DPG Vortrag in Berlin Maerz 2005

1
Three roads to neutrino masses
or evidence?
complementary
or evidence?
2
Absolute Neutrino Mass MeasurementsBeate
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 MeasurementsBeate
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) lt 190 keV (PDG2006)
m(nt) lt 18.2 MeV (PDG2006)
m(ne) lt 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) lt 190 keV (PDG2006)
m(nt) lt 18.2 MeV (PDG2006)
m(ne) lt 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) lt 190 keV (PDG2006)
m(nt) lt 18.2 MeV (PDG2006)
m(ne) lt 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) lt 190 keV (PDG2006)
m(nt) lt 18.2 MeV (PDG2006)
m(ne) lt 2 eV (PDG2006)
21
Electron neutrino mass - again a look into PDG2006
22
Neutrino mass from SN1987A
Time of flight measurement
SN1987A
L ? 1.5 1018 km ? 1.6 105 light years
One neutrino with m, E (m2 ltlt 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) 063002, 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

• ß-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 ?m2ij

29
ß-decay and neutrino mass
kinematic measurement of electron neutrino mass
m(ne)
E0 18.57 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
calorimeter source detector

• ß-detection requirements
• - high resolution (DElt few eV)
• - large solid angle (DW 2p)
• - low background

spectrometer source ? detector
30
Based on Andrea Giuliani, MARE collaboration
31
Tritium ß-decay experiment
3H ? 3He e- ?e with E018.6 keV
Measurement of T2 ß-decay spectrum in the region
around the endpoint E0
32
Why tritium?
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 ß-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
withmagnetic 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
withmagnetic 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
withmagnetic 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

• MAC-E Filter - method
• Scanning ß spectrum and background region by
  varyingspectrometer voltage U0
• All ß electrons with an energy higher than the
  filter energy eU0 accepted and counted
• Measuring time per data pointis experiment
  specificTypical values 20 to 60 s per voltage
  set

-eU0
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 10-10 mbar

QCTS Quench Condensed Tritium
Source
40
The Mainz neutrino mass experiment (1997-2001)
KATRIN 2006
Mainz neutrinogroup 2001 J. Bonn
B. Bornschein L. BornscheinB.
FlattCh. KrausB. Müller E.W. OttenJ.P.
SchallTh. ThümmlerCh. Weinheimer ? FZ K
U Karlsruhe ? U Münster
41
Source systematics

• 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
• ?t ?t0 ? exp(? W / kT)
• (Arrhenius-law)
• ?t characteristic dewetting time
• ?W activation energy
• Dewetting time ?t (T1.9 K) gt 1.2 a (95 C. L.)
• ? long term measurements are possible with
  quench condensed tritium films if Tlt
  1.9 K

?t
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 cross sectionstot
(2.980.16) 10-18 cm2 Det. of energy loss
function V.N. Aseev et al., Eur. Phys.J. D10
(2000) 39

• Determination of dynamics ?E (456) 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

? Self-charging of T2 film
? Long time behavior of T2 film
Rest gas condensation evaporation gtEffect
limits measurement time
Determination of critical field Ecrit (634)
MV/mgt slight broadening of energy resolution H.
Barth et al., Prog. Part. Nucl. Phys. 40 (1998)
353B. Bornschein et al., J. Low Temp. Phys. 131
(2003) 69
48
Self-charging of QCTS

• First hint
• shift of the ß-endpoint
• energy (1997)
• Idea
• Charging of the tritium
• film (40 mCi 1.5E9 electrons/s)

?Measurement with Kr-83m conversion
electrons
49
Time dependencyof charging
Assumption tritium ß-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.
ß-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)
lt 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)lt 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
• L3 m, Ø 5 cm
• T2HTH2 682
• column density 1017cm-2

• Spectrometer
• 3 ring lectrodes
• 3.5 eV resolution
• L6 m, Ø1.2 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 ß-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
• 1994-98 results (6 parameter fit)
• m?2 -1.9 3.4 2.2 eV2/c4 gt m? lt 2.5
  eV/c2 (95 C.L.)
• V. Lobashev et al., Phys.
  Lett. B 460 (1999) 227
• 1994-99/01 results (6 parameter fit)
• m?2 -2.3 2.5 2.0 eV2/c4 gt m? lt 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
• gt 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 MeasurementsBeate
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 lt 2 K ? no mobility!
• Charging
• additional el. Field
• movement of charges at Ecrit