Hamish Robertson, CENPA, University of Washington Progress toward measuring the mass of the neutrino The Ohio State University, February 3, 2015

THE NEUTRINO IS SUMMONED BY PAULI Bi 210 Po e-e- 210 Bi 210 Po e-e- e 1930

F. Wilson, Am. J. Phys. 36, 1150 (1968) “Hence, we conclude that the rest mass of the neutrino is either zero, or, in any case, very small in comparison to the mass of the electron.” 3 E. Fermi

NEUTRINOS OSCILLATE, HAVE MASS 5 Earth cos  = -1 cos  = +1 SK Super-Kamiokande (1998)  m 32 2 | = x eV 2 (2013)

6 Super-Kamiokande KamLAND SNO Neutrinos oscillate, have mass

MASS MAKES MIXING MANIFEST 7 Free-particle wave functions have a de Broglie wavelength. If there are two (or more) components with different masses, relative phase shifts develop with time or distance. After a while, not e any more. Depends on mass-squared differences  distance: and on the sizes of the U ei

v1,v2,v3v1,v2,v3

NEUTRINO MASSES AND FLAVOR CONTENT 9 Mass (eV) 00 3 e mu tau Atmospheric 2 1 Solar Atmospheric 2 1 Solar 0 ??  m 23 2  m 12 2

Particle Physics Cosmology What is the neutrino mass scale? Some things are simply missing from the standard model (dark matter, gravity…) but neutrino mass is the only contradiction to the SM.

NEUTRINO MASS FROM BETA SPECTRA neutrino masses mixing With flavor mixing : from oscillationsmass scale 11

PRESENT LABORATORY LIMIT FROM 2 TRITIUM EXPERIMENTS: 12 Together:… m v < 1.8 eV (95% CL)

TLK KATRIN At Karlsruhe Institute of Technology unique facility for closed T 2 cycle: Tritium Laboratory Karlsruhe 13 A direct, model- independent, kinematic method, based on β decay of tritium. ~ 75 m long with 40 s.c. solenoids

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Overview of KArlsruhe TRItium Neutrino Experiment Windowless gaseous sourceTransport sectionPre-spectrometer Main-spectrometerDetector V Monitor-spectrometer 70 m mbar mbar

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mbar mbar Radon!

NEUTRINO MASS SIGNAL 18

KATRIN’S UNCERTAINTY BUDGET Statistical Final-state spectrum T - ions in T 2 gas Unfolding energy loss Column density Background slope HV variation Potential variation in source B-field variation in source Elastic scattering in T 2 gas σ(m v 2 ) eV 2 σ(m v 2 ) total = eV 2 19 m v < 0.2 eV (90 % CL)

MOLECULAR FINAL-STATE SPECTRUM 20 Saenz et al. PRL 84 (2000) T 2  3 HeT + Q A = 18.6 keV

21 MOLECULAR FINAL-STATE SPECTRUM Saenz et al. PRL 84 (2000) Fackler et al. PRL 55 (1985) KATRIN 0.2 eV eV 2 LANL 1991, LLNL 1995

MASS RANGE ACCESSIBLE Present Lab Limit 1.8 eV starting 2016 KATRIN 22

THE LAST ORDER OF MAGNITUDE If the mass is below 0.2 eV, how can we measure it? KATRIN may be the largest such experiment possible. Size of experiment now: Diameter 10 m. Rovibrational states of THe +, HHe + molecule Source T 2 column density near max Next diameter: 300 m! σ(m v ) 2 ~ 0.38 eV 2

8751 hours x mg (AgReO 4 ) MIBETA: Kurie plot of 6.2 × Re ß-decay events (E > 700 eV) 10 crystals: E 0 = ( ± 0.5 stat ± 1.6 syst ) eV MANU2 (Genoa) metallic Rhenium m( ) < 26 eV Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293 MIBETA (Milano) AgReO 4 m( ) < 15 eV MARE (Milano, Como, Genoa, Trento, US, D) Phase I : m( ) < 2.5 eV m 2 = (-112 ± 207 ± 90) eV 2 Nucl. Instr. Meth. 125 (2004) 125 hep-ex/ MICROCALORIMETERS FOR 187 RE ß- DECAY 24

ELECTRON CAPTURE HOLMIUM EXPT (ECHo) 25 Gastaldo et al. NIM A711, 150 (2013) 163 Ho implanted in Metallic Magnetic Calorimeters Au:Er paramagnetic sensors

26 Ranitzsch et al De Rujula & Lusignoli PL 118B 429 (1982) Energy resolution 8.3 eV

27 Spectrum with both single and double vacancies in the 163 Dy daughter. HR

28 We need… a new idea.

CYCLOTRON RADIATION FROM TRITIUM BETA DECAY 29 (B. Monreal and J. Formaggio, PRD 80:051301, 2009) Surprisingly, this has never been observed for a single electron. “Never measure anything but frequency.” A. Schawlow

83m Kr: NICE TEST SOURCE d 83 Rb 83 Kr 41 keV 9 keV 1.83 h Conversion e - K: eV L 2 : eV L 3 : eV …

THE ENERGY IS MEASURED AS A FREQUENCY 31 Tritium endpoint

POWER RADIATED 32

ENERGY RESOLUTION 33 ~30 For 1 eV energy resolution, you need about 2 ppm frequency. For 2 ppm frequency, you need 500,000 cycles, or 15 μs. Electron travels 2 km. You need a trap!

