KATRIN: status and prospects for the neutrino mass and beyond

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2010

The Karlsruhe Tritium Neutrino experiment (KATRIN) aims to measure the mass of electron neutrinos from betadecay of tritium with an unprecedented sensitivity of 0.2 eV /c 2 improving present limits by one order of magnitude. The decay electrons will originate from a 10 m long windowless, gaseous tritium source. Super-conducting magnets guide the electrons through differential and cryogenic pumping sections to the electro-static tandem spectrometer (MAC-E-filter), where the kinetic energy will be measured. The experiment is presently being built at the Forschungszentrum Karlsruhe by an international collaboration of more than 120 scientists. The largest component, the 1240 m 3 main spectrometer, was delivered end of 2006 and first commissioning tests have been performed. This presentation describes the goals and technological challenges of the experiment and reports on the progress in commissioning first major components. The start of first measurements is expected in 2012.

AIP Conference Proceedings, 2012

The Karlsruhe Tritium Neutrino (KATRIN) experiment is the next generation tritium beta decay experiment with sub-eV sensitivity to make a direct, model independent measurement of the neutrino mass. The principle of the experiment is to look for a distortion at the high energy endpoint of the electron spectrum of tritium beta decay. KATRIN will reach a final sensitivity of 200 meV at 90% C.L. on the absolute neutrino mass scale.

Physics Letters B, 2011

The KArlsruhe TRItium Neutrino experiment (KATRIN) combines an ultra-luminous molecular tritium source with an integrating high-resolution spectrometer to gain sensitivity to the absolute mass scale of neutrinos. The projected sensitivity of the experiment on the electron neutrino mass is 200 meV at 90% C.L. With such unprecedented resolution, the experiment is also sensitive to physics beyond the Standard Model, particularly to the existence of additional sterile neutrinos at the eV mass scale. A recent analysis of available reactor data appears to favor the existence of such a sterile neutrino with a mass splitting of | m sterile | 2 1.5 eV 2 and mixing strength of sin 2 2θ sterile = 0.17 ± 0.08 at 95% C.L. Upcoming tritium beta decay experiments should be able to rule out or confirm the presence of the new phenomenon for a substantial fraction of the allowed parameter space.

2021

We report the results of the second measurement campaign of the Karlsruhe Tritium Neutrino (KATRIN) experiment. KATRIN probes the effective electron anti-neutrino mass, mν, via a high-precision measurement of the tritium β-decay spectrum close to its endpoint at 18.6 keV. In the second physics run presented here, the source activity was increased by a factor of 3.8 and the background was reduced by 25% with respect to the first campaign. A sensitivity on mν of 0.7 eV/c2 at 90% confidence level (CL) was reached. This is the first sub-eV sensitivity from a direct neutrino-mass experiment. The best fit to the spectral data yields mν2=(0.26±0.34) eV2/c4, resulting in an upper limit of mν<0.9 eV/c2 (90% CL). By combining this result with the first neutrino mass campaign, we find an upper limit of mν<0.8 eV/c2 (90% CL).

The European Physical Journal C

In this work we present a keV-scale sterile-neutrino search with a low-tritium-activity data set of the KATRIN experiment, acquired in a commissioning run in 2018. KATRIN performs a spectroscopic measurement of the tritium $$\upbeta $$ β -decay spectrum with the main goal of directly determining the effective electron anti-neutrino mass. During this commissioning phase a lower tritium activity facilitated the measurement of a wider part of the tritium spectrum and thus the search for sterile neutrinos with a mass of up to $$1.6\, \textrm{keV}$$ 1.6 keV . We do not find a signal and set an exclusion limit on the sterile-to-active mixing amplitude of $$\sin ^2\theta < 5\times 10^{-4}$$ sin 2 θ < 5 × 10 - 4 ($$95\%$$ 95 % C.L.) at a mass of 0.3 keV. This result improves current laboratory-based bounds in the sterile-neutrino mass range between 0.1 and 1.0 keV.

Physical Review D, 2012

The presence of light sterile neutrinos would strongly modify the energy spectrum of the tritium electrons. We perform an analysis of the KArlsruhe TRItium Neutrino (KATRIN) experiment's sensitivity by scanning almost all the allowed region of neutrino mass-squared difference and mixing angles of the 3 þ 1 scenario. We consider the effect of the unknown absolute mass scale of active neutrinos on the sensitivity of KATRIN to the sterile neutrino mass. We show that after 3 years of data-taking, the KATRIN experiment can be sensitive to mixing angles as small as sin 2 2 s $ 10 À2 . Particularly we show that for small mixing angles, sin 2 2 s & 0:1, the KATRIN experiment can give the strongest limit on active-sterile mass-squared difference.

