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E. Otten

Publications and source records attributed to E. Otten.

15 recordsLinked to original sources
arXiv2020

KATRIN background due to surface radioimpurities

The goal of the KArlsruhe TRItrium Neutrino (KATRIN) experiment is the determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c$^2$ at 90% C.L. This goal can only be achieved with a very low background level in the order of 0.01 counts per second. A possible background source is $α$-decays on the inner surface of the KATRIN Main Spectrometer. Two $α$-sources, $^{223}$Ra and $^{228}$Th, were installed at the KATRIN Main Spectrometer with the purpose of temporarily increasing the background in order to study $α$-decay induced background processes. In this paper, we present a possible background generation mechanism and measurements performed with these two radioactive sources. Our results show a clear correlation between $α$-activity on the inner spectrometer surface and background from the volume of the spectrometer. Two key characteristics of the Main Spectrometer background -the dependency on the inner electrode offset potential, and the radial distribution - could be reproduced with this artificially induced background. These findings indicate a high contribution of $α$-decay induced events to the residual KATRIN background.

physics.ins-det↗
arXiv2020

Suppression of Penning discharges between the KATRIN spectrometers

The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to determine the effective electron (anti)neutrino mass with a sensitivity of $0.2\textrm{ eV/c}^2$ (90$\%$ C.L.) by precisely measuring the endpoint region of the tritium $β$-decay spectrum. It uses a tandem of electrostatic spectrometers working as MAC-E (magnetic adiabatic collimation combined with an electrostatic) filters. In the space between the pre-spectrometer and the main spectrometer, an unavoidable Penning trap is created when the superconducting magnet between the two spectrometers, biased at their respective nominal potentials, is energized. The electrons accumulated in this trap can lead to discharges, which create additional background electrons and endanger the spectrometer and detector section downstream. To counteract this problem, "electron catchers" were installed in the beamline inside the magnet bore between the two spectrometers. These catchers can be moved across the magnetic-flux tube and intercept on a sub-ms time scale the stored electrons along their magnetron motion paths. In this paper, we report on the design and the successful commissioning of the electron catchers and present results on their efficiency in reducing the experimental background.

physics.ins-det↗
arXiv2019

Gamma-induced background in the KATRIN main spectrometer

The KATRIN experiment aims to measure the effective electron antineutrino mass $m_{\overlineν_e}$ with a sensitivity of 0.2 eV/c$^2$ using a gaseous tritium source combined with the MAC-E filter technique. A low background rate is crucial to achieving the proposed sensitivity, and dedicated measurements have been performed to study possible sources of background electrons. In this work, we test the hypothesis that gamma radiation from external radioactive sources significantly increases the rate of background events created in the main spectrometer (MS) and observed in the focal-plane detector. Using detailed simulations of the gamma flux in the experimental hall, combined with a series of experimental tests that artificially increased or decreased the local gamma flux to the MS, we set an upper limit of 0.006 count/s (90% C.L.) from this mechanism. Our results indicate the effectiveness of the electrostatic and magnetic shielding used to block secondary electrons emitted from the inner surface of the MS.

physics.ins-det↗
arXiv2019

High-resolution spectroscopy of gaseous $^\mathrm{83m}$Kr conversion electrons with the KATRIN experiment

In this work, we present the first spectroscopic measurements of conversion electrons originating from the decay of metastable gaseous $^\mathrm{83m}$Kr with the Karlsruhe Tritium Neutrino (KATRIN) experiment. The results obtained in this calibration measurement represent a major commissioning milestone for the upcoming direct neutrino mass measurement with KATRIN. The successful campaign demonstrates the functionalities of the full KATRIN beamline. The KATRIN main spectrometer's excellent energy resolution of ~ 1 eV made it possible to determine the narrow K-32 and L$_3$-32 conversion electron line widths with an unprecedented precision of ~ 1 %.

physics.ins-det↗
arXiv2018

Muon-induced background in the KATRIN main spectrometer

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c$^{2}$. It investigates the kinematics of $β$-particles from tritium $β$-decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about $12\%$ of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than $17\%$ ($90\%$ confidence level) of the overall MS background.

physics.ins-det↗
arXiv2018

First transmission of electrons and ions through the KATRIN beamline

The Karlsruhe Tritium Neutrino (KATRIN) experiment is a large-scale effort to probe the absolute neutrino mass scale with a sensitivity of 0.2 eV (90% confidence level), via a precise measurement of the endpoint spectrum of tritium beta decay. This work documents several KATRIN commissioning milestones: the complete assembly of the experimental beamline, the successful transmission of electrons from three sources through the beamline to the primary detector, and tests of ion transport and retention. In the First Light commissioning campaign of Autumn 2016, photoelectrons were generated at the rear wall and ions were created by a dedicated ion source attached to the rear section; in July 2017, gaseous Kr-83m was injected into the KATRIN source section, and a condensed Kr-83m source was deployed in the transport section. In this paper we describe the technical details of the apparatus and the configuration for each measurement, and give first results on source and system performance. We have successfully achieved transmission from all four sources, established system stability, and characterized many aspects of the apparatus.

