Model independent search for the neutrino
mass with the KATRIN experiment
D. Vénos
for electron spectroscopy group
Nuclear Physics Institute of the Czech Acad. Sci.
Řež near Prague
71th NuPECC meeting mini-workshop, Prague, June 17-18, 2011
Supported by the Czech Ministry of Education - contr. LC07050
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Some neutrino features
- Together with photons, the neutrinos are the most abundant
particles in the Universe
- Neutrino fluxes on the earth surface in cm-2s-1:
relic - 3·1012, sun - 6·1010, earth - 6·106, reactor(1 km dist.) - 1·1010,
human body - 4000/s into 4π due to 40K decay
(140 g of K, 0.01 % of 40K, T1/2= 1.2· 109 y)
- Three flavor of neutrinos νe, νμ, ντ with masses mν < exp. limit,
neutrinos are weak interacting electrically neutral particles with spin 1/2
incorporated in standard model of particle physics as massless
- Deficit in νe and νμ fluxes from sun and atmosphere → oscillation →
the three weak interacting flavor states are mixings of three neutrino mass
states m1, m2, m3
The knowledge of the neutrino mass is of great importance for particle physics,
cosmology and astrophysics
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Current values of the neutrino masses
Model independent methods based on kinematics , E2 = p2c2 + m2c4
β-decay mνe < 2 eV
π decay mνμ < 190 keV
τ decay mντ < 18.2 MeV
Model dependent methods:
- T1/2(0νββ), depends on the nuclear models: mee = 0.1 - 0.9 eV
- time of flight, depends on the supernova models: mνe < 5.7 eV/
- anisotropy of the cosmic microwave background and the large scale
structure of galaxies,
depends on the cosmological models: ∑mi < 0.6 eV
Neutrino oscillations:
not mν but | mi2 – mj2| and 3 x 3 elements of neutrino mixing matrix Uai ,
m22 – m12 = 8.0(0.4) x 10-5 eV2, |m32 – m22| = 2.40(26) x 10-3 eV2
i.e. the heaviest mj ≥ 0.05 eV
Values from E.W. Otten et al., Rep. Prog. Phys. 71(2008)086201
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KATRIN - Karlsruhe Tritium Neutrino Experiment:
direct β-spectroscopic search for mν
Founded by institutions from Germany, Russia, USA, Czech Republic
Measured quantity :
mνe2 = Σ|Uei|2 · mi2
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Neutrino
mixing
matrix
Mass
eigenstates
dN/dE = K × F(E,Z+1) × p × (Ee+me) × (E0-Ee) × [ (E0-Ee)2 – mνe2 ]1/2
After 1000 measuring days: mν < 0.2 eV at 90 % C.L. if no effect is observed
mν = 0.35 eV would be seen as 5σ effect
KATRIN Collaboration, /http://www-ik.fzk.de/katrin/
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KATRIN setup - with MAC-E filter spectrometers
For sensitivity of 200 meV:
-high resolution: 0.9 eV
-high luminosity: 19% of 4p
-low detector back.: 10 mHz
-T2 injection of 40 g/day, 4.7 Ci/s
-1000 measurement days
-high stability of key parameters
e.g.: ± 3 ppm for retar. HV
calibration electron sources are developed at NPI
First test run is expected in Dec 2012
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Tritium β-electrons in KATRIN beam line
tritium part, inside TLK
no tritium part, out of TLK
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KATRIN – not only neutrino mass
• There are indications from ῡμ → ῡe accelerator oscillation
experiments and reanalysis of the reactor oscillation
experiments that sterile neutrinos at eV scale exist. It was
shown that KATRIN is enough sensitive to observe directly
these sterile neutrinos [1]
• Due to the strong tritium source KATRIN can serve as a target
for process νe + T→3He+ + e- induced by cosmic relict
neutrinos with a sensitivity of 2x109 x 56 cm-3. If process will
be not observed hypotheses about certain local neutrino
gravitation clustering will be rejected [2]
[1] A.S. Riis et al. arXiv: 1008.1495v2[astro-ph] 8Feb2011
C. Giunti et al. PRD 82(2010)053005
[2] A. Kaboth et al. arXiv: 1006.1886v1 [hep-ex] 9Jun2010
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HV stability monitoring at KATRIN main spectrometer
– principal scheme
- HV power supply, common for monitoring and main spectrometers, will be set to
a constant value of 18575 V
- separate scaning low voltages will be applied on the electron sources of both
spectrometers– the line and continuous spectra will be measured independently
Shift of line energy will indicate a possible shift of voltages
determined by common system HV divider + voltmeter
