or evidence?

Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

61st Scottish University Summer School in Physics: Absolute Neutrino Mass Measurements Beate Bornschein, Tritium Laboratory Karlsruhe # 1

HVT-TLK

or evidence?

or evidence?

complementary

Three roads to neutrino masses



HVT-TLK

Lecture I

Introduction

Electron neutrino mass measurements - methods

Status at the begin of the 3rd millennium

sensitivity 0.2 eV/c2

Absolute Neutrino Mass MeasurementsBeate Bornschein



HVT-TLK

Lecture II

Future of Re experiments – MARE

Fixing the neutrino mass scale with KATRIN

Summary & Perspectives





HVT-TLK

Absolute neutrino masses

---Particle

Data Group



HVT-TLK

Absolute neutrino masses – PDG (May 2006)



HVT-TLK

Absolute neutrino masses – the ‚traditional‘ way

m(e) : tritium ß-decay 3H → 3He + e- + e

m(µ) : pion-decay + → µ+ + µ

m() : tau hadr. decay → 5 +

kinematic phasespace studies

m() < 190 keV (PDG2006)

m() < 18.2 MeV (PDG2006)

m(e) < 2 eV (PDG2006)



HVT-TLK

Neutrino oscillations: linking -masses

mass offset?mass offset?



HVT-TLK






m() < 190 keV (PDG2006)

m() < 18.2 MeV (PDG2006)

m(e) < 2 eV (PDG2006)

neutrino oscillations with large mixing angles -

all -masses are linked to lightest by oscillations



HVT-TLK






m() < 190 keV (PDG2006)

m() < 18.2 MeV (PDG2006)

m(e) < 2 eV (PDG2006)

Therefore, concentration on m(e),

especially -decay experiments



HVT-TLK

A short step into the past

myon neutrino mass

tau neutrino mass



HVT-TLK

Myon neutrino mass

Three different quantities needs to be measured with very high precision

Done in three different experiments!

Principle:Principle:

22422 cpcmE 22422 cpcmE



HVT-TLK

1) 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

2) Measurement of

Myon neutrino mass

mmm

p

m

Mohr and Taylor, CODATA, RevModPhys 77 (2005)

Mohr and Taylor, CODATA, RevModPhys 77 (2005)

Jeckelmann et al., PhysLettB335 (1994)326

Jeckelmann et al., PhysLettB335 (1994)326



HVT-TLK

3) Measurement of at Paul-Scherrer Institute (PSI)

Myon neutrino mass

p

Assamagan et al., PhyRevD 53 (1996)6065




HVT-TLK

Setup at PSI





HVT-TLK

Different neutrino mass states i



HVT-TLK

Myon neutrino mass

PDG2006PDG2006

PDG2006PDG2006



HVT-TLK

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



HVT-TLK

Tau neutrino mass – ALEPH collaboration

Barate et al.,

Eur. Phys. J. C2 (1998)395

Barate et al.,

Eur. Phys. J. C2 (1998)395



HVT-TLK

Tau neutrino massPDG2006PDG2006

(23 entries …)



HVT-TLK






m() < 190 keV (PDG2006)

m() < 18.2 MeV (PDG2006)

m(e) < 2 eV (PDG2006)

Therefore, concentration on m(e),

especially -decay experiments



HVT-TLK

Electron neutrino mass - again a look into PDG2006



HVT-TLK

Neutrino mass from SN1987A

2

42

21

E

cm

c

Lttt SNE

2

42

21

E

cm

c

Lttt SNE

Time of flight measurement:Time of flight measurement:

One neutrino with m, E (m2 << E2)

SN1987A

22422 cpcmE

2

2

2

1

42

2121

11

2)(

EE

cm

c

Ltttt SNSNEE

2

2

2

1

42

2121

11

2)(

EE

cm

c

Ltttt SNSNEE

Two neutrinos with m, E1, E2

L 1.5 ∙ 1018 km 1.6 ∙ 105 light years



HVT-TLK

Neutrino mass from SN1987A

2

42

21

E

cm

c

Lttt SNE

2

42

21

E

cm

c

Lttt SNE

Time of flight measurement:Time of flight measurement:

One neutrino with m, E

22422 cpcmE

2

2

2

1

42

2121

11

2)(

EE

cm

c

Ltttt SNSNEE

2

2

2

1

42

2121

11

2)(

EE

cm

c

Ltttt SNSNEE

Two neutrinos with m, E1, E2

Dependent on SN model !



