1. Direct Determination of Neutrino Mass
The mass is needed for
Particle physics
Interpretation of supernova n signal
Cosmology
Beta Decay
Tritium
187Re
Other ideas?
Neutrino Oscillations
Supernova timing
Double beta decay
Cosmology
Z-bursts
Hamish Robertson -- Carolina Symposium 5/08

2. Masses linked by oscillations
Average mass > 20 meV
Present
Lab Limit
2.3 eV ?
m232
m122

3. Claim of Evidence for 0 in 76Ge
<m> ~ 0.2 to 0.3 eV
Looks good to me…
Single-site events in detectors 2, 3, 4, 5 (56.6 kg-y).
H.V. Klapdor-Kleingrothaus, Int. J. Mod. Phys. E17, 505 (2008)

4. Beta decay and neutrino mass3H
Requirements:
Strong source
Excellent energy resolution
Small endpoint energy E0
Long term stability
Low background rate
Task:
Investigate 3H or 187Re endpoint with sub-eV precision
KATRIN Aim:
Improve mn sensitivity tenfold (2eV  0.2eV )

5. What are we measuring?
Writing the transition probability as the matrix element of some operator T,
In the degenerate regime where all the masses are the same, the unitarity of U gives us back the original expression for a single massive neutrino, an “electron neutrino with mass”

6. Final Mainz Result -- Kraus et al. hep-ex/0412056
Improved S/N tenfold over 1994 data
20 weeks of data in 1998, 1999, 2001
Stable background: pulsed RF clearing field applied at 20-s intervals

7. The next generation experiment
Assemble everyone who has done a tritium experiment. Then…
aim : improve mn by one order of magnitude (2 eV ® 0.2 eV )
requires : improve mn by two orders of magnitude (4 eV2 ® 0.04 eV2 )
problem : count rate close to ß-end point drops very fast (~dE3)
improve statistics :
stronger tritium source (factor 80) (& large analysing plane, Ø=10m)
- longer measuring period (~100 days ® ~1000 days)
improve energy resolution :
large electrostatic spectrometer with DE=0.93 eV (factor 4 improvement)
reduce systematic errors :
- better control of systematics, energy losses (reduce to less than 1/10) 2

8. KATRIN 5 countries 13 institutions 100 scientists
at Forschungszentrum Karlsruhe
unique facility for closed T2 cycle:
Tritium Laboratory Karlsruhe
5 countries
13 institutions
100 scientists
TLK
~ 75 m long with 40 s.c. solenoids

9. Windowless Gaseous T2 Source

10. Principle of MAC-E Filter
Adiabatic magnetic guiding
of b´s along field lines
in stray B-field of
s.c. solenoids:
Bmax = 6 T
Bmin = 3×10-4 T
Energy analysis by
static retarding E-field
with varying strength:
High pass filter with
integral b transmission
for E>qU

11. KATRIN Experiment 70 m 10-11 mbar - 1 - 18.4 kV Pre-spectrometer Rear
Rejection of low-energy electrons and adiabatic guiding of electrons
Rear
3He
Rear System:
Monitor source
parameters
1010 e- /s e-
3•10-3 mbar
- 1 ± 1 kV
Source 3H
β-decay
3He
Source:
Provide the
required tritium
column density
Transp/Pump
3He
1010 e- /s e-
Transp. & Pump system:
Transport the electrons,
adiabatically and reduce
the tritium density
significantly
0 kV
1 e- /s e-
10-11 mbar kV
Main spectrometer
Main-spectrometer:
Rejection of electrons
below endpoint and
adiabatic guiding of
electrons
Detector
Detector:
Count electrons
and measure their
energy

12. Pre-spectrometer Parameters: Length: 3.4 m (flange to flange)
Diameter:1.7 m
Vacuum: < mbar
Material: Stainless steel
Magnets: 4.5 T
Status:
Vacuum 7•10-11 mbar (without getter)
Outgassing 7•10-14 mbar l/ s cm2
Measurements in progress

13. Tandem design: -- Pre-filter, Energy analysis
Pre-spectrometer
Filters low energy -decay electrons E<18.4 keV
Moderate energy resolution E80 eV
Test bed for vacuum, electrode design, detector.
detector
Pre- spectrometer
Main spectrometer
1010 e-/sec
103 e-/sec
10i e-/sec
Detector
145 pixel Si PIN diode
~1keV resolution
Image source
 systematics
 backgrounds
Main spectrometer
23 m long, 10 m diameter
High luminosity: dN/dt~Aspect.
high energy resolution: E/E~Aspect
Vacuum 3x10-11 mbar (reduce backgrounds)
use non-evaporable getter pumps
Inner wire electrode (shape field, reduce backgrounds)
External air coil - compensate for Earths magnetic field

14. Main Spectrometer Manufacture
2 conical end pieces
Danube
assembly hall DWE
1 cylindrical centre piece

15. Voyage of the main spectrometer

16. Arrival in Leopoldshafen: Nov 24, 2006

17. Inside the Spectrometer

18. Detector Section (Univ. of Washington, MIT)
Silicon PIN diode detector
9 cm active diameter
500 m thick
148 segments
detector magnet
B = 3-6 T
“flux tube” e-
The last, but not least, part of our apparatus is the detector section, which is UW's contribution to the project. The detector itself is a 9 cm diameter silicon p-i-n diode, with 145 individual pixels. It sits at the end of the section, and is shown enlarged in the inset. Note that there is also a post acceleration electrode. This allows us the possibility to apply an additional accelerating field to enhance our signal to background to ratio.
pinch magnet
B = 6 T
shielding & veto
post-acceleration electrode