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Electron source for the monitoring spectrometer
Our suggestion: solid 83Rb(86d)/83mKr(2h) source with K-shell internal conversion
electrons of krypton isomeric state transition 32.2 keV
electron
K-32 line: energy E = 17824.3(5) eV
source
intensity I = 17%,
line width Γ = 2.8 eV
Development of the source with main properties:
- stability energy K-32 at level of ±3 ppm/(2 months)
non trivial – electron energy standard do not exist
- very high retention of Rb in source substrate
- reasonable retention of 83mKr in substrate
- high amount of no energy loss electrons (i.e. thin source, low contamination)
Steps:
- Production of 83Rb at Řež U-120M cyclotron, 83Rb/83mKr sources prepared by
vacuum evaporation, long term measurement of L1-9.4 keV line energy stability
at Řež ESA12 spectrometer, the line energy was increasing with time linearly
with a drifts of 2,4 - 12 ppm/month – not satisfactory
- Long term energy K-32 stability measurement using 2 vacuum evaporated sources
(produced at Řež) and 4 implanted sources (produced at ISOLDE) at Mainz
MAC-E filter spectrometer – drifts compatible with KATRIN demand
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Results, conclusions from measurement at Mainz
spectrometer
- technique of up to 4 electron sources on one holder simultaneously in spectrometer
was successfully proved
- careful spectrometer bake up necessary for stability of the spectr. work function
- 83mKr retention in implanted sources amounts to ~ 90 % (vac. evap. only of ~15 %)
- stability of K-32 energy:
●measured value of K-32 energy for all 6 sources depends on time linearly
●linear drift amounts maximally of 2.4 ppm/month; specifically, for both vacuum
evaporated and two implanted Pt15 and Pt#1 sources maximally of 0.4 ppm/month
i.e. all drifts < ±3 ppm/month
●the scatter of K-32 energy values along the line dependence amounts to ±1 ppm
(source activity of 2 MBq, time of line measurement of 1.5 h)
●energy of conversion electrons from implanted sources does not depend on the
temporary vacuum deterioration in source part
Generally: K-32 energy stability was sufficient, the problems were with stabilities
of spectrometer vacuum, 220 V and high voltage divider
Next stability tests of system “spectrometer + 83Rb/83mKr source” are planned
at monitoring spectrometer at Karlsruhe
Remark: tested source 241Am/Co providing photolectrons of 18631.68(23) eV energy was
abandoned for too low electron rate for continuous monitoring
D. Venos et al. Meas. Tech. 53(2010)573
O. Dragoun et al. App. Rad. Isot. 69(2011)672
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Stability of K-32 conversion electrons energy
measured at Mainz – 2nd period, 3 sources
venting of sources:
10-9 → 10-3 mbar , 10-9 → 10-1 mbar
corrected drifts of E(K-32) for sources: +1.2, +0.3, +0.4 ppm/month
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Stability of K-32 conversion electrons energy
measured at Mainz – 3nd period, 4 imp. sources
corrected drifts of E(K-32) for sources: -0.3, +0.6, +0.2 +2.4 ppm/month
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Stability of K-32 conversion electrons energy measured
at Mainz – 2nd period, 3 sources: failures and bake out
(red=implanted, blue, green=vac. evaporated)
220 V fail
vac.fail
bake out
220 V fail
source venting
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1 GBq electron source for the KATRIN gaseous source based on
83Rb deposition in zeolite
Motivation: studies of WGTS space charging and main
spectrometer response function
Gas target
Zeolite (aluminosilicate) based source vacuum properties :
- 83Rb firmly kept in the source, escape < 0.2mBq (from 2 MBq)
- 83mKr released from the source substrate, ≥ 50% is released
For production of ≈1 GBq 83Rb/83mKr source:
- cooling with helium gas has to be developed for existing krypton gas
target at NPI U-120M cyclotron [reaction natKr(p,xn)83Rb, 7.5 bar,
Ep = 26.2 MeV ]
- method for measurement of degree of 83mKr release from source
zeolite
Remark: 83Rb in zeolite is also very suitable for the space calibration
of xenon dark matter detector (collab. XENON – 15 samples)
D. Venos et al. App.Rad Isot. 63(2005)323
V. Hannen et al. KATRIN workshop, Münster, May 2010
A. Manalaysay et al., Rev. Sci. Inst. 81(2010) 073303
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Thank you for your attention
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