1. Absolute neutrino mass determination with the experiment KATRIN
F. Glück
(on behalf of the KATRIN collaboration)
Johannes Gutenberg-Universität, Mainz

2. Neutrino mass value important for: particle physics,
astrophysics, cosmology
Information for neutrino mass:
neutrino oscillation experiments
direct kinematical measurements
neutrinoless double beta decay
supernovae
cosmological observations (galaxy redshift,
microwave background radiation)

3. Neutrino oscillation results:
At least 2 neutrino masses are finite; lepton mixing matrix has large off-diagonal elements
SNO, KAMLAND:
D m122 ≈7·10-5 eV2, θ12 ≈33°
3. SuperKamiokande:
D m232 ≈ 2.5·10-3 eV2, θ23 ≈45°
→ mν(max) ≈ 50 meV
m1 => m2 , m3
No information about absolute mass scale (m1) !

4. neutrino masses and schemes
„normal“ mass hierarchy m1<m2<m3
quasi-degenerate
hierarchical

5. Neutrino Mass Measurements
Strategies
cosmology &
structure formation
astrophysics:
SN ToF measurements
0nbb decay:
b decay kinematics:
microcalorimeters
MAC-E spectrometers
NEMO3
LNGS ´90-´03
(71.7 kg×y)
2nbb
D.N. Spergel et al: Smn < 0.69 eV (95%CL)
S.W. Allen et al: Smn = 0.56 eV (best fit)
|mee|= eV
187Re 3H
SuperK, SNO, OMNIS + grav.waves:
potential for ~1eV sensitivity?

6. Neutrino mass limit from cosmology:
free-streaming of neutrinos in universe
(because of their small interaction)
massive neutrinos: gravitational effect,
they can reduce the matter density fluctuations
large neutrino mass → no small scale structure
in universe
neutrino mass limit from cosmology is model
dependent (correlations with many other
parameters)

7. mn = 0 eV
mn = 1 eV
Ma ’96
mn = 7 eV
mn = 4 eV

8. 2dFGRS analysis & n-mass limit
redshifts for 32 point galaxy power spectrum
c2 = 32.9
large scales small scales
~900 Mpc ~90 Mpc

9. Cosmology: n-masses from WMAP & 2dFGRS & Ly a
CMBR
WMAP
galaxies with <z>=0.11
Powerspectrum of CMBR
Combined result :
mn < 0.23 eV (95 % CL.)
astro-ph/
a challenge for KATRIN ?! How are these results derived, and are they realistic?

10. 2dFGRS analysis & n-mass limit
adding priors for cosmological parameters
Inference of neutrino mass depends on priors for
Hubble parameter h, baryon density Wb h2, Wtot,
flat prior on
0.1 < Wm < 0.5

11. WMAP results- a critical review
3 main lines of criticism:
- Systematic problems of the WMAP result itself
at large and small scales, compatibility with BBN,
the role of the LCDM model (PL-LCDM or RSI-LCDM)
- The role of priors and combination of different data
sets (Hannestad, Elgaroy & Lahav)
- ‚Massive attack‘ on LCDM: the role of H0 and the need
for L and their influence on Wn (Rowan-Robinson & Sarkar)

13. need lab experiments with sub-eV mass sensitivity

14. Heidelberg Moscow (enriched 76Ge)
Double  decay Z
 E
normal (2) neutrinoless (0) _
needed: a)  ν (Majorana) b) helicity flip: m()  or other new physics
Heidelberg Moscow (enriched 76Ge)

15. Evidence for 0 at Heidelberg Moscow Exp.?
Klapdor-Kleingrothaus et al., MPLA 37 (2001) 2409
(s.also comments: hep-ex/ , hep-ph/ , hep-ph/ )
Nearly same data as earlier (54kgy: 8/ /2000),
but now asumptions of peaks in [2000,2080] keV:
 background level is lower
fit only [2032,2046] keV with background and peak
 peak at 0 signal position (2039 keV)
single side events
expected peak position
„Single-Side-Events“
erwartete Position
T1/20 = ( ) 1025 y
mee = ( ) eV
m(e) = ( ) eV
 (fast) degenerierte?
New, data up to 2003: 72 kgy, with new data selection, new calibration Klapdor-Kleingrothaus et al., PL B586 (2004)  Peak at (5) keV (expected: (50) keV) Multi-Gauss. Fit: 4.2 significance for 0 T1/20 = ( ) 1025 y mee = eV (99.7% C.L.)

16. τ0ν-1 ~ mee2 · M0ν2 (1) mee = Σi Uei2 miν (2)
If 0νββ due to light Majorana neutrino:
τ0ν-1 ~ mee2 · M0ν (1)
mee = Σi Uei2 miν (2)
τ0ν → miν model dependent, because of:
-nuclear matrix element
sign (complex phase) of Uei2
possibility for beyond Standard Model mechanism
of 0νββ process (supersymmetry, …) → Eq. 1
not valid any more
Possible:
present HM signal confirmed, but hierarchical neutrino masses
( miν < 0.2 eV)
Test by KATRIN !

17. b – decay kinematics
phase space determines energy spectrum
transition energy E0 = Ee + En (+ recoil corrections)
dN/dE = K × F(E,Z) × p × Etot × (E0-Ee) × [ (E0-Ee)2 – mn2 ]1/2
theoretical b spectrum near endpoint
experimental observable 1
0.8
0.6
0.4
0.2
rel. rate [a.u.]
strong source
(high count rate near E0)
small endpoint energy E0
excellent energy resolution
long term stability
low bg rate
mn = 0eV
mn = 1eV
Ee-E0 [eV]

18. m calorimeters for 187Re b decay
neutrino mass measurement with
array of 10 AgReO4 crystals
lower pile up
higher statistics
MIBETA experiment
(Milano, Como, Trento)
M.Sisti et al, NIM A520(2004)125
A.Nucciotti et al, NIM A520(2004)148
C. Arnaboldi et al, PRL 91, (2003)
E0 = 2.46 keV
Top ~ mK

19. m calorimeters for 187Re b decay
Kurie plot of 6.2 × Re b decay events above 700 eV
fit with function
free fit parameters:
b endpoint energy
mn2
b spectrum normal.
pile-up amplitude
background level

20. 187Re b decay endpoint and mn
E0 = ± 0.5stat ± 1.6syst eV
(8751 h*mg, NIMA520, 2004)
= ± 0.8stat ± 1.5syst eV
(4485 h*mg, PRL91,2003)
Flavio Gatti (Genoa):
0.5g Re  1—1.7eV sensitivity expected
Expt. Under construction
mn2 = -112 ± 207 ± 90 eV2
mn < 15 eV (90%CL)
future:
proposal for a new
calorimeter expt. with
~2-3 eV sensitivity
foreseen 2007 (?)
fit range: 0.9 to 4 keV
fit function

21. Direct determination of mν by tritium β decay
super allowed
E0 = 18.6 keV
t1/2 = 12.3 a
tritium  decay: 3H  3He+ +e-+e _
average neutrino
mass
Need: very high energy resolution &
very high luminosity &  MAC-E-Filter
very low background }

22. magnetic spectrometers & MAC-E filters

23. Principle of the MAC-E-Filter
Magnetic Adiabatic Collimation + Electrostatic Filter (A. Picard et al., Nucl. Instr. Meth. 63 (1992) 345)
Two supercond. solenoids compose magnetic guiding field
Electron source (T2) in left solenoid
e- in forward direction: magnetically guided
adiabatic transformation:  = E/B = const.  parallel e-beam
Energy analysis by electrostat. retarding field E = EBmin/Bmax = EAs,eff/Aanalyse  4.8 eV (Mainz)

24. principle of an electrostatic filter with
magnetic adiabatic collimation (MAC-E)
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

25. The Mainz Neutrino Mass Experiment 1997-2001
Mainzer
-Gruppe
2001:
tilded solenoids
new cryostat
J. Bonn B. Bornschein*
L. Bornschein*
B. Flatt
Ch. Kraus
B. Müller**
E.W. Otten
J.P.Schall
Th. Thümmler**
Ch. Weinheimer**
* FZ Karlsruhe
**  Univ. Bonn
T2 film at 1.86 K
quench-condensed on graphite (HOPG)
45 nm thick (130ML), area 2cm2
thickness determination by ellipsometry

27. From current to future experiments
Mainz: Troitsk:
mn2 = -1.2(-0.7) ± 2.2 ± 2.1 eV2 mn2 = -2.3 ± 2.5 ± 2.0 eV2
mn < 2.2(2.3) eV (95%CL) mn < 2.1 eV (95%CL)
C. Weinheimer, Nucl. Phys. B (Proc. Suppl.) 118 (2003) 279 V. Lobashev, private communication
C. Kraus, EPS HEP2003 (neighbour excitations self-consistent) (allowing for a step function near endpoint)
aim: improvement of mn by one order of magnitude (2eV  0.2eV )
 improvement of uncertainty on mn2 by 100 (4eV2  0.04eV2)
statistics:
stronger Tritium source (>>1010 b´s/sec)
longer measurement
(~100 days  ~1000 days)
energy resolution:
DE/E=Bmin/Bmax
 spectrometer with DE=1eV
 Ø 10m UHV vessel

