Sterile neutrino search with KATRIN - modeling and design-criteria of a novel detector system

A fundamental phenomenon in particle physics is the absence of massive objects in our universe: Dark Matter. A promising candidate that could explain these observations are sterile neutrinos with a mass of several $\mathrm{keV}/c^2$. While it is presumed that sterile neutrinos do not interact via the weak force, they, due to their mass, still partake in neutrino oscillation. Consequently, it is experimentally possible to investigate their imprint in beta-decay experiments, such as the Karlsruhe tritium neutrino experiment (KATRIN). A dedicated search for sterile neutrinos however ensues a steep increase in the electron rate and thus requires the development of a new detector system, the TRISTAN detector. In addition, as the imprint of sterile neutrinos is presumably $<10^{-7}$, systematic uncertainties have to be understood and modeled with high precision. In this thesis systematics prevalent at the detector and spectrometer section of KATRIN will be discussed and their impact to a sterile neutrino sensitivity illuminated. The derived model is compared with data of the current KATRIN detector and with characterization measurements of the first TRISTAN prototype detectors, seven pixel silicon drift detectors. It is shown that the final TRISTAN detector requires a sophisticated redesign of the KATRIN detector section. Moreover, the combined impact of the back-scattering and electron charge-sharing systematic lead to an optimal detector magnetic field of $B_\mathrm{det}=0.7\dots0.8\,\mathrm{T}$, which translates to a pixel radius of $r_\mathrm{px}=1.5\dots1.6\,\mathrm{mm}$. The sensitivity analysis discusses individual effects as well as the combined impact of systematic uncertainties. It is demonstrated that the individual effects can be largely mitigated by shifting the tritium \bd energy spectrum above the \bd endpoint. In contrast, their combined impact to the sensitivity leads to an overall degradation and only mixing amplitudes of $\sin^2\theta_4<3\cdot10^{-6}$ would be reachable, even in an optimized case with very low and homogeneous detection deadlayer $z_\mathrm{dl}=20\pm1\,\mathrm{nm}$. Assessing sterile neutrino mixing amplitudes of $\sin^2\theta_4<10^{-7}$ thus requires disentangling of systematic effects. In a future measurement this could be for example achieved by vetoing detector events with large signal rise-times and small inter-event times

Impact of ADC non-linearities on the sensitivity to sterile keV neutrinos with a KATRIN-like experiment

International audienceADC non-linearities are a major systematic effect in the search for keV-scale sterile neutrinos with tritium β -decay experiments like KATRIN. They can significantly distort the spectral shape and thereby obscure the tiny kink-like signature of a sterile neutrino. In this work we demonstrate various mitigation techniques to reduce the impact of ADC non-linearities on the tritium β -decay spectrum to a level of <ppm . The best results are achieved with a multi-pixel ( ≥104 pixels) detector using full waveform digitization. In this case, active-to-sterile mixing angles of the order of sin2θ=10−7 would be accessible from the viewpoint of ADC non-linearities. With purely peak-sensing ADCs a comparable sensitivity could be reached with highly linear ADCs, sufficient non-linearity corrections or by increasing the number of pixels to ≥105

A novel detector system for KATRIN to search for keV-scale sterile neutrinos

International audienceSterile neutrinos appear in minimal extensions of the Standard Model of particle physics. If their mass is in the keV regime, they are viable dark matter candidates. One way to search for sterile neutrinos in a laboratory-based experiment is via the analysis of β-decay spectra, where the new neutrino mass eigenstate would manifest itself as a kink-like distortion of the β-decay spectrum. The objective of the TRISTAN project is to extend the KATRIN setup with a new multi-pixel silicon drift detector system to search for a keV-scale sterile neutrino signal. In this paper we describe the requirements of such a new detector, and present first characterization measurement results obtained with a 7 pixel prototype system

Detector Development for a Sterile Neutrino Search with the KATRIN Experiment

International audienceThe 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 precision of $200\,\mathrm{meV}$ ($90\,\%$ C.L.) after an effective data taking time of three years. The TRISTAN (tritium $\beta$-decay to search for sterile neutrinos) group aims to detect 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 multi-pixel silicon drift detector is being designed, which is able to handle rates up to $10^{8}\,\mathrm{cps}$ with an excellent energy resolution of $<200\,\mathrm{eV}$ (FWHM) at $10\,\mathrm{keV}$. This work gives an overview of the ongoing detector development and test results of the first seven pixel prototype detectors

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

International audienceSterile 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

First operation of the KATRIN experiment with tritium

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 β β -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 0.2 eV (90% 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 the theoretical prediction with the recorded spectra was found and stable conditions over a time period of 13 days could be established. These results are an essential prerequisite for the subsequent neutrino mass measurements with KATRIN in 2019

Quantitative Long-Term Monitoring of the Circulating Gases in the KATRIN Experiment Using Raman Spectroscopy.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c2, i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experiment's windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritium-one of the key parameters required in the derivation of the electron neutrino mass. The concentrations cx for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10-3 or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, εT, is derived with precision of &lt;10-3 and trueness of &lt;3 × 10-3, being within and surpassing the actual requirements for KATRIN, respectively

Quantitative Long-Term Monitoring of the Circulating Gases in the KATRIN Experiment Using Raman Spectroscopy.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c2, i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experiment's windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritium-one of the key parameters required in the derivation of the electron neutrino mass. The concentrations cx for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10-3 or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, εT, is derived with precision of &lt;10-3 and trueness of &lt;3 × 10-3, being within and surpassing the actual requirements for KATRIN, respectively