1. Three roads to neutrino masses
or evidence?
complementary
or evidence?

2. Absolute Neutrino Mass Measurements Beate Bornschein
Lecture I
Introduction
Electron neutrino mass measurements - methods
Status at the begin of the 3rd millennium
sensitivity 0.2 eV/c2

3. Absolute Neutrino Mass Measurements Beate Bornschein
Lecture II
Future of Re experiments – MARE
Fixing the neutrino mass scale with KATRIN
Summary & Perspectives
sensitivity 0.2 eV/c2

4. Absolute neutrino masses --- Particle Data Group

5. Absolute neutrino masses – PDG (May 2006)

6. Absolute neutrino masses – the ‚traditional‘ way
m(ne) : tritium ß-decay 3H → 3He + e- + ne
m(nµ) : pion-decay p+ → µ+ + nµ
m(nt) : tau hadr. decay t → 5p + nt
kinematic phase
space studies
m(nm) < 190 keV (PDG2006)
m(nt) < 18.2 MeV (PDG2006)
m(ne) < 2 eV (PDG2006)

7. Neutrino oscillations: linking -masses
n-mass offset?

8. Absolute neutrino masses – the ‚traditional‘ way
m(ne) : tritium ß-decay 3H → 3He + e- + ne
m(nµ) : pion-decay p+ → µ+ + nµ
m(nt) : tau hadr. decay t → 5p + nt
kinematic phase
space studies
neutrino oscillations with large mixing angles -
all -masses are linked to lightest by oscillations
m(nm) < 190 keV (PDG2006)
m(nt) < 18.2 MeV (PDG2006)
m(ne) < 2 eV (PDG2006)

9. Absolute neutrino masses – the ‚traditional‘ way
m(ne) : tritium ß-decay 3H → 3He + e- + ne
m(nµ) : pion-decay p+ → µ+ + nµ
m(nt) : tau hadr. decay t → 5p + nt
kinematic phase
space studies
Therefore, concentration on m(e),
especially -decay experiments
m(nm) < 190 keV (PDG2006)
m(nt) < 18.2 MeV (PDG2006)
m(ne) < 2 eV (PDG2006)

10. A short step into the past
myon neutrino mass
tau neutrino mass

11. Myon neutrino mass Principle:
Three different quantities needs to be measured with very high precision
Done in three different experiments!

12. Myon neutrino mass Measurement of , with CPT theorem: =
Pionic atom: negative pion is stopped in matter and captured by an atom.
Example: Measurement of the 4f-3d transition in pionic 24Mg with a crystal spectrometer
Measurement of
Jeckelmann et al., PhysLettB335 (1994)326
Mohr and Taylor, CODATA, RevModPhys 77 (2005)

13. Myon neutrino mass Measurement of at Paul-Scherrer Institute (PSI)
Assamagan et al., PhyRevD 53 (1996)6065

14. Setup at PSI
Assamagan et al., PhyRevD 53 (1996)6065

15. Different neutrino mass states i

16. Myon neutrino mass
PDG2006
PDG2006

17. Tau neutrino mass Method:
 Hadronic system is composed of 3, 5 or 6 pions
 In tau rest frame energy of hadronic system is fixed:
 m() can computed for given values of mh and Eh*
 mh and Eh* are determined from the measured momenta of the particles
composing the hadronic system

18. Tau neutrino mass – ALEPH collaboration
Barate et al.,
Eur. Phys. J. C2 (1998)395

19. Tau neutrino mass
PDG2006
(23 entries …)

20. Absolute neutrino masses – the ‚traditional‘ way
m(ne) : tritium ß-decay 3H → 3He + e- + ne
m(nµ) : pion-decay p+ → µ+ + nµ
m(nt) : tau hadr. decay t → 5p + nt
kinematic phase
space studies
Therefore, concentration on m(e),
especially -decay experiments
m(nm) < 190 keV (PDG2006)
m(nt) < 18.2 MeV (PDG2006)
m(ne) < 2 eV (PDG2006)

21. Electron neutrino mass - again a look into PDG2006

22. Neutrino mass from SN1987A Time of flight measurement:
L  1.5 ∙ 1018 km
 1.6 ∙ 105 light years
One neutrino with m, E (m2 << E2)
Two neutrinos with m, E1, E2

23. Neutrino mass from SN1987A Time of flight measurement:
One neutrino with m, E
Two neutrinos with m, E1, E2
Dependent on SN model !