28. The KArlsruhe TRItium Neutrino
Experiment
Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft

29. Pre and main spectrometer
transport
magnets
spectrometer
solenoids
Main spectrometer
Energy resolution: E = 0.93 eV
high luminosity: L = ASeff /4 = Aanalyse E/(2E) = 20 cm2
Ultrahigh vacuum requirements (Background) p < mbar
„simple“ construction: vacuum vessel at HV = electrode + „massless“ screening electrode
industry study
Pre spectrometer:
Transmission of electron with highest energy only (10-7 part in last 100 eV)  Reduction of scattering probaility in main spectrometer  Reduction of background
only moderate energy resolution required: E = 50 eV
Test of new ideas (XHV, shape of electrodes, avoid and remove of trapped particles, ...)
1010 e-/s
103 e-/s

30. KATRIN Main Spectrometer
stainless steel vessel (Ø=10m & l=22m) on HV potential
minimisation of bg  UHV: p ≤ mbar
 „massless“ inner electrode system
Mainz V results
2.8mHz
inner electrode
installed in Mainz
spectrometer for
background tests
UHV requirements:
outgassing < mbar l/s
inner surface ~ 800m2
volume to pump ~ 1500m3
intrinsic det. bg 1.6mHz

31. Detector

34. WGTS source characteristics
pinj = 3.0 × 10-3 mbar ( at T=27K)
qinj = 1.85 mbar l/s = 1020 mol./s = 4.7 Ci/s
(~ 40g T2 per day if no closed loop)
isotopic purity (±2‰)
monitored by Laser Raman spectroscopy

36. Statistical uncertainty
design optimisation ´01 -´03
tritium purity by tritium laboratory (>95%)
2× stronger gaseous source (Ø=75mm  Ø=90mm) requires Ø=10m spectrometer)
optimised measuring point distribution (~5 eV below E0)
active background reduction by inner electrode system, low background detector (needs further detailed tests)
LoI
reference

37. KATRIN sensitivity & discovery potential
expectation:
after 3 full beam years
ssyst ~ sstat
mn = 0.35eV (5s)
mn = 0.3eV (3s) 5s
discovery potential
mn < 0.2eV (90%CL)
sensitivity

38. Systematic uncertainties
any not accounted variance s2 leads to negative shift of mn2:
D mn2 = -2 s2
1. inelastic scatterings of ß´s inside WGTS
- requires dedicated e-gun measurements, unfolding techniques for response fct.
2. fluctuations of WGTS column density (required < 0.1%)
- rear detector, Laser-Raman spectroscopy, T=30K stabilisation, e-gun measurements
3. HV stability of retarding potential on ~3ppm level required
- precision HV divider (PTB), monitor spectrometer beamline
4. WGTS charging due to remaining ions (MC:  < 20mV)
- inject low energy meV electrons from rear side, diagnostic tools available
5. final state distribution
- reliable quantum chem. calculations }
a few contributions with each:
m2 0.007 eV2

39. Status and schedule of Katrin
2001 Presentation of project to community (Bad Liebenzell Workshop)
Foundation of KATRIN collaboration
Letter of Intent (hep-ex/ )
First, but significant funds by BMBF, FZ Karlsruhe
2002 Very positive report of International Review Panel
2003 X-Vat Workshop in Bad Liebenzell
Background investigations at Mainz
Setup of pre spectrometer at FZK
2004 Reviewing, proposal and funding
Setup of major KATRIN components:
WGTS, transport system, main spectrometer, detector
Commissioning at start of data taking with complete setup

40. Status of hardware components

41. Setup of pre-spectrometer at FZ Karlsruhe

42. Electric screening by „massless“ wire electrode 
Secondary electrons from wall/electrode
by cosmic rays, environmental radioactivity, ...
wire electrode on slightly more negative potential
U-U U
test installation at Mainz

43. Electric screening by „massless“ wire electrode
First realisation: Mainz III
total
background
rate:
2.8mHz
detector background rate 1.6mHz
New record !
April 04
Mainz V (2004-
PhD thesis: B. Flatt/Mz
KATRIN pre spectrometer

44. Summary
KATRIN:
A large tritium  decay neutrino mass experiment at FZ Karlsruhe performed by a strong international collaboration with sub-eV sensitivity (<0.20 eV)
probes in a unique model independent way: degenerate and cosmologically relevant neutrino masses
complementary to oscillation experiments, 0nbb, cosmology
 key experiment w.r.t. neutrino mass scale