34 G-M cooler (35K) 26-GHz amplifiers 83m Kr source (behind) SC Magnet (0.95 T) Prototype at University of Washington

35 Gas cell is a small section of WR-42 waveguide

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SUPERHETERODYNE RECEIVER 37

WHAT WOULD A SIGNAL FROM AN ELECTRON LOOK LIKE? 38 Digitize the amplifier output. Make short-time Fourier transforms. Plot the spectra sequentially (a “spectrogram”). Simulation: M. Leber

FIRST OBSERVATION OF SINGLE- ELECTRON CYCLOTRON RADIATION June 6, 2014

UNEXPECTED DETAIL! 40 Electron slowly loses energy from cyclotron emission ~ 1 fW radiative loss Electron scatters off gas molecule, losing energy, possibly changing pitch angle Track start gives initial electron kinetic energy

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44 Short-time Fourier transform spectrogram Find tracks Join segments vertically to map complete electron event

ENERGY SPECTRUM 45 83m Kr

“JUMP” SPECTRUM 46 83m Kr 30.4 keV line Most probable jump is 14 eV.

WHY IS THIS SO IMPORTANT? 47 Source is transparent to microwaves: can make it as big as necessary. Whole spectrum is recorded at once, not point-by-point. Excellent resolution should be obtainable. An atomic source of T (rather than molecular T 2 ) may be possible. Eliminates the final- state theory input.

NEXT: A TRITIUM EXPERIMENT 48 Fill a volume with tritium gas at low pressure Add antennas and receivers Apply uniform magnetic field Measure mass of neutrino

PROJECT 8 SENSITIVITY 49 and OPTIMISTIC

PROJECT 8 SENSITIVITY 50 Existing mass limit Normal vs inverted hierarchy Current system volume

PROJECT 8: A PHASED APPROACH

NEUTRINO MASS LIMITS FROM BETA DECAY 52 KATRIN

SUMMARY Direct mass measurements are largely model independent: Majorana or Dirac No nuclear matrix elements No complex phases No cosmological degrees of freedom One experiment in construction (KATRIN); 2016 start. Four experiments in R&D (Project 8, ECHo, HOLMES, PTOLEMY) Success of Project 8 proof-of-concept. New spectroscopy based on frequency First step toward frequency-based determination of neutrino mass 53

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56 Fin

ConstructionRunning KATRIN: Phase IProof concept Prototype Project 8: NEUTRINO MASS: SOME MILESTONES 57

NEUTRINO MASS PHYSICS IMPACT 58

59 Battye and Moss, PRL 112, (2014)  Planck  SPT Lensing power spectrum Shear correlation spectrum  CFHTLenS Some tensions in ΛCDM resolved with neutrino mass:

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MASS AND MIXING PARAMETERS  m x eV 2  m 32 2 | x eV 2 mimi > eV (90% CL)< 5.4 eV (95% CL)*  deg  deg  deg sin 2  Marginalized 1-D 1-  uncertainties. *C. Kraus et al., Eur. Phys. J. C40, 447 (2005); V. Aseev et al. PRD 84 (2011) Other refs, see Fogli et al OscillationKinematic

SENSITIVITY WITH TIME 62

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64 52 mm

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IS AN ATOMIC SOURCE FEASIBLE? Must reject molecules to (endpoint is 8 eV higher) Produce T in RF discharge: 90:10 T 2 :T Cool to 140 K in aluminum or sapphire tube. Inject into trap, trap low-field seeking polarization. Trap and cool to ~1 K by scattering from 4 He. Trap in same magnetic field configuration that is trapping the electrons: bathtub axial trap + added barrel conductors. High fields are essential: complicated SC magnet. 5T ~ 3.1 K. Neither T 2 nor 4 He are trapped magnetically. Surprisingly, all of this looks sort of feasible, not easy. The statistical accuracy alone doesn’t convey the added confidence an atomic source would give.

MAGNETIC CONFIGURATION OF TRAP Solenoidal uniform field for electron cyclotron motion Pinch coils to reflect electrons Ioffe conductors (multipole magnetic field) to reflect radially moving atoms. The ALPHA antihydrogen trap parameters: Magnetic well depth 0.54 K (50 μeV) Trap density initially ~10 7 cm -3 Trap lifetime ~ 1000 s

AN EARLY H TRAP (AT&T, MIT) Hess et al. PRL 59, 672 [1987] 6 x cm mK 400 s Effect of dipolar spin flips

ALPHA’s antihydrogen trap ALPHA Collaboration: Nature Phys.7: ,2011; arXiv

CURRENT STATUS: Mainz: solid T 2, MAC-E filter C. Kraus et al., Eur. Phys. J. C40, 447 (2005) Troitsk: gaseous T 2, MAC-E filter V. Aseev et al., PRD 84 (2011) Together:… m v < 1.8 eV (95% CL) 70

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Molecular excitations 75 Energy loss A WINDOW TO WORK IN

KATRIN’S STATISTICAL POWER 76

MASS RANGE ACCESSIBLE Present Lab Limit 1.8 eV starting 2016 KATRIN 77