19. Pixelized Detector Corrects Focal Plane Resolution

20. KATRIN Statistical Sensitivity
Improved over original design (7 m diameter main spectrometer, source luminosity)
Reduction in background
Only shows statistical uncertainty

21. Optimized run time at each energy

22. Tritium Beta Decay History

23. A window to work in
Molecular Excitations

24. Precision Voltage Divider test at PTB, 2006
preliminary
preliminary
preliminary

25. Improved sensitivity with larger system
Discovery
90% CL UL

26. Mass Range Accessible KATRIN Present Average mass > 20 meV
Lab Limit
2.3 eV
m232
m122

27. Microcalorimeters for 187Re ß-decay
MIBETA: Kurie plot of 6.2 × Re ß-decay events (E > 700 eV)
MANU2 (Genoa)
metallic Rhenium
m(n) < 26 eV
Nucl. Phys. B (Proc.Suppl.) 91 (2001) 293
MIBETA (Milano)
AgReO4
m(n) < 15 eV
10 crystals:
8751 hours x mg (AgReO4)
Nucl. Instr. Meth. 125 (2004) 125
MARE (Milano, Como,
Genoa, Trento, US, D)
Phase I : m(n) < 2.5 eV
E0 = ( ± 0.5stat ± 1.6syst) eV
mn2 = (-112 ± 207 ± 90) eV2
hep-ex/

28. KATRIN outlook
KATRIN can measure neutrino mass directly via kinematics of beta decay -- model independent
Improvement of order of magnitude over previous best
Challenging goal of m < 0.2 eV (90% C.L.) looks achievable
German funding (33.5 M€) is in place
US DOE funding ($2.6 M) is in place
Initial operation 2010.
Thanks, Peter

29. Fin

30. Supernova Neutrino Time-of-flight
For a supernova at distance D (in 10 kpc) the time delay for a neutrino of mass m (eV) and energy E (MeV) is:
Beacom & Vogel hep-ph/
The delay must be ~ the duration of the neutrino signal to avoid model dependence at short times and not to be drowned in background at long times. For a 1 eV result with 30-MeV neutrinos, need D = 175 Mpc. Scaling Kamiokande for the same rate as SN1987a, detector mass must be 12 Gt.
IceCube will be “only” 1 Gt, and not very sensitive at these low energies.

31. Z-bursts Gelmini, Varieschi & Weiler, hep-ph/0404272
Hypothesis: the extreme-energy CR spectrum is produced by neutrinos from distant sources. The neutrinos can annihilate at the Z pole on relic neutrinos to produce the observable EE CR. (A GZK-style cutoff for neutrinos).
If cutoff is at 2 x 1020 eV, then m > 20 eV, in disagreement with expt. EE CR thus likely not neutrino Z-burst debris.
Abbasi et al., PRL 92,

32. Future tritium measurements?
Ultimate sensitivity of spectrometers
require instrumental resolution of ~
Linear size X of instrument scales with resolution:
Differential spectrometers
Integral spectrometers
spectral fraction per decay in the last mn of the spectrum is ~ (m/Eo )3
source thickness is set by the inelastic scattering cross-section (3.4 x cm2 ), n ≤ 1. Can’t make it thicker, only wider.
If one wants ~1 event/day in last m of the spectrum
for a 10 m magnetic spectrometer m ~ 1.7 eV
for a 3 m dia. solenoid retarding field spectrometer m ~ 0.3 eV
KATRIN is probably the end of the road for tritium beta decay

33. NEXTEX Sensitivity ~ 0.8 eV Not funded, it’s over U of Texas (1 M$)
Pure electrostatics
Possibility for electron diffr.
no magnetic fields <0.1 mG
Sensitivity ~ 0.8 eV
Required funding 6.5M$
Not funded, it’s over

34. Sensitivity with run time

35. Systematic Uncertainties

37. Status of KATRIN Hardware Activities
Pre-spectrometer magnets
Delivered in February 2005
Main spectrometer
Final designs by MAN-DWE
Delivered December 2006
WGTS
Manufacturing Started
Delivery 2007
Pre-spectrometer
Delivered in Oct. 2003
Vacuum tests started May 2004
El. mag. test start 2006
DPS2-F
Manufacturing started
Delivery 2007

38. MC Using Stopping Power (M. Steidl)
Arrows show 99% intensity windows

39. Figure-of-merit
2 mHz
“Better”
1 mHz

41. Final States Red: 3HeT+ Blue: 3HeH+
1% uncertainty in rovib spectrum  m2 = 6 x 10-3 eV2

42. Even small mn influences structure
2DF Galaxy Survey
PRL
Smn
2.4 eV
0.5 eV
Large
Scale
Small
Scale

43. Neutrino mass spectrum and flavor content
Minimum Neutrino Masses and Flavor Content
Mass (eV)
e mu tau
Atmospheric n3
0.058
Solar
0.050 n2
0.049 n1
m232
Solar n2
0.009
Atmospheric
m122 n1 0 0 n3 ? ?