HVT-TLK

Neutrino mass from SN1987A: results

T.J. Loredo et al., PRD65 (2002) 063002, 39 pp

improved SN model

improved data modeling

PDG2006PDG2006



HVT-TLK

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



HVT-TLK

β-decay and neutrino mass



HVT-TLK

ß-decay and neutrino mass

kinematic measurement ofelectron neutrino mass m(e):



HVT-TLK



scaling in ß-decay: experimental observable is mscaling in ß-decay: experimental observable is m22

mass eigenstates mi too close to be resolved experimentally with

E ~ 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 Δm2

ij



HVT-TLK



E0 = 18.57 keVT1/2 = 12.3 ysuperallowed

E0 = 18.57 keVT1/2 = 12.3 ysuperallowed

3H

187ReE0 = 2.47 keVT1/2 = 43.2 Gyunique 1st forbidden

E0 = 2.47 keVT1/2 = 43.2 Gyunique 1st forbidden

calorimeter:source = detector

calorimeter:source = detector

spectrometer:source ≠ detector

spectrometer:source ≠ detector

ß-source requirements : high ß-decay rate

low ß-endpoint energy E0

no strongly forbidden transition

…, see further discussion,

dependent on experiment

ß-detection requirements : - high resolution (E< few eV)

- large solid angle ( ~ 2)

- low background



HVT-TLK

Source Electron analyzer Electron counter

T2

high activityhigh energy resolution integral spectrum: select Ee > Eth

high efficiency low background

spectrometers MAINZ-TROITSK KATRIN

electron

excitation energies

When in presence of decays toexcited states, the calorimeter

measures both the electron and the de-excitation energy

bolometer high energy resolution differential spectrum: dN/dE

microcalorimeters MIBETA, MANU MARE

Based on

Andrea Giuliani,

MARE collaboration

Based on

Andrea Giuliani,

MARE collaboration



HVT-TLK

Tritium β-decay experiment

3H 3He+ + e- + e with E0=18.6 keV

m > 0

m = 0

10 -13

-3 -2 -1 0E - E0 [eV]

cou

nt

rat

e [

a.u

.]

0 5 10 15 20energy E [keV]

0

0.2

0.4

0.6

0.8

1.0

1.2

Measurement of T2 β-decay spectrum in the region around the endpoint E0



HVT-TLK

Why tritium?

42200

22)())((),(const)( cmEEEEcmEpEZFMEN e

recoil energy and excitation neglected

nuclear matrix element

Fermi function

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

Tritium: E0 = 18.6 keV, TH = 12.3 a



HVT-TLK

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

m = 1 eV

m = 0 eV

2 10 * -13

-3 -2.5 -2 -1 0-1.5 -0.5 0.5E - E0 [eV]

0

2

4

6

8

10

N

[a.u

.]

Best solution: tritium source combined with MAC-E filter



HVT-TLK

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



HVT-TLK


MAC-E Filter:



2

inhomogen B-Field:


electrostatic retarding field:

high pass filter !

E = Bmin/Bmax E0



HVT-TLK


MAC-E Filter:



2

inhomogen B-Field:


electrostatic retarding field:

high pass filter !

E = Bmin/Bmax E0

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

-2 0 2 4 6

tran

smis

sio

n f

un

ctio

n

E - qU [eV]

E = 4.8 eV0° 45°



HVT-TLK

Principle of a MAC-E filter II

MAC-E Filter - method

Scanning β spectrum and background region by varyingspectrometer voltage U0

All β 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

amp

litu

de

energy

E0

spectrum region

rejected

- eU0

accepted

bg region

E0

-eU0



HVT-TLK

Principle set-up of a tritium -decay experiment

TritiumSource

(Magnetic) TransportSystem

Spectrometer(Energy Filter) Detector

1) No disturbance of kinetic energy of beta decay electrons (adiabatic transport)

2) No loss of electrons

3) Elimination of residual tritium molecules

1) Very high energy resolution

2) Very low background

1) Very low background

2) Segmented

1) Very high source strength

2) Very good understanding of systematic effects



HVT-TLK

The Mainz neutrino mass experiment (1997-2001)

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

Detector

5 segments silicon

e-continuous flowcryostat: 1.9K

laser for ellipsometry LHe cooled shield

graphitesubstrate

tritiumfilm



graphitesubstrate

tritiumfilm

QCTS = Quench Condensed Tritium Source

QCTS = Quench Condensed Tritium Source



HVT-TLK

The Mainz neutrino mass experiment (1997-2001)

Mainz neutrinogroup 2001:

J. Bonn B. Bornschein*

L. Bornschein*

B. FlattCh. KrausB. Müller ** E.W. OttenJ.P. SchallTh. Thümmler**

Ch. Weinheimer**

* FZ K + U Karlsruhe** U Münster

Mainz neutrinogroup 2001:

J. Bonn B. Bornschein*

L. Bornschein*

B. FlattCh. KrausB. Müller ** E.W. OttenJ.P. SchallTh. Thümmler**

Ch. Weinheimer**

* FZ K + U Karlsruhe** U Münster

KATRIN 2006

KATRIN 2006



HVT-TLK

Source systematics



graphitesubstrate

tritiumfilm

time

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…

Investigation of source effect in Mainz:

Entering the solid state physics…



HVT-TLK

Stray light measurements

700

800

900

1000

1100

1200

0 1000 2000 3000 4000 5000

inte

nsi

ty [

a.u

.]

time [s]

quench condensedfilm

dewetting state of equilibrium

desorption

1.6 Kcondensation

4.2 Kdewetting

> 5 Kdesorption



HVT-TLK

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

Results of stray light measurements

Δt

time [s]

0 1000 2000 3000 4000

T = 4.4 K

800

600

400

1200

1400

str

ay

lig

ht

[a.u

.]

T = 3.8 K

T > 5 Kdesorption

T = 4.0 K

T = 1.6 Kcondensation

1000



HVT-TLK

Source systematics & negative mass squares



graphitesubstrate

tritiumfilm

-150

-100

-50

0

50

100

150

18.3 18.4 18.5 18.6

m2

[eV

2/c

4]

E low

run91

-150

-100

-50

0

50

100

150

18.3 18.4 18.5 18.6

m2

[eV

2/c

4]

E low

run91

-150

-100

-50

0

50

100

150

18.3 18.4 18.5 18.6

m2

[eV

2/c

4]

E low

run91run98, Q5

-150

-100

-50

0

50

100

150

18.3 18.4 18.5 18.6

m2

[eV

2/c

4]

E low

run91run98, Q5

time

fit

lower limit of fit

fit

lower limit of fit

Quench Condensed Tritium Source QCTS, before 1997:

Source temperature 4.2K, 2.8 K Roughening transition ! Increased energy loss



HVT-TLK

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)

-3 -2 -1 0E - E0 [eV]

E0 E0 of fit

undisturbed spectrum

spectrum with additional energy loss



HVT-TLK

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)

year20001998199619941992199019881986

-350

-300

-250

-200

-150

-100

-50

0

50

100

m2

c4 [

eV2]

(MAC-E Filters)

magnetic spectrometers

Livermoore

Los Alamos

Mainz

Tokyo

Troitsk

Troitsk (step)

Zürich

electrostatic spectrometers



HVT-TLK

QCTS - investigations of systematic effects

time

timeH2: +0.1 nm/d

T2: -0.06 nm/d

e-

-

2 V, d = 350 A

Roughening transition of T2 film Roughening transition of T2 film

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

Inelastic scattering Inelastic scattering

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 Self-charging of T2 film Long time behavior 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) 353B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69

Rest gas condensation & evaporation =>Effect limits measurement time



HVT-TLK

Self-charging of QCTS

10

15

20

25

30

35

40

45

17.81 17.815 17.82 17.825 17.83 17.835 17.84 17.845

3000

3200

3400

3600

3800

4000

4200

4400

4600

4800

17.81 17.815 17.82 17.825 17.83 17.835 17.84 17.845

data

fit

data

fit

shift e * U

co

un

ts [

1/s

]c

ou

nts

[1

/s]

energy [keV]

e

e

Kr-83 submonolayeron 240 ML deuterium

Kr-83 submonolayeron 120 ML tritium

dEU

Measurement with Kr-83m conversion electrons

First hint: shift of the β-endpoint energy (1997)

Idea: Charging of the tritium film (40 mCi ≈ 1.5E9 electrons/s)



HVT-TLK

Time dependencyof charging

d1

d1

d 0

d 0

d 0

d 0

d 0

d 0

d1

d1

EC

EC

d 0

-----

d 0

d 0

EC

d 0

EC

++ +

+

+

---

------

+ ++++

E

E

E+++

+ ++

++

++

+

------

-

------

++++++

E

E

dd

d

dd

d d

d d

d tcrit

equal distributionof charges

capacitor

Assumption:

tritium β-decay

&

existence of critical field

Assumption:

tritium β-decay

&

existence of critical field



HVT-TLK

Result of measurement

-7

-6

-5

-4

-3

-2

-1

0

0 200 400 600 800 1000

ener

gy

shif

t [e

V]

film thickness [ Å ]

Q2

Q5

Q8

test films

E c = 62.6 4.0 MV/m

Steady state is characterized by a practically constant, critical electric field strength Ecrit ≈ 62 MV/m

≈ 20mV/monolayerover the film, at which the residual positive charges attain sufficient mobility to penetrate the film towards the conducting substrate.

Steady state is characterized by a practically constant, critical electric field strength Ecrit ≈ 62 MV/m

≈ 20mV/monolayerover the film, at which the residual positive charges attain sufficient mobility to penetrate the film towards the conducting substrate.

B. Bornschein et al., J. Low Temp. Phys. 131 (2003) 69

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!

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!



HVT-TLK

Results of Mainz experiment (1998/1999 + 2001)

-150

-100

-50

0

50

100

150

18.3 18.4 18.5 18.6

m2

[eV

2/c

4]

E low

run91run98, Q5

-150

-100

-50

0

50

100

150

18.3 18.4 18.5 18.6

m2

[eV

2/c

4]

E low

run91run98, Q5

lower limit of fit interval Elow [keV]18.3 18.4 18.5 18.6

-10

-5

0

5

10

m2

[e

V2 /

c4]

1998/1999 data

2001 data

lower limit of fit interval Elow [keV]18.3 18.4 18.5 18.6

-10

-5

0

5

10

m2

[e

V2 /

c4]

1998/1999 data

2001 data



HVT-TLK

Results of Mainz experiment

With neighbour excitation from calculation (Kolos et al., Phys. Rev. A37 (1988) 2297)

m2() = -1.2 ± 2.2 ± 2.1 eV2

m() < 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() = -0.6 ± 2.2 ± 2.1 eV2

m()< 2.3 eV (95% C.L.)C. Kraus et al., Eur. Phys. J. C40 (2005) 447

With neighbour excitation from calculation (Kolos et al., Phys. Rev. A37 (1988) 2297)

m2() = -1.2 ± 2.2 ± 2.1 eV2

m() < 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() = -0.6 ± 2.2 ± 2.1 eV2

m()< 2.3 eV (95% C.L.)C. Kraus et al., Eur. Phys. J. C40 (2005) 447

Data of 20 weeks run time added for evaluation

PDG2006PDG2006



HVT-TLK

Troitsk neutrino mass experiment

tritium gas injection

28K

5T0.8T

5T

e- to spectro-meter

Principle of WGTS:

= Windowless Gaseous Tritium Source & MAC-E Filter= Windowless Gaseous Tritium Source & MAC-E Filter

Dominant systematic uncertainty:Energy loss due to inelastic scattering of decay electrons



HVT-TLK

0.5-1 mT8 T 2.6 T

5 T 5 T0.8 T

Windowless GaseousTritium Source

MAC-E-Filter

Hg pump

T2 purification

Ti pump

Detector

e-gun

Magnetic Transport System+ Differential Pumping Section 0 1m 2m

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)



HVT-TLK

0.5-1 mT8 T 2.6 T

5 T 5 T0.8 T

Windowless GaseousTritium Source

MAC-E-Filter

Hg pump

T2 purification

Ti pump

Detector

e-gun

Magnetic Transport System+ Differential Pumping Section 0 1m 2m

Troitsk setup



HVT-TLK

Troitsk Anomaly

dEU

E0

dEU

E0

month in the yearst

ep p

os

itio

n b

elo

w E

0 [

eV]

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 ?

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 ?



HVT-TLK

Troitsk Results

Strong correlation between step parameters (anomaly) and m2

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):

m2 = -1.9 ± 3.4 ± 2.2 eV2/c4 => m < 2.5 eV/c2 (95% C.L.)

V. Lobashev et al., Phys. Lett. B 460 (1999) 227

1994-99/01 results (6 parameter fit):

m2 = -2.3 ± 2.5 ± 2.0 eV2/c4 => 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

Strong correlation between step parameters (anomaly) and m2

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):

m2 = -1.9 ± 3.4 ± 2.2 eV2/c4 => m < 2.5 eV/c2 (95% C.L.)

V. Lobashev et al., Phys. Lett. B 460 (1999) 227

1994-99/01 results (6 parameter fit):

m2 = -2.3 ± 2.5 ± 2.0 eV2/c4 => 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

PDG2006PDG2006



HVT-TLK

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

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



HVT-TLK

PDG2006PDG2006



HVT-TLK

Electron neutrino mass

^

PDG2006PDG2006



HVT-TLK

Lecture II

Future of Re experiments – MARE

Fixing the neutrino mass scale with KATRIN

Summary & Perspectives





HVT-TLK

Additional transparencies



HVT-TLK

Model for charging

-300

-200

-100

0

100

200

300

400

n-1

e * Ecrit * g

n+1

W [

kB

K]

monolayer

+

n

g

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

Documents

or evidence?