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Register a new userHigh-resolution spectroscopy of gaseous $^mathrm{83m}$Kr conversion electrons with the KATRIN experiment
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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 spectrometers 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 %.
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The NEXT-White (NEW) detector is currently the largest radio-pure high-pressure xenon gas time projection chamber with electroluminescent readout in the world. NEXT-White has been operating at Laboratorio Subterraneo de Canfranc (LSC) since October 2016. This paper describes the calibrations performed with $^{83m}mathrm{Kr}$ decays during a long run taken from March to November 2017 (Run II). Krypton calibrations are used to correct for the finite drift-electron lifetime as well as for the dependence of the measured energy on the event position which is mainly caused by variations in solid angle coverage. After producing calibration maps to correct for both effects we measure an excellent energy resolution for 41.5 keV point-like deposits of (4.553 $pm$ 0.010 (stat.) $pm$ 0.324 (sys.)) % FWHM in the full chamber and (3.804 $pm$ 0.013 (stat.) $pm$ 0.112 (sys.)) % FWHM in a restricted fiducial volume. Using naive 1/$sqrt{E}$ scaling, these values translate into resolutions of (0.516 $pm$ 0.0014 (stat.) $pm$ 0.0421 (sys.)) % FWHM and (0.4943 $pm$ 0.0017 (stat.) $pm$ 0.0146 (sys.)) % FWHM at the $Q_{betabeta}$ energy of xenon double beta decay (2458 keV), well within range of our target value of 1%.
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 $^{83mathrm{m}}$Kr conversion electron lines with the KATRIN setup, which was demonstrated during KATRINs 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.
We report the preparation of a Kr-83m source and its subsequent use in calibrating a liquid xenon detector. Kr-83m atoms were produced through the decay of Rb-83 atoms trapped in zeolite molecular sieve and were then introduced into liquid xenon. Decaying Kr-83m nuclei were detected through liquid xenon scintillation. Conversion electrons with energies of 9.4 keV and 32.1 keV from the decay of Kr-83m were both observed. This calibration source will allow the characterization of the scintillation and ionization response of noble liquid detectors at low energies, highly valuable for the search for WIMP dark matter. Kr-83m may also be useful for measuring fluid flow dynamics, both to understand purification in noble liquid-based particle detectors, as well as for studies of classical and quantum turbulence in superfluid helium.
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.
Prompt scintillation signals from $^{83m}$Kr calibration sources are a useful metric to calibrate the spatial variation of light collection efficiency and electric field magnitude of a two phase liquid-gas xenon time projection chamber. Because $^{83m}$Kr decays in two steps, there are two prompt scintillation pulses for each calibration event, denoted S1a and S1b. We study the ratio of S1b to S1a signal sizes in the Particle Identification in Xenon at Yale (PIXeY) experiment and its dependence on the time separation between the two signals ($Delta t$), notably its increase at low $Delta t$. In PIXeY data, the $Delta t$ dependence of S1b/S1a is observed to exhibit two exponential components: one with a time constant of $0.05 pm 0.02mu s$, which can be attributed to processing effects and pulse overlap and one with a time constant of $10.2 pm 2.2mu s$ that increases in amplitude with electric drift field, the origin of which is not yet understood.
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