24. Neutrino mass from SN1987A: results
PDG2006
T.J. Loredo et al., PRD65 (2002) , 39 pp
improved SN model
improved data modeling

25. Neutrino mass from SN20xx ???
Actually no competition with -decay experiments:
not sensitive to sub-eV neutrino masses (uncertainty in emission time at SN)
galactic SN only expected every 40 years

26. β-decay and neutrino mass

27. ß-decay and neutrino mass
kinematic measurement of
electron neutrino mass m(ne):

28. ß-decay and neutrino mass
kinematic measurement of
electron neutrino mass m(ne):
scaling in ß-decay: experimental observable is mn2
n-mass eigenstates mi too close to be resolved experimentally with
DE ~ 1 eV for single electrons at ß-decay endpoint
ß-decay & -oscillation experiments allow to fully reconstruct
mass eigenstates mj as -oscillations provide Uei and Δm2ij

29. ß-decay and neutrino mass
kinematic measurement of
electron neutrino mass m(ne):
E0 = keV
T1/2 = 12.3 y
superallowed 3H
ß-source requirements :
high ß-decay rate
low ß-endpoint energy E0
no strongly forbidden transition
…, see further discussion,
dependent on experiment
E0 = 2.47 keV
T1/2 = 43.2 Gy
unique 1st forbidden
187Re
ß-detection requirements :
- high resolution (DE< few eV)
- large solid angle (DW ~ 2p)
- low background
calorimeter:
source = detector
spectrometer:
source ≠ detector

30. spectrometers MAINZ-TROITSK  KATRIN
Based on
Andrea Giuliani,
MARE collaboration
Source
Electron analyzer
Electron counter T2
high activity
high energy resolution
integral spectrum: select Ee > Eth
high efficiency
low background
spectrometers MAINZ-TROITSK  KATRIN b n
electron
excitation
energies
When in presence of decays to
excited states, the calorimeter
measures both the electron and
the de-excitation energy
bolometer
high energy resolution
differential spectrum: dN/dE
microcalorimeters MIBETA, MANU  MARE

31. Tritium β-decay experiment
3H  3He+ + e- + e with E0=18.6 keV
Measurement of T2 β-decay spectrum in the region around the endpoint E0

32. Why tritium? Tritium: E0 = 18.6 keV, TH = 12.3 a
recoil energy and excitation neglected
Fermi function
nuclear matrix element
Tritium: E0 = 18.6 keV, TH = 12.3 a
Superallowed transition:  matrix element M is not energy dependent
Low endpoint energy:  relative decay fraction at the endpoint is comparatively high
Short half life:  specific activity is high  low amount of source material  low fraction of inelastic scattered electrons
Hydrogen isotope:  simple atomic shell  final states precisely calculable

33. Tritium β-decay experiment: basic requirements
very high energy resolution
very high luminosity
L = ASeff /4
- large source area
- large accepted solid angle
high -decay rate
very low background
Best solution: tritium source combined with MAC-E filter

34. Principle of an electrostatic filter with magnetic adiabatic collimation (MAC-E)
MAC-E Filter:
adiabatic guiding of  particles along the magnetic field lines
large accepted solid angle
  2
inhomogen B-Field:
adiabatic transformation

35. Principle of an electrostatic filter with magnetic adiabatic collimation (MAC-E)
MAC-E Filter:
adiabatic guiding of  particles along the magnetic field lines
large accepted solid angle
  2
inhomogen B-Field:
adiabatic transformation
electrostatic retarding field:
high pass filter !
E = Bmin/Bmax E0

