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Model independent search for the neutrino mass with the KATRIN experiment

D. Vénosfor electron spectroscopy group

Nuclear Physics Institute of the Czech Acad. Sci.Řež near Prague

71th NuPECC meeting mini-workshop, Prague, June 17-18, 2011Supported by the Czech Ministry of Education - contr. LC07050

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- 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

Some neutrino features

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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 – mj

2| and 3 x 3 elements of neutrino mixing matrix Uai , m2

2 – m12 = 8.0(0.4) x 10-5 eV2, |m3

2 – m22| = 2.40(26) x 10-3 eV2

i.e. the heaviest mj ≥ 0.05 eVValues 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 · mi

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i

mν < 0.2 eV at 90 % C.L. if no effect is observed mν = 0.35 eV would be seen as 5σ effect

After 1000 measuring days:

Neutrino mixingmatrix

Masseigenstates

KATRIN Collaboration, /http://www-ik.fzk.de/katrin/

dN/dE = K × F(E,Z+1) × p × (Ee+me) × (E0-Ee) × [ (E0-Ee)2 – mνe2 ]1/2

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KATRIN setup - with MAC-E filter spectrometers

HV stability monitor

spectrometer

main spectrometer

rear

section

3T2 source

differ.&cryo pump.pre-

spec.

detecto

r

calibration electron sources are developed at NPI

For sensitivity of 200 meV:-high resolution: 0.9 eV-high luminosity: 19% of 4-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

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 spectrometerOur suggestion: solid 83Rb(86d)/83mKr(2h) source with K-shell internal conversion

electrons of krypton isomeric state transition 32.2 keV K-32 line: energy E = 17824.3(5) eV 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

electronsource

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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)573O. 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

corrected drifts of E(K-32) for sources: +1.2, +0.3, +0.4 ppm/month

venting of sources:10-9 → 10-3 mbar , 10-9 → 10-1 mbar

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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

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

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)323V. Hannen et al. KATRIN workshop, Münster, May 2010A. Manalaysay et al., Rev. Sci. Inst. 81(2010) 073303

Gas target

zeolite

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Thank you for your attention