physics.ins-det↗
arXiv2018

Nuclear hyperpolarization of 3He by magnetized plasmas

We describe a method to hyperpolarize 3He nuclear spins at high magnetic fields (4.7 Tesla) solely by a magnetized plasma. The conditions for such a magnetized plasma are fulfilled when the mean free path of the free electrons is much larger than their gyration radius in the rf gas discharge. Investigations are carried out in the 1-15 mbar pressure range with rf excitation at ~100 MHz. Quantitative NMR measurements show that for different cell sizes and 3He densities nuclear polarizations in the range 1% to 9% are observed. We explain this phenomenon by an alignment-to-orientation conversion mechanism in the excited 2 3P state of 3He which is most efficient when the Zeeman and the spin-orbit energies are comparable. The method appears as a very attractive alternative to established laser polarization techniques (spin exchange or metastability exchange optical pumping). Application to 3He nuclear magnetometry with a relative precision of 10-12 is demonstrated.

physics.atom-ph↗
arXiv2018

Calibration of high voltages at the ppm level by the difference of $^{83\mathrm{m}}$Kr conversion electron lines at the KATRIN experiment

The neutrino mass experiment KATRIN requires a stability of 3 ppm for the retarding potential at -18.6 kV of the main spectrometer. To monitor the stability, two custom-made ultra-precise high-voltage dividers were developed and built in cooperation with the German national metrology institute Physikalisch-Technische Bundesanstalt (PTB). Until now, regular absolute calibration of the voltage dividers required bringing the equipment to the specialised metrology laboratory. Here we present a new method based on measuring the energy difference of two $^{83\mathrm{m}}$Kr conversion electron lines with the KATRIN setup, which was demonstrated during KATRIN's commissioning measurements in July 2017. The measured scale factor $M=1972.449(10)$ of the high-voltage divider K35 is in agreement with the last PTB calibration four years ago. This result demonstrates the utility of the calibration method, as well as the long-term stability of the voltage divider.

physics.ins-det↗
arXiv2018

Reduction of stored-particle background by a magnetic pulse method at the KATRIN experiment

The KATRIN experiment aims to determine the effective electron neutrino mass with a sensitivity of $0.2\,{\text{eV}/c^2}$ (90\% C.L.) by precision measurement of the shape of the tritium \textbeta-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. A common background source in this setup is the decay of short-lived isotopes, such as $\textsuperscript{219}$Rn and $\textsuperscript{220}$Rn, in the spectrometer volume. Active and passive countermeasures have been implemented and tested at the KATRIN main spectrometer. One of these is the magnetic pulse method, which employs the existing air coil system to reduce the magnetic guiding field in the spectrometer on a short timescale in order to remove low- and high-energy stored electrons. Here we describe the working principle of this method and present results from commissioning measurements at the main spectrometer. Simulations with the particle-tracking software Kassiopeia were carried out to gain a detailed understanding of the electron storage conditions and removal processes.

physics.ins-det↗
arXiv2017

A White Paper on keV Sterile Neutrino Dark Matter

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.

hep-ph↗
arXiv2016

Commissioning of the vacuum system of the KATRIN Main Spectrometer

The KATRIN experiment will probe the neutrino mass by measuring the beta-electron energy spectrum near the endpoint of tritium beta-decay. An integral energy analysis will be performed by an electro-static spectrometer (Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m^3, and a complex inner electrode system with about 120000 individual parts. The strong magnetic field that guides the beta-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. A system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter strips has been deployed and was tested during the commissioning of the spectrometer. In this paper the configuration, the commissioning with bake-out at 300°C, and the performance of this system are presented in detail. The vacuum system has to maintain a pressure in the 10^{-11} mbar range. It is demonstrated that the performance of the system is already close to these stringent functional requirements for the KATRIN experiment, which will start at the end of 2016.

physics.ins-det↗
arXiv2014

Ultrasensitive 3He magnetometer for measurements of high magnetic fields

We describe a 3He magnetometer capable to measure high magnetic fields (B > 0.1 Tesla) with a relative accuracy of better than 10^-12. Our approach is based on the measurement of the free induction decay of gaseous, nuclear spin polarized 3He following a resonant radio frequency pulse excitation. The measurement sensitivity can be attributed to the long coherent spin precession time T2* being of order minutes which is achieved for spherical sample cells in the regime of motional narrowing where the disturbing influence of field inhomogeneities is strongly suppressed. The 3He gas is spin polarized in-situ using a new, non-standard variant of the metastability exchange optical pumping. We show that miniaturization helps to increase T2* further and that the measurement sensitivity is not significantly affected by temporal field fluctuations of order 10^-4.

physics.ins-det↗
arXiv2005

Measurement of the asymmetries in 3He(e,e'p)d and 3He(e,e'p)np

The electron-target-asymmetries A_parallel and A_perpendicular with target spin parallel and perpendicular to the momentum transfer q were measured for both the two-- and three-body breakup of 3He in the 3He(e,e'p)-reaction. Polarized electrons were scattered off polarized 3He in the quasielastic regime in parallel kinematics with the scattered electron and the knocked-out proton detected using the Three-Spectrometer-Facility at MAMI. The results are compared to Faddeev calculations which take into account Final State Interactions as well as Meson Exchange Currents. The experiment confirms the prediction of a large effect of Final State Interactions in the asymmetry of the three-body breakup and of an almost negligible one for the two-body breakup.

nucl-ex↗
arXiv2003

Final State Interaction Effects in pol 3He(pol e,e'p)

Asymmetries in quasi-elastic pol 3He(pol e,e'p) have been measured at a momentum transfer of 0.67 (GeV/c)^2 and are compared to a calculation which takes into account relativistic kinematics in the final state and a relativistic one-body current operator. With an exact solution of the Faddeev equation for the 3He-ground state and an approximate treatment of final state interactions in the continuum good agreement is found with the experimental data.

nucl-ex↗