36. Principle of an electrostatic filter with magnetic adiabatic collimation (MAC-E)
MAC-E Filter:
adiabatic guiding of  particles along the magnetic field lines
large accepted solid angle
  2
inhomogen B-Field:
adiabatic transformation
electrostatic retarding field:
high pass filter !
E = Bmin/Bmax E0

37. Principle of a MAC-E filter II
-eU0
MAC-E Filter - method
Scanning β spectrum and background region by varying spectrometer voltage U0
All β electrons with an energy higher than the filter energy –eU0 accepted and counted
Measuring time per data point is experiment specific Typical values: to 60 s per voltage set E0

38. Principle set-up of a tritium -decay experiment

39. The Mainz neutrino mass experiment (1997-2001)
Detector
5 segments
silicon
Molecular T2 source
T2 film at 1.9 K
Quench condensed on graphite (HOPG)
d  480Å (140 ML) A = 2 cm2
20 mCi activity
Spectrometer
23 ring electrodes
4.8 eV resolution
L = 4 m, Ø = 1 m
Vacuum better mbar
QCTS = Quench Condensed Tritium Source

40. The Mainz neutrino mass experiment (1997-2001)
KATRIN
2006
Mainz neutrino group 2001:
J. Bonn B. Bornschein* L. Bornschein* B. Flatt Ch. Kraus B. Müller ** E.W. Otten J.P. Schall Th. Thümmler** Ch. Weinheimer**
*  FZ K + U Karlsruhe **  U Münster

41. Source systematics Investigation of source effect in Mainz:
Quench Condensed Tritium Source QCTS, before 1997:
Source temperature 4.2K, 2.8 K
Roughening transition !
Increased energy loss
Investigation of source effect in Mainz:
Entering the solid state physics…

42. Stray light measurements

43. Results of stray light measurements
Fleischmann et al. Eur. Phys. J. B 16 (2000) 521
Model of surface diffusion
Δt ≈ Δt0  exp(Δ W / kT)
(Arrhenius-law)
Δt = characteristic dewetting time
ΔW = activation energy
Dewetting time Δt (T=1.9 K) > 1.2 a (95% C. L.)
 long term measurements are possible with quench condensed tritium films if T< 1.9 K Δt

44. Source systematics & negative mass squares
Quench Condensed Tritium Source QCTS, before 1997:
Source temperature 4.2K, 2.8 K
Roughening transition !
Increased energy loss

45. Underestimated energy loss – the most often reason for negative mass squares
If we have underestimated or just missed some energy loss mechanism,
then the fit finds a too low endpoint which shifts the squared neutrino mass towards negative values (count rate “above” the endpoint)

46. Results of neutrino mass measurements of last 2 decades
Long series of tritium -decay experiments
“Problem of negative mass squares” disappeared due to better understanding of systematic effects
Troitsk:
Gaseous tritium source (WGTS)
Mainz:
Quench condensed tritium source (QCTS)

47. QCTS - investigations of systematic effects
 Roughening transition of T2 film
 Inelastic scattering
Determination of dynamics: ΔE = (45±6) kBK
no roughening transition below 2 K
L. Fleischmann et al., J. Low Temp. Phys. 119 (2000) 615, L. Fleischmann et al., Eur. Phys. J. B16 (2000) 521
Determination of cross section: σtot = (2.98±0.16) 10‑18 cm2
Det. of energy loss function
V.N. Aseev et al., Eur. Phys.J. D10 (2000) 39
 Self-charging of T2 film
 Long time behavior of T2 film
Determination of critical field: Ecrit = (63±4) MV/m => slight broadening of energy resolution
H. Barth et al., Prog. Part. Nucl. Phys. 40 (1998) 353 B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69
Rest gas condensation & evaporation =>Effect limits measurement time

48. Self-charging of QCTS First hint: shift of the β-endpoint
energy (1997)
Idea:
Charging of the tritium
film (40 mCi ≈ 1.5E9 electrons/s)
Measurement with
Kr-83m conversion
electrons

49. Time dependency of charging
Assumption:
tritium β-decay
&
existence of critical field

50. Result of measurement
Steady state is characterized by a practically constant, critical electric field strength
Ecrit ≈ 62 MV/m
≈ 20mV/monolayer
over the film, at which the residual positive charges attain sufficient mobility to penetrate the film towards the conducting substrate.
β-spectroscopy:
Limits either resolution (in case of thick films) or count rate (in case of thin films).
Reason for using gaseous
source in KATRIN experiment!
B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69

51. Results of Mainz experiment (1998/1999 + 2001)

52. Results of Mainz experiment
Data of 20 weeks run time added for evaluation
With neighbour excitation from
calculation
(Kolos et al., Phys. Rev. A37 (1988) 2297)
m2(n) = -1.2 ± 2.2 ± 2.1 eV2
Þ m(n) < 2.2 eV (95% C.L.)
Ch. Weinheimer, Nucl. Phys. B
(Proc. Suppl.) 118 (2003) 279,
C. Kraus et al., Nucl. Phys. B
(Proc. Suppl.) 118 (2003) 482
Neighbour excitation fitted from
own data
m2(n) = -0.6 ± 2.2 ± 2.1 eV2 Þ m(n)< 2.3 eV (95% C.L.)
C. Kraus et al., Eur. Phys. J. C40 (2005) 447
PDG2006

53. Troitsk neutrino mass experiment
= Windowless Gaseous Tritium Source & MAC-E Filter
Dominant systematic uncertainty:
Energy loss due to inelastic scattering of decay electrons

54. Troitsk setup WGTS 26-28 K L=3 m, Ø= 5 cm T2:HT:H2 = 6:8:2
column density: 1017cm‑2
Spectrometer
3 ring lectrodes
3.5 eV resolution
L=6 m, Ø=1.2 m
P = 10‑9 mbar
Detector
Si(Li)

55. Troitsk setup

56. Troitsk Anomaly
Observation of an excess count rate (‘step’) close to the endpoint (equivalent to a mono energetic line in original β-spectrum)
Location: 5 – 15 eV below E0, intensity: ≈ 10‑10 of total T2-decay rate
Periodicity = 0.5 years ?

57. Troitsk Results
Strong correlation between step parameters (anomaly) and m2
Requires description of anomaly phenomenologically by adding 2 additional fit parameters (standard: E0, m2, Amp, Bg):
step_position, step_amplitude
results (6 parameter fit):
m2 = -1.9 ± 3.4 ± 2.2 eV2/c => m < 2.5 eV/c2 (95% C.L.)
V. Lobashev et al., Phys. Lett. B 460 (1999) 227
/01 results (6 parameter fit):
m2 = -2.3 ± 2.5 ± 2.0 eV2/c => m < 2.2 eV/c2 (95% C.L.)
V. Lobashev, Proceedings 17th International Conference on Nuclear Physics in Astrophysics, Debrecen/Hungary, 2002, Nucl. Phys. A 719 (2003) 153
PDG2006

58. Coincident measurements in Troitsk and Mainz
Mainz results:
No significant change of 2
=> no indication of an anomaly
Troitsk anomaly is very likely an experimental artefact which is not present in Mainz

59. PDG2006

60. Electron neutrino mass
PDG2006 ^

61. Absolute Neutrino Mass Measurements Beate Bornschein
Lecture II
Future of Re experiments – MARE
Fixing the neutrino mass scale with KATRIN
Summary & Perspectives
sensitivity 0.2 eV/c2

62. Additional transparencies

63. Model for charging electrons are leaving the T2 film
pos. Ions are remaining in the film
need charge compensating current from/to substrate
mobility of charges:
proportional to
exp (-W/kT)
T < 2 K  no mobility!
Charging
additional el. Field
movement of charges at Ecrit