Journal of Physics: Conference Series

Nuclear and Particle Physics Proceedings, 2015

2004

* Full texts of the report of the working group. For the summary report of the APS Multidivisional Neutrino Study, 'The Neutrino Matrix', see physics/0411216 0νββ decay, independent of its rate, would show that neutrinos, unlike all the other constituents of matter, are their own antiparticles. There is no other realistic way to determine the nature-Dirac or Majorana, of massive neutrinos. This would be a discovery of major importance, with impact not only on this fundamental question, but also on the determination of the absolute neutrino mass scale, and on the pattern of neutrino masses, and possibly on the problem of CP violation in the lepton sector, associated with Majorana neutrinos. There is a consensus on this basic point which we translate into the recommendations how to proceed with experiments dedicated to the search of the 0νββ decay, and how to fund them. • To reach our conclusion, we have to consider past achievements, the size of previous experiments, and the existing proposals. There is a considerable community of physicists worldwide as well as in the US interested in pursuing the search for the 0νββ decay. Past experiments were of relatively modest size. Clearly, the scope of future experiments should be considerably larger, and will require advances in experimental techniques, larger collaborations and additional funding. In terms of m ββ , the effective neutrino Majorana mass that can be extracted from the observed 0νββ decay rate, there are three ranges of increasing sensitivity, related to known neutrino-mass scales of neutrino oscillations. • The ∼100-500 meV m ββ range corresponds to the quasi-degenerate spectrum of neutrino masses. The motivation for reaching this scale has been strengthened by the recent claim of an observation of 0νββ decay in 76 Ge; a claim that obviously requires further investigation. To reach this scale and perform reliable measurements, the size of the experiment should be approximately 200 kg of the decaying isotope, with a corresponding reduction of the background. This quasi-degenerate scale is achievable in the relatively near term, ∼ 3-5 years. Several groups with considerable US participation have well established plans to build ∼ 200-kg devices that could scale straightforwardly to 1 ton (Majorana using 76 Ge, Cuore using 130 Te, and EXO using 136 Xe). There are also other proposed experiments worldwide which offer to study a number of other isotopes and could reach similar sensitivity after further R&D. Several among them (e.g. Super-NEMO, MOON) have US participation. By making measurements in several nuclei the uncertainty arising from the nuclear matrix elements would be reduced. The development of different detection techniques, and measurements in several nuclei, is invaluable for establishing the existence (or lack thereof) of the 0νββ decay at this effective neutrino mass range. • The ∼20-55 meV range arises from the atmospheric neutrino oscillation results. Observation of m ββ at this mass scale would imply the inverted neutrino mass hierarchy or the normal-hierarchy ν mass spectrum very near the quasidegenerate region. If either this or the quasi-degenerate spectrum is established, it would be invaluable not only for the understanding of the origin of neutrino mass, but also as input to the overall neutrino physics program (long baseline oscillations, search for CP violations, search for neutrino mass in tritium beta decay and astrophysics/cosmology, etc.) To study the 20-50 meV mass range will require about 1 ton of the isotope mass, a challenge of its own. Given the importance, and the points discussed above, more than one experiment of that size is desirable. • The ∼2-5 meV range arises from the solar neutrino oscillation results and will almost certainly lead to the 0νββ decay, provided neutrinos are Majorana particles. To reach this goal will require ∼100 tons of the decaying isotope, and no current technique provides such a leap in sensitivity. • The qualitative physics results that arise from an observation of 0νββ decay are profound. Hence, the program described above is vital and fundamentally important even if the resulting m ββ would be rather uncertain in value. However, by making measurements in several nuclei the uncertainty arising from the nuclear matrix elements would be reduced. • Unlike double-beta decay, beta-decay endpoint measurements search for a kinematic effect due to neutrino mass and thus are "direct searches" for neutrino mass. This technique, which is essentially free of theoretical assumptions about neutrino properties, is not just complementary. In fact, both types of measurements will be required to fully untangle the nature of the neutrino mass. Excitingly, a very large new beta spectrometer is being built in Germany. This KATRIN experiment has a design sensitivity approaching 200 meV. If the neutrino masses are quasi-degenerate, as would be the case if the recent double-beta decay claim proves true, KATRIN will see the effect. In this case the 0νββ-decay experiments can provide, in principle, unique information about CP-violation in the lepton sector, associated with Majorana neutrinos. • Cosmology can also provide crucial information on the sum of the neutrino masses. This topic is summarized in a different section of the report, but it should be mentioned here that the next generation of measurements hope to be able to observe a sum of neutrino masses as small as 40 meV. We would like to emphasize the complementarity of the three approaches, 0νββ , β decay, and cosmology. Recommendations: We conclude that such a double-beta-decay program can be summarized as having three components and our recommendations can be summarized as follows: