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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
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Need for absolute mass determination
e
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?Results of recent oscillation experiments:
23,
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
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