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 CRACOW EPIPHANY CONFERENCEON NEUTRINOS AND DARK MATTER5 - 7 January 2006, Cracow, Poland

 

● Introduction

● Neutrino mass determination

● The Karlsruhe TRItium Neutrino experiment KATRIN

● Conclusions

Status of the KATRIN experiment

Jochen Bonn

Johannes Gutenberg Universität Mainz

Jochen.Bonn@uni-mainz.de

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Need for absolute mass determination

e

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?Results of recent oscillation experiments:

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12, m2

23, m2

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hierarchical masses

degenerated masses

cosmological relevant

m2solar

m2atmos

normal hierarchy

mi KATRIN sensitivity

limit

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Previous β-spectroscopic searches for mν

Enrico Fermi (1934):dN/dE = K × F(E,Z) × p × Etot × (E0-Ee) × [ (E0-Ee)2 – mν

2 ]1/2

Theoretical β-spectrum near endpoint Eo → no dependency on nuclear

structure for tritium β-decay

→ no need for absolute intensity

calibration mν = 0eV

mν = 1eV

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

Experimental requirements:• high count rate near E0

• excellent energy resolution• long term stability• low back ground rate

~ mν2

~ mν

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Principle of an electrostatic filter withPrinciple of an electrostatic filter withmagnetic adiabatic collimationmagnetic adiabatic collimation (MAC-E) (MAC-E)

adiabatic magnetic guiding of ´s along field lines in stray B-field of s.c. solenoids:Bmax = 6 TBmin = 3×10-4 T

energy analysis bystatic retarding E-fieldwith varying strength:

high pass filter withintegral transmissionfor E>qU

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Electron spectrometers of MAC-E-Filter Type

Advantages:• High luminosity and high resolution simultaneously• No scattering on slits defining electron beam• No high energy tail of the response function

Disadvantages:• Danger of magnetic traps for charged particles

Integral spectra: low energy features superimposed on background from high energy part)

not important for endpoint region of β-spectrum

MAC-E-TOF mode is possibleMonoenergetic line at 17.8 keV

83Rb/83mKr

10 eV

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The Mainz neutrino mass experiment

frozen T2 on HOP graphite at T=1.86 K A=2cm2, d~130 monolayers (~45nm)20 mCi activity

spectrometer: 4 m lenght, 0.9 m diameterE=4.8 eV

mν2 = -0.7 ± 2.2 ± 2.1 eV2

mν < 2.3 eV @ 95% C.L.

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The requirements for a new direct mν experimentwith sub-eV sensitivity

The tritium β-decay is the best possible source:

• The low endpoint energy E0= 18.6 keV

dN/dE ≈ (1/E3) in the mass sensitive region

• No dependence on nuclear structure superalloved transition ½+ → ½+

• Known excited states for gaseous daughter ion (T3He)+

the first excited electronic state is at 27 eV but rotational-vibrational excitations of the ground (T3He)+ state with average energy of 1.6 eV and width of 0.4 eV

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• Known electron energy losses in gaseous tritium the last 12 eV of β-spectrum are free of inelastically scattered

electrons

• Tritium T½ = 12.3 y still acceptable specific activity of the source

Electron spectrometer: a very large MAC-E-Filter with superior parameters

In comparison with the present experiments at Mainz and Troitsk:10x better sensitivity on mν (2eV → 0.2eV)100 x better sensitivity on mν

2 (3eV2 →0.03eV2)

Improve both resolution and luminosity!

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The Karlsruhe TRItium Neutrino Experiment

Academy of Sciencesof the Czech Republic Forschungszentrum Karlsruhe

in der Helmholtz-Gemeinschaft

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KATRIN location at FZKarlsruhe

TLK now

TLK expanded (+ 2/3 of transport hall)

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Hole in the wall of the TritiumLaboratory KarlsruheSeptember 2005

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T2 injection rate:

1.8 cm3/s (± 0.1%)

Windowless Gaseous Tritium Source (WGTS)

16 m

T2 injectionT2 pumping

Total pumping speed: 12000 l/s

Magnetic field: 3.6 Tesla (± 2%)

Source tube temperature: 27 K (± 0.1% stable)

at pressure of 3.4 ·10-3 mbar

Isotopicpurity>95%

WGTS tube: stainless steel,10 m length, 90 mm diameter

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Requirements:adiabatic electron guiding T2 reduction factor of ~1011

Background due to tritium decay in the main spectrometer <1 mHz !

Filling rate of 1.7 · 1011Bq/s

4.7 · 1010 β-particles /sec are guided to spectrometers

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Test of the inner loop of the tritium gaseous source

Summer 2005

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Tandem of electrostatic spectrometers

pre-spectrometer main spectrometerfixed retarding potential ≈ 18.45kV variable retarding potential 18.5 – 18.6 kVØ = 1.7m; length = 3.5m Ø = 10m; length = 24mE ≈ 60 eV E = 0.93 eV (18.575keV)

electrostatic pre-filtering & analysis of tritium ß-decay electrons~1010 ´s/sec ~103 ´s/sec ~10 ´s/sec (qU=E0-25eV)

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• UHV: p ≤ 10-11 mbar • „massless“ inner electrode system to protect against secondary electrons from the walls

inner electrodeinstalled in Mainzspectrometer for background tests

intrinsic det. bg 1.6mHz

2.8mHz

Results from the Mainz spectrometer:

Minimisation of spectrometer background

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Vacuum in the main spectrometer

• UHV: p ≤ 10-11 mbar

• Bake up at 350º C for outgassing rate 10-12

mbar l s-1 cm-2 (400 kW power is needed, 12 cm increase in length)

• Non-evaporable getter pumps: 5 ·105 l s-1

(mainly for hydrogen from the walls)

• Turbomolecular pumps: 10 000 l s-1 (mainly for hydrogen set free during NEG activation)

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CU + PB SHIELD

SCINTILLATOR VETO

The elements of the detector design

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Calibration and monitoring of the energy scale

Two independent ways of monitoring:

1) Precise measurement of the retarding high voltage but no HV dividers for tens of kV on ppm level

are commercially available

2) Monitor spectrometer on the same HV+ physical standard of monoenergetic electrons but no precision standards for region of tens keV

Reason: Ekin = Eexc- Ebin

and Ebin is sensitive to phys. & chem. environment

Ebin up to a few eV!

Calibration with gaseous 83mKr admixed to T2

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The high precision HV divider

The first test at Sept 2005:stable on sub-ppm level at 32 kV for 16 hours

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Monitor Spectrometer

Precise monitoring of the main spectrometer energy scale: precise measurement of retarding potential + comparison to reference energy

pre spectrometer

main spectrometer

detector

HV-supply

voltage divider/voltage measurement

monitor spectrometer(magnified)

reference sourceof nuclear or atomic transition

reference detector

Mainz spectrometer modified to 1 eV resolution

β-particles

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Systematic uncertaintiesany not accounted variance 2 leads to negative shift of m

2: m2 = -2 2

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. transmission function

- spatially resolved e-gun measurements

4. HV stability of retarding potential on ~3ppm level required

- precision HV divider (PTB), monitor spectrometer beamline

5. WGTS charging due to remaining ions (MC: < 20mV)

- inject low energy meV electrons from rear side, diagnostic tools available

6. final state distribution

- reliable quantum chem. calculations

a fewcontributions

with each:m

2 0.007 eV2

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KATRIN sensitivity & discovery potential

m < 0.2eV (90%CL)

m = 0.35eV (5)

m = 0.3eV (3)

sensitivity

discovery potential

expectation:

after 3 full beam years syst ~ stat

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6.5

H.-V. Klapdor-Kleingrothaus et al., NIM A 522 (2004) 371

claim for <mee> = 0.4 eV (4.2)

[0.1-0.9eV] including matrix el.

E0=2039 keV

KATRIN sensitivity & discovery potential

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Absolute neutrino mass scale needed for particle physics and astrophysics/cosmologyby direct neutrino mass measurement (less model dependent & complementary)

Directmassmeasurement from tritiumdecay:●Mainz finished (all problems solved):

m(e) < 2.3 eV (95% C.L.)

● KATRIN: A large tritium neutrino mass experiment with sub-eV sensitivity m(

e) < 0.2 eV or m(

e) > 0 eV (for m(

e) 0.30 eV @ 3)

key experiment to fix the absolute neutrino mass scale design for most parts finished, first parts of the setup already installedmajor compenents have been ordered

Summary