Progress toward measuring the mass of the neutrino

The Ohio State University, February 3, 2015

Hamish Robertson, CENPA, University of Washington

THE NEUTRINO IS SUMMONED BY PAULI...

210 Bi e 210 Po 210 Bi e n e 210 Po

1930 2

“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.”

E. Fermi

F. Wilson, Am. J. Phys. 36, 1150 (1968) 3

NEUTRINOS OSCILLATE, HAVE MASS

Super-Kamiokande (1998) cos q = +1 SK Earth cos q = -1  m 32 2 | = 2.42

+0.12

-0.11

(2013) x 10 -3 eV 2

5

Neutrinos oscillate, have mass

SNO Super-Kamiokande KamLAND 6

MASS MAKES MIXING MANIFEST

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 .

l After a while, not n e any more.

Depends on

mass-squared differences

 =

h p

distance :

E

2 »

p i

2 >>

m i

2

p i

-

p j

» (

m j

2 -

m i

2 )

L

2

E

and on the

sizes of the U ei 7

v 1 , v 2 , v 3

NEUTRINO MASSES AND FLAVOR CONTENT Mass (eV)

e mu tau

Atmospheric n

3

0.058

0.050

0.049

Solar  m 23 2 n

2

n

1

n

2

n

1

Solar  m 12 2 ?

0.009

 0  0 Atmospheric ?

9

n

3

What is the neutrino mass scale?

Particle Physics Cosmology 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

With flavor mixing : from oscillations mass scale mixing neutrino masses

11

PRESENT LABORATORY LIMIT FROM 2 TRITIUM EXPERIMENTS:

Together:… m v < 1.8 eV (95% CL)

12

KATRIN

TLK

At Karlsruhe Institute of Technology unique facility for closed T 2 cycle: Tritium Laboratory Karlsruhe

A direct, model independent , kinematic method, based on

β

decay of tritium.

~ 75 m long with 40 s.c. solenoids

13

ES

14

Overview of KA rlsruhe TRI tium N eutrino Experiment

Windowless gaseous source 10 -3 mbar Transport section Pre-spectrometer 10 -11 mbar Main-spectrometer Detector 70 m V Monitor-spectrometer

K. Valerius

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Radon!

10 -10 mbar 10 -9 mbar

NEUTRINO MASS SIGNAL 18

KATRIN

’

S UNCERTAINTY BUDGET

σ(m v 2 ) 0 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 0.01 eV 2 σ(m v 2 ) total = 0.025 eV 2 m v < 0.2 eV (90 % CL)

19

MOLECULAR FINAL-STATE SPECTRUM

Saenz et al. PRL 84 (2000) T 2  3 HeT + Q A = 18.6 keV

20

MOLECULAR FINAL-STATE SPECTRUM

Saenz et al. PRL 84 (2000) Fackler et al. PRL 55 (1985) 0.2 eV 2 694 eV 2 LANL 1991, LLNL 1995 KATRIN

21

MASS RANGE ACCESSIBLE KATRIN starting 2016 Present Lab Limit 1.8 eV

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. σ(m v ) 2 ~ 0.38 eV 2 Size of experiment now: Diameter 10 m. Next diameter: 300 m!

Source T 2 column density near max Rovibrational states of THe + , HHe + molecule

MICROCALORIMETERS FOR 187 RE ß DECAY

MIBETA:

Kurie plot of 6.2 × 10 6 187 Re ß-decay events (E > 700 eV) 10 crystals: 8751 hours x mg (AgReO 4 ) E 0 = (2465.3 ± 0.5

stat ± 1.6

syst ) eV m n 2 = (-112 ± 207 ± 90) eV 2 MANU2 (Genoa) metallic Rhenium m( n ) < 26 eV Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293 MIBETA (Milano) AgReO 4 m( n ) < 15 eV Nucl. Instr. Meth. 125 (2004) 125 MARE (Milano, Como, Genoa, Trento, US, D) Phase I : m( n ) < 2.5 eV hep-ex/0509038

24

ELECTRON CAPTURE HOLMIUM EXPT (ECHo)

Gastaldo et al. NIM A711, 150 (2013) 163 Ho implanted in Metallic Magnetic Calorimeters Au:Er paramagnetic sensors

25

Ranitzsch et al. 1409.0071

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

Spectrum with both single and double vacancies in the 163 Dy daughter. HR 2014 1411.2906

27

We need… a new idea.

28

CYCLOTRON RADIATION FROM TRITIUM BETA DECAY

(B. Monreal and J. Formaggio, PRD 80:051301, 2009) “Never measure anything but frequency.”

A. Schawlow

Surprisingly, this has never been observed for a single electron.

29

83m

Kr: NICE TEST SOURCE

86.2 d 83 Rb 1.83 h 41 keV 9 keV 83 Kr Conversion e K: 17824.3 eV L 2 : 30424.4 eV L 3 : 30477.2 eV …

30

THE ENERGY IS MEASURED AS A FREQUENCY

Tritium endpoint

31

POWER RADIATED

32

ENERGY RESOLUTION

D

E kin E kin

= æ 1 +

m e c

2

E kin

æ æ D

f f

~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 !

33

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

34

Gas cell is a small section of WR-42 waveguide

35

36

SUPERHETERODYNE RECEIVER 37

WHAT WOULD A SIGNAL FROM AN ELECTRON LOOK LIKE?

Digitize the amplifier output. Make short-time Fourier transforms. Plot the spectra sequentially (a “spectrogram”).

FIRST OBSERVATION OF SINGLE ELECTRON CYCLOTRON RADIATION

June 6, 2014 1408.5362

39

UNEXPECTED DETAIL!

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

41

42

43

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

44

ENERGY SPECTRUM

83m Kr

45

“JUMP” SPECTRUM

83m Kr 30.4 keV line Track Energy (keV) Counts (a.u.) Counts (a.u.) Most probable jump is 14 eV.

46

WHY IS THIS SO IMPORTANT?

• 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.

47

NEXT: A TRITIUM EXPERIMENT

Fill a volume with tritium gas at low pressure Add antennas and receivers Apply uniform magnetic field Measure mass of neutrino

48

PROJECT 8 SENSITIVITY

and OPTIMISTIC

49

PROJECT 8 SENSITIVITY

Existing mass limit Current system volume Normal vs inverted hierarchy

50

PROJECT 8: A PHASED APPROACH

NEUTRINO MASS LIMITS FROM BETA DECAY

KATRIN

52

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

54

55

Fin

56

NEUTRINO MASS: SOME MILESTONES

Construction

KATRIN:

Running

Project 8:

Proof concept Prototype Phase I 2013 2014 2015 2016 2017 2018 2019

57

NEUTRINO MASS PHYSICS IMPACT

58

Lensing power spectrum   Planck SPT Battye and Moss, PRL 112, 051303 (2014) Some tensions in ΛCDM resolved with neutrino mass: Shear correlation spectrum  CFHTLenS 59

60

MASS AND MIXING PARAMETERS

Oscillation Kinematic  m 21 2  m 32 2 |  m i q 12 7.54

2.42

+0.21

+0.12

-0.21

-0.11

x 10 x 10 34.1

+0.9

-0.9

deg -5 -3 q 23 39.2

+1.8

-1.8

deg q 13 sin 2 q 13 9.1

+0.6

-0.7

deg 0.025

+.003

-.003

Marginalized 1-D 1  uncertainties. eV eV > 0.055 eV (90% CL) 2 2 < 5.4 eV (95% CL)* *C. Kraus et al., Eur. Phys. J. C40, 447 (2005); V. Aseev et al. PRD 84 (2011) 112003.

Other refs, see Fogli et al. 1205.5254

61

SENSITIVITY WITH TIME 62

63

52 mm

64

65

IS AN ATOMIC SOURCE FEASIBLE?

• Must reject molecules to 10 -5 (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)

6 x 10 12 cm -3 40 mK 400 s Effect of dipolar spin flips Hess et al. PRL 59, 672 [1987]

ALPHA’s antihydrogen trap

ALPHA Collaboration: Nature Phys.7:558-564,2011; arXiv 1104.4982

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) 112003 Together:… m v < 1.8 eV (95% CL)

70

K. Valerius

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K. Valerius

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K. Valerius

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K. Valerius

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A WINDOW TO WORK IN Molecular excitations Energy loss 75

KATRIN’S STATISTICAL POWER 76

MASS RANGE ACCESSIBLE KATRIN starting 2016 Present Lab Limit 1.8 eV

77