The Project 8 collaboration seeks to measure the absolute neutrino mass scale
by means of precision spectroscopy of the beta decay of tritium. Our technique,
cyclotron radiation emission spectroscopy, measures the frequency of the
radiation emitted by electrons produced by decays in an ambient magnetic field.
Because the cyclotron frequency is inversely proportional to the electron's
Lorentz factor, this is also a measurement of the electron's energy. In order
to demonstrate the viability of this technique, we have assembled and
successfully operated a prototype system, which uses a rectangular waveguide to
collect the cyclotron radiation from internal conversion electrons emitted from
a gaseous $^{83m}$Kr source. Here we present the main design aspects of the
first phase prototype, which was operated during parts of 2014 and 2015. We
will also discuss the procedures used to analyze these data, along with the
features which have been observed and the performance achieved to date.Comment: 3 pages; 2 figures; Proceedings of Neutrino 2016, XXVII International
  Conference on Neutrino Physics and Astrophysics, 4-9 July 2016, London, U

Böser, S

Claessens, C

de Viveiros, L

Doe, P J

Doeleman, S

Esfahani, A Ashtari

Fertl, M

Finn, E C

Formaggio, J A

Guigue, M

Heeger, K M

Jones, A M

Kazkaz, K

LaRoque, B H

Machado, E

Monreal, B

Nikkel, J A

Oblath, N S

Robertson, R G H

Rosenberg, L J

Rybka, G

Saldaña, L

Slocum, P L

Tedeschi, J R

Thümmler, T

Vandevender, B A

Wachtendonk, M

Weintroub, J

Young, A

Zayas, E

Journal of Physics Conference Series

English

arXiv

A Ashtari Esfahani

S Böser

C Claessens

L de Viveiros

P J Doe

S Doeleman

M Fertl

E C Finn

J A Formaggio

M Guigue

K M Heeger

A M Jones

K Kazkaz

B H LaRoque

E Machado

B Monreal

J A Nikkel

N S Oblath

R G H Robertson

L J Rosenberg

G Rybka

L Saldaña

P L Slocum

J R Tedeschi

T Thümmler

B A Vandevender

M Wachtendonk

J Weintroub

A Young

E Zayas

Crossref

Results from the Project 8 phase-1 cyclotron radiation emission spectroscopy detector

Ashtari Esfahani, A.

Böser, S.

Claessens, C.

De Viveiros, L.

Doe, P. J.

Doeleman, S.

Fertl, M.

Finn, E. C.

Formaggio, J. A.

Guigue, M.

Heeger, K. M.

Jones, A. M.

Kazkaz, K.

Laroque, B. H.

Machado, E.

Monreal, B.

Nikkel, J. A.

Oblath, N. S.

Robertson, R. G. H.

Rosenberg, L. J.

Rybka, G.

Saldaña, L.

Slocum, P. L.

Tedeschi, J. R.

Thümmler, T.

Vandevender, B. A.

Wachtendonk, M.

Weintroub, J.

Young, A.

Zayas, E.

KITopen

Journal of Physics: Conference SeriesPAPER • OPEN ACCESSResults from the Project 8 phase-1 cyclotronradiation emission spectroscopy detectorTo cite this article: A Ashtari Esfahani et al 2017 J. Phys.: Conf. Ser. 888 012074 View the article online for updates and enhancements.Related contentDetermining the neutrino mass withCyclotron Radiation EmissionSpectroscopy—Project 8Ali Ashtari Esfahani, David M Asner,Sebastian Böser et al.-Project 8 Phase III Design ConceptA Ashtari Esfahani, S Böser, C Claessenset al.-Recent advances in precisionspectroscopy of ultracold atoms and ionsA V Taichenachev, V I Yudin and S NBagayev-This content was downloaded from IP address 129.13.72.197 on 23/11/2017 at 09:361Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd1234567890Neutrino2016 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 888 (2017) 012074  doi :10.1088/1742-6596/888/1/012074Results from the Project 8 phase-1 cyclotronradiation emission spectroscopy detectorA Ashtari Esfahani1, S Böser2, C Claessens2, L de Viveiros3,P J Doe1, S Doeleman4, M Fertl1, E C Finn5, J A Formaggio6,M Guigue5, K M Heeger7, A M Jones5, K Kazkaz8, B H LaRoque3,E Machado1, B Monreal3, J A Nikkel7, N S Oblath5,R G H Robertson1, L J Rosenberg1, G Rybka1, L Saldaña7,P L Slocum7, J R Tedeschi5, T Thümmler9, B A Vandevender5,M Wachtendonk1, J Weintroub4, A Young4 and E Zayas61 Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics,University of Washington, Seattle, WA, USA2 Johannes Guttenberg University, Mainz, Germany3 Department of Physics, University of California, Santa Barbara, CA, USA4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA5 Pacific Northwest National Laboratory, Richland, WA, USA6 Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA,USA7 Department of Physics, Yale University, New Haven, CT, USA8 Lawrence Livermore National Laboratory, Livermore, CA, USA9 Karlsruhe Institute for Technology, Karlsruhe, GermanyE-mail: laroque@physics.ucsb.eduAbstract. The Project 8 collaboration seeks to measure the absolute neutrino mass scale bymeans of precision spectroscopy of the beta decay of tritium. Our technique, cyclotron radiationemission spectroscopy, measures the frequency of the radiation emitted by electrons produced bydecays in an ambient magnetic field. Because the cyclotron frequency is inversely proportionalto the electron’s Lorentz factor, this is also a measurement of the electron’s energy. In orderto demonstrate the viability of this technique, we have assembled and successfully operated aprototype system, which uses a rectangular waveguide to collect the cyclotron radiation frominternal conversion electrons emitted from a gaseous 83mKr source. Here we present the maindesign aspects of the first phase prototype, which was operated during parts of 2014 and 2015.We will also discuss the procedures used to analyze these data, along with the features whichhave been observed and the performance achieved to date.1. IntroductionThe absolute scale of the neutrino masses is a significant gap in our understanding of fundamentalparticle physics. While it is possible to derive stringent limits from cosmological observations orsearches for neutrinoless double-beta decay, these limits depend implicitly on the models usedin their determination. On the other hand, kinematically derived limits are agnostic to theunderlying physics and therefore offer a complementary approach. The Project 8 collaborationwill use a novel technique known as Cyclotron Radiation Emission Spectroscopy (CRES), which21234567890Neutrino2016 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 888 (2017) 012074  doi :10.1088/1742-6596/888/1/012074was first proposed in 2009 [1], to make such a direct measurement through spectroscopy oftritium beta decay.Spectroscopy of tritium beta decay is well established as a technique for such directmeasurements, providing both the current best limits from the Mainz and Troitsk experiments,[2, 3] and KATRIN, the current generation experiment [4]. While established technologies useelectrostatic barrier potentials and counting detectors to measure the energy spectrum, theCRES technique leverages the fact that there are relativistic corrections to a particle’s cyclotronfrequency, and therefore a frequency measurement can be used to determine a particle’s totalenergy. CRES therefore provides a complementary approach to traditional techniques, subjectto different systematic effects and sensitivity scaling constraints.The Project 8 collaboration constructed the phase I detector with the primary goal ofdemonstrating the CRES technique. The prototype uses a section of waveguide, sealed withkapton foil windows, to contain 83mKr gas, a source of internal-conversion electrons. The emittedcyclotron radiation is colleted by the waveguide and propagates to a receiver. Coils wrappedaround the waveguide provide magnetic field perturbations which confine electron motionparallel to the local magnetic field, while the cyclotron motion itself confines perpendicularmotion. The entire waveguide assembly is inserted into an nuclear magnetic resonance magnetwhich provides an axial magnetic field of 0.9467T. We initially operated the detector during2014, with the first results published in early 2015 [5]. Given the success of phase I, the prototypehas been used to study the performance of the technique as an R&D effort prior to phase II,where CRES will be applied to the tritium spectrum for the first time. Here we discuss progressmade with the phase I detector since publication of our first results.2. Hardware changes and improvementsThe essential features of the phase I detector systems were described in the publication offirst results [5]. After collection was completed in 2014, a comprehensive survey of the analogsignal path was conducted. Several components in the first analog mixing stage, whichdownconverts signals which start around 26GHz by 24.2GHz, were upgraded. Additionally,standard maintenance procedures to the cryocooler resulted in a significant improvement tothermal stability of the cryogenic system, including the low noise amplifiers.For the initial data collection, both a continuously streaming digitizer and a real timespectrum analyzer, with the ability to trigger on electron events, were used to collect data.The streaming acquisition system can be used to study triggering systematics since it is immuneto them, at the cost of producing a much large volume of data; however, the system had to bedecommissioned due to unexpected hardware failures. All data taken since our initial publicationhas been conducted using the triggered data acquisition system exclusively. A new acquisitionsystem with support for both streaming and triggered modes will be commissioned for phaseII. Studies of trigger efficiency and investigations related to event rate will be done using thatsystem.Finally, the initial data collected in the phase I system were all taken using a single trappingcoil, which generated a local region of slightly reduced magnetic field magnitude. A careful surveyof the magnetic properties of all materials near the trapping region was conducted and severalmagnetic components were identified and relocated or replaced with non-magnetic alternatives.As a result, we were able to achieve axial confinement between two coils, each producing a locallyincreased magnetic field. This configuration is expected to provide a more uniform mean fieldfor trapped electrons, and is more naturally scalable to an extended trapping region for futurephases. Data taken in this new configuration provide the new results in the following section.31234567890Neutrino2016 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 888 (2017) 012074  doi :10.1088/1742-6596/888/1/0120743. Latest results and conclusionsIn the spectra from the initial phase I release, we demonstrated a full-width at half maximum(FWHM) of 140 eV for the conversion electron lines near 30 keV using a single coil fieldperturbation of −3.2mT. This was improved to 15 eV when using a smaller trapping fieldof −1.6mT at a cost of reduced trapping efficiency, and therefore event rate. After the changesdescribed in the previous section, data were collected using the two-coil trapping configuration,with each coil providing a 3.5mT perturbation. The result for the same pair of lines near 30 keVis shown in figure 1, where the FWHM is measured to be less than 4 eV.Figure 1. Electron energy spectrum ofthe conversion electrons near 30 keV. TheFWHM measured in these data is less than4 eV, a significant improvement over the15 eV we have previously demonstrated.Figure 2. Spectrogram of a single electrontrapped using the two coil configuration.The cyclotron emission starts at 0 s and85MHz while the sideband begins roughly40MHz higher and runs parallel to thecyclotron emission.Furthermore, trapping between two coils results in a lower axial motion frequency, bringingthe sidebands produced by modulation of the cyclotron frequency within the receiver’sbandwidth as shown in figure 2. Because sidebands were not previously apparent, they hadpreviously not been considered in the event reconstruction software. A significant change to thatalgorithm detects tracks with common start and stop times and groups them into single events,rather than falsely reconstructing the sidebands as independent electron events. The sidebandsare a result of an electron’s axial motion, and detailed reconstruction of the sidebands providesan additional handle to the magnetic field experienced by confined electron. Investigations intothe use of sideband information for improved energy reconstruction are ongoing.In conclusion, the Project 8 collaboration has previously demonstrated the feasibility of CRESfor electrons energies near the 18.6 keV endpoint of tritium. Since then, we have achieved roughlya factor of 4 improvement in energy resolution, while moving to a more sophisticated trappingfield configuration. We have observed power modulation into sidebands and are investigatinguse of this additional information to improve event reconstruction. The ongoing commissioningand operation of phase II will benefit from the analysis lessons learned from phase I.References[1] B. Monreal and J. A. Formaggio, “Relativistic cyclotron radiation detection of tritium decay electrons as anew technique for measuring the neutrino mass”, Phys. Rev. D 80, 051301 (2009).[2] C. Kraus et al., “Final results from phase II of the Mainz neutrino mass search in tritium beta decay”, Eur.Phys. J. C40, 447-468 (2005).[3] V. N. Aseev et al., “An upper limit on electron antineutrino mass from Troitsk experiment”, Phys Rev. D 84112003 (2011).[4] J. Angrik et al.. 2005. FZK Scientific Report 7090.[5] D. M. Asner, et al. (Project 8 collaboration), “Single-electron detection and spectroscopy via relativisticcyclotron radiation”, Phys Rev. Lett. 114, 162501 (2015).

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