the coherent elastic neutrino-…
We study the effect of exotic charged current interactions on the electron energy spectrum in tritium decay, focussing on the KATRIN experiment and a possible modified setup that has access to the full spectrum. Both sub-eV and keV neutrino masses are considered. We perform a fully relativistic calculation and take all possible new interactions into account, demonstrating the possible sizable distortions in the energy spectrum.
We propose a new experiment to search for a sterile neutrino in a few keV mass range at the "Troitsk nu-mass" facility. The expected signature corresponds to a kink in the electron energy spectrum in tritium beta-decay. The new goal compared to our previous experiment will be precision spectrum measurements well below end point. The experimental installation consists of a windowless gaseous tritium source and a high resolution electromagnetic spectrometer. We estimate that the current bounds on the sterile neutrino mixing parameter can be improved by an order of magnitude in